prEN 481

Workplace exposure - Size fraction definitions for measurement of airborne particles (ISO 7708:1995, modified)

This document defines sampling conventions for airborne particle size fractions for use in assessing the health relevant exposure from inhalation of particles in the workplace. Conventions are defined for the inhalable, thoracic and respirable fractions. The sampling conventions only describe the inhalation of particles and their penetration in the respiratory tract as governed by inertia (impaction). Deposition in the respiratory tract by other mechanisms, e.g. diffusion, is not considered in this document. The sampling conventions defined in this document apply to both indoor and outdoor workplaces.
The assumptions on which the sampling conventions are defined are given in Clause 6. The convention chosen for a specific application will depend on the region of the health effect of the component of interest in the airborne particles (see Clause 5). The conventions can be used with whatever metric is of interest, including particle count, length, surface area, volume or mass. The metric depends on the kind of particle analysis carried out on the sampled aerosol fraction. The health-related fraction concentrations defined in this document are often expressed in mass of the sampled particles per volume of sampled air in order to compare with mass-based occupational exposure limit values.
The conventions are not applicable in association with limit values expressed in a different metric, e.g. for fibre limit values defined in terms of the length and diameter of airborne fibres and the ratio of the two (aspect ratio), unless a measurement procedure explicitly requires that a specific health related size fraction is to be sampled/collected [13].
The main purpose of this document is to provide agreement on the particle size fractions to sample and their definitions. Sampling is generally carried out using dedicated samplers, for which there is no need to measure the aerodynamic size distribution of the airborne particles to be sampled. Samplers including a separation into one or more relevant sampling conventions(s) are currently available. In general, no assumptions or pre-knowledge are needed on the number of modes, modal diameter(s) or width of the particle aerodynamic size distribution of the airborne particles to be sampled.
Because there is a wide variation from one person to another in the probability of particle inhalation, deposition, reaction to deposition and clearance, this document is not applicable for determining the deposited dose taken up by an individual worker.
The conventions are primarily intended for determining workers’ exposure to airborne particles by sampling the airborne particles. This document is not applicable to large particles emitted at high speed that are travelling under the momentum from their emission, instead of being carried by the air (airborne) and aspirated into humans and aerosol samplers by their suction (see Annex B).

Exposition am Arbeitsplatz - Festlegung der Größenfraktionen zur Messung luftgetragener Partikel (ISO 7708:1995, modifiziert)

Atmosphères des lieux de travail - Définition des fractions de taille pour le mesurage des particules en suspension dans l'air (ISO 7708:1995, modifée)

Le présent document définit des conventions d’échantillonnage pour les fractions de taille des particules en suspension dans l’air qui sont destinées à être utilisées pour évaluer les effets éventuels sur la santé dus à l’inhalation de particules sur le lieu de travail. Des conventions sont définies pour les fractions inhalable, thoracique et alvéolaire. Les conventions d’échantillonnage décrivent uniquement l’inhalation de particules et leur pénétration dans les voies respiratoires régie par l’inertie (impaction). Le présent document ne traite pas du dépôt des particules dans les voies respiratoires par d’autres mécanismes, par exemple par diffusion. Les conventions d’échantillonnage définies dans le présent document s’appliquent aux lieux de travail intérieurs et extérieurs.
Les hypothèses sur lesquelles sont fondées les conventions d’échantillonnage sont données à l’Article 6. La convention choisie pour une application spécifique dépend de la région d’action sur la santé du composé intéressant dans les particules en suspension dans l’air (voir Article 5). Les conventions peuvent être utilisées avec n’importe quelle métrique pertinente, y compris le nombre de particules, leur longueur, surface, volume ou masse. La métrique dépend du type d’analyse des particules menée sur la fraction d’aérosol prélevée. Les concentrations de fractions liées à la santé définies dans le présent document sont souvent exprimées en masse de particules échantillonnées par volume d’air prélevé, ce qui permet la comparaison avec les valeurs de limite d’exposition professionnelle basées sur la masse.
Les conventions ne s’appliquent pas en association avec des valeurs limites exprimées dans une autre métrique, par exemple pour des valeurs limites de fibres définies en termes de longueur et diamètre des fibres en suspension dans l’air et de rapport entre les deux (rapport d’aspect), sauf si une procédure de mesure exige explicitement qu’une fraction spécifique de taille liée à la santé soit prélevée/collectée [13].
L’objectif principal du présent document est d’uniformiser les fractions de taille des particules à prélever et leur définition. L’échantillonnage est généralement effectué à l’aide de dispositifs de prélèvement dédiés, pour lesquels il n’est pas utile de mesurer la distribution granulométrique en diamètre aérodynamique des particules en suspension dans l’air à prélever. Des dispositifs de prélèvement incluant une séparation en une ou plusieurs conventions d’échantillonnage pertinentes sont actuellement disponibles. En général, aucune hypothèse ou connaissance préalable n’est requise en matière de nombre de modes, de diamètre modal ou de largeur de la distribution granulométrique en diamètre aérodynamique des particules en suspension dans l’air à prélever.
Dans la mesure où l’on constate une variation importante de la probabilité d’inhalation, de dépôt, de réaction au dépôt, et d’élimination des particules d’une personne à l’autre, le présent document ne s’applique pas à la détermination de la dose déposée absorbée par un travailleur individuel.
Les conventions sont principalement destinées à déterminer l’exposition des travailleurs aux particules en suspension dans l’air en prélevant les particules en suspension dans l’air. Le présent document ne s’applique pas aux grosses particules émises à vitesse élevée qui se déplacent sous l’impulsion de leur émission au lieu d’être transportées par l’air (en suspension dans l’air) et aspirées par les humains et les dispositifs de prélèvement d’aérosol (voir Annexe B).

