ISO/FDIS 10298

• Abstract:

  ISO 10298:2018 lists the best available acute-toxicity data of gases taken from a search of the current literature to allow the classification of gases and gas mixtures for toxicity by inhalation.

• Status: Not Published
• ICS: 71.100.20 - Gases for industrial application
• Technical Committee: ISO/TC 58/SC 2 - Cylinder fittings
• Drafting Committee: ISO/TC 58/SC 2/WG 7 - Determination of properties of gases and gas mixtures
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 16-Sep-2026
• Completion Date: 16-Sep-2026

• Consolidates: FprEN ISO 10298 - Gas cylinders - Gases and gas mixtures - Determination of toxicity for the selection of cylinder valve outlets (ISO/FDIS 10298:2026)
• Effective Date: 12-Feb-2026
• Consolidates: ISO 10893-11:2011/Amd 1:2020 - Non-destructive testing of steel tubes — Part 11: Automated ultrasonic testing of the weld seam of welded steel tubes for the detection of longitudinal and/or transverse imperfections — Amendment 1: Change of ultrasonic test frequency; change of acceptance criteria
• Effective Date: 21-Oct-2023
• Revises: ISO 10298:2018 - Gas cylinders — Gases and gas mixtures — Determination of toxicity for the selection of cylinder valve outlets
• Effective Date: 28-Oct-2023
• Revises: ISO 10298:2018/Amd 1:2021 - Gas cylinders — Gases and gas mixtures — Determination of toxicity for the selection of cylinder valve outlets — Amendment 1
• Effective Date: 28-Oct-2023

ISO/FDIS 10298 is an ISO document for gas cylinders that lists acute inhalation toxicity data for gases and gas mixtures and explains how to determine toxicity for selecting cylinder valve outlets. It is written for people who need to classify gases, calculate the toxicity of mixtures, and choose a compatible outlet in practical cylinder design and supply work.

What does ISO/FDIS 10298 specify?

ISO/FDIS 10298 specifies how to use acute inhalation toxicity data for gases and gas mixtures so they can be classified for the selection of cylinder valve outlets. Clause 1 gives the scope, Clause 2 names the normative reference, Clause 3 defines the key terms, and Clause 4 sets out the toxicity determination method.

Annex	What it covers
Annex A	Selection of an LC value for a particular gas, including time adjustment, choice of animal, effect adjustment, read-across, other routes of application, and a conclusion with a selection algorithm
Annex B	LC values for toxic gases and toxic vapours used in gas mixtures, with literature sources

The document is organized so that the main text gives the method and the annexes provide the supporting data and selection logic. That matters in practice because users can either calculate a mixture result from component data or look up gas-specific LC values and the basis used to select them.

What are the key requirements of ISO/FDIS 10298?

ISO/FDIS 10298 uses two routes to determine toxicity: a test method and a calculation method. Clause 4 states that toxicity may be determined by test for gas mixtures where data exist, or by calculation when the component data are available. In practice, this means users should not run new inhalation tests on mixtures if the toxicity of each component is already known.

Test data and pure gases

Clause 4.2 points users to a recognized inhalation test method for new toxicity data, such as OECD TG 403. The document treats LC50 as equivalent to 1-hour exposure to albino rats for its own purposes. Annex B then lists the toxicity of pure gases as 1-hour LC50 values, and some of those values are estimated rather than directly measured.

Gas mixtures

Clause 4.3 gives the calculation method for gas mixtures. The LC value of a mixture is calculated from the mole fraction of each toxic component and the LC50 of that component, using only toxic components with LC50 below 5 000 ppm by volume. After the calculation, the mixture is classified according to the toxicity level in Clause 3.2. The note says synergistic effects are not considered, so users need to know that the result is a calculation-based classification, not a full interaction study.

Selecting an LC value for a gas

Annex A is the practical guide for choosing an LC value for a particular gas. It explains how literature data are time-adjusted, why 1-hour rat data are preferred, and how other animal data are used when the preferred data are not available. It also covers how LCLO and approximate values are treated, how read-across can be used for related substances, and why other application routes are only a last resort. In practice, Annex A helps a reader justify the LC value they use in a mixture calculation or in a classification file.

Using the data in the document

Clause 4 and Annex B together give the data needed to classify pure gases and mixtures. Annex B includes the gas name, CAS Registry Number, UN No., LC50 value, remarks, and literature reference. That means a user can trace a value back to its published basis instead of relying on a number with no explanation.

Why the document matters in use

The introduction explains that compatible gas groups for valve outlets are defined using practical criteria from ISO 14456 and that toxicity is one of those criteria. It also says the document has been used beyond outlet selection, including for transport classification and dangerous substances regulations. For users, that means the same toxicity method may support both equipment selection and regulatory classification work.

