ISO 13571-1

• Abstract:

  This International Standard is one of many tools available for use in fire safety engineering. It is intended to be used in conjunction with models for analysis of the initiation and development of fire, fire spread, smoke formation and movement, chemical species generation, transport and decay, and people movement, as well as fire detection and suppression. This International Standard is to be used only within this context.

• Status: Not Published
• ICS: 13.220.01 - Protection against fire in general
• Technical Committee: ISO/TC 92/SC 3 - Fire threat to people and environment
• Drafting Committee: ISO/TC 92/SC 3 - Fire threat to people and environment
• Current Stage: 6000 - International Standard under publication
• Start Date: 10-Sep-2026
• Completion Date: 12-Sep-2026

• Revises: ISO 13571:2012 - Life-threatening components of fire — Guidelines for the estimation of time to compromised tenability in fires
• Effective Date: 06-Jun-2022

Overview

ISO 13571-1: Life-threatening components of fire - Part 1: Guidelines for method based on tenability endpoints for the estimation of time to compromised escape capability from exposure to smoke toxicants is an international standard developed by ISO/TC 92/SC 3. This standard provides guidelines for estimating the time to compromised tenability-when escape capability has been reduced or lost-due to exposure to smoke toxicants in fire scenarios. It forms a core component of fire safety engineering, offering a scientific framework for assessing the effects of exposure to life-threatening components of fire, specifically focusing on the toxicological impacts of smoke.

ISO 13571-1 is intended to be used in conjunction with fire models that analyze fire growth, smoke production and movement, toxic gas generation, and occupant movement, as well as with methods for fire detection and suppression. The standard integrates fire effluent analysis with human tenability thresholds, addressing different occupant vulnerabilities, including children, older adults, and individuals with health concerns.

Key Topics

• Tenability and Escape Capability: Defines the ability of occupants to maintain cognitive and physical functions necessary for safe escape when exposed to a fire.
• Toxic Smoke Exposure: Provides methods to determine at what point exposure to smoke toxicants, like carbon monoxide and hydrogen cyanide, compromises escape capability.
• Activity Levels and Susceptibility: Incorporates varying activity levels (e.g., at rest, walking, running) and accounts for sensitive subpopulations.
• Thresholds and Endpoints: Describes how to estimate the critical exposure limits-called tenability endpoints-for both median and susceptible populations.
• Fire Modeling Integration: Assumes results from detailed fire scenarios (typically from fire dynamics modeling) to apply tenability calculations.
• Post-exposure Health Effects: Includes informative guidance on the estimation of adverse health effects occurring after escape or rescue.

Applications

ISO 13571-1 serves as a vital tool for professionals and organizations involved in fire safety engineering and risk assessment. Common practical applications include:

• Fire Risk Assessment: Estimation of the time period during which occupants can safely escape in building and transport scenarios.
• Performance-based Fire Safety Design: Integration in calculations of Available Safe Escape Time (ASET) and Required Safe Escape Time (RSET).
• Fire Modeling: Supports hazard assessments where time-concentration curves of toxic gases are generated from fire dynamics simulation or large-scale experiments.
• Hazard Analysis for Vulnerable Occupants: Provides methods to estimate increased risk for sensitive groups, informing evacuation strategies for diverse occupants.
• Incident Investigation and Regulatory Compliance: Assists in the evaluation and demonstration of building safety and compliance with fire safety standards.

Related Standards

ISO 13571-1 is part of a broader family of ISO fire safety standards, each covering different aspects of life-threatening fire components:

• ISO 13571-3: Focuses on smoke toxicity assessment based on lethality endpoints, providing an alternative approach to estimating risk.
• ISO TR 13571-2: Offers technical reports and practical examples of the application of the ISO 13571 series.
• ISO/TR 13571-4: Provides comparative analyses of tenability and lethality endpoints across different fire scenarios.
• ISO 13571-5: Expands on models related to heat exposure, smoke exposure, and introduces a simplified toxicity model based on combustible mass loss.
• ISO/TR 16738: Offers broader guidance on fire safety engineering, including occupant characteristics and escape modeling.
• ISO 13943: Defines critical terms and concepts in fire safety, including incapacitation and tenability.

Summary

ISO 13571-1 is a key international standard in fire safety engineering, enabling the robust estimation of time to compromised escape capability from exposure to smoke toxicants. Its structured approach provides the necessary methodology for integrating fire effluent analysis, human behavioral and physiological response, and the latest fire modeling data, forming a foundation for risk-informed fire safety design and assessment. This enhances occupant protection and supports compliance with modern fire safety objectives across buildings and transportation environments.

DRAFT
International
Standard
ISO/DIS 13571-1
ISO/TC 92/SC 3
Life-threatening components of
Secretariat: AFNOR
fire —
Voting begins on:
Part 1: 2025-05-20
Guidelines for the estimation of
Voting terminates on:
2025-08-12
time to compromised tenability and
escape capability from exposure to
smoke toxicants — Method A
ICS: 13.220.01
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
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Reference number
ISO/DIS 13571-1:2025(en)
DRAFT
ISO/DIS 13571-1:2025(en)
International
Standard
ISO/DIS 13571-1
ISO/TC 92/SC 3
Life-threatening components of fire —
Secretariat: AFNOR
Part 1:
Voting begins on:
Guidelines for the estimation of
time to compromised tenability and
Voting terminates on:
escape capability from exposure to
smoke toxicants — Method A
ICS: 13.220.01
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland Reference number
ISO/DIS 13571-1:2025(en)
ii
ISO/DIS 13571-1:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 General principles . 2
4.1 Time to compromised tenability .2
4.2 Toxic-gas model . .2
5 Significance and use . 4
6 Toxic gas models . 6
6.1 Asphyxiant-gas fractional effective dose model .6
6.2 Irritancy model . 12
7 Post-exposure injury and lethality .13
8 Report . 14
Annex A (informative) Context and mechanism of toxic potency .15
Annex B (informative) Asphyxiant model expanded for different activity levels incorporating
V as a variable .37
E
Annex C (informative) Post-exposure injury and lethality .40
Bibliography .43

iii
ISO/DIS 13571-1:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
people and environment.
This first edition cancels and replaces the second edition (ISO 13571 :2012), which has been technically
revised.
The main changes are as follows:
— Additional expressions for enabling calculation of asphyxiant tenability over are range of activity levels
from at rest to heavy work.
— Guidance on estimation of asphyxiant and irritant tenability threshold (Point of Departure) levels have
been revised and further developed.
— Informative guidance on estimation of post-exposure health effects has been included.
— Further information has been included to extend and clarify the basis of the derivation of threshold
levels and application to different occupant populations, including children, the elderly and those with
health conditions.
iv
ISO/DIS 13571-1:2025(en)
Introduction
ISO 13571 series is a set of standards developed for estimation of time to compromised tenability and escape
capability for occupants when exposed to a fire environment. Different threats are evaluated separately
for exposure to acute toxicants, heat and smoke. The time to compromised tenability is the shortest of the
determined times to compromised tenability for each individual threat.
ISO 13571 series is composed of 5 parts:
— ISO 13571-1 describes a model for smoke toxicity assessment of time to compromised tenability and
escape capability of 50 % of an exposed occupant population, and threshold tenability limits for the
sensitive members of an exposed population including children, elderly and health compromised.
— ISO/TR 13571-2 (Technical report) describes examples of application of ISO 13571 series [TO BE REVISED].
— ISO 13571-3 describes a model for smoke toxicity assessment of time to compromised tenability based
on lethality endpoints for an exposed occupant population (excluding hypersensitive).
— ISO/TR 13571-4 (Technical report) gives examples of comparisons between parts 1 and 3 in different
fire scenarios.
— ISO 13571-5 describes models for heat exposure, smoke exposure, and a simplified model for toxicity
assessment based on mass loss of combustible.
Chronic or environmental exposure are not covered in ISO 13571 series.
This document is intended for estimation of time to compromised tenability and escape capability for
occupants when exposed to a fire environment for applications where the time-concentration curves for
fire scenarios are available (for example from fire dynamics modelling or large-scale fire experiments). The
standard may be used for hazard calculations and modelling as applied to Available Safe Escape time (ASET)
and Required Safe Escape time (RSET) calculations and models.
The document provides expressions for calculation of time and exposure doses to tenability endpoints
for 50 % of an exposed occupant population and for estimation of threshold limits designed to protect
essentially all occupants. This includes mixed general populations with children, the elderly and adults with
health conditions in all occupancies including buildings and transport systems.
The calculation expressions in this document have been derived as far as possible from human behavioural
and physiological tenability data obtained from experimental and accidental exposures, especially data from
exposures during fire incidents, data from experiments on non-human primates, and experiments involving
rodents (rats and mice). The expressions and endpoints derived from these data have been developed to
provide assessment methods most relevant to the tenability and particularly the escape capability of human
occupants of building or transport fire scenarios.
The main areas of revision in this edition from ISO 13571:2012 are as follows:
— For this third edition the main expressions for calculation of tenability endpoints for active walking
adults have been retained, as in the second edition, but additional expressions have been provided for
which the volume of air breathed each minute (V ) has been separated out as user defined term. This
E
provides more versatility to enable the user to calculate tenability times for occupants over a range of
activity levels including at rest, moderate activity (such as rapid walking to evacuate) or heavy work
(such as running along a tunnel). This also incorporates the stimulatory effect of inhaled high CO
concentrations, enabling V to be calculated throughout the physiological range (~8-70 l/min) and the
E
resulting effects on the uptake and time to compromised tenability from asphyxiants. Expressions for
the asphyxiant effects and time to compromised tenability for decreased oxygen concentrations and.
— For the narcotic effects of inhaled CO at high concentrations (which were referenced in the second
edition) have now been included in this edition.
— For this edition, although the main endpoints for asphyxiant and irritant tenability are the same as for
the previous edition the guidance on estimation of threshold, Point of Departure (POD), levels have

v
ISO/DIS 13571-1:2025(en)
been revised and further developed. For asphyxiants tenability is compromised by confusion and loss
of consciousness after inhalation of a sufficient exposure dose. For smoke irritants, tenability depends
on exposure concentration and is compromised by eye and respiratory tract pain, visual and breathing
difficulties sufficient to result in a high probability of escaping occupants turning back or being unable
to continue through irritant smoke.
— As with the previous edition the main intended application of this standard is the calculation to times of
compromised tenability during exposure at a fire incident, for application to time up to which occupants
are able to escape or shelter without compromised tenability. For this reason, the main application
does not include consideration of potential post-exposure adverse health effects in fire survivors. In
general, it is considered that such effects should be minimal providing the limits for compromised
tenability during the incident are not exceeded. In order to enable consideration of such potential post-
exposure hazards in survivors when appropriate (for example when threshold limits may be exceeded),
guidance has been included in an informative Annex C in this edition for estimation of threshold level
for asphyxiant exposures above which there may be significant risk of post-exposure neurological or
cardiovascular health effects and expressions for calculation of threshold exposure doses of irritant
gases and particulates for risk of inhalation injury from lung inflammation.
— Further information has been included, mainly in the Appendices, to extend and clarify the basis of the
derivation of the calculation expressions and endpoints, the derivation of threshold levels and application
to different occupant populations. The guidance in this standard draws on that derived independently for
[6]
the AEGL (National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances),
[7][25][26][27][28][29][30][31]
and comparisons are presented in ISO/TR 13571-4.
The guidance in this International Standard (ISO 13571-1) is based on the best available scientific judgment
in using a state-of-the-art but less-than-complete knowledge base of the consequences of human exposure to
fire effluents. For ethical reasons, much of the methodology described has not been and cannot be validated
experimentally with humans. However, for carbon monoxide, the major contributor to prevention of escape
and the most frequent cause of fire fatalities, the database is actually quite extensive and well-validated
with human experience.
Estimation of occupants’ tenability when exposed to a fire environment ultimately involves their ability
to perform behavioural, cognitive and motor-skill functions at an acceptable level. Generally, acceptable
performance may include any of a number of desirable outcomes, including escape to a place of refuge, or
if escape is not a viable option, continued functioning in place as necessary. The latter situation includes
occupants who are not mobile or whose egress is prohibited for a variety of reasons, e.g., from an aircraft
in flight. The time from initiation of a fire to the point when tenability is compromised such that acceptable
performance is not possible is a central component of fire safety design.
The time required to reach compromised tenability can depend upon each occupant’s location and
movement, along with numerous other characteristics specific to the occupant. As a result, each occupant
may have a different time to compromised tenability. Guidance for consideration of these factors is provided
in other sources, e.g. ISO/TR 16738.
Each occupant may also have a different time to compromised tenability, depending on their particular
exposure to heat and fire effluent combustion products and their individual susceptibility to such exposures
(see A.2.3). The purpose of the methodology described in this International Standard (ISO 13571-1) is to
provide a framework for use in estimating the time at which compromised tenability may occur.
The methodology described cannot be used alone to evaluate the overall fire safety performance of specific
materials or products and cannot, therefore, constitute criteria for a test method. Rather, the formulae are
to be used as input to a fire hazard or risk analysis. In such an analysis, the estimated time to compromised
tenability also depends on the nature both of the fire (e.g. heat release rate, quantity and types of
combustibles, fuel chemistry) and of the enclosure (e.g. dimensions, ventilation). These determine the toxic-
gas concentrations, the gas and wall temperatures and the density of smoke throughout the enclosure as a
function of time. Furthermore, estimation of exposure is determined, in part, by assumptions regarding the
position of the occupants' heads relative to the hot smoke layer that forms near ceilings and descends as the
fire grows.
Although the concept of compromised tenability is consistent with the definition of incapacitation
(see ISO 13943), the latter term is not used in this International Standard due to its potentially broad

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ISO/DIS 13571-1:2025(en)
interpretation to include many effects, including collapse and unconsciousness, that are not addressed. This
International Standard focuses specifically on compromised tenability as influenced by both physiological
and behavioural responses resulting from exposure to a fire’s life-threatening components.
As with all predictive methodology, uncertainty exists in the application of this International Standard. An
estimation of the uncertainty for each procedure is provided, with the user being encouraged to determine
the significance of these uncertainties in the estimation of the outcome of a given fire scenario.