Izpostavljenost na delovnem mestu - Definicije velikostnih razredov za merjenje lebdečih delcev

General Information

• Status: Not Published
• Publication Date: 16-Sep-2026
• ICS: 13.040.30 - Workplace atmospheres
• Technical Committee: CEN/TC 137 - Assessment of workplace exposure
• Drafting Committee: CEN/TC 137/WG 3 - Particulate matter
• Current Stage: 4060 - Closure of enquiry - Enquiry
• Start Date: 19-Dec-2024
• Due Date: 24-Oct-2024
• Completion Date: 19-Dec-2024
• Ref Project: oSIST prEN 481:2024 - Workplace exposure - Size fraction definitions for measurement of airborne particles

Relations

• Revises: EN 481:1993 - Workplace atmospheres - Size fraction definitions for measurement of airborne particles
• Effective Date: 04-Oct-2023

Overview

The prEN 481:2024 standard, developed by CEN, establishes size fraction definitions for measurement of airborne particles for workplace exposure assessment. This document supersedes the EN 481:1993 and provides updated sampling conventions for inhalable, thoracic, and respirable particle fractions. These conventions are essential for evaluating health-relevant exposure to airborne particles through inhalation in occupational settings.

This standard focuses on sampling airborne particles based on their aerodynamic diameter, considering impaction-driven penetration into the respiratory tract, and excludes other deposition mechanisms such as diffusion. The definitions apply to both indoor and outdoor workplaces and are designed to support occupational hygiene practices and compliance sampling.

Key Topics

• Sampling Conventions: prEN 481 defines conventions for three key particle size fractions relevant to worker health:

  • Inhalable fraction: Particles entering the respiratory tract through mouth and nose.
  • Thoracic fraction: Particles penetrating beyond the larynx into the thoracic region.
  • Respirable fraction: Particles depositing in the gas exchange region of the lungs (alveolar region).

• Particle Aerodynamic Diameter: Measurement and classification use the aerodynamic diameter, which relates to particle behavior during inhalation under airflow conditions.

• Health Exposure Assessment: The standard supports estimating health-relevant exposure by defining sampling efficiencies that approximate the fraction of airborne particles likely to deposit in various parts of the respiratory tract under typical breathing conditions.

• Applicability and Limitations:

  • Applies to airborne particles suspended in air, excluding particles propelled by momentum (particle projectiles).
  • Sampling conventions focus on impaction deposition only.
  • Not intended for individual dose assessment due to variability in deposition and clearance among workers.
  • Compatible with various particle metrics including mass, count, surface area, or volume depending on analysis methods.

• Sampler Design and Use: The document guides the use of samplers designed to selectively capture size fractions without measuring the complete aerodynamic size distribution, simplifying workplace monitoring.

Applications

• Occupational Hygiene: prEN 481 is crucial for assessing worker exposure to airborne particles and hazardous aerosols in various industrial environments such as manufacturing, construction, mining, and healthcare.

• Compliance Monitoring: Enables sampling aligned with health-related exposure limits, supporting compliance with mass-based occupational exposure limits (OELs).

• Risk Assessment: By using defined size fractions, occupational health professionals can better correlate measured particle concentrations with potential respiratory health risks.

• Air Quality Management: The conventions assist in measuring airborne particulates both indoors and outdoors, contributing to effective workplace air quality control.

• Sampler Development and Testing: Standard references provide a foundation for manufacturers and laboratories to develop and validate aerosol samplers consistent with size-selective sampling conventions.

Related Standards

• EN 1540:2021 – Terminology relating to workplace exposure, providing essential definitions referenced by prEN 481.

• CEN/TR 15230 – Guidance for sampling aerosol fractions defined in prEN 481.

• EN 13205 Series (Parts 1 to 6) – Performance testing standards for aerosol samplers used in workplace environments.

• EN 482 – General requirements and guidance for performance testing of occupational hygiene samplers, instruments, and analytical methods.

• EN 689 – Strategy for assessing compliance with occupational exposure limits, closely linked to measurement methods.

• EN ISO 13138 – Sampling conventions for respiratory tract deposition, complementing prEN 481 definitions on particle penetration.

Keywords

Workplace exposure, airborne particles, particle size fractions, inhalable fraction, thoracic fraction, respirable fraction, occupational hygiene, aerosol sampling, aerodynamic diameter, occupational exposure limits, particle inhalation, respiratory tract deposition, CEN standards, prEN 481.

---

By adhering to prEN 481:2024, workplaces and occupational health professionals can ensure consistent, reliable measurement of airborne particles related to worker health risks, improving exposure assessment accuracy and supporting regulatory compliance efforts.