What terms does ISO/FDIS 10298 define?

• Lethal concentration 50 (LC50) - the concentration of a substance in air expected to cause death in 50% of a defined experimental animal population after a specified exposure time.
• Toxicity level - the degree to which a gas or gas mixture is poisonous; the document notes that ISO 14456 divides this into non-toxic, toxic, and very toxic groupings.
• Lethal dose 50 (LD50) - the amount of a material given at once that causes death in 50% of a test-animal group.
• Lethal concentration low value (LCLO) - the lowest concentration, other than the LC50, reported as causing death in humans or animals.
• Globally Harmonized System (GHS) - the hazard classification framework referenced in the introduction and in the notes on inhalation toxicity categories.

These terms matter because the document’s calculations, tables, and classification choices all depend on them.

Who uses ISO/FDIS 10298?

ISO/FDIS 10298 is used by people who classify gases and gas mixtures by inhalation toxicity and by those who choose cylinder valve outlets for those gases. Typical users include gas cylinder manufacturers, valve and fitting designers, gas suppliers, toxicologists, regulatory and transport classification specialists, and quality or compliance managers.

In practice, they use it to decide whether a gas or mixture is treated as non-toxic, toxic, or very toxic, to select or verify LC values, and to document the basis for a classification. It is also useful when a mixture has to be assessed from component data rather than from a direct test.

What changed in ISO/FDIS 10298 from the previous edition?

This fourth edition cancels and replaces ISO 10298:2018. The foreword says it also incorporates Amendment 1:2021.

The stated changes are:

• Annex B has been updated to include new toxic gases being added to ISO 14456.
• Some LC values have been updated.
• Amendment 1 has been incorporated into the calculation method in Clause 4.3.

Which standards are used with ISO/FDIS 10298?

Standard	How it is used with ISO/FDIS 10298
ISO 10286	The normative reference for Gas cylinders vocabulary
ISO 14456	Gives the gas properties and associated classification codes that the introduction uses to describe compatible gas groups
ISO 5145	Defines cylinder valve outlet dimensions for compatible gas groups, which is the practical application context for the toxicity classification
ISO 10156	Covers fire potential and oxidizing ability for cylinder valve outlet selection and sits alongside toxicity in the broader selection framework

What does the ISO/FDIS 10298 document contain?

ISO/FDIS 10298 contains a clause on determining toxicity, including a test method and a calculation method for gas mixtures. It also contains a worked calculation structure in Clause 4, including the variables used in the LC formula. Annex A provides a selection algorithm and explanatory text for choosing an LC value from literature data, including time adjustment and animal selection.

Annex B contains tabulated LC50 values for toxic gases and toxic vapours used in gas mixtures, together with references and remarks that explain how some values were derived. The figure in Annex A summarizes the LC selection logic, and the bibliography supports the values and methods used throughout the document.

FINAL DRAFT
International
Standard
ISO/TC 58/SC 2
Gas cylinders — Gases and gas
Secretariat: AFNOR
mixtures — Determination of
Voting begins on:
toxicity for the selection of cylinder
2026-09-16
valve outlets
Voting terminates on:
2026-11-11
Bouteilles à gaz — Gaz et mélanges de gaz — Détermination de
la toxicité pour le choix des raccords de sortie de robinets
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.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/CEN PARALLEL PROCESSING LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 58/SC 2
Gas cylinders — Gases and gas
Secretariat: AFNOR
mixtures — Determination of
Voting begins on:
toxicity for the selection of cylinder
valve outlets
Voting terminates on:
Bouteilles à gaz — Gaz et mélanges de gaz — Détermination de
la toxicité pour le choix des raccords de sortie de robinets
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
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Determination of toxicity . 2
4.1 General .2
4.2 Test method .2
4.2.1 Test procedure.2
4.2.2 Results for pure gases . . .2
4.3 Calculation method.3
Annex A (informative) Selection of an LC value for a particular gas . 4
Annex B (informative) LC values for toxic gases and toxic vapours used in gas mixtures . 7
Bibliography .12

iii
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 documents 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.
This document was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 2, Cylinder
fittings, in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/
TC 23, Transportable gas cylinders, in accordance with the Agreement on technical cooperation between ISO
and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 10298:2018), which has been technically
revised. It also incorporates the Amendment ISO 10298:2018/Amd 1:2021.
The main changes are as follows:
— update of Annex B to include new toxic gases which are being added to ISO 14456;
— some LC values have been updated;
— incorporated Amendment 1 into 4.3.
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
Introduction
ISO 5145 specifies the dimensions of different valve outlets for different compatible gas groups. These
compatible gas groups are determined according to practical criteria defined in ISO 14456.
These criteria are based on certain physical, chemical, toxic and corrosive properties of the gases. In
particular, the tissue corrosiveness is considered in this document.
The aim of this document is to assign for each gas a classification category that takes into account the toxicity
by inhalation of the gas. For gas mixtures containing toxic components, a calculation based on the method
specified in the Globally Harmonized System (GHS) is proposed.
Since the publication of the first edition of ISO 10298, this document has been used for other purposes
than the selection of cylinder valve outlets, e.g. providing toxicity data for the classification of gas and
gas mixtures according to the international transport regulations and according to the classification of
dangerous substances regulations, which, since 2003, is under the umbrella of the GHS.