vii
DRAFT International Standard ISO/DIS 13571-1:2025(en)
Life-threatening components of fire —
Part 1:
Guidelines for the estimation of time to compromised
tenability and escape capability from exposure to smoke
toxicants — Method A
1 Scope
This International Standard (ISO 13571-1) is one of many tools available for use in fire safety engineering.
It is intended to be used in conjunction with fire test data such as those detailed in ISO 13571-5 and models
for analysis of the initiation and development of fire, fire spread, smoke formation and movement, chemical
species generation, transport and decay, and people movement, as well as fire detection and suppression.
This International Standard is to be used only within this context.
This International Standard is intended to address the consequences of human exposure to the life-
threatening components of fire. The time-dependent concentrations of fire effluents and the thermal
environment of a fire are determined by the rate of fire growth, the yields of the various fire gases produced
from the involved fuels, the decay characteristics of those fire gases and the ventilation pattern (see B.1).
Once these are determined, the methodology presented in this International Standard can be used for the
estimation of the time at which individuals can be expected to experience compromised tenability.
This guidance can also be applied to estimation of the time limit for rescuing people who are immobile due
to injury, medical condition, etc.
This International Standard establishes formulae to evaluate the life-threatening components of fire hazard
analysis in terms of the status of exposed human subjects at discrete time intervals. It makes possible the
estimation of the time at which occupants can experience compromised tenability (see A.2). It enables
estimation of a compromised tenability endpoint for each of the fire effluent components, with the most
important endpoint being the earliest to occur.
The life-threatening components addressed in the 13571 series include fire-effluent toxicity, heat, and
visual obscuration due to smoke. In cases where the effluent composition is available, the toxic gas model is
used for assessment of fire-effluent toxicity. For those cases where the effluent composition is unknown, an
additional mass-loss model using generic toxic potency values is provided in ISO 13571-5.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 19701, Methods for sampling and analysis of fire effluents
ISO 19702, Sampling and analysis of toxic gases and vapours in fire effluents using Fourier Transform Infrared
(FTIR) spectroscopy
ISO 13943, Fire safety — Vocabulary
ISO/TR 16738, Fire-safety engineering — Technical information on methods for evaluating behaviour and
movement of people
ISO/DIS 13571-1:2025(en)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
tenability
ability of humans to perform cognitive and motor skill functions at an acceptable level when exposed to a
fire environment
Note 1 to entry: If exposed individuals are able to perform cognitive and motor-skill functions at an acceptable level,
the exposure is said to be tenable. If not, the exposure is said to result in compromised tenability.
3.2
adjustment factor
factor for the incorporation of quantitative data on interspecies differences or on human variability in either
toxico-kinetics (variability in inhaled dose and metabolism) or toxico-dynamics (mode of action causing the
critical effect) into the risk assessment procedure
4 General principles
4.1 Time to compromised tenability
The time to compromised tenability for individuals is the shortest of four distinct times estimated from
consideration of asphyxiant fire gases, irritant fire gases, heat, and visual obscuration due to smoke.
The context and mechanisms of the fire-effluent toxicity component of life threat are discussed in Annex A.
Effects of the asphyxiant toxicants, carbon monoxide and hydrogen cyanide (see A.3), as well as those of eye
and upper-respiratory tract sensory irritants (see A.4), are described in detail.
Responses to these exposures involve functions of the human sensory, cardiovascular, respiratory and
neurological systems that are dependent upon inherent physical characteristics (e.g., age, body weight, pre-
existing cardiopulmonary conditions), along with environmental considerations and physical activity at the
time of exposure. As a result, individual human responses can be highly variable and, therefore, not readily
reduced to usable engineering formulae for prediction of compromised tenability without considerable
simplification, application of numerous assumptions, and exclusion of unusual circumstances.
With regard to the susceptibilities of individuals to the insults of fire exposure, a primary assumption of
this International Standard is that all occupant responses are treated as a log-normal or probit statistical
distribution with respect to a median time, with half of the population experiencing a tenable exposure
and half experiencing compromised tenability (see 5.3). Threshold levels estimated to affect tenability for
approximately 1 % of an exposed population are derived from Point of Departure (POD) animal toxicity data
[2][6][9][25][26][27][28][29][30][31]
and reported findings from human exposure data .
4.2 Toxic-gas model
4.2.1 The toxic-gas models described in this International Standard address effects that are considered
detrimental to human tenability. Because they are physiologically unrelated and mechanistically
independent, asphyxiant toxicants and irritant toxicants are treated separately (see A.3 and A.4).
With irritant toxicants, only those that cause eye and upper-respiratory tract sensory irritation are
considered in this International Standard as having effects on tenability (see A.4.2). Serious effects of
pulmonary irritation resulting in lung injury are manifested from a few hours up to several days after

ISO/DIS 13571-1:2025(en)
exposure and are not normally expected to have a direct impact on tenability during exposure at a fire scene
(see A.4.3).
Providing asphyxiant and irritancy thresholds are not exceeded during exposure then significant post-
exposure lung injury from irritants and significant post-exposure neurological or cardiovascular injury
from asphyxiants are considered unlikely to occur. Additional guidance on threshold exposure doses that
may result in post-exposure injury is given (see A.4).
4.2.2 The basic principle for estimating the asphyxiant component of toxic hazard analysis involves the
exposure dose of each toxicant, i.e. the integrated area under each concentration-time curve. Fractional
effective doses (FEDs) are determined for each asphyxiant at each discrete increment of time, whereby the
accumulated exposure dose is expressed as a fraction of the exposure dose required to cause compromised
tenability. The time at which their accumulated sum exceeds a specified threshold value represents the time
to compromised tenability relative to chosen safety criteria.
4.2.3 The basic principle for estimating the eye and upper respiratory tract sensory irritant component of
toxic hazard analysis involves the concentration of each irritant. Fractional effective concentrations (FECs)
are determined for each irritant at each discrete increment of time. The time at which their sum exceeds
a specified threshold value represents the time to compromised tenability relative to the chosen safety
criteria.
4.2.4 Relevant assumptions and exclusions are as follows:
a) Asphyxiant toxicants, irritants, heat and visual obscuration are each considered as acting independently.
Some degrees of interaction between these insults are known to occur (see A.6), but are considered
secondary.
b) Exposed occupants are considered to be at relatively normal ambient environmental conditions and at
altitudes below which reduced ambient oxygen could be a factor, and performing at a moderate level of
physical activity. Deviation from these conditions can affect susceptibility.
c) Any interactions between aerosols, particulates and gaseous fire-effluent components are not
considered. The physical form of toxic effluents is known to have some influencing effects, but in
this International Standard they are considered secondary to the direct effects of vapour-phase and
particulate effluents.
d) Adverse health effects subsequent to exposure to fire atmospheres are not considered in relation to
tenably during exposure, although it is recognized that post-exposure effects occur where tenability
limits during exposure are exceeded. Pre-existing health conditions may be exacerbated and potentially
life-threatening sequelae may develop from exposure both to asphyxiants and to pulmonary irritants
(see A.3 and A.4.3). Lower respiratory tract effects are typically manifested at time scales much
longer than those of the actual fire and, although noted, are not considered in the requirements of this
International Standard with respect to tenability during exposure at a fire scene. Additional guidance
has been provided on post exposure adverse health effects from inhaled doses of asphyxiants with
risk of post-exposure cardiovascular and neurological effects and to inhaled doses of lung irritants
associated with a risk of lung injury.
e) The early impacts of visual obscuration due to smoke (e.g., recognition that a fire exists, seeing exit
paths clearly) are behavioural in nature and are not included. However, smoke obscuration of such
severity that occupants become disoriented or show a high probability of turning back rather than enter
or continue through smoke places a limitation on the time during which escape may be attempted and is
considered.
The formulae in the methodology described in this International Standard enable estimation of the status
of exposed occupants at discrete time intervals throughout the progress of a fire scenario, up to the time
at which such exposure can result in compromised tenability. If the estimated time is deemed excessively
limiting, a variety of protection strategies then require consideration by the fire safety professional.

ISO/DIS 13571-1:2025(en)
5 Significance and use
5.1 The objective of this International Standard is to provide simplified, but robust, guidance for engineers
in estimating occupants’ time to compromised tenability as part of an assessment of a structure’s fire safety
capabilities when subjected to fire conditions specified in terms of time-concertation profiles for toxic gases
and smoke particulates. Such estimation of occupants’ tenability ultimately involves their ability to perform
cognitive and motor-skill functions at an acceptable level. Generally, acceptable performance may include
any of a number of desirable outcomes, including escape to a place of refuge, or if escape is not a viable
option, continued functioning in place as necessary.
NOTE If escape to a place of refuge or final exit is the outcome to be considered, the time to compromised
tenability can reasonably be equated to the available safe escape time (ASET).
The method has been developed specifically to address issues relating to exposure of occupants to
developing fires.
The main purpose of the expressions is to enable calculation of time to compromised tenability during
exposure to fire scenarios. The particular endpoint addressed is the time at which a significant proportion of
an exposed population becomes incapacitated to the extent that they are unable to make a safe escape. The
expressions are also protective against significant post exposure injury and death providing the endpoints
for compromised tenability are not exceeded.
During fire incidents enclosure occupants (occupants of buildings and transport systems) are typically
[1][2]
exposed to one of three types of exposure scenario :
1. Occupants in the same enclosure as a fire exposed to smoke particulates, irritants and asphyxiant gases
(and or heat) starting from low concentrations then increasing rapidly over a period of a few minutes to
incapacitating concentrations.
2. Occupants leaving a relatively clear enclosure to enter a smoke-filled escape route containing
concentrations varying from low levels to those capable of causing incapacitation within a short period
(a few minutes, a few seconds or even after a single breath). Occupants are in such cases exposed to a
near square wave effluent concentration profile.
3. Occupants trapped in an enclosure (or remaining in a designated refuge) which is initially clear but
gradually fills with smoke and toxic gases by infiltration over an extended period of up to (but rarely
exceeding) an hour.
In these scenarios occupants are exposed to and affected by a sequence of hazards, typically beginning with
the immediate effects of exposure to irritant smoke, then followed by effects of exposure to asphyxiant gases
and/or heat. Key aspects of these exposure scenarios in relation to the development of tenability expressions
are that they generally involve short exposure periods of a few minutes, and that conditions can change very
rapidly, so that the expressions need to be able to address effects of high exposure concentrations and short
tenability times. An advantage when estimating tenability times in such situations is that due the exponential
increase in gas concentrations at a certain time during most fires, calculated times to incapacitation may
show only small changes when model parameters are varied.
5.2 Operating under a considerable number of simplifying assumptions, this International Standard deals
with responses of the overall population as represented by a statistical distribution. It is not intended to
provide guidance for a detailed assessment of the insult to specific individuals that might be exposed to a
given fire atmosphere ― such as is commonly required in forensic investigations. Furthermore, the focus
of this International Standard is on assessment of an occupant’s tenability, while forensic investigations
generally focus on the consequences of compromised tenability. These are quite different objectives.
Forensic investigations can also be extremely complicated, involving detailed characterization of specific
exposed occupants, along with interpretive expertise far beyond that which can reasonably be taught in a
guidance standard.
[3] [4]
5.3 The concepts of Fractional Effective Dose (FED) and Fractional effective concentration (FEC) are
fundamental to the methodology of this International Standard. Both concepts relate to the manifestation of
physiological and behavioural effects exhibited by exposed subjects.

ISO/DIS 13571-1:2025(en)
5.4 The variability of human responses to toxicological insults is best represented by a statistical
distribution that takes into account varying susceptibility to the insult. Some people are more susceptible
than the average, while others may be less susceptible (see A.5). In this International Standard, FED and/or
FEC values of 1,0 correspond, by definition, to the median value of a log-normal distribution of responses,
with one-half of the population being less susceptible and one-half being more susceptible. This means
that, statistically, 50 % of the population would be expected to experience tenable conditions (able to
perform cognitive and motor-skill functions at an acceptable level), with 50 % then expected to experience
compromised tenability (unable to perform cognitive and motor-skill functions at an acceptable level).
Recognizing that threshold criteria of 1,0 FED and/or FEC statistically serve to protect only one-half of the
population, users of this International Standard may use reduced FED and/or FEC threshold criteria in order
to satisfy more conservative fire safety objectives. This International Standard provides the flexibility to
choose FED and/or FEC threshold criteria as may be appropriate. While a threshold level of 0,3 FED or FEC
is recommended, further guidance is provided in A.5.2. Whatever the rationale used when choosing FED
and FEC threshold criteria, it is necessary to use a single value for both FED and FEC thresholds in a given
estimation of the time to compromised tenability.
5.5 The exposure of occupants to tenable conditions should not be construed as equating to no post-
exposure harm. Exposure to fire-gas toxicants that do not cause compromised tenability can still result in
a variety of effects that may prolong escape and thus increase exposure intensity to fire effluents and lead
to post-exposure health problems; (see Annex A.3 and A.4). Although the primary purpose of this standard
is estimation of compromised tenability during exposure at a fire incident, guidance is given on the risk
of significant post-exposure health effects. Providing the compromised tenability limits in this standard
are not exceeded during the period of exposure, post-exposure heath effect are likely to be minor. However
quantification of these effects, especially under conditions where effective post-traumatic measures are
common practice through medical intervention, is beyond the scope of this International Standard.
5.6 The time-dependent concentrations of fire effluents to which occupants, who are often on the
move, are exposed can only be determined using computational fire models and/or a series of real-scale
experiments. It is not valid to insert the concentrations of fire effluents or values of smoke optical density
obtained from bench-scale test methods in the formulae presented in this International Standard.
5.7 The methodology described for toxic gas exposures can be validated only to a limited extent from
human data. It is necessary to recognize that uncertainty exists in the precision of the experimental data
upon which the formulas are based, the representation of those data by algebraic functions, the accuracy
of assumptions regarding non-interaction of fire gases with each other and with heat, the susceptibility
of people relative to that of test animals, etc. These uncertainties are estimated in the following sections.
As with any engineering calculation, uncertainties should be included in the estimation of the overall
uncertainty of a fire hazard or risk analysis. This enables the user to determine whether the difference
between the outcomes of two such analyses are truly different or are irresolvable.
NOTE The resulting uncertainty in the estimated time to compromised tenability depends in a non-linear manner
upon the uncertainty in the FED and FEC calculations (for instance, these uncertainties can have reduced impact on
the estimated outcome of rapidly developing fires).
5.8 There is very little reliable information on asphyxiant gas exposures of less than 1 min or longer than
1 h. Thus, the accuracy of the formulas in this International Standard and the resulting estimations for either
very short or very long fire scenarios are uncertain. Due to these uncertainties, estimations of time available
to escape of less than 1 min are to be reported as <1 min, with caution exercised when making estimations
that involve occupant exposures longer than 1 h.
NOTE Due to the uncertainties involved, differences between comparative estimations of time to compromised
tenability of less than 1 min are typically insignificant.