Standards Content (Sample)

SLOVENSKI STANDARD
01-oktober-2024
Zrak na delovnem mestu - Definicije velikostnih razredov za merjenje lebdečih
delcev
Workplace exposure - Size fraction definitions for measurement of airborne particles
Arbeitsplatzatmosphäre - Feslegung der Größenfraktionen zur Messung luftgetragener
Partikel
Atmosphères des lieux de travail - Définition des fractions de taille pour le mesurage des
particules en suspension dans l'air
Ta slovenski standard je istoveten z: prEN 481
ICS:
13.040.30 Kakovost zraka na delovnem Workplace atmospheres
mestu
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2024
ICS 13.040.30 Will supersede EN 481:1993
English Version
Workplace exposure - Size fraction definitions for
measurement of airborne particles
Atmosphères des lieux de travail - Définition des Arbeitsplatzatmosphäre - Feslegung der
fractions de taille pour le mesurage des particules en Größenfraktionen zur Messung luftgetragener Partikel
suspension dans l'air
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 137.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
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 supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 481:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Symbols and abbreviations . 10
5 Principle of conventions . 11
6 Assumptions and approximations . 12
7 Specifications for conventions and corresponding fraction concentrations . 13
7.1 Conventions . 13
7.1.1 Inhalable convention . 13
7.1.2 Thoracic convention . 15
7.1.3 Respirable convention . 16
7.2 Relative inhalable, thoracic or respirable fraction . 18
7.3 Fraction concentrations . 18
7.3.1 General . 18
7.3.2 Inhalable fraction concentration . 18
7.3.3 Thoracic fraction concentration . 19
7.3.4 Respirable fraction concentration . 19
8 Application to samplers for use in occupational hygiene surveys . 20
Annex A (informative) Main arguments for revision and significant technical changes . 23
Annex B (informative) Sampling situations for which the definitions of health-related
fractions are NOT directly applicable . 28
Annex C (informative) General information on particle inhalability and penetration,
and on sampling conventions . 30
Bibliography . 32

European foreword
This document (prEN 481:2024) has been prepared by Technical Committee CEN/TC 137 “Assessment
of workplace exposure to chemical and biological agents”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 481:1993
This document includes the following significant technical changes with regard to EN 481:1993:
—
Introduction
The proportion of total particulate matter that is inhaled into a human body depends on properties
of the particles, on the speed and direction of air movement near the body, on breathing rate, and whether
breathing is through the nose or mouth. Inhaled particles can then deposit somewhere in the respiratory
tract, or can be exhaled. The site and amount of deposition, or probability of exhalation, depends
on properties of the particle, respiratory tract, breathing pattern, and other factors.
Human tissues can absorb liquid particles or soluble components of solid particles wherever they deposit
in the respiratory tract. Particles can cause damage close to the deposition site if they are chemically
reactive, corrosive, radioactive, or capable of initiating some other type of damage. Insoluble particles
can be transported to another part of the respiratory tract or body, where they can be taken up by cells
and tissues and detrimental to health.
There is a wide variation from one person to another in the probability of particle inhalation, deposition,
reaction to deposition, and clearance. Nevertheless, it is necessary to define conventions for size selective
sampling of airborne particles when the purpose of sampling is health-related, e.g. in compliance
sampling.
The respirable and thoracic sampling conventions defined in this document are for the penetration
of particles in the inhaled air into deeper regions of the respiratory tract. In this document the
penetration is only based on airborne particles depositing onto the enclosing tissue in the respiratory
tract due to impaction. The particles are characterized by the aerodynamic diameter. Separation of
particles from the inhaled air and deposition onto the enclosing tissue in the respiratory tract by other
mechanisms, i.e. mainly diffusion, is disregarded in this document.
These conventions are relationships between particle aerodynamic diameter and the fractions to be
collected or measured. These fractions approximate the fraction of particles that penetrate to regions
of the respiratory tract under average breathing conditions.
Measurements conducted according to these conventions will yield a better relationship between
measured concentration and risk of disease than measurement of the total airborne particle
concentration.
Guidance for sampling the defined aerosol fractions is given in CEN/TR 15230 [1]. EN 13205-1 to −6 [2 to
7] describe performance tests for candidate aerosol samplers for any of the sampling conventions defined
in this document whereas EN 482 [8] gives general guidance for performance testing of samplers,
instruments and analytical methods used in occupational hygiene. A strategy for testing compliance with
occupational exposure limits is given in EN 689 [9]. EN ISO 13138 [10] describes sampling conventions
for fractions deposited in regions of the respiratory tract.
1 Scope
This document defines sampling conventions for airborne particle size fractions for use in assessing
the health relevant exposure from inhalation of particles in the workplace. Conventions are defined
for the inhalable, thoracic and respirable fractions. The sampling conventions only describe the
inhalation of particles and their penetration in the respiratory tract as governed by inertia (impaction).
Deposition in the respiratory tract by other mechanisms, e.g. diffusion, is not considered in this document.
The sampling conventions defined in this document apply to both indoor and outdoor workplaces.
The assumptions on which the sampling conventions are defined are given in Clause 6. The convention
chosen for a specific application will depend on the region of the health effect of the component of interest
in the airborne particles (see Clause 5). The conventions can be used with whatever metric is of interest,
including particle count, length, surface area, volume or mass. The metric depends on the kind of particle
analysis carried out on the sampled aerosol fraction. The health-related fraction concentrations defined
in this document are often expressed in mass of the sampled particles per volume of sampled air in order
to compare with mass-based occupational exposure limit values.
The conventions are not applicable in association with limit values expressed in a different metric, e.g. for
fibre limit values defined in terms of the length and diameter of airborne fibres and the ratio of the two
(aspect ratio), unless a measurement procedure explicitly requires that a specific health related size
fraction is to be sampled/collected [13].
The main purpose of this document is to provide agreement on the particle size fractions to sample
and their definitions. Sampling is generally carried out using dedicated samplers, for which there is no
need to measure the aerodynamic size distribution of the airborne particles to be sampled. Samplers
including a separation into one or more relevant sampling conventions(s) are currently available.
In general, no assumptions or pre-knowledge are needed on the number of modes, modal diameter(s) or
width of the particle aerodynamic size distribution of the airborne particles to be sampled.
Because there is a wide variation from one person to another in the probability of particle inhalation,
deposition, reaction to deposition and clearance, this document is not applicable for determining
the deposited dose taken up by an individual worker.
The conventions are primarily intended for determining workers’ exposure to airborne particles
by sampling the airborne particles. This document is not applicable to large particles emitted at high
speed that are travelling under the momentum from their emission, instead of being carried by the air
(airborne) and aspirated into humans and aerosol samplers by their suction (see Annex B).
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.
EN 1540:2021, Workplace exposure — Terminology
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1540 and the following apply.
NOTE The definitions given in EN 1540:2024 are reproduced here for improved readability.
ISO and IEC maintain terminological 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
airborne particle
chemical or biological agent, in solid or liquid form, dispersed in air
Note 1 to entry: Smoke, fume, mist and fog consist of airborne particles.
Note 2 to entry: This term describes a class of particles with a specific property, namely those that are airborne
while being measured or sampled. The document is not applicable to particles that are not airborne, whether they
have been airborne in the past or will be airborne in the future.
Note 3 to entry: Particle projectiles are a specific class of particles that move through air under its own
momentum, which they obtained when they were ejected into air. A typical example is particles generated by using
grinding wheels. In order to be able to travel a long distance under its own momentum, a particle projectile needs
to be large (much larger than 100 µm) and have been emitted at high speeds (exceeding 5 m/s to 10 m/s). Once
drag has consumed all the original momentum of a particle projectile, it moves in the air as any other airborne
particle, under the influence of air currents, air suction, drag and external forces, e.g. gravity.
3.2
alveolar region
compartment of the human respiratory tract consisting of respiratory bronchioles, alveolar ducts,
alveolar sacs and alveoli
Note 1 to entry: The American Conference of Governmental Industrial Hygienists uses the term Gas-Exchange
region and the (US) National Commission on Radiological Protection uses the term Pulmonary region [12].
3.3
cut-size of a sampler
d
ae,,p=0 50
particle size corresponding to the sampling efficiency of a sampler being equal to 0,50
3.4
cut-size of sampling convention X