v
FINAL DRAFT International Standard ISO/FDIS 10298:2026(en)
Gas cylinders — Gases and gas mixtures — Determination of
toxicity for the selection of cylinder valve outlets
1 Scope
This document lists acute inhalation toxicity data for gases and gas mixtures to enable their classification
for the selection of cylinder valve outlets.
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 10286, Gas cylinders — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 10286 and the following 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
lethal concentration 50
LC
concentration of a substance in air exposure to which, for a specified length of time, it is expected to cause
the death of 50 % of the entire defined experimental animal population after a defined time period
Note 1 to entry: See Annex A for the selection of this LC value.
3.2
toxicity level
quality, state, or relative degree of being poisonous of gases and gas mixtures
Note 1 to entry: In ISO 14456, the toxicity level is divided into three groups:
— subdivision 1: non-toxic [LC > 5 000 ppm (volume fraction)];
— subdivision 2: toxic [200 ppm (volume fraction) < LC ≤ 5 000 ppm (volume fraction)];
— subdivision 3: very toxic [LC ≤ 200 ppm (volume fraction)].
These subdivisions are sometimes used in transport regulations.
where
LC values correspond to 1 h exposure to gas;
ppm (volume fraction) indicates parts per million, by volume.
Note 2 to entry: In the GHS, the inhalation toxicity levels are:

Category 1: Fatal if inhaled 0 ppm < LC ≤ 100 ppm (volume fraction)
Category 2: Fatal if inhaled 100 ppm (volume fraction) < LC ≤ 500 ppm (volume fraction)
Category 3: Toxic if inhaled 500 ppm (volume fraction) < LC ≤ 2 500 ppm (volume fraction)
Category 4: Harmful if inhaled 2 500 ppm (volume fraction) < LC ≤ 20 000 ppm (volume fraction)
Note 3 to entry: In GHS, the LC values correspond to 4-h exposure. Consequently, the LC50 values given in Annex B
(see 4.2.2) are divided by 2 (i.e. 41/ ). The reasoning behind the division by 2 is given in Clause A.2.
3.3
lethal dose 50
LD
amount of a material, given all at once, which causes the death of 50 % of a group of test animals
3.4
lethal concentration low value
LC
LO
lowest concentration of a substance in air, other than the LC , which was reported in the original reference
paper as having caused death in humans or animals
4 Determination of toxicity
4.1 General
Toxicity may be determined through a test method (see 4.2) for gas mixtures where the data for the
components exist, or through a calculation method (see 4.3).
For reasons of animal welfare, inhalation toxicity tests geared only for the classification of gas mixtures
should be avoided if the toxicity of each of the components is available. In this case, toxicity is determined in
accordance with 4.3.
4.2 Test method
4.2.1 Test procedure
When new toxicity data are being considered for inclusion in this document, an internationally recognized
[43]
test method such as OECD TG 403 should be used.
NOTE For this document, LC is equivalent to 1-h exposure to albino rats.
4.2.2 Results for pure gases
The toxicity of pure gases is listed in Annex B, in which LC values correspond to 1-h exposure. Some of
these values have been estimated. See Annex A.

4.3 Calculation method
The LC value of a gas mixture is calculated using Formula (1):
LC  (1)
C
i

i
LC
50i
where
C is the mole fraction of the ith toxic component present in the gas mixture;
i
LC is the lethal concentration of the ith toxic component [LC < 5 000 ppm (by volume)].
50i 50
After the LC of the gas mixture has been calculated, this mixture is classified in accordance with 3.2.
NOTE Potential synergistic effects are not considered in Formula (1).