ISO/DIS 13571-1:2025(en)
6 Toxic gas models
6.1 Asphyxiant-gas fractional effective dose model
6.1.1 Fractional effective doses (FEDs) are determined for each asphyxiant at each discrete increment of
time. The time at which their accumulated sum exceeds a specified threshold value represents the time to
compromised tenability relative to chosen safety criteria (see 5.3). The principle of the model in its simplest
form for calculating the fractional effective dose, X , is shown in Formula (1):
FED
t
n
C
i
X = Δt (1)
FED ∑∑
Ct⋅
()
i
i=1 t
where
−1
C is the average concentration, expressed in µl·l , of an asphyxiant gas “i ” over the chosen time
i
increment;
Δt is the chosen time increment, expressed in minutes;
(C·t) is the exposure dose causing occupants’ compromised tenability, expressed in minutes multiplied
i
−1
by µl·l ;
t Is the exposure period expressed in minutes.
In estimating incremental effects, ΔX , on the fractional effective doses (FEDs), X , for each discrete
FED FED
increment of time, Δt, C = C, and Formula (1) reduces to:
i
t
n
X =⋅Δt (2)
FED ∑∑
t
i
i=1 t
where the time, t , to compromised tenability due to component “i” is a function of its concentration, with the
i
units of time cancelling to give a dimensionless fraction for X
FED.
For asphyxiant gases the dose inhaled depends on three main variables:
— Exposure concentration C
— Volume of air breathed per minute (V ) in relation to body size
E
— Exposure time Δt
The main case used for the asphyxiant expressions is for an adult human engaged in moderate physical work
such as rapid walking horizontally of down stairs during an evacuation, with a V under ambient conditions
E
of 20 litres/minute. In Annex B, general case versions of the asphyxiant expressions are presented in which
V is included as a variable to enable uptake calculations for resting and heavy work conditions (such as
E
running). In all mammals V for a given activity level varies as a function of body surface area to mass
E
[2][5]
ratio so that the rate of dose uptake is greater for smaller humans or animals. To the extent that the
following asphyxiant expressions are derived from animal studies (such as primates or rodents) the effects
of body size on uptake is taken into account. Some inhaled fire gases, especially CO , further increase V by
2 E
stimulating breathing. This effect is also included in the uptake expressions.
The main asphyxiant gases occurring in fire effluents are CO and HCN, which cause hypoxic asphyxia by
impairing the carriage of oxygen in the blood and its delivery to and use in body tissues, especially brain and
[1][2]
heart, resulting in incapacitation due to collapse and loss of consciousness. The effects of CO and HCN
are considered to be additive on a fractional dose basis. Decreased oxygen concentration in fire effluents is
also a potential additive contributor to hypoxia, but is considered unlikely to make a significant contribution
at inhaled concentrations above 13 % oxygen. Inhaled nitrogen oxides can also contribute to hypoxia due to
methaemoglobin formation, decreasing the carriage of blood oxygen, but concentrations occurring in mixed
fuel fires are too low for NOx to make a significant contribution to hypoxia. Methaemoglobin also detoxifies

ISO/DIS 13571-1:2025(en)
[6]
inhaled cyanide somewhat due to the formation of cyanomethaemoglobin. The main contribution of
carbon dioxide to developing asphyxia is that it stimulates respiration and thereby increases the rate of
[1][2]
uptake of CO and HCN. High inhaled concentrations of CO above 5 % also cause incapacitation due to
dose-dependent respiratory distress and narcosis. This narcosis does not result from hypoxia so is treated
as a separate potential cause of incapacitation. During compartment fires, incapacitation due to effects of
asphyxiant gases is generally predicted before the narcotic effects of CO are likely to be significant. On
this basis the main asphyxiant model considers the effects of CO and HCN in conjunction with effects on
V depending on physical activity level of exposed subjects and inhaled CO concentrations. An expression
E 2
for the calculation of asphyxiant FED from oxygen depletion (Formula 8) is also presented for use as an
additive term with the FEDs for CO and HCN where necessary, and an expression for the calculation to FED
for narcosis from CO for use as a separate term with situations of exposure to high concentrations of CO in
2 2
the
...

FINAL DRAFT
International
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ISO/FDIS 13571-1
ISO/TC 92/SC 3
Life-threatening components of
Secretariat: AFNOR
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Voting begins on:
2026-07-15
Part 1:
Guidelines for method based
Voting terminates on:
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on tenability endpoints for the
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smoke toxicants
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MADE IN NATIONAL REGULATIONS.
Reference number
ISO/FDIS 13571-1:2026(en) © ISO 2026

FINAL DRAFT
ISO/FDIS 13571-1:2026(en)
International
Standard
ISO/FDIS 13571-1
ISO/TC 92/SC 3
Life-threatening components of
Secretariat: AFNOR
fire —
Voting begins on:
Part 1:
Guidelines for method based
Voting terminates on:
on tenability endpoints for the
estimation of time to compromised
escape capability from exposure to
smoke toxicants
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
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INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
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TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
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ISO/FDIS 13571-1:2026(en) © ISO 2026

ii
ISO/FDIS 13571-1:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3  Terms and definitions . 1
4 General principles . 2
4.1 Time to compromised tenability .2
4.2 Toxic-gas model . .2
5  Significance and use . 3
6 Toxic gas models . 5
6.1 Asphyxiant-gas fractional effective dose model .5
6.2 Irritancy model . 12
7 Post-exposure injury and lethality .13
8 Report . 14
Annex A (informative) Context and mechanism of toxic potency .15
Annex B (informative) Asphyxiant model expanded for different activity levels incorporating
V as a variable .37
E
Annex C (informative) Post-exposure injury and lethality .40
Bibliography .42

iii
ISO/FDIS 13571-1:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
people and environment.
This first edition of ISO 13571-1 cancels and replaces the second edition of ISO 13571:2012, which has been
technically revised.
The main changes are as follows:
— deletion of the terms not used;
— addition of the terms currently used in the portfolio of TC 96 standards;
— addition of the terms referenced in ISO/TC 96/SC 5 standards;
— addition of figures illustrating the definitions.
A list of all parts in the ISO 13571 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO/FDIS 13571-1:2026(en)
Introduction
The ISO 13571 series is a set of standards developed for estimation of time to compromised tenability
and escape capability for occupants when exposed to a fire environment. Different threats are evaluated
separately for exposure to acute toxicants, heat and smoke. The time to compromised tenability is the
shortest of the determined times to compromised tenability for each individual threat.
The ISO 13571 series is composed of 5 parts:
— ISO 13571-1 describes a model for smoke toxicity assessment of time to compromised tenability and
escape capability of 50 % of an exposed occupant population, and threshold tenability limits for the
sensitive members of an exposed population including children, elderly and health compromised.
— ISO/TR 13571-2 describes examples of application of ISO 13571 series.
— ISO 13571-3 describes a model for smoke toxicity assessment of time to compromised tenability based
on lethality endpoints for an exposed occupant population
— ISO/TR 13571-4 gives examples of comparisons between ISO 13571-1 and ISO 13571-3 in different fire
scenarios.
— ISO 13571-5 describes models for heat exposure, smoke exposure, and a simplified model for toxicity
assessment based on mass loss of combustible.
Chronic or environmental exposures and their potential health effects are not covered in the ISO 13571
series.
This document is intended for estimation of time to compromised tenability and escape capability for
occupants when exposed to a fire environment for applications where the time-concentration curves for
fire scenarios are available (for example from fire dynamics modelling or large-scale fire experiments). The
standard may be used for hazard calculations and modelling as applied to Available Safe Escape time (ASET)
and Required Safe Escape time (RSET) calculations and models.
The document provides expressions for calculation of time and exposure doses to tenability endpoints
for 50 % of an exposed occupant population and for estimation of threshold limits designed to protect
essentially all occupants. This includes mixed general populations with children, the elderly and adults with
health conditions in all occupancies including buildings and transport systems.
The calculation expressions in this document have been derived as far as possible from human behavioural
and physiological tenability data obtained from experimental and accidental exposures, especially data from
exposures during fire incidents, data from experiments on non-human primates, and experiments involving
rodents (rats and mice). The expressions and endpoints derived from these data have been developed to
provide assessment methods most relevant to the tenability and particularly the escape capability of human
occupants of building or transport fire scenarios.
The guidance in this document is based on the best available scientific judgment in using a state-of-the-art
but less-than-complete knowledge base of the consequences of human exposure to fire effluents. For ethical
reasons, much of the methodology described has not been and cannot be validated experimentally with
humans. However, for carbon monoxide, the major contributor to prevention of escape and the most frequent
cause of fire fatalities, the database is actually quite extensive and well-validated with human experience.
Estimation of occupants’ tenability when exposed to a fire environment ultimately involves their ability
to perform behavioural, cognitive and motor-skill functions at an acceptable level. Generally, acceptable
performance may include any of a number of desirable outcomes, including escape to a place of refuge, or
if escape is not a viable option, continued functioning in place as necessary. The latter situation includes
occupants who are not mobile or whose egress is prohibited for a variety of reasons, e.g., from an aircraft
in flight. The time from initiation of a fire to the point when tenability is compromised such that acceptable
performance is not possible is a central component of fire safety design.
The time required to reach compromised tenability can depend upon each occupant’s location and
movement, along with numerous other characteristics specific to the occupant. As a result, each occupant

v
ISO/FDIS 13571-1:2026(en)
may have a different time to compromised tenability. Guidance for consideration of these factors is provided
in other sources, e.g. ISO/TR 16738.
Each occupant may also have a different time to compromised tenability, depending on their particular
exposure to heat and fire effluent combustion products and their individual susceptibility to such exposures
(see A.2.3). The purpose of the methodology described in this document is to provide a framework for use in
estimating the time at which compromised tenability may occur.
The methodology described cannot be used alone to evaluate the overall fire safety performance of specific
materials or products and cannot, therefore, constitute criteria for a test method. Rather, the formulae are
to be used as input to a fire hazard or risk analysis. In such an analysis, the estimated time to compromised
tenability also depends on the nature both of the fire (e.g. heat release rate, quantity and types of
combustibles, fuel chemistry) and of the enclosure (e.g. dimensions, ventilation). These determine the toxic-
gas concentrations, the gas and wall temperatures and the density of smoke throughout the enclosure as a
function of time. Furthermore, estimation of exposure is determined, in part, by assumptions regarding the
position of the occupants' heads relative to the hot smoke layer that forms near ceilings and descends as the
fire grows.
Although the concept of compromised tenability is consistent with the definition of incapacitation
(see ISO 13943), the latter term is not used in this document due to its potentially broad interpretation to
include many effects, including collapse and unconsciousness, that are not addressed. This document focuses
specifically on compromised tenability as influenced by both physiological and behavioural responses
resulting from exposure to a fire’s life-threatening components.
As with all predictive methodology, uncertainty exists in the application of this document. An estimation of
the uncertainty for each procedure is provided, with the user being encouraged to determine the significance
of these uncertainties in the estimation of the outcome of a given fire scenario.

vi
FINAL DRAFT International Standard ISO/FDIS 13571-1:2026(en)
Life-threatening components of fire —
Part 1:
Guidelines for method based on tenability endpoints for the
estimation of time to compromised escape capability from
exposure to smoke toxicants
1 Scope
This document is one of many tools available for use in fire safety engineering. It is intended to be used in
conjunction with fire test data such as those detailed in ISO 13571-5 and models for analysis of the initiation
and development of fire, fire spread, smoke formation and movement, chemical species generation, transport
and decay, and people movement, as well as fire detection and suppression. This document is to be used only
within this context.
This document is intended to address the consequences of human exposure to the life-threatening
components of fire. The time-dependent concentrations of fire effluents and the thermal environment
of a fire are determined by the rate of fire growth, the yields of the various fire gases produced from the
involved fuels, the decay characteristics of those fire gases and the ventilation pattern (see A.1). Once these
are determined, the methodology presented in this document can be used for the estimation of the time at
which individuals can be expected to experience compromised tenability from exposure to smoke toxicants.
This guidance can also be applied to estimation of the time limit for rescuing people who are immobile due
to injury, medical condition, etc.
This document establishes formulae to evaluate the life-threatening components of fire hazard analysis in
terms of the status of exposed human subjects at discrete time intervals. It makes possible the estimation
of the time at which occupants can experience compromised tenability (see A.2). It enables estimation of a
compromised tenability endpoint for each of the fire effluent components, with the most important endpoint
being the earliest to occur.
The life-threatening components addressed in the 13571 series include fire-effluent toxicity, heat, and visual
obscuration due to smoke. In cases where the effluent composition is available, the toxic gas model is used
for assessment of fire-effluent toxicity. Effects of heat and smoke obscuration are addressed in ISO 13571-5.
For those cases where the effluent composition is unknown, an additional mass-loss model using generic
toxic potency values is also provided in ISO 13571-5.
2 Normative references
No normative references are cited in this document.
3  Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/

ISO/FDIS 13571-1:2026(en)
3.1
tenability
ability of humans to perform cognitive and motor skill functions at an acceptable level when exposed to a
fire environment
Note 1 to entry: If exposed individuals are able to perform cognitive and motor-skill functions at an acceptable level,
the exposure is said to be tenable. If not, the exposure is said to result in compromised tenability.
3.2
adjustment factor
factor for the incorporation of quantitative data on interspecies differences or on human variability in either
toxico-kinetics (variability in inhaled dose and metabolism) or toxico-dynamics (mode of action causing the
critical effect) into the risk assessment procedure
3.3
V
E
volume of air breathed each minute
Note 1 to entry: In air this depends on the activity level of the subject (V ). In the presence of inhaled CO V is
Eair 2 E
increased by a hyperventilatory stimulus factor (VCO ) depending on the inhaled CO2 concentration.
4 General principles
4.1 Time to compromised tenability
The time to compromised tenability for individuals is the shortest of four distinct times estimated from
consideration of asphyxiant fire gases, irritant fire gases, heat, and visual obscuration due to smoke.
The context and mechanisms of the fire-effluent toxicity component of life threat are discussed in Annex A.
Effects of the asphyxiant toxicants, carbon monoxide and hydrogen cyanide (see A.4), as well as those of eye
and upper-respiratory tract sensory irritants (see A.5), are described in detail.
Responses to these exposures involve functions of the human sensory, cardiovascular, respiratory and
neurological systems that are dependent upon inherent physical characteristics (e.g., age, body weight, pre-
existing cardiopulmonary conditions), along with environmental considerations and physical activity at the
time of exposure. As a result, individual human responses can be highly variable and, therefore, not readily
reduced to usable engineering formulae for prediction of compromised tenability without considerable
simplification, application of numerous assumptions, and exclusion of unusual circumstances.
With regard to the susceptibilities of individuals to the insults of fire exposure, a primary assumption of this
document is that all occupant responses are treated as a log-normal or probit statistical distribution with
respect to a median time, with half of the population experiencing a tenable exposure and half experiencing
compromised tenability (see 5.3). Threshold levels estimated to affect tenability for approximately 1 % of an
exposed population are derived from Point of Departure (POD) animal toxicity data and reported findings
[2][6][9][25][26][27][28][29][30][31]
from human exposure data .
4.2 Toxic-gas model
4.2.1 The toxic-gas models described in this document address effects that are considered detrimental to
human tenability. Because they are physiologically unrelated and mechanistically independent, asphyxiant
toxicants and irritant toxicants are treated separately (see A.4 and A.5).
With irritant toxicants, only those that cause eye and upper-respiratory tract sensory irritation are
considered in this document as having effects on tenability (see A.5.2). Serious effects of pulmonary
irritation resulting in lung injury are manifested from a few hours up to several days after exposure and are
not normally expected to have a direct impact on tenability during exposure at a fire scene (see A.5.3).
Providing asphyxiant and irritancy thresholds are not exceeded during exposure then significant post-
exposure lung injury from irritants and significant post-exposure neurological or cardiovascular injury