d
ae,,X p=0,50
particle size corresponding to sampling convention X being equal to 0,50, where X is either the thoracic
or the respirable sampling convention
3.5
inhalability
ratio of the concentration of particles entering the respiratory tract (by inhalation through the nose or
mouth) to the corresponding concentration in the air before the particles are affected by the presence of
the exposed individual and inhalation (i.e., the total airborne particle concentration)
Note 1 to entry: For the definition of “total airborne particle composition”, see 3.15.
Note 2 to entry: The numerical definition of inhalability is given as a function of the aerodynamic particle
diameter.
3.6
inhalable convention
inhalable sampling convention
E
I
sampling convention describing the ratio of the concentration of particles entering the respiratory tract
(by inhalation through the nose or mouth) to the corresponding concentration in the air before
the particles are affected by the presence of the exposed individual and inhalation (i.e., the total airborne
particle concentration) as a function of the aerodynamic particle diameter (i.e., inhalability)
Note 1 to entry: For the definition of “inhalability”, see 3.5.
Note 2 to entry: The mathematical definition of the inhalable convention is given in 7.1.1.
Note 3 to entry: The mathematical definition of the inhalable convention depends on the wind speed range
at the actual workplace, see 7.1.1.
Note 4 to entry: The concentration can be related to the number, surface area or mass of the airborne particles.
3.7
inhalable fraction concentration
inhalable aerosol fraction concentration
inhalable dust fraction concentration
concentration of the sub-set of the total airborne particle concentration collected by an ideal sampler
with a sampling efficiency perfectly matching the inhalable sampling convention
Note 1 to entry: For any specific worker, the actual inhaled fraction depends on the speed and direction of the air
movement, on breathing rate and other factors. This fraction of an individual person can deviate from the measured
inhalable fraction concentration.
Note 2 to entry: For the definition of “total airborne particle concentration”, see 3.15.
Note 3 to entry: The concentration obtained using a validated sampler is an approximation to this concentration.
Note 4 to entry: The inhalable fraction is sometimes called inspirable; the terms are equivalent.
Note 5 to entry: The inhalable fraction concentration is also applicable to liquid particles.
3.8
particle aerodynamic diameter
d
ae
diameter of a sphere of 1 g/cm density with the same terminal settling velocity in calm air as the particle,
under the prevailing conditions of temperature, pressure and relative humidity
Note 1 to entry: The particle aerodynamic diameter depends on the size, density and shape of the particle
and, to a small degree, on the mean free path of the air carrying the particles.
Note 2 to entry: In the human respiratory tract, the separation of particles from the inhaled air for particles
of aerodynamic diameter less than 0,5 µm does not primarily depend on aerodynamics (impaction or settling
by gravity). For these particles, the separation mechanism is instead mainly governed by diffusion, and the size
of these particles is best described by the particle diffusive (equivalent) diameter. The particle diffusive (equivalent)
diameter equals the diameter of a sphere with the same diffusion coefficient as the particle under the prevailing
conditions of temperature, pressure and relative humidity.
Note 3 to entry: This document disregards the influence of diffusion on the penetration of particle sizes (
d ≤ 0,5 µm) in the human respiratory tract.
ae
Note 4 to entry: The particle aerodynamic equivalent diameter is an equivalent diameter, because it is not a real
diameter. It is based on particles with equivalent diameters have equal amount of some property, in this case
settling speed in air.
3.9
relative inhalable, thoracic or respirable fraction
sum of all amount, according to selected metric, of (relevant) particle sizes of a normalised particle size
distribution weighted by the selected sampling convention
Note 1 to entry: The relative (health-related) fraction can be determined for any of the defined sampling
conventions; inhalable in the low wind speed range, inhalable in the medium wind speed range, thoracic
and respirable, respectively.
3.10
respirable convention
respirable sampling convention
E
R
sampling convention describing the ratio of the concentration of particles penetrating to the alveolar
region (for average breathing conditions and light to moderate physical activity) to the corresponding
concentration in the air before the particles are affected by the presence of the exposed individual
and inhalation (i.e., the total airborne particle concentration)
Note 1 to entry: These experiments were carried out with humans often inhaling radioactive particles [13].
Note 2 to entry: For the definition of “total airborne particle concentration”, see 3.15.
Note 3 to entry: The numerical definition of the respirable convention is given as a function of the aerodynamic
particle diameter (see 7.1.3).
Note 4 to entry: The workload and breathing parameters are those defined for the ACGIH “Reference worker”
[15].
3.11
respirable fraction concentration
respirable aerosol fraction concentration
respirable dust fraction concentration
concentration of the sub-set of the total airborne particle concentration collected by an ideal sampler
with a sampling efficiency perfectly matching the respirable sampling convention
Note 1 to entry: For any specific worker, the actual fraction that penetrates to the alveolar region depends