ISO/FDIS 13571-1:2026(en)
from asphyxiants are considered unlikely to occur. Additional guidance on threshold exposure doses that
may result in post-exposure injury is given (see C.3).
4.2.2 The basic principle for estimating the asphyxiant component of toxic hazard analysis involves the
exposure dose of each toxicant, i.e. the integrated area under each concentration-time curve. Fractional
effective doses (FEDs) are determined for each asphyxiant at each discrete increment of time, whereby the
accumulated exposure dose is expressed as a fraction of the exposure dose required to cause compromised
tenability. The time at which their accumulated sum exceeds a specified threshold value represents the time
to compromised tenability relative to chosen safety criteria.
4.2.3 The basic principle for estimating the eye and upper respiratory tract sensory irritant component of
toxic hazard analysis involves the concentration of each irritant. Fractional effective concentrations (FECs)
are determined for each irritant at each discrete increment of time. The time at which their sum exceeds
a specified threshold value represents the time to compromised tenability relative to the chosen safety
criteria.
4.2.4 Relevant assumptions and exclusions are as follows:
a) Asphyxiant toxicants, irritants, heat and visual obscuration are each considered as acting independently.
Some degrees of interaction between these insults are known to occur (see A.7) but are considered
secondary.
b) Exposed occupants are considered to be at relatively normal ambient environmental conditions and at
altitudes below which reduced ambient oxygen could be a factor, and performing at a moderate level of
physical activity. Deviation from these conditions can affect susceptibility.
c) Any interactions between aerosols, particulates and gaseous fire-effluent components are not
considered. The physical form of toxic effluents is known to have some influencing effects, but in
this document, they are considered secondary to the direct effects of vapour-phase and particulate
effluents.
d) Adverse health effects subsequent to exposure to fire atmospheres are not considered in relation to
tenability during exposure, although it is recognized that post-exposure effects occur where tenability
limits during exposure are exceeded. Pre-existing health conditions may be exacerbated and potentially
life-threatening sequelae may develop from exposure both to asphyxiants and to pulmonary irritants
(see A.4 and A.5.3). Lower respiratory tract effects are typically manifested at time scales much longer
than those of the actual fire and, although noted, are not considered in the requirements of this document
with respect to tenability during exposure at a fire scene. Additional guidance has been provided on
post exposure adverse health effects from inhaled doses of asphyxiants with risk of post-exposure
cardiovascular and neurological effects and to inhaled doses of lung irritants associated with a risk of
lung injury.
e) The early impacts of visual obscuration due to smoke (e.g., recognition that a fire exists, seeing exit
paths clearly) are behavioural in nature and are not included. However, smoke obscuration of such
severity that occupants become disoriented or show a high probability of turning back rather than enter
or continue through smoke places a limitation on the time during which escape may be attempted and is
considered in ISO 13571-5.
The formulae in the methodology described in this document enable estimation of the status of exposed
occupants at discrete time intervals throughout the progress of a fire scenario, up to the time at which
such exposure can result in compromised tenability. If the estimated time is deemed excessively limiting, a
variety of protection strategies then require consideration by the fire safety professional.
5  Significance and use
5.1 The objective of this document is to provide simplified, but robust, guidance for engineers in
estimating occupants’ time to compromised tenability as part of an assessment of a structure’s fire safety
capabilities when subjected to fire conditions specified in terms of time-concertation profiles for toxic gases

ISO/FDIS 13571-1:2026(en)
and smoke particulates. Such estimation of occupants’ tenability ultimately involves their ability to perform
cognitive and motor-skill functions at an acceptable level. Generally, acceptable performance may include
any of a number of desirable outcomes, including escape to a place of refuge, or if escape is not a viable
option, continued functioning in place as necessary.
NOTE If escape to a place of refuge or final exit is the outcome to be considered, the time to compromised
tenability can reasonably be equated to the available safe escape time (ASET).
The method has been developed specifically to address issues relating to exposure of occupants to
developing fires.
The main purpose of the expressions is to enable calculation of time to compromised tenability during
exposure to fire scenarios. The particular endpoint addressed is the time at which a significant proportion of
an exposed population becomes incapacitated to the extent that they are unable to make a safe escape. The
expressions are also protective against significant post exposure injury and death providing the endpoints
for compromised tenability are not exceeded.
During fire incidents enclosure occupants (occupants of buildings and transport systems) are typically
[1][2]
exposed to one of three types of exposure scenario :
a) Occupants in the same enclosure as a fire exposed to smoke particulates, irritants and asphyxiant gases
(and or heat) starting from low concentrations then increasing rapidly over a period of a few minutes to
incapacitating concentrations.
b) Occupants leaving a relatively clear enclosure to enter a smoke-filled escape route containing
concentrations varying from low levels to those capable of causing incapacitation within a short period
(a few minutes, a few seconds or even after a single breath). Occupants are in such cases exposed to a
near square wave effluent concentration profile.
c) Occupants trapped in an enclosure (or remaining in a designated refuge) which is initially clear but
gradually fills with smoke and toxic gases by infiltration over an extended period of up to (but rarely
exceeding) an hour.
In these scenarios occupants are exposed to and affected by a sequence of hazards, typically beginning with
the immediate effects of exposure to irritant smoke, then followed by effects of exposure to asphyxiant gases
and/or heat. Key aspects of these exposure scenarios in relation to the development of tenability expressions
are that they generally involve short exposure periods of a few minutes, and that conditions can change
very rapidly, so that the expressions need to be able to address effects of high exposure concentrations
and short tenability times. An advantage when estimating tenability times in such situations is that due
to the exponential increase in gas concentrations at a certain time during most fires, calculated times to
incapacitation may show only small changes when model parameters are varied.
5.2 Operating under a considerable number of simplifying assumptions, this document deals with
responses of the overall population as represented by a statistical distribution. It is not intended to provide
guidance for a detailed assessment of the insult to specific individuals that might be exposed to a given
fire atmosphere ― such as is commonly required in forensic investigations. Furthermore, the focus of this
document is on assessment of an occupant’s tenability, while forensic investigations generally focus on the
consequences of compromised tenability. These are quite different objectives. Forensic investigations can
also be extremely complicated, involving detailed characterization of specific exposed occupants, along
with interpretive expertise far beyond that which can reasonably be taught in a guidance standard.
[3] [4]
5.3 The concepts of Fractional Effective Dose (FED) and Fractional effective concentration (FEC) are
fundamental to the methodology of this document. Both concepts relate to the manifestation of physiological
and behavioural effects exhibited by exposed subjects.
5.4 The variability of human responses to toxicological insults is best represented by a statistical
distribution that takes into account varying susceptibility to the insult. Some people are more susceptible
than the average, while others may be less susceptible (see A.6). In this document, FED and/or FEC values of
1,0 correspond, by definition, to the median value of a log-normal distribution of responses, with one-half
of the population being less susceptible and one-half being more susceptible. This means that, statistically,

ISO/FDIS 13571-1:2026(en)
50 % of the population would be expected to experience tenable conditions (able to perform cognitive and
motor-skill functions at an acceptable level), with 50 % then expected to experience compromised tenability
(unable to perform cognitive and motor-skill functions at an acceptable level).
Recognizing that threshold criteria of 1,0 FED and/or FEC statistically serve to protect only one-half of the
population, users of this document may use reduced FED and/or FEC threshold criteria in order to satisfy
more conservative fire safety objectives. This document provides the flexibility to choose FED and/or FEC
threshold criteria as may be appropriate. While a threshold level of 0,3 FED or FEC is recommended, further
guidance is provided in A.6.2. Whatever the rationale used when choosing FED and FEC threshold criteria,
it is necessary to use a single value for both FED and FEC thresholds in a given estimation of the time to
compromised tenability.
5.5 The exposure of occupants to tenable conditions should not be construed as equating to no post-
exposure harm. Exposure to fire-gas toxicants that do not cause compromised tenability can still result in a
variety of effects that may prolong escape and thus increase exposure intensity to fire effluents and lead to
post-exposure health problems; (see Annex A.4, A.5 and C). Although the primary purpose of this standard
is estimation of compromised tenability during exposure at a fire incident, guidance is given on the risk
of significant post-exposure health effects. Providing the compromised tenability limits in this standard
are not exceeded during the period of exposure, post-exposure heath effect are likely to be minor. However
quantification of these effects, especially under conditions where effective post-traumatic measures are
common practice through medical intervention, is beyond the scope of this document.
5.6 The time-dependent concentrations of fire effluents to which occupants, who are often on the move, are
exposed can only be determined using computational fire models and/or a series of real-scale experiments.
It is not valid to insert the concentrations of fire effluents obtained from bench-scale test methods in the
formulae presented in this document.
5.7 The methodology described for toxic gas exposures can be validated only to a limited extent from
human data. It is necessary to recognize that uncertainty exists in the precision of the experimental data
upon which the formulas are based, the representation of those data by algebraic functions, the accuracy
of assumptions regarding non-interaction of fire gases with each other and with heat, the susceptibility
of people relative to that of test animals, etc. These uncertainties are estimated in the following sections.
As with any engineering calculation, uncertainties should be included in the estimation of the overall
uncertainty of a fire hazard or risk analysis. This enables the user to determine whether the difference
between the outcomes of two such analyses are truly different or are irresolvable.
NOTE The resulting uncertainty in the estimated time to compromised tenability depends in a non-linear manner
upon the uncertainty in the FED and FEC calculations (for instance, these uncertainties can have reduced impact on
the estimated outcome of rapidly developing fires).
5.8 There is very little reliable information on asphyxiant gas exposures of less than 1 min or longer than
1 h. Thus, the accuracy of the formulas in this document and the resulting estimations for either very short
or very long fire scenarios are uncertain. Due to these uncertainties, estimations of time available to escape
of less than 1 min are to be reported as <1 min, with caution exercised when making estimations that involve
occupant exposures longer than 1 h.
NOTE Due to the uncertainties involved, differences between comparative estimations of time to compromised
tenability of less than 1 min are typically insignificant.
6 Toxic gas models
6.1 Asphyxiant-gas fractional effective dose model
6.1.1 Fractional effective doses (FEDs) are determined for each asphyxiant at each discrete increment of
time. The time at which their accumulated sum exceeds a specified threshold value represents the time to

ISO/FDIS 13571-1:2026(en)
compromised tenability relative to chosen safety criteria (see 5.3). The principle of the model in its simplest
form for calculating the fractional effective dose, X , is shown in Formula (1):
FED
t
n
C
i
X  t (1)

FED
Ct

i1 t i
where
−1
C is the average concentration, expressed in µl·l , of an asphyxiant gas “i ” over the chosen time
i
increment;
Δt is the chosen time increment, expressed in minutes;
(C·t) is the exposure dose causing occupants’ compromised tenability, expressed in minutes
i
−1
multiplied by µl·l ;
t Is the exposure period expressed in minutes.
In estimating incremental effects, ΔX , on the fractional effective doses (FEDs), X , for each discrete
FED FED
increment of time, Δt, C = C, and Formula (1) reduces to Formula (2):
i
t
n
X t (2)

FED
t
i
i1 t
where the time, t , to compromised tenability due to component “i” is a function of its concentration, with the
i
units of time cancelling to give a dimensionless fraction for X
FED.
For asphyxiant gases the dose inhaled depends on three main variables:
— Exposure concentration C
— Volume of air breathed per minute (V ) in relation to body size
E
— Exposure time Δt
The main case used for the asphyxiant expressions is for an adult human engaged in moderate physical work
such as rapid walking horizontally of down stairs during an evacuation, with a V under ambient conditions
E
(breathing air) of 20 litres/minute. In Annex B, general case versions of the asphyxiant expressions are
presented in which V is included as a variable to enable uptake calculations for resting and heavy work
E
conditions (such as running). In all mammals V for a given activity level varies as a function of body surface
E
[2][5]
area to mass ratio so that the rate of dose uptake is greater for smaller humans or animals . To the extent
that the following asphyxiant expressions are derived from animal studies (such as primates or rodents) the
effects of body size on uptake is taken into account. Some inhaled fire gases, especially CO , further increase
V by stimulating breathing. This effect is also included in the uptake expressions.
E
The main asphyxiant gases occurring in fire effluents are CO and HCN, which cause hypoxic asphyxia by
impairing the carriage of oxygen in the blood and its delivery to and use in body tissues, especially brain and
[ ][ ]
heart, resulting in incapacitation due to collapse and loss of consciousness 1 2 . The effects of CO and HCN
are considered to be additive on a fractional dose basis. Decreased oxygen concentration in fire effluents is
also a potential additive contributor to hypoxia but is considered unlikely to make a significant contribution
at inhaled concentrations above 13 % oxygen. Inhaled nitrogen oxides can also contribute to hypoxia due to
methaemoglobin formation, decreasing the carriage of blood oxygen, but concentrations occurring in mixed
fuel fires are too low for NOx to make a significant contribution to hypoxia. Methaemoglobin also detoxifies
[6]
inhaled cyanide somewhat due to the formation of cyanomethaemoglobin . The main contribution of
carbon dioxide to developing asphyxia is that it stimulates respiration and thereby increases the rate of
[1][2]
uptake of CO and HCN . High inhaled concentrations of CO above 5 % also cause incapacitation due to
dose-dependent respiratory distress and narcosis. This narcosis does not result from hypoxia so is treated
as a separate potential cause of incapacitation. During compartment fires, incapacitation due to effects of
asphyxiant gases is generally predicted before the narcotic effects of CO are likely to be significant. On
this basis the main asphyxiant model considers the effects of CO and HCN in conjunction with effects on
V depending on physical activity level of exposed subjects and inhaled CO concentrations. An expression
E 2
for the calculation of asphyxiant FED from oxygen depletion (Formula 7) is also presented for use as an