both on the breathing rate and other factors, and on speed and direction of the air movement. This fraction
of an individual person can deviate from the measured respirable fraction concentration.
Note 2 to entry: For the definition of “total airborne particle concentration”, see 3.15.
Note 3 to entry: The concentration obtained using a validated sampler is an approximation to this concentration.
Note 4 to entry: The respirable fraction concentration is also applicable to liquid particles.
3.12
sampling convention
collection efficiency function of the ratio of particle concentrations, describing the probability
(as a function of particle aerodynamic diameter) of the total airborne concentration that constitutes
the health-related fraction in question
Note 1 to entry: In the case of the inhalable convention, this probability is defined as the ratio of the concentration
of particles entering the respiratory tract to the corresponding homogeneous total airborne particle concentration
in the air before the particles are affected by the presence of the exposed individual and inhalation.
Note 2 to entry: In the case of the other conventions, this probability is defined as the ratio of the concentration
of particles entering the specified region of the respiratory tract to the corresponding homogeneous total airborne
particle concentration in the air before the particles are affected by the presence of the exposed individual and
inhalation.
Note 3 to entry: This definition specifies how the inhalability and penetration data, upon which the collection
efficiency functions are based, originally were determined.
Note 4 to entry: This document defines four sampling conventions; the inhalable in the low wind-speed range,
the inhalable in the medium wind-speed range, the thoracic and the respirable.
3.13
thoracic convention
thoracic sampling convention
E
T
sampling convention describing the ratio of the concentration of particles penetrating beyond the larynx
(for average breathing conditions and light to moderate physical activity) to the corresponding
concentration in the air before the particles are affected by the presence of the exposed individual
and inhalation (i.e., the total airborne particle concentration)
Note 1 to entry: These experiments were carried out with humans, often inhaling radioactive particles [13].
Note 2 to entry: For the definition of “total airborne particle concentration”, see 3.15.
Note 3 to entry: The numerical definition of the thoracic convention is given as a function of the aerodynamic
particle (see 7.1.2).
Note 4 to entry: The workload and breathing parameters are those defined for the ACGIH “Reference worker”
[15].
Note 5 to entry: The thoracic convention approximates to the thoracic fraction during oral breathing. During nose
breathing, the fraction of particles penetrating the larynx is lower due to deposition in the nose.
3.14
thoracic fraction concentration
thoracic aerosol fraction concentration
thoracic dust fraction concentration
concentration of the sub-set of the total airborne particle concentration collected by an ideal sampler
with a sampling efficiency perfectly matching the thoracic sampling convention
Note 1 to entry: For any specific worker, the actual fraction that penetrates the larynx depends both on the
breathing rate and other factors, and on the speed and direction of the air movement. This fraction of an individual
person can deviate from the measured thoracic fraction concentration.
Note 2 to entry: For the definition of “total airborne particle concentration”, see 3.15.
Note 3 to entry: The concentration obtained using a validated sampler is an approximation to this concentration.
Note 4 to entry: The thoracic fraction concentration is also applicable to liquid particles.
3.15
total airborne particle concentration
concentration of all airborne particles present in the air before the particles are affected by the presence
of the sampler, or in the case of a personal sampler (mounted on a mannequin/person) by the presence
of the mannequin/person
[SOURCE: EN 13205-2:2014, 3.2, modified – “aerosol particles present” has been changed to “all airborne
particles present”. The wording “by the presence of the person wearing the sampler” has been replaced
by “.(mounted on a mannequin/person) by the presence of the mannequin/person” [3].]
Note 1 to entry: The total airborne particle concentration is a function of particle size.
Note 2 to entry: This quantity is generally only measured in laboratory experiments using monodisperse
or polydisperse test aerosols to determine the inhalability or sampling efficiency of samplers, and is measured
per particle aerodynamic size.
Note 3 to entry: Because all measuring instruments/ samplers are size-selective to some extent, it is often
impossible to measure correctly the total airborne particle concentration at workplaces. However, in laboratory
experiments, ideal measurement/sampling situations can be designed so that the total airborne particle
concentration can be determined using either isokinetic or pseudo-isokinetic samplers or tubular nozzles
with known high aspiration efficiencies.
Note 4 to entry: This is not equal to the “total dust” (fraction) used in many countries, with different definitions
in different countries. The definition in each country was mainly defined by what is sampled by a specified national
sampler. See e.g. the NIOSH method 0500 [16].
4 Symbols and abbreviations
total airborne particle concentration
C
TA
concentration of all airborne particles in worker's breathing zone
C
BZap
particle aerodynamic diameter
d
ae
particle size for which the penetration of the thoracic sampling convention
d
ae,,50 T
equals 0,50; = 10 µm
d
ae,,50 T
particle size for which the penetration of the respirable sampling convention