ISO/FDIS 13571-1:2026(en)
additive term with the FEDs for CO and HCN where necessary, and an expression for the calculation to FED
for narcosis from CO for use as a separate term with situations of exposure to high concentrations of CO in
2 2
the absence of significant concentrations of asphyxiant gases.
6.1.2 Allowance for activity and ventilation levels for asphyxiant uptake models
For any given exposure concentration the uptake rates of asphyxiant gases are directly proportional to
an occupant’s activity level expressed in terms of volume of air breathed each minute (V ). The volume
E
of air breathed each minute under normal circumstances (breathing air) (V ) depends on the level of
Eair
activity driven mainly by endogenous carbon dioxide production. This varies between approximately 6 l/
min for sleeping adults to maximum levels of up to approximately 100 l/min for maximal exercise in air (or
a maximum level of approximately 70 l/minute for the general adult population). Inhalation of increased
concentrations of carbon dioxide during exposure to fire atmospheres further stimulates breathing beyond
the volumes for the specific activity level (up the maximum limit) so needs to be allowed for in asphyxiant
uptake calculations. The first consideration in asphyxiant uptake calculations is the V relating to the activity
E
level. The main case considered for this standard is for occupants engaged in moderate activity involving
rapid horizontal walking or walking down stairs in order to escape from an occupancy at a baseline level
for this activity (in the absence of elevated inhaled CO ) V of 20 l/min. The asphyxiant expressions in the
2 Eair
following sections are designed for this specified case. Inhaled CO causes hyperventilation so an adjustment
factor for the increase in V resulting from inhalation of elevated CO is presented in paragraph 6.1.6 For
E 2
application to a full range of scenarios including occupants at rest (V ~8,5 l/min), in moderate activity
Eaur
(V ~20 l/min) or engaged in heavy work such as running on the level or climbing up stairs (V ~40 l/
Eair Eair
min) a general case set of expressions is presented in informative Annex B, for which V is included as a
E
variable (subject to further increases up to a maximum of 70 l/min depending on inhaled CO concentration).
This may be useful for the evaluation of cumulative uptake and tenability in scenarios such as for occupants
exposed for a period while sheltering at rest, then engaged in moderate of heavy activity while walking
or running to escape. Both the main and general case models include expressions to calculate the effect of
further increases in V from different activity levels in air due to the hyperventilatory effect of increased
E
inhaled carbon dioxide concentrations.
6.1.3 Adjustment factors for asphyxiant models
The asphyxiant models provide an estimate of the exposure dose predicted to cause compromised tenability
n
for 50 % of an exposed mixed human population (IC t ), but also includes an estimate of the Point of
Departure (POD) (exposure threshold with 1 % incidence) for more sensitive subjects including children,
the elderly and those with health impairments.
Estimates for these parameters had been derived using human experimental or incident data to the extent
available, combined with measured incapacitation data from animal experiments, mainly using non-human
primates and also rats. Where human data have been obtained from subjects with a limited range of
characteristics (for example adults rather than children), or under differing activity conditions (for example
at rest rather than walking) then it is necessary to apply adjustment factors to allow for these variations.
Where data are obtained using animal models it is necessary to consider inter-species differences in
toxic sensitivity, representing differences between the inhaled dose resulting in incapacitation between
humans and animals, and to apply compensatory adjustment factors (AF) where appropriate. Where I%
POD threshold levels are estimated from animal data it is also necessary to consider impl
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ISO/TC 92/SC 3
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Date: 2025-11-21
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Secretariat: AFNOR
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Life-threatening components of fire —
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Part 1:
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Guidelines for method based on tenability endpoints for the
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estimation of time to compromised tenability and escape capability
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from exposure to smoke toxicants — Method based on tenability
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St l D fi iti
ISO/FDIS 13571-1:2026(en)
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All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
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or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
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ii
ISO/DISFDIS 13571-1:20252026(en)
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Contents
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Foreword . iv
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Introduction . viii
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1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 General principles . 2
4.1 Time to compromised tenability . 2
4.2 Toxic-gas model . 3
5 Significance and use . 4
6 Toxic gas models . 6
6.1 Asphyxiant-gas fractional effective dose model . 6
6.2 Irritancy model . 14
7 Post-exposure injury and lethality . 16
8 Report . 16
Annex A (informative) Context and mechanism of toxic potency . 17
Annex B (informative) Asphyxiant model expanded for different activity levels incorporating V
E
as a variable . 47
Annex C (informative) Post-exposure injury and lethality . 51
Bibliography . 54

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iii
ISO/FDIS 13571-1:2026(en)
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Foreword
Foreword . v
Introduction . vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General principles . 2
4.1 Time to compromised tenability . 2
4.2 Toxic-gas model . 2
5 Significance and use . 4
6 Toxic gas models . 6
6.1 Asphyxiant-gas fractional effective dose model . 6
6.2 Irritancy model . 13
7 Post-exposure injury and lethality . 14
8 Report . 15
Annex A (informative) Context and mechanism of toxic potency . 16
A.1 Overview
A.2 Elements of fire hazard analysis. 16
A.3 Compromised tenability . 17
A.3.1 General . 17
A.3.2 Behavioural effects . 17
A.3.3 Physiological effects . 18
A.4 Asphyxiant toxicants . 18
A.4.1 General . 17
A.4.2 Consideration of effects of activity levels on breathing and interactions between
asphyxiant gases . 20
A.4.3 Carbon monoxide . 21
A.4.4 Hydrogen cyanide . 23
A.4.5 Effects of activity level and inhaled CO on V and time to compromised tenability due to
2 E
CO narcosis . 26
A.4.6 Adjustment factors applied to derivation of human thresholds from primate and human
and data . 28
A.5 Irritant toxicants . 30
A.5.1 General . 30
A.5.2 Eye and upper-respiratory tract irritants . 30
A.5.3 Pulmonary irritation . 36
A.6 Susceptibility of subpopulations . 36
A.6.1 General . 36
A.6.2 Accommodating susceptible subpopulations . 36
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iv
ISO/DISFDIS 13571-1:20252026(en)
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A.7 Interactions of toxicological insults . 37
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Annex B (informative) Asphyxiant model expanded for different activity levels incorporating VE
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as a variable . 38
B.1 General . 38
B.2 General case asphyxiant model for carbon monoxide . 38
B.3 General case asphyxiant model for HCN . 39
B.4 General case model for combined effect of activity level and inhaled carbon dioxide on
ventilation and uptake of asphyxiants . 39
B.5 General case model for Fractional Effective dose expression for asphyxia from CO and
HCN . 40
Annex C (informative) Post-exposure injury and lethality . 41
C.1 General . 41
C.2 Post-exposure injury from asphyxiants . 41
C.3 Post-exposure injury from irritant gases and vapours . 41
C.4 Post-exposure injury from irritant smoke particulates . 42
Bibliography . 44
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v
ISO/FDIS 13571-1:2026(en)
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for identifying any or all such
patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
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people and environment.
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This first edition of ISO 13571-1 cancels and replaces the second edition of ISO 13571:2012, which has been
technically revised.
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The main changes are as follows:
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— additional expressions for enabling calculation of asphyxiant tenability over a range of activity levels Formatted: Default Paragraph Font
from at rest to heavy work; For this edition the main expressions for calculation of tenability endpoints
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for active walking adults have been retained, as in 13571-:2012, but additional expressions have been
provided for which the volume of air breathed each minute (VE) has been separated out as user defined
term. This provides more versatility to enable the user to calculate tenability times for occupants over a
range of activity levels including at rest, moderate activity (such as rapid walking to evacuate) or heavy
work (such as running along a tunnel). This also incorporates the stimulatory effect on breathing of
inhaled high CO concentrations, enabling V to be calculated throughout the physiological range (~8 to
2 E
70 l/min) and the resulting effects on the uptake and time to compromised tenability from asphyxiants.
Expressions for the asphyxiant effects and time to compromised tenability for decreased oxygen
concentrations and an expression for o the narcotic effects of inhaled CO at high concentrations (which
were referenced in the second edition) have now been included in this edition.
— guidance on estimation of asphyxiant and irritant tenability threshold (point of departure) levels have
been revised and further developed. For this edition, although the main endpoints for asphyxiant and
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vi
ISO/DISFDIS 13571-1:20252026(en)
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irritant tenability are the same as for the previous edition, the guidance on estimation of threshold, Point
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of Departure (POD), levels have been revised and further developed. For asphyxiants tenability is
compromised by confusion and loss of consciousness after inhalation of a sufficient exposure dose. For
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smoke irritants, tenability depends on exposure concentration and is compromised by eye and respiratory
tract pain, visual and breathing difficulties sufficient to result in a high probability of escaping occupants
turning back or being unable to continue through irritant smoke.
— informative guidance on estimation of post-exposure health effects has been included; As with the
previous edition (ISO13571 2012) the main intended application of this standard is the calculation of
times to compromised tenability during exposure at a fire incident, for application to time up to which
occupants are able to escape or shelter without compromised tenability. For this reason, the main
application does not include consideration of potential post-exposure adverse health effects in fire
survivors. However, since escape cannot be considered safe if significant post exposure injury is likely,
some guidance on the risk of post exposure health effects has been included in informative Annex C of this
edition.  In general, it is considered that such effects should be minimal providing the limits for
compromised tenability during the incident are not exceeded. In order to enable consideration of such
potential post-exposure hazards in survivors when appropriate (for example when threshold limits may
be exceeded), guidance has been included in informative Annex C for estimation of threshold doses for
asphyxiant exposures above which there may be significant risk of post-exposure neurological or
cardiovascular health effects and expressions for calculation of threshold exposure doses of irritant gases
and particulates above which there may be significant risk of inhalation injury from lung inflammation.
.— further information has been included to extend and clarify the basis of the derivation of the
calculation expressions and endpoints, threshold levels and application to different occupant populations,
including children, the elderly and those with health conditions. The guidance in this standard draws on
that derived independently for the AEGL (National Advisory Committee for Acute Exposure Guideline Levels
[6][7][25][26][27][28][29][30][31]
for Hazardous Substances), and comparisons are presented in ISO/TR 13571-4.

— deletion of the terms not used;
— addition of the terms currently used in the portfolio of TC 96 standards;
— addition of the terms referenced in ISO/TC 96/SC 5 standards;
— addition of figures illustrating the definitions.
— A list of all parts in the ISO 13571 series can be found on the ISO website.
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Any feedback or questions on this document should be directed to the user’s national standards body. A
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complete listing of these bodies can be found at www.iso.org/members.html.
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vii
ISO/FDIS 13571-1:2026(en)
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Introduction
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The ISO 13571 series is a set of standards developed for estimation of time to compromised tenability and
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escape capability for occupants when exposed to a fire environment. Different threats are evaluated separately
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for exposure to acute toxicants, heat and smoke. The time to compromised tenability is the shortest of the
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determined times to compromised tenability for each individual threat.
The ISO 13571 series is composed of 5 parts:
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— — ISO 13571-1 describes a model for smoke toxicity assessment of time to compromised tenability and
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escape capability of 50 % of an exposed occupant population, and threshold tenability limits for the
sensitive members of an exposed population including children, elderly and health compromised.
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— — ISO/TR 13571-2 (Technical report) describes examples of application of ISO 13571 series
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— — ISO 13571-3 describes a model for smoke toxicity assessment of time to compromised tenability based
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on lethality endpoints for an exposed occupant population
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
— — ISO/TR 13571-4 (Technical report) gives examples of comparisons between parts ISO 13571-1 and
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ISO 13571-3 in different fire scenarios.
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— — ISO 13571-5 describes models for heat exposure, smoke exposure, and a simplified model for toxicity
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assessment based on mass loss of combustible.
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Chronic or environmental exposures and their potential health effects are not covered in the ISO 13571 series.
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This document is intended for estimation of time to compromised tenability and escape capability for
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occupants when exposed to a fire environment for applications where the time-concentration curves for fire
scenarios are available (for example from fire dynamics modelling or large-scale fire experiments). The
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standard may be used for hazard calculations and modelling as applied to Available Safe Escape time (ASET)
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and Required Safe Escape time (RSET) calculations and models.
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The document provides expressions for calculation of time and exposure doses to tenability endpoints for
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50 % of an exposed occupant population and for estimation of threshold limits designed to protect essentially
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all occupants. This includes mixed general populations with children, the elderly and adults with health
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The calculation expressions in this document have been derived as far as possible from human behavioural
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and physiological tenability data obtained from experimental and accidental exposures, especially data from
exposures during fire incidents, data from experiments on non-human primates, and experiments involving
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rodents (rats and mice). The expressions and endpoints derived from these data have been developed to
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provide assessment methods most relevant to the tenability and particularly the escape capability of human
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occupants of building or transport fire scenarios.
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The guidance in this document (ISO 13571-1) is based on the best available scientific judgment in using a
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state-of-the-art but less-than-complete knowledge base of the consequences of human exposure to fire
effluents. For ethical reasons, much of the methodology described has not been and cannot be validated Formatted: Adjust space between Latin and Asian text,
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experimentally with humans. However, for carbon monoxide, the major contributor to prevention of escape
and the most frequent cause of fire fatalities, the database is actually quite extensive and well-validated with
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human experience.
Estimation of occupants’ tenability when exposed to a fire environment ultimately involves their ability to
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perform behavioural, cognitive and motor-skill functions at an acceptable level. Generally, acceptable
performance may include any of a number of desirable outcomes, including escape to a place of refuge, or if
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viii
ISO/DISFDIS 13571-1:20252026(en)
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escape is not a viable option, continued functioning in place as necessary. The latter situation includes
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occupants who are not mobile or whose egress is prohibited for a variety of reasons, e.g., from an aircraft in
flight. The time from initiation of a fire to the point when tenability is compromised such that acceptable
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performance is not possible is a central component of fire safety design.
The time required to reach compromised tenability can depend upon each occupant’s location and movement,
along with numerous other characteristics specific to the occupant. As a result, each occupant may have a
different time to compromised tenability. Guidance for consideration of these factors is provided in other
sources, e.g. ISO/TR 16738.
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Each occupant may also have a different time to compromised tenability, depending on their particular
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exposure to heat and fire effluent combustion products and their individual susceptibility to such exposures
(see A.2.3). The purpose of the methodology described in this document (ISO 13571-1) is to provide a
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framework for use in estimating the time at which compromised tenability may occur.
The methodology described cannot be used alone to evaluate the overall fire safety performance of specific
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materials or products and cannot, therefore, constitute criteria for a test method. Rather, the formulae are to
be used as input to a fire hazard or risk analysis. In such an analysis, the estimated time to compromised
tenability also depends on the nature both of the fire (e.g. heat release rate, quantity and types of combustibles,
fuel chemistry) and of the enclosure (e.g. dimensions, ventilation). These determine the toxic-gas
concentrations, the gas and wall temperatures and the density of smoke throughout the enclosure as a
function of time. Furthermore, estimation of exposure is determined, in part, by assumptions regarding the
position of the occupants' heads relative to the hot smoke layer that forms near ceilings and descends as the
fire grows.
Although the concept of compromised tenability is consistent with the definition of incapacitation
(see ISO 13943), the latter term is not used in this document due to its potentially broad interpretation to
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include many effects, including collapse and unconsciousness, that are not addressed. This document focuses
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specifically on compromised tenability as influenced by both physiological and behavioural responses
resulting from exposure to a fire’s life-threatening components.
As with all predictive methodology, uncertainty exists in the application of this document. An estimation of
the uncertainty for each procedure is provided, with the user being encouraged to determine the significance
of these uncertainties in the estimation of the outcome of a given fire scenario.
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ix
DRAFT International Standard ISO/DIS 13571-1:2025(en)