d
ae,,50 R
equals 0,50; d = 4,0 µm
ae,,50 R
inhalable sampling convention
E = Ed(
I I ae)
thoracic sampling convention
E = Ed(
T T ae)
respirable sampling convention

E = Ed(
R R ae)
geometric standard deviation used in the definition of the thoracic sampling
GSD
T
GSD
convention; = 1,55
T
geometric standard deviation used in the definition of the respirable
GSD
R
sampling convention; GSD = 1,55
T
relative inhalable fraction for the particle size distribution of interest
h SizeDistribution
( )
I
relative thoracic fraction for the particle size distribution of interest
h SizeDistribution
( )
T
relative respirable fraction for the particle size distribution of interest
h SizeDistribution
( )
R
inhalable fraction concentration for a particle size distribution of interest
H SizeDistribution
( )
I
thoracic fraction concentration for a particle size distribution of interest
H SizeDistribution
( )
I
respirable fraction concentration for a particle size distribution of interest
H SizeDistribution
( )
I
NOAA nano-objects and their aggregates and agglomerates
p probability
Φ function for the cumulative normal distribution for a standardized variable,
i.e. for which the expectation value equals zero and the standard deviation
equals one
w local (relative) wind speed at the position of the worker
z argument for the cumulative normal distribution for a standardized variable,
i.e. it has an expectation value equal to zero and a standard deviation equal
to one
5 Principle of conventions
The sampling conventions are based on the fact that only a fraction of the total airborne particle
concentration will be inhaled into the nose and/or mouth during breathing. This fraction is estimated
by the inhalable fraction (see 3.7). For some substances, other fractions of the airborne particles that
penetrate beyond the larynx or to the alveolar region are of special significance for health. This document
presents conventionalized curves approximating to the fraction inhaled and the fractions reaching
beyond the larynx or to the alveolar region. These curves are called the inhalable convention (see 3.6),
the thoracic convention (see 3.13) and the respirable convention (see 3.10), respectively.
A short description on how the data upon which the sampling conventions are based is presented
in Annex C.
The conventions for the respirable and thoracic fractions are for the fraction that can penetrate to that
respective region of the respiratory tract. These conventions are therefore considered to be penetration-
based. Conventions for the deposited fraction in the extra-thoracic, tracheobronchial and alveolar regions
are given in EN ISO 13138 [10].
Aerosol samplers/instruments used for sampling need to conform with the sampling convention
appropriate to the region of the respiratory tract where deposition of the substance being measured
might lead to a negative health effect. For example, the inhalable convention would be chosen
if the substance might lead to a health effect wherever it deposited, the thoracic convention would be
chosen if the region were the bronchi, and the respirable convention if the region were the alveoli.
Aerosol samplers/instruments can be used to collect a specific fraction according to the conventions,
or to collect several fractions simultaneously. For example, an instrument could collect particles from
the air according to the inhalable convention, and then separate this material into portions according to
the thoracic and respirable conventions. Alternatively, an instrument might just collect the respirable
fraction from the air. In this case, the design would have to ensure that selection at the entry due to
aerodynamic effects, and subsequently within the instrument, were such that the overall selection was
in accordance with the conventions.
The health-related fractions defined by the sampling conventions are to be measured externally
in the breathing zone of the exposed worker. The measured concentration is a property of the air quality
at the workplace, and not what the individual worker inhales or what penetrates to a specific region
of the individual respiratory tract.
6 Assumptions and approximations
Approximations and assumptions are unavoidable to define the sampling conventions in simulating
the very complex interaction of variables that governs respiratory tract entry and penetration.
The conventions are necessarily only approximations to particle behaviour in the respiratory tract,
and the following assumptions are particularly important:
— The fraction actually inhaled by a worker depends on air movement (speed and direction),
on breathing rate, and on whether breathing is through the nose or mouth. The values given in the
inhalable convention are for representative values of breathing rate, and averaged for all wind
directions. This is appropriate for an individual uniformly exposed to all wind directions
or predominantly to wind from behind. See the experimentally determined aspiration efficiencies
of a model human head and a simplified torso [17]. The convention usually underestimates
the inhalable fraction of larger particles for an individual who usually works facing the wind,
particularly in wind speeds greater than 4 m/s.
— The definition of the inhalable convention is defined for two ranges of workplace wind speeds,
the low wind speed range (wind speed less than 0,2 m/s, see 7.1 NOTE 2 for the basis of this value)
and the medium wind speed range (wind speeds in the range 0,2 m/s < w ≤ 4 m/s). High wind speeds
(>4 m/s) are out of the scope of this document as inhalability has not been sufficiently investigated
at these wind speeds.
— The fractions that actually penetrate the larynx or penetrate down to the alveolar region of a worker
vary from individual to individual and with breathing pattern, and the conventions are necessarily
approximations to the average case. For any specific worker, the actual fraction that penetrates
the larynx or to the alveolar region depends both on the breathing rate and other individual factors,
and on speed and direction of the air movement. Both actual fractions can deviate from the measured
thoracic or respirable fraction.
— Each convention (as a function of aerodynamic particle diameter) approximates to the fraction
penetrating to a specific region of the respiratory tract, not to the fraction depositing there.
In general, particles must deposit to have a biological effect. In this respect, the conventions can lead
to an overestimate of the potential health effect. The most important example is that the respirable
fraction is larger than the fraction of particles with an aerodynamic diameter smaller than 1 µm that
deposit in the alveolar region, because a part of these particles is exhaled without being deposited.
In many workplaces, these very small particles do not contribute much to the respirable mass.
If the median aerodynamic diameter of the relevant number, length, surface area, volume or mass
size distribution of the sampled workplace aerosol has an aerodynamic equivalent diameter smaller
than 0,5 µm, the respirable fraction will grossly overestimate the aerosol fraction that can deposit
in this region of the respiratory tract.
NOTE 1 In occupational hygiene measurement, this bias is of most concern when the same substance occurs
at some workplaces from processes emitting (small) airborne particles that mainly deposit in the respiratory
tract of workers by diffusion and at other workplaces from processes emitting (larger) airborne particles that
mainly deposit in the respiratory tract of workers by aerodynamics (impaction and gravitation). A typical
example is mineral particles (airborne as dust (i.e. larger particles) which are separated in the human
respiratory tract by aerodynamics) consisting of e.g. metal oxides. At a blast furnace the mineral particles are
reduced to a liquid metal in a hot process. This process generates metal fumes (consisting of smaller particles
that are separated in the human respiratory tract mainly by diffusion). Deposition of the smaller particles
by diffusion in the alveolar region is considerably lower than the respirable fraction corresponding to these
smaller particles.
— The thoracic convention approximates to the thoracic fraction during oral breathing. During nose
breathing, the fraction of particles penetrating the larynx is lower due to deposition in the nose.
— This document is also applicable to airborne (nano-)objects if they consist of an agglomerate
or aggregate of smaller (nano-)objects (e.g. nanoparticles) with an aerodynamic diameter exceeding
approximately 0,5 µm. As the density of an agglomerate/aggregate is much lower than the material
density of its compounds, its physical size generally is considerably larger than usual for non-
agglomerate/non-aggregate mineral particles in the size range of respirable particles. Nevertheless
all (nano-)objects, their aggregates and agglomerates (NOAA) contribute to the three fractions,
although its mass contribution can be low.
NOTE 2 The critical aerodynamic diameter is an approximation for the size of inhaled unit-density spheres
which in the alveolar region of the human respiratory tract has the same estimated separation efficiency due
to combined diffusion and interception, as due to aerodynamics. For larger particle sizes aerodynamics
dominate separation, whereas combined diffusion and interception dominate separation for smaller particle
sizes.
7 Specifications for conventions and corresponding fraction concentrations
7.1 Conventions
7.1.1 Inhalable convention
7.1.1.1 General
The shape and magnitude of inhalability are a function of the local wind speed at the worker’s breathing
d
ae
zone (w), apart from the major dependence on . In the low wind speed range, this inhalability is high
and almost independent of w. In the medium wind speed range, the ratio is decreased but levels out
from w ≈ 0,5 m/s, and it is approximately constant up to w ≈ 4 m/s.
The definition is explicitly split depending on the wind speed range at the position of sampling
(static or personal).
NOTE 1 The critical wind speeds of 0,5 m/s and 4 m/s are based on the relative speed between the worker
and the air.
NOTE 2 The limit between the low wind speed region and medium wind speed region (0,2 m/s) is based on two
different investigations: 1) Sleeth and Vincent [18] found that the inhalability for oral breathing at a minute volume
of 20 L did not significantly change between the wind speeds of 0,08 m/s and 0,24 m/s; and 2) Baldwin and
Maynard [19] investigated the relative average wind speed measured on the worker at indoor workplaces and
found it generally was below 0,2 m/s away from open doors and strong forced ventilation.
7.1.1.2 Inhalable convention in low wind speed range
Sampling of the inhalable fraction in the low wind speed range (w ≤ 0,2 m/s) shall conform to the
E
I−lwsr
following convention: the fraction of the total airborne particle concentration, at an aerodynamic
d
ae
diameter that is to be collected, shall be given by:
E 1+ ad (1)
( )
I, lwsr 1 ae
where
is the inhalable sampling convention in the low wind speed range;

E
I, lwsr
d is the particle aerodynamic diameter with 0,5 µm ≤ d ≤ 100 µm, in micrometres (µm);
ae ae
is a constant with a value of – 0,0038.
a
Some values for these two equations are given in Table 1 and illustrated in Figure 1.
Experimental data on the inhalable fraction do not yet exist for d > 100 µm, and the convention should
ae
be applied with caution to larger particles.
The current edition of EN 13205-2 [3], Table 1 states that the performance test of samplers for the
inhalable fraction in the low wind speed range shall be carried out at 0,1 m/s. This document defines the
upper wind speed for the low wind speed range at 0,2 m/s.
The mathematical formulas in Formula (1) are only valid in the size range stated, i.e.
0,5 µm ≤ d ≤ 100 µm. The functional form outside this particle size range is unknown and cannot be
ae
expected to be a continuation of the formulas valid in this size range. The mathematical formulas in
Formula (1) shall not be extrapolated.
7.1.1.3 Inhalable convention in medium wind speed range
Sampling of the inhalable fraction in the medium wind speed range (0,2 m/s < w ≤ 4 m/s) shall conform
E
I,mwsr
to the following convention: the fraction of the total airborne particle concentration, at an
d
ae
aerodynamic diameter that is to be collected, shall be given by:
E d 1+ b d (2)
( )
I,mwsr ae 1 ae
d
ae
when < 4,485 µm
E d cc+ ln d (3)
( ) ( )
I,mwsr ae 0 1 ae
d
ae
when ≥ 4,485 µm
where
is the inhalable sampling convention in the medium wind speed range;