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Life-threatening components of fire — Part 1: Guidelines for the
estimation of time to compromised tenability and escape capability
from exposure to smoke toxicants — Method based on tenability
endpoints —
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Part 1:
distance from edge: 1.27 cm, Footer distance from
Guidelines for method based on tenability endpoints for the
edge: 0.5 cm
estimation of time to compromised escape capability from exposure
to smoke toxicants
1 Scope
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This document is one of many tools available for use in fire safety engineering. It is intended to be used in
conjunction with fire test data such as those detailed in ISO 13571-5 and models for analysis of the initiation
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and development of fire, fire spread, smoke formation and movement, chemical species generation, transport
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and decay, and people movement, as well as fire detection and suppression. This document is to be used only
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within this context.
This document is intended to address the consequences of human exposure to the life-threatening
components of fire. The time-dependent concentrations of fire effluents and the thermal environment of a fire
are determined by the rate of fire growth, the yields of the various fire gases produced from the involved fuels,
the decay characteristics of those fire gases and the ventilation pattern (see A.1).A.1). Once these are
determined, the methodology presented in this document can be used for the estimation of the time at which
individuals can be expected to experience compromised tenability from exposure to smoke toxicants.
This guidance can also be applied to estimation of the time limit for rescuing people who are immobile due to
injury, medical condition, etc.
This document establishes formulae to evaluate the life-threatening components of fire hazard analysis in
terms of the status of exposed human subjects at discrete time intervals. It makes possible the estimation of
the time at which occupants can experience compromised tenability (see A.2).A.2). It enables estimation of a
compromised tenability endpoint for each of the fire effluent components, with the most important endpoint
being the earliest to occur.
The life-threatening components addressed in the 13571 series include fire-effluent toxicity, heat, and visual
obscuration due to smoke. In cases where the effluent composition is available, the toxic gas model is used for
assessment of fire-effluent toxicity. Effects of heat and smoke obscuration are addressed in ISO 13571-5. For
those cases where the effluent composition is unknown, an additional mass-loss model using generic toxic
potency values is also provided in ISO 13571-5.
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2 Normative references
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No normative references are cited in this document.
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ISO/FDIS 13571-1:2026(en)
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3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
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— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
3.1 3.1
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tenability
and Asian text, Adjust space between Asian text and
ability of humans to perform cognitive and motor skill functions at an acceptable level when exposed to a fire
numbers
environment
Note 1 to entry: If exposed individuals are able to perform cognitive and motor-skill functions at an acceptable level,
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the exposure is said to be tenable. If not, the exposure is said to result in compromised tenability.
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stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
3.2 3.2
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
adjustment factor
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factor for the incorporation of quantitative data on interspecies differences or on human variability in either
and Asian text, Adjust space between Asian text and
toxico--kinetics (variability in inhaled dose and metabolism) or toxico-dynamics (mode of action causing the
numbers
critical effect) into the risk assessment procedure
3.3 3.3
VE -
volume of air breathed each minute.
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Note 1 to entry:  In air this depends on the activity level of the subject (V ). In the presence of inhaled CO V is
Eair 2 E
increased by a hyperventilatory stimulus factor (VCO2) depending on the inhaled CO2 concentration.
4 General principles
4.1 Time to compromised tenability
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The time to compromised tenability for individuals is the shortest of four distinct times estimated from
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consideration of asphyxiant fire gases, irritant fire gases, heat, and visual obscuration due to smoke.
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The context and mechanisms of the fire-effluent toxicity component of life threat are discussed in
Annex A.Annex A. Effects of the asphyxiant toxicants, carbon monoxide and hydrogen cyanide (see A.4),A.4),
as well as those of eye and upper-respiratory tract sensory irritants (see A.5), A.5), are described in detail.
Responses to these exposures involve functions of the human sensory, cardiovascular, respiratory and
neurological systems that are dependent upon inherent physical characteristics (e.g., age, body weight, pre-
existing cardiopulmonary conditions), along with environmental considerations and physical activity at the
time of exposure. As a result, individual human responses can be highly variable and, therefore, not readily
reduced to usable engineering formulae for prediction of compromised tenability without considerable
simplification, application of numerous assumptions, and exclusion of unusual circumstances.
With regard to the susceptibilities of individuals to the insults of fire exposure, a primary assumption of this
document is that all occupant responses are treated as a log-normal or probit statistical distribution with
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respect to a median time, with half of the population experiencing a tenable exposure and half experiencing
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compromised tenability (see 5.3). 5.3). Threshold levels estimated to affect tenability for approximately 1 %
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of an exposed population are derived from Point of Departure (POD) animal toxicity data and reported
[2][6][9][25][26][27][28][29][30][31] [2][6][9][25][26][27][28][29][30][31]
findings from human exposure data . .
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spacing: single
2 © ISO #### 2026 – All rights reserved
ISO/DISFDIS 13571-1:20252026(en)
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4.2 Toxic-gas model
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4.2.1 4.2.1 The toxic-gas models described in this document address effects that are considered
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detrimental to human tenability. Because they are physiologically unrelated and mechanistically independent,
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asphyxiant toxicants and irritant toxicants are treated separately (see A.4 and A.5). A.4 and A.5).
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stops: Not at 0.71 cm
With irritant toxicants, only those that cause eye and upper-respiratory tract sensory irritation are considered
in this document as having effects on tenability (see A.5.2). A.5.2). Serious effects of pulmonary irritation
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resulting in lung injury are manifested from a few hours up to several days after exposure and are not normally
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expected to have a direct impact on tenability during exposure at a fire scene (see A.5.3). A.5.3).
Adjust space between Asian text and numbers, Tab
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
Providing asphyxiant and irritancy thresholds are not exceeded during exposure then significant post-
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
exposure lung injury from irritants and significant post-exposure neurological or cardiovascular injury from
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asphyxiants are considered unlikely to occur. Additional guidance on threshold exposure doses that may
result in post-exposure injury is given (see C.3). C.3). Formatted: Adjust space between Latin and Asian text,
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4.2.2 4.2.2 The basic principle for estimating the asphyxiant component of toxic hazard analysis involves
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the exposure dose of each toxicant, i.e. the integrated area under each concentration-time curve. Fractional
effective doses (FEDs) are determined for each asphyxiant at each discrete increment of time, whereby the Formatted: Adjust space between Latin and Asian text,
accumulated exposure dose is expressed as a fraction of the exposure dose required to cause compromised
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tenability. The time at which their accumulated sum exceeds a specified threshold value represents the time
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
to compromised tenability relative to chosen safety criteria.
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
4.2.3 4.2.3 The basic principle for estimating the eye and upper respiratory tract sensory irritant
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component of toxic hazard analysis involves the concentration of each irritant. Fractional effective
concentrations (FECs) are determined for each irritant at each discrete increment of time. The time at which
their sum exceeds a specified threshold value represents the time to compromised tenability relative to the
chosen safety criteria.
4.2.4 4.2.4 Relevant assumptions and exclusions are as follows:
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a) a) Asphyxiant toxicants, irritants, heat and visual obscuration are each considered as acting
independently. Some degrees of interaction between these insults are known to occur (see A.7),A.7) but
are considered secondary.
b) b) Exposed occupants are considered to be at relatively normal ambient environmental
conditions and at altitudes below which reduced ambient oxygen could be a factor, and performing at a
moderate level of physical activity. Deviation from these conditions can affect susceptibility.
c) c) Any interactions between aerosols, particulates and gaseous fire-effluent components are not
considered. The physical form of toxic effluents is known to have some influencing effects, but in this
document, they are considered secondary to the direct effects of vapour-phase and particulate effluents.
d) d) Adverse health effects subsequent to exposure to fire atmospheres are not considered in
relation to tenability during exposure, although it is recognized that post-exposure effects occur where
tenability limits during exposure are exceeded. Pre-existing health conditions may be exacerbated and
potentially life--threatening sequelae may develop from exposure both to asphyxiants and to pulmonary
irritants (see A.4A.4 and A.5.3).A.5.3). Lower respiratory tract effects are typically manifested at time
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scales much longer than those of the actual fire and, although noted, are not considered in the
requirements of this document with respect to tenabili
...

PROJET FINAL
Norme
internationale
ISO/FDIS 13571-1
ISO/TC 92/SC 3
Composants dangereux du feu —
Secrétariat: AFNOR
Partie 1:
Début de vote:
2026-07-15
Lignes directrices relatives à une
méthode fondée sur des critères
Vote clos le:
2026-09-09
de tenabilité pour l'estimation
du temps avant que la capacité
d'évacuation ne soit compromise du
fait de l'exposition aux substances
toxiques de la fumée
Life-threatening components of fire —
Part 1: Guidelines for method based on tenability endpoints for
the estimation of time to compromised escape capability from
exposure to smoke toxicants
LES DESTINATAIRES DU PRÉSENT PROJET SONT
INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS,
NOTIFICATION DES DROITS DE PROPRIÉTÉ DONT ILS
AURAIENT ÉVENTUELLEMENT CONNAISSANCE ET À
FOURNIR UNE DOCUMENTATION EXPLICATIVE.
OUTRE LE FAIT D’ÊTRE EXAMINÉS POUR
ÉTABLIR S’ILS SONT ACCEPTABLES À DES FINS
INDUSTRIELLES, TECHNOLOGIQUES ET COM-MERCIALES,
AINSI QUE DU POINT DE VUE DES UTILISATEURS, LES
PROJETS DE NORMES
INTERNATIONALES DOIVENT PARFOIS ÊTRE CONSIDÉRÉS
DU POINT DE VUE DE LEUR POSSI BILITÉ DE DEVENIR DES
NORMES POUVANT
SERVIR DE RÉFÉRENCE DANS LA RÉGLEMENTATION
NATIONALE.
Numéro de référence
ISO/FDIS 13571-1:2026(fr) © ISO 2026

PROJET FINAL
ISO/FDIS 13571-1:2026(fr)
Norme
internationale
ISO/FDIS 13571-1
ISO/TC 92/SC 3
Composants dangereux du feu —
Secrétariat: AFNOR
Partie 1:
Début de vote:
Lignes directrices relatives à une 2026-07-15
méthode fondée sur des critères
Vote clos le:
2026-09-09
de tenabilité pour l'estimation
du temps avant que la capacité
d'évacuation ne soit compromise du
fait de l'exposition aux substances
toxiques de la fumée
Life-threatening components of fire —
Part 1: Guidelines for method based on tenability endpoints for
the estimation of time to compromised escape capability from
exposure to smoke toxicants
LES DESTINATAIRES DU PRÉSENT PROJET SONT
INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS,
NOTIFICATION DES DROITS DE PROPRIÉTÉ DONT ILS
AURAIENT ÉVENTUELLEMENT CONNAISSANCE ET À
FOURNIR UNE DOCUMENTATION EXPLICATIVE.
DOCUMENT PROTÉGÉ PAR COPYRIGHT
OUTRE LE FAIT D’ÊTRE EXAMINÉS POUR
ÉTABLIR S’ILS SONT ACCEPTABLES À DES FINS
© ISO 2026 INDUSTRIELLES, TECHNOLOGIQUES ET COM-MERCIALES,
AINSI QUE DU POINT DE VUE DES UTILISATEURS, LES
Tous droits réservés. Sauf prescription différente ou nécessité dans le contexte de sa mise en œuvre, aucune partie de cette
PROJETS DE NORMES
INTERNATIONALES DOIVENT PARFOIS ÊTRE CONSIDÉRÉS
publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,
DU POINT DE VUE DE LEUR POSSI BILITÉ DE DEVENIR DES
y compris la photocopie, ou la diffusion sur l’internet ou sur un intranet, sans autorisation écrite préalable. Une autorisation peut
NORMES POUVANT
être demandée à l’ISO à l’adresse ci-après ou au comité membre de l’ISO dans le pays du demandeur.
SERVIR DE RÉFÉRENCE DANS LA RÉGLEMENTATION
NATIONALE.
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Publié en Suisse Numéro de référence
ISO/FDIS 13571-1:2026(fr) © ISO 2026

ii
ISO/FDIS 13571-1:2026(fr)
Sommaire Page
Avant-propos .iv
Introduction .v
1 Domaine d'application . 1
2 Références normatives . 1
3 Termes et définitions . 1
4 Principes généraux . 2
4.1 Temps disponible avant que les conditions de tenabilité ne soient compromises .2
4.2 Modèle de gaz toxiques .3
5 Portée et utilisation . 4
6 Modèles de gaz toxiques . 6
6.1 Modèle de dose effective fractionnelle de gaz asphyxiants .6
6.2 Modèle d'irritation . 13
7 Lésions et létalité après exposition .15
8 Rapport .15
Annexe A (informative) Contexte et mécanisme du potentiel toxique . 17
Annexe B (informative) Modèle étendu relatif aux asphyxiant pour différents niveaux d'activité
intégrant V comme variable . 41
E
Annexe C (informative) Lésion et létalité après exposition .44
Bibliographie . 47

iii
ISO/FDIS 13571-1:2026(fr)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux
de normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général
confiée aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire
partie du comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents
critères d'approbation requis pour les différents types de documents ISO. Le présent document
a été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2
(voir www.iso.org/directives).
L'ISO attire l'attention sur le fait que la mise en application du présent document peut entraîner l'utilisation
d'un ou de plusieurs brevets. L'ISO ne prend pas position quant à la preuve, à la validité et à l'applicabilité
de tout droit de propriété revendiqué à cet égard. À la date de publication du présent document, l'ISO
n'avait pas reçu notification qu'un ou plusieurs brevets pouvaient être nécessaires à sa mise en application.
Toutefois, il y a lieu d'avertir les responsables de la mise en application du présent document que des
informations plus récentes sont susceptibles de figurer dans la base de données de brevets, disponible à
l'adresse www.iso.org/brevets. L'ISO ne saurait être tenue pour responsable de ne pas avoir identifié tout ou
partie de tels droits de brevet.
Les appellations commerciales éventuellement mentionnées dans le présent document sont données pour
information, par souci de commodité, à l'intention des utilisateurs et ne sauraient constituer un engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l'ISO liés à l'évaluation de la conformité, ou pour toute information au sujet de l'adhésion de
l'ISO aux principes de l'Organisation mondiale du commerce (OMC) concernant les obstacles techniques au
commerce (OTC), voir www.iso.org/avant-propos.
L'ISO 13571-1 a été élaborée par le comité technique ISO/TC 92, Sécurité au feu, sous-comité SC 3, Dangers
pour les personnes et l'environnement dus au feu.
Cette première édition de l'ISO 13571-1 annule et remplace la deuxième édition de l'ISO 13571:2012, qui a
fait l'objet d'une révision technique.
Les principales modifications sont les suivantes:
— suppression des termes non utilisés;
— ajout des termes actuellement utilisés dans le portefeuille de normes TC 96;
— ajout des termes référencés dans les normes ISO/TC 96/SC 5;
— ajout de chiffres pour illustrer les définitions.
— Une liste de toutes les parties de la série ISO 13571 se trouve sur le site web de l'ISO.
Il convient que l'utilisateur adresse tout retour d'information ou toute question concernant le présent
document à l'organisme national de normalisation de son pays. Une liste exhaustive desdits organismes se
trouve à l'adresse www.iso.org/fr/members.html.