E
I, mwsr
d is the particle aerodynamic diameter with 0,5 µm ≤ d ≤ 100 µm, in micrometres
ae ae
(µm);
is a constant with a value of – 0,0038;
b
is a constant with a value of 1,289;
c
is a constant with a value of – 0,204.
c
Some values for these two equations are given in Table 1 and illustrated in Figure 1.
=
=
=
7.1.2 Thoracic convention
7.1.2.1 General
The thoracic convention is defined as a sub-fraction of the inhalable fraction. As there are two different
definitions of the inhalable fraction in the low wind speed range and medium wind speed range,
respectively, the actual definitions of the thoracic fraction in these two wind speed ranges are somewhat
different. However, the direct relation between the inhalable and thoracic conventions is independent
of the wind speed (w).
Sampling of the thoracic sub-fraction (of the inhalable fraction) shall conform to the following:
E d
T ae
the fraction of the total airborne particle concentration, at an aerodynamic diameter that is to be
collected, shall be given by:
Ed 1− Φ z (4)
( ) ( )
T ae
d
ae
ln
d
ae,,T p=0,50
z= (5)
ln GSD
T
where
is the thoracic sub-sampling convention;
E
T
d is the particle aerodynamic diameter with 0,5 µm ≤ d ≤ 36 µm, in micrometres
ae ae
(µm);
is the cumulative normal distribution function with argument z;

Φ z
( )
z is the argument of the cumulative normal distribution function;
is the median of the lognormal distribution expressing the definition of the thoracic
d
ae,,T p=0,50
sub-sampling convention, in micrometres (µm) where d = 10,203 µm;
ae,,T p=0,50
is the geometric standard deviation of the lognormal distribution expressing the
GSD
T
definition of the thoracic sub-sampling convention.
NOTE 1 In this definition the cumulative normal distribution function is used just as any mathematical function
describing a functional relation between the independent variable(s) and the dependent variable. The definition
does not in any way imply that the particle size distribution of the thoracic fraction (3.13) has a median size equal
to d and a geometric standard deviation equal to GSDT. In order to determine the particle size
ae,,T p=0,50
distribution of a specific sampled thoracic fraction, one would need to investigate it specifically.
NOTE 2 The minimum aerodynamic diameter, 0,5 µm, approximates the smallest particle size at which
aerodynamics dominates the separation in the alveolar region of the human respiratory tract. The maximum
aerodynamic diameter, 40 µm, approximates the particle size at which the thoracic sampling convention equals
0,001.
7.1.2.2 Thoracic convention in low wind speed range
Sampling of the thoracic fraction (of the total airborne particle concentration) in the low wind speed
range shall conform to the following: the fraction E of the total airborne particle concentration
T,lwsr
at an aerodynamic diameter d that is to be collected shall be given by:
ae
=
E d = Ed E d (6)
( ) ( ) ( )
T,,lwsr ae T ae I lwsr ae
where
is the thoracic sampling convention in the low wind speed range;

E
T,lwsr
is the particle aerodynamic diameter in micrometres
...