iv
ISO/FDIS 13571-1:2026(fr)
Introduction
La série ISO 13571 est un ensemble de normes élaborées pour estimer le temps avant que la tenabilité ne
soit compromise et la capacité d’évacuation des occupants lorsqu'ils sont exposés à un environnement
d'incendie. Les différentes menaces liées à l’exposition à des toxiques aigus, à la chaleur et à la fumée sont
évaluées séparément. Le temps disponible avant que les conditions de tenabilité ne soient compromises est
le plus court des temps disponibles avant que les conditions de tenabilité ne soient compromises déterminés
pour chaque menace individuelle.
La série ISO 13571 est composée de 5 parties:
— L'ISO 13571-1 décrit un modèle d'évaluation de la toxicité de la fumée pour déterminer le temps disponible
avant que les conditions de tenabilité ne soient compromises et la capacité d'évacuation de 50 % d’une
population d’occupants exposée, et les limites de tenabilité pour les membres sensibles d'une population
exposée, y compris les enfants, les personnes âgées et les personnes dont l’état de santé est altéré.
— L'ISO/TR 13571-2 décrit des exemples d'application de la série ISO 13571.
— L'ISO 13571-3 décrit un modèle d'évaluation de la toxicité de la fumée pour déterminer le temps disponible
avant que les conditions de tenabilité ne soient compromises sur la base des critères de létalité pour une
population d'occupants exposée
— L'ISO/TR 13571-4 donne des exemples de comparaisons entre l'ISO 13571-1 et l'ISO 13571-3 dans
différents scénarios de feux.
— L'ISO 13571-5 décrit des modèles d'exposition à la chaleur, d'exposition aux fumées et un modèle simplifié
d'évaluation de la toxicité basé sur la perte de masse de combustible.
Les expositions chroniques ou environnementales et leurs effets potentiels sur la santé ne sont pas couverts
par la série ISO 13571.
Le présent document est destiné à l'estimation du temps disponible avant que les conditions de tenabilité ne
soient compromises et la capacité d'évacuation des occupants lorsqu'ils sont exposés à un environnement
d'incendie pour des applications où les courbes concentration-temps pour les scénarios de feux sont
disponibles (par exemple, dans le cadre d'une modélisation de la dynamique de l’incendie ou d'expériences
de feu à grande échelle). La norme peut être utilisée pour les calculs de danger et la modélisation, tels
qu’appliqués au calcul et à la modélisation du temps disponible pour l’évacuation en sécurité (ASET) et du
temps requis pour l’évacuation en sécurité (RSET).
Le document fournit des expressions pour calculer le temps et les doses d'exposition aux seuils de tenabilité
pour 50 % d'une population d'occupants exposée et pour l'estimation des limites de seuil conçues pour
protéger essentiellement tous les occupants. Sont incluses les populations générales mixtes avec enfants,
personnes âgées et adultes dont l’état de santé est altéré, dans tous les types d’occupation, y compris les
bâtiments et les systèmes de transport.
Les expressions de calcul du présent document ont été déduites autant que possible des données de tenabilité
comportementale et physiologique humaine obtenues à partir d'expositions expérimentales et accidentelles,
notamment des données d'expositions lors d'incendies, des données d'expériences sur des primates non
humains et des expériences impliquant des rongeurs (rats et souris). Les expressions et les critères d’effet
déduits de ces données ont été développés pour fournir des méthodes d'évaluation les plus pertinentes pour
la tenabilité et, en particulier, la capacité d'évacuation des occupants humains dans des scénarios d’incendie
de bâtiment ou de transport.
Les lignes directrices fournies dans le présent document sont fondées sur le meilleur jugement scientifique
disponible en utilisant une base de connaissances récente, mais non exhaustive, sur les conséquences d'une
exposition humaine aux effluents du feu. Pour des raisons éthiques, une grande partie de la méthodologie
décrite n'a pas été et ne peut pas être validée expérimentalement sur des êtres humains. Toutefois, en ce
qui concerne le monoxyde de carbone qui est le principal facteur entravant l'évacuation et la cause la plus
fréquente des accidents mortels dus au feu, la base de données est en réalité assez complète et bien validée
par un retour d’expérience sur l'homme.

v
ISO/FDIS 13571-1:2026(fr)
L'estimation de la tenabilité pour les occupants, lorsqu'ils sont exposés à un environnement d'incendie,
concerne en dernier ressort leur aptitude à assurer les fonctions comportementales, cognitives et motrices
à un niveau acceptable. En général, les performances acceptables peuvent inclure l'un quelconque des
nombreux résultats souhaitables, notamment l'évacuation vers un refuge sûr ou, si l'évacuation n'est pas une
option envisageable, le maintien de ces fonctions sur place si nécessaire. Cette dernière situation concerne
les occupants qui ne sont pas mobiles ou dont l'évacuation est empêchée pour diverses raisons, par exemple
un avion en vol. Le temps qui s'écoule entre le déclenchement d'un incendie et le moment où la tenabilité est
compromise à tel point que des performances acceptables sont impossibles est un élément essentiel de la
conception de la sécurité au feu.
Le temps disponible avant que les conditions de tenabilité ne soient compromises peut dépendre de la
position et du déplacement de chaque occupant ainsi que de nombreuses autres caractéristiques propres à
l'occupant. Chaque occupant peut donc disposer d'un délai différent avant que les conditions de tenabilité ne
soient compromises. Des lignes directrices relatives à la prise en compte de ces facteurs sont fournies dans
d'autres sources, par exemple l'ISO/TR 16738.
Chaque occupant peut également disposer d'un délai différent avant que les conditions de tenabilité ne soient
compromises selon son exposition particulière à la chaleur et aux effluents du feu et produits de combustion
et sa sensibilité individuelle à de telles expositions (voir A.2.3). La méthodologie décrite dans le présent
document a pour objectif de fournir un cadre pour l'estimation du temps disponible avant que les conditions
de tenabilité ne soient compromises.
La méthodologie décrite ne peut pas être utilisée seule pour évaluer la performance globale en matière
de sécurité au feu de matériaux ou produits spécifiques et ne peut donc pas fournir de critères pour une
méthode d'essai. Les formules doivent plutôt être utilisées comme données d'entrée pour une analyse des
dangers du feu ou des risques d'incendie. Dans une telle analyse, le temps estimé disponible avant que les
conditions de tenabilité ne soient compromises dépend également de la nature du feu (par exemple débit
thermique, quantité et types de combustibles, composition chimique du combustible) et du volume considéré
(par exemple dimensions, ventilation). Ces facteurs déterminent les concentrations de gaz toxiques, les
températures des gaz et des parois et la densité de fumée dans le volume considéré en fonction du temps.
De plus, l'estimation de l'exposition est déterminée en partie par les hypothèses concernant la position de la
tête des occupants par rapport à la couche de fumée chaude qui se forme à proximité des plafonds et descend
au fur et à mesure que l'incendie se développe.
Bien que le concept de conditions de tenabilité compromises soit compatible avec la définition de
l'incapacitation (voir l'ISO 13943), ce dernier terme n'est pas utilisé dans le présent document en raison de
son interprétation potentiellement large permettant d'inclure de nombreux effets, y compris un collapsus
cardiovasculaire et une perte de connaissance qui ne sont pas traités. Le présent document se concentre
spécifiquement sur les conditions de tenabilité compromises qui sont influencées par les réponses
physiologiques et comportementales engendrées par une exposition aux composants dangereux du feu.
Comme pour toute méthodologie prédictive, une incertitude est associée à l'application du présent
document. Une estimation de l'incertitude associée à chaque procédure est fournie, l'utilisateur étant invité
à déterminer l'importance de ces incertitudes dans l'estimation du résultat d'un scénario feu donné.

vi
PROJET FINAL Norme internationale ISO/FDIS 13571-1:2026(fr)
Composants dangereux du feu —
Partie 1:
Lignes directrices relatives à une méthode fondée sur des
critères de tenabilité pour l'estimation du temps avant
que la capacité d'évacuation ne soit compromise du fait de
l'exposition aux substances toxiques de la fumée
1 Domaine d'application
Le présent document constitue l'un des nombreux outils pouvant être utilisés en ingénierie de la sécurité
incendie. Il est destiné à être utilisé conjointement à des données d'essai d'incendie telles que celles
détaillées dans l'ISO 13571-5 et à des modèles pour l'analyse du déclenchement et du développement du feu,
de la propagation du feu, de la formation et du déplacement des fumées, de la génération, du transport et de
la décroissance des espèces chimiques, et du déplacement des personnes, ainsi que pour la détection et la
suppression de l'incendie. Le présent document ne doit être utilisé que dans ce contexte.
Le présent document est destiné à traiter des conséquences d'une exposition humaine aux composants
dangereux du feu. Les concentrations des effluents du feu en fonction du temps et l'environnement thermique
d'un feu sont déterminées par la vitesse de développement du feu, les taux de production des divers gaz
de combustion produits par les combustibles impliqués, les caractéristiques de décroissance de ces gaz
de combustion et le modèle de ventilation (voir A.1). Une fois ces paramètres déterminés, la méthodologie
présentée dans le présent document peut être utilisée pour estimer le temps dont les individus peuvent
disposer avant que les conditions de tenabilité ne soient compromises en raison de leur exposition aux
substances toxiques présentes dans la fumée.
Ces lignes directrices peuvent également s'appliquer à l'estimation du délai imparti pour le sauvetage de
personnes immobilisées par des lésions, un état pathologique, etc.
Le présent document établit des formules permettant d'évaluer les composants dangereux lors d'une analyse
des dangers du feu en termes d'état des êtres humains exposés à des intervalles de temps discrets. Il permet
d'estimer le temps dont disposent les occupants avant que les conditions de tenabilité ne soient compromises
(voir A.2). Il permet d'estimer un critère de compromission de la tenabilité pour chacun des composants des
effluents du feu, l'effet le plus important étant celui qui se manifeste en premier.
Les composants dangereux traités dans la série 13571 comprennent la toxicité des effluents du feu, la
chaleur et l'obscurcissement par la fumée. Lorsque la composition des effluents est disponible, le modèle
de gaz toxique est utilisé pour l'évaluation de la toxicité des effluents du feu. Les effets de la chaleur et de
l'obscurcissement par la fumée sont traités dans l'ISO 13571-5. Lorsque la composition des effluents est
inconnue, un modèle supplémentaire de perte de masse utilisant des valeurs génériques de potentiel toxique
est fourni dans l'ISO 13571-5.
2 Références normatives
Aucune référence normative n'est citée dans le présent document.
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions suivants s'appliquent.

ISO/FDIS 13571-1:2026(fr)
L'ISO et l'IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en normalisation,
consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l'adresse https:// www .iso .org/ obp
— IEC Electropedia: disponible à l'adresse https:// www .electropedia .org/
3.1
tenabilité
aptitude des individus à assurer des fonctions cognitives et motrices à un niveau acceptable lorsqu'ils sont
exposés à un environnement d'incendie
Note 1 à l'article: Si les individus exposés sont capables d'assurer des fonctions cognitives et motrices à un niveau
acceptable, l'exposition est dite supportable. Sinon, l'exposition est dans des conditions de tenabilité compromises.
3.2
facteur d'ajustement
facteur d'incorporation de données quantitatives sur les différences interespèces ou sur la variabilité
interindividuelle chez l’être humain, en toxicocinétique (variabilité de la dose inhalée et du métabolisme)
ou en toxicodynamique (mode d'action provoquant l'effet critique) dans la procédure d'évaluation du risque
3.3
V
E
volume d'air respiré par minute
Note 1 à l'article: Dans l'air, cela dépend du niveau d'activité du sujet (V ). En présence de CO inhalé, le V est
Eair 2 E
augmenté par un facteur de stimulation hyperventilatoire (VCO ) en fonction de la concentration de CO2 inhalée.
4 Principes généraux
4.1 Temps disponible avant que les conditions de tenabilité ne soient compromises
Le temps dont disposent les individus avant que les conditions de tenabilité ne soient compromises est
le plus court des quatre temps estimés en tenant compte des gaz de combustion asphyxiants, des gaz de
combustion irritants, de la chaleur et de l'obscurcissement par la fumée.
Le contexte et les mécanismes de la composante du danger pour la vie liée à la toxicité des effluents du
feu sont traités dans l'Annexe A. Les effets des toxiques asphyxiants, du monoxyde de carbone et du
cyanure d'hydrogène (voir A.4), ainsi que ceux des irritants sensoriels pouvant affecter les yeux et les voies
respiratoires supérieures (voir A.5), sont décrits en détail.
Les réactions à ces expositions concernent les fonctions des systèmes sensoriel, cardiovasculaire, respiratoire
et neurologique de l'homme, qui dépendent des caractéristiques physiques intrinsèques (par exemple âge,
masse corporelle, état cardio-pulmonaire préexistant) ainsi que de considérations environnementales et de
l'activité physique au moment de l'exposition. De ce fait, les réactions humaines individuelles peuvent être
extrêmement variables et il est donc difficile de les réduire à des formules techniques utiles pour prédire
les conditions de tenabilité compromises sans une simplification considérable, l'application de nombreuses
hypothèses et l'exclusion de circonstances inhabituelles.
En ce qui concerne la sensibilité des individus aux agressions d'une exposition au feu, la principale hypothèse
du présent document est que toutes les réactions des occupants sont traitées comme une distribution
statistique log-normale analysée par une méthode probit par rapport à un temps médian, la moitié de la
population subissant une exposition supportable et l'autre moitié subissant des conditions de tenabilité
compromises (voir 5.3). Les niveaux de seuil estimés pour affecter la tenabilité pour environ 1 % d'une
population exposée sont dérivés des données de toxicité animale au point de départ (POD) et des résultats
[2][6][9][25][26][27][28][29][30][31]
rapportés des données d'exposition humaine ·

ISO/FDIS 13571-1:2026(fr)
4.2 Modèle de gaz toxiques
4.2.1 Les modèles de gaz toxique décrits dans le présent document traitent d’effets qui sont considérés
comme préjudiciables pour la tenabilité. Du fait qu'ils ne sont pas liés physiologiquement et qu'ils sont
indépendants du point de vue de leur mécanisme, les toxiques asphyxiants et les toxiques irritants sont
traités séparément (voir A.4 et A.5).
En ce qui concerne les toxiques irritants, seuls ceux qui provoquent une irritation sensorielle des yeux et
des voies respiratoires supérieures sont considérés dans le présent document comme ayant des effets sur
la tenabilité (voir A.5.2). Les graves effets d'une irritation pulmonaire entraînant des lésions pulmonaires
se manifestent dans un délai de quelques heures à plusieurs jours après l'exposition et ne sont normalement
pas censés avoir une incidence directe sur la tenabilité lors d'une exposition sur les lieux d'un incendie
(voir A.5.3).
À condition que les seuils d'asphyxie et d'irritation ne soient pas dépassés pendant l'exposition, il est jugé
peu probable que surviennent des lésions pulmonaires importantes après l'exposition dues aux substances
irritantes, ni des lésions neurologiques ou cardiovasculaires importantes dues aux substances asphyxiantes.
Des recommandations supplémentaires concernant les doses d'exposition seuils susceptibles d'entraîner
des lésions après exposition sont fournies (voir C.3).
4.2.2 Le principe de base pour estimer le composant asphyxiant dans une analyse du risque toxique
concerne la dose d'exposition de chaque toxique, c'est-à-dire l'aire intégrée sous chaque courbe concentration-
temps. Les doses effectives fractionnelles (FED, fractional effective doses) sont déterminées pour chaque
asphyxiant à chaque incrément de temps discret, où la dose d'exposition cumulée est exprimée sous la forme
d'une fraction de la dose d'exposition requise pour provoquer des conditions de tenabilité compromises. Le
temps auquel leur somme cumulée dépasse une valeur seuil spécifiée représente le temps disponible avant
que les conditions de tenabilité ne soient compromises par rapport à des critères de sécurité choisis.
4.2.3 Le principe de base pour estimer le composant irritant sensoriel pour les yeux et les voies
respiratoires supérieures dans une analyse du risque toxique concerne la concentration de chaque irritant.
Les concentrations effectives fractionnelles (FEC, fractional effective concentrations) sont déterminées pour
chaque irritant à chaque incrément de temps discret. Le temps auquel leur somme dépasse une valeur seuil
spécifiée représente le temps disponible avant que les conditions de tenabilité ne soient compromises par
rapport à des critères de sécurité choisis.
4.2.4 Les hypothèses et exclusions pertinentes sont les suivantes:
a) Les toxiques asphyxiants, les irritants, la chaleur et la réduction de la visibilité sont chacun considérés
comme agissant séparément. On sait qu'il existe un certain degré d'interaction entre ces agressions
(voir A.7), mais il est jugé secondaire.
b) Les occupants exposés sont considérés comme se trouvant dans des conditions environnementales
ambiantes relativement normales et à des altitudes inférieures à celles où une concentration réduite
d'oxygène ambiant pourrait être un facteur, et comme effectuant un niveau modéré d'activité physique.
L'écart par rapport à ces conditions peut affecter la susceptibilité.
c) Toute interaction entre les aérosols, les particules et les composants des effluents gazeux d'incendie
n'est pas prise en compte. La forme physique des effluents toxiques est connue pour avoir certains effets
notables mais, dans le présent document, ils sont considérés comme secondaires par rapport aux effets
directs des effluents en phase vapeur et des particules.
d) Les effets nocifs pour la santé consécutifs à l'exposition aux atmosphères de feu ne sont pas pris en compte
en ce qui concerne la tenabilité pendant l'exposition, bien qu'il soit reconnu que les effets postérieurs
à l'exposition se produisent lorsque les limites de tenabilité sont dépassées pendant l'exposition. Des
affections préexistantes peuvent être aggravées et des séquelles potentiellement mortelles peuvent
apparaître à la suite d'une exposition à des asphyxiants et à des irritants pulmonaires (voir A.4 et
A.5.3). Les effets sur les voies respiratoires inférieures se manifestent généralement à beaucoup plus
longue échéance que ceux de l'incendie et, bien que mentionnés, ne sont pas pris en compte dans les
exigences du présent document concernant la tenabilité lors d'une exposition sur les lieux d'un incendie.

ISO/FDIS 13571-1:2026(fr)
Des recommandations supplémentaires ont été fournies concernant les effets indésirables sur la santé
après exposition des doses inhalées d'asphyxiants présentant un risque d'effets cardiovasculaires et
neurologiques après exposition et sur les doses inhalées d'irritants pulmonaires associées à un risque
de lésion pulmonaire.
e) Les premières conséquences d'une réduction de la visibilité par la fumée (par exemple reconnaissance
de la présence d'un feu, vue claire des chemins d'évacuation) sont de nature comportementale et ne sont
pas incluses. Cependant, l'obscurcissement par la fumée d'une telle gravité que les occupants deviennent
désorientés ou présentent une forte probabilité de faire demi-tour plutôt que d’entrer dans la fumée ou
de continuer à la traverser, impose une limitation du temps pendant lequel l'évacuation peut être tentée
et est pris en compte dans l'ISO 13571-5.
Les formules fournies dans la méthodologie décrite dans le présent document permettent d'estimer l'état
des occupants exposés à des intervalles de temps discrets pendant le déroulement d'un scénario feu jusqu'au
moment où une telle exposition peut compromettre les conditions de tenabilité. Si le temps estimé est jugé
excessivement limité, diverses stratégies de protection doivent alors être envisagées par le professionnel en
sécurité incendie.
5 Portée et utilisation
5.1 Le présent document a pour objet de fournir aux ingénieurs des lignes directrices simplifiées, mais
robustes, leur permettant d'estimer le temps dont disposent les occupants avant que les conditions de
tenabilité ne soient compromises, dans le cadre de l'évaluation des capacités de sécurité incendie d'une
structure soumise à des conditions d'incendie définies en termes de profils temporels de concentration des
gaz toxiques et des particules de fumée. Une telle estimation de la tenabilité pour les occupants concerne
en dernier ressort leur aptitude à assurer des fonctions cognitives et motrices à un niveau acceptable. En
général, les performances acceptables peuvent inclure l'un quelconque des nombreux résultats souhaitables,
notamment l'évacuation vers un lieu de refuge ou, si l'évacuation n'est pas une option envisageable, le
maintien de ces fonctions sur place si nécessaire.
NOTE Si l'évacuation vers un lieu de refuge ou la sortie finale est le résultat à prendre en considération, le temps
disponible avant que les conditions de tenabilité ne soient compromises peut raisonnablement être assimilé au temps
disponible pour l'évacuation en sécurité (ASET, available safe escape time).
La méthode a été développée spécifiquement afin de traiter les problèmes liés à l'exposition des occupants
au feu.
L'objectif principal des expressions est de permettre le calcul du temps disponible avant que les conditions
de tenabilité ne soient compromises pendant l'exposition aux scénarios de feux. Le critère particulier traité
est le moment auquel une proportion significative d'une population exposée devient incapable dans la
mesure où elle n'est pas en mesure de s'échapper en toute sécurité. Les expressions protègent aussi contre
les lésions et les décès postérieurs à l'exposition, à condition que les critères d'évaluation de la tenabilité
compromise ne soient pas dépassés.
En cas d'incendie, les occupants de l'enceinte (occupants de bâtiments et systèmes de transport) sont
[1][2]
généralement exposés à l'un des trois types de scénarios d'exposition :
a) Occupants dans la même enceinte qu'un feu exposés à des particules de fumée, à des irritants et à des
gaz asphyxiants (ou à la chaleur) à partir de faibles concentrations puis augmentant rapidement sur une
période de quelques minutes jusqu'à des concentrations incapacitantes.
b) Occupants quittant une enceinte relativement claire afin de pénétrer dans une voie d'évacuation remplie
de fumée contenant des concentrations variant de faibles niveaux à celles susceptibles de provoquer
une incapacité dans une courte période (quelques minutes, quelques secondes ou même après une seule
respiration). Dans de tels cas, les occupants sont exposés à un profil de concentration d'effluent quasi-
rectangulaire.
c) Occupants piégés dans une enceinte (ou restant dans un refuge désigné) qui est initialement exempte de
fumée mais qui se remplit progressivement de fumée et de gaz toxiques par infiltration sur une période
prolongée allant jusqu'à (mais dépassant rarement) une heure.

ISO/FDIS 13571-1:2026(fr)
Dans ces scénarios, les occupants sont exposés et affectés par une séquence de phénomènes dangereux, en
commençant généralement par les effets immédiats de l'exposition à la fumée irritante, puis par les effets
de l'exposition aux gaz asphyxiants ou à la chaleur. Les principaux aspects de ces scénarios d'exposition en
relation avec le développement d'expressions de tenabilité sont qu'ils impliquent généralement de courtes
périodes d'exposition de quelques minutes, et que les conditions peuvent changer très rapidement, si bien
que les expressions doivent être en mesure de traiter les effets de concentrations d'exposition élevées et de
courts temps de tenabilité. Un avantage lors de l'estimation des temps de tenabilité dans de telles situations
est qu'en raison de l'augmentation exponentielle des concentrations en gaz à un certain moment pendant la
plupart des feux, les temps calculés de l'incapacité peuvent ne présenter que de faibles variations lorsque les
paramètres du modèle sont modifiés.
5.2 Le présent document étant utilisé avec un nombre considérable d'hypothèses de simplification,
il traite des réactions de la population globale telle que représentée par une distribution statistique. Elle
n'est pas destinée à fournir des lignes directrices pour une évaluation détaillée de l'agression subie par des
individus spécifiques susceptibles d'être exposés à une atmosphère de combustion donnée, comme cela est
généralement nécessaire dans les enquêtes de médecine légale. Par ailleurs, le présent document est axé
sur l'évaluation de la tenabilité pour un occupant, alors que les enquêtes de médecine légale s'intéressent
généralement aux conséquences de conditions de tenabilité compromises. Ces objectifs sont assez
différents. Les enquêtes de médecine légale peuvent aussi être extrêmement compliquées, impliquant une
caractérisation détaillée des occupants spécifiques exposés ainsi qu'une expertise en termes d'interprétation
allant bien au-delà de ce qui peut raisonnablement figurer dans une norme donnant des lignes directrices.
[3]
5.3 Les concepts de dose effective fractionnelle (FED) et de concentration effective fractionnelle (FEC)
[4]
sont fondamentaux pour la méthodologie du présent document. Ces deux concepts se rapportent à la
manifestation des effets physiologiques et comportementaux que présentent les sujets exposés.
5.4 La variabilité des réponses humaines aux agressions toxicologiques est mieux représentée par une
distribution statistique qui prend en compte la sensibilité variable à l’agression. Certaines personnes sont
plus sensibles que la moyenne alors que d'autres peuvent être moins sensibles (voir A.6). Dans le présent
document, les valeurs de FED ou FEC de 1,0 correspondent, par définition, à la valeur médiane d'une
distribution log-normale des réactions, la moitié de la population étant moins sensible et l'autre moitié
étant plus sensible. Cela signifie que, statistiquement, 50 % de la population devraient subir des conditions
supportables (c'est-à-dire être capables d'assurer des fonctions cognitives et motrices à un niveau
acceptable) et 50 % des conditions de tenabilité compromises (c'est-à-dire être incapables d'assurer des
fonctions cognitives et motrices à un niveau acceptable).
Sachant que les critères de seuil de FED ou FEC de 1,0 servent statistiquement à protéger uniquement la
moitié de la population, les utilisateurs du présent document doivent utiliser des critères de seuil de FED
ou FEC réduits pour répondre à des objectifs de sécurité incendie plus conservateurs. Le présent document
offre la possibilité de choisir des critères de seuil de FED ou FEC appropriés selon le cas. Un seuil de 0,3 FED
ou FEC est recommandé, mais des recommandations supplémentaires sont données en A.6.2. Quelle que soit
la justification des critères de seuil de FED et FEC choisis, il est nécessaire d'utiliser une seule valeur pour les
seuils de FED et FEC dans une estimation donnée du temps disponible avant que les conditions de tenabilité
ne soient compromises.
5.5 Il convient de ne pas interpréter l'exposition des occupants à des conditions supportables comme
équivalente à l'absence de préjudice après exposition. L'exposition à des toxiques présents dans les gaz
de combustion qui n'entraînent pas de dégradation de la tenabilité peut encore entraîner divers effets
susceptibles de prolonger l'évacuation et donc d'augmenter l'intensité d'exposition aux effluents du feu et
de provoquer des problèmes de santé après exposition (voir les Annexes A.4, A.5 et C). Bien que l'objectif
principal de la présente norme soit l'estimation de la tenabilité compromise lors d'une exposition à un
incendie, des recommandations sont données sur le risque d'effets significatifs sur la santé après exposition.
À condition que les limites de tenabilité compromises de la présente norme ne soient pas dépassées pendant
la période d'exposition, les effets sur la santé après exposition sont susceptibles d'être faibles. Toutefois,
la quantification de ces effets, en particulier dans des conditions où des mesures thérapeutiques efficaces
après exposition, notamment grâce à une intervention médicale, ne relève pas du domaine d'application du
présent document.
ISO/FDIS 13571-1:2026(fr)
5.6 Les concentrations en fonction du temps des effluents du feu auxquelles sont exposés les occupants,
éventuellement en mouvement, ne peuvent être déterminées qu'en utilisant des modèles numériques de
feu ou une série d'expérimentations en vraie grandeur. Il n'est pas valable d'insérer les concentrations des
effluents du feu obtenues par des méthodes d'essai au banc dans les formules présentées dans le présent
document.
5.7 La méthodologie décrite pour les expositions aux gaz toxiques ne peut être validée que dans une
mesure limitée à partir de données humaines. Il est nécessaire de reconnaître qu'une incertitude est associée
à la précision des données expérimentales sur lesquelles sont fondées les formules, à la représentation de
ces données par des fonctions algébriques, à l'exactitude des hypothèses concernant l'absence d'interaction
des gaz de combustion les uns avec les autres et avec la chaleur, à la sensibilité des personnes par rapport
à celle des animaux d'essai, etc. Ces incertitudes sont estimées dans les paragraphes suivants. Comme pour
tout calcul technique, il convient d'inclure les incertitudes dans l'estimation de l'incertitude globale d'une
analyse des dangers du feu ou des risques d'incendie. L'utilisateur peut ainsi déterminer si les résultats de
ces deux analyses sont vraiment différents ou s'il est impossible de les différencier.
NOTE L'incertitude résultante associée au temps estimé disponible avant que les conditions de tenabilité ne soient
compromises dépend d'une manière non linéaire de l'incertitude associée aux calculs de FED et de FEC (par exemple,
ces incertitudes peuvent avoir une incidence réduite sur le résultat estimé de feux se développant rapidement.)
5.8 Il existe très peu d'informations fiables sur les expositions à des gaz asphyxiants de moins de 1 min ou
de plus de 1 h. Par conséquent, l'exactitude des formules du présent document et les estimations obtenues
pour des scénarios de feux de très courte durée ou de très longue durée sont incertaines. En raison de
ces incertitudes, les estimations du temps disponible pour l'évacuation inférieures à 1 min doivent être
rapportées sous la forme < 1 min, et des précautions doivent être prises lors des estimations relatives à des
expositions des occupants de plus de 1 h.
NOTE En raison des incertitudes impliquées, les différences inférieures à 1 min entre des estimations
comparatives du temps disponible avant que les conditions de tenabilité ne soient compromises sont généralement
insignifiantes.
6 Modèles de gaz toxiques
6.1 Modèle de dose effective fractionnelle de gaz asphyxiants
6.1.1 Les doses effectives fractionnelles (FED, fractional effective doses) sont déterminées pour chaque
asphyxiant à chaque incrément de temps discret. Le temps auquel leur somme cumulée dépasse une valeur
seuil spécifiée représente le temps disponible avant que les conditions de tenabilité ne soient compromises
par rapport à des critères de sécurité choisis (voir 5.3). Le principe du modèle, dans sa forme la plus simple
pour calculer la dose effective fractionnelle, X , est illustré dans la Formule (1):
FED
t
n
C
i
X  t (1)

FED
Ct

i1 t i
où
−1
C est la concentration moyenne, exprimée en µl·l , d'un gaz asphyxiant «i» sur l'incrément de
i
temps choisi;
Δt est l'incrément de temps choisi, exprimé en minutes;
(C·t) est la dose d'exposition entraînant une compromission des conditions de tenabilité pour les
i
−1
occupants, exprimée en minutes multipliées par µl·l ;
t est la durée d'exposition, exprimée en minutes.

ISO/FDIS 13571-1:2026(fr)
En estimant les effets différentiels, ΔX , sur les doses effectives fractionnelles (FED), X , pour chaque
FED FED
incrément de temps discret, Δt, C = C,, et la Formule (1) se réduit à Formule (2):
i
t
n
X t (2)

FED
t
i
i1
...