Annex A
(informative)
Selection of an LC value for a particular gas
A.1 General
When collecting data from the open literature on the acute inhalation toxicity of gases, some difficulties are
experienced. For example, taking into account that in the very early years after the publication of toxicity
data, results of standardized tests cannot be expected to be obtained. Moreover, data from reporting sources
have to be validated with respect to their details in handling and summarizing information. Furthermore,
there is a lack of information on inhalation toxicity for several gases. Thus, particular attention is needed to
incorporate all the available facts to complete the toxicological characteristics of gases.
A.2 Time adjustment
In inhalation toxicity tests, the dose-response relationship can be described by Formula (A.1):
W = c ⋅ t (A.1)
where
W is a constant which is specific for any given effect, e.g. the deaths of 50 % of the animals exposed;
c ⋅ t is the applied dose expressed as the product of concentration and exposure time.
This equation, called Haber's rule, is applicable as long as the biological half-life of the substance in question
is reasonably longer than the exposure time.
For gases and vapours with appreciable rates of detoxification or excretion over the time in question, it was
found that the relationship between concentration and time is better described by Formula (A.2).
0,5
W = c ⋅ t (A.2)
When extrapolating from 4 h to 1 h, Formula (A.2) predicts lower LC values than does Haber's rule. This
[73]
principle was applied by the UN Transport Recommendations in adopting the conversion factor 2 (i.e.
41/ ) to allow classification of materials on the basis of 1-h LC data. On the other hand, Haber's rule
predicts a lower LC when going from a 1-h to a 4-h LC . To make use of all the available data on acute
50 50
inhalation toxicity under the different exposure schemes, a more generalized version was applied.
Using 1 h as the point of reference,
— going up from shorter periods, linear extrapolation was preferred;
— coming down from longer periods, the conversion factor x hh/1 was used.
However, test results for a period less than 0,5 h were not used, as this was deemed unreliable.
A.3 Choice of animal
Since data on humans, if available, are usually not sufficient to derive any dose-response relationship,
laboratory animals are used to investigate the toxicity of substances on warm-blooded animals.

Unless there are counter indications, such as extraordinarily high or low susceptibility of the rat compared
to other animals or humans, the rat is the preferred species in the most common toxicity tests. Therefore,
LC data in rats are the most likely to be found. If they are missing, data from animals close to the rat in
body weight are evaluated.
A.4 Adjustment for effects
Instead of LC , often the term LC is found in the reporting literature and in databases.
50 LO
Unfortunately, the use of this term is not consistent enough to make any assumptions as to whether the
LC is below or above that value. Nevertheless, it seems reasonable to make the same use of the LC as if it
50 LO
were information about an approximate lethal concentration (ALC). For the classification of gases, no higher
precision is required, but the calculation formula for gas mixtures requires a definite LC value to be set.
Another LC value has been taken as LC when additional information proved it plausible to do so.
A.5 Read across
Some substances had to be characterized as analogous to chemically related structures with known
physiological properties. Structure-activity relationships have been taken into consideration as far as
possible. Moreover, in several instances, the toxicological impact on the respiratory tract is based on
fundamental reactions such as the hydrolysis of different gases in the presence of moisture leading to the
same reactive principle.
A.6 Other routes of application
This route should only be used as a very last option.
Sometimes the inhalation toxicity of volatile liquids has to be assessed on the basis of other parenteral,
especially intraperitoneal (i.p.), LD values. There is a good correlation between the LC and LD i.p. as far
50 50 50
as systemically active substances are concerned. Taking toxic pesticides as an example, it can be shown that
an LD i.p. corresponds in aerosol studies by far and large with the same body weight-related dose inhaled
by rats during a 4-h period. For instance, an LD i.p. of 100 mg/kg can be assumed to be equivalent to a
4 h-LC of about 1 mg/l air.
A.7 Conclusion
The selection of an LC value for a particular gas follows the logic algorithm shown in Figure A.1. The
preferred measurement standard is LC RAT for 1 h. Lacking good data for these exact parameters,
LC RAT values for times different from, but closest to, 1 h were selected, eliminating all data for exposures
less than 0,5 h. If no reliable LC data from RAT were available, the next animal of choice was MUS (mouse),
then in the following order: rabbit, guinea-pig, cat, dog and monkey. Data for 1-h exposures were preferred.
If no reliable LC data were found for any animal, then a search was made for a reliable LC value, utilizing
50 LO
the same hiera
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St l D fi iti
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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
distance from edge: 1.27 cm, Footer distance from
at the address below or ISO’s member body in the country of the requester.
edge: 0.5 cm
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
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ii © ISO #### 2026 – All rights reserved
ii
ISO/DISFDIS 10298:2026(en)
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Contents
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Foreword . iv
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Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Determination of toxicity . 2
4.1 General . 2
4.2 Test method . 2
4.3 Calculation method . 2
Annex A (informative) Selection of an LC value for a particular gas . 4
Annex B (informative) LC values for toxic gases and toxic vapours used in gas mixtures . 9
Bibliography . 14

Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Determination of toxicity . 2
4.1 General . 2
4.2 Test method . 2
4.2.1 Test procedure . 2
4.2.2 Results for pure gases . 2
4.2.3 Calculation method . 2
Annex A (informative) Selection of an LC value for a particular gas . 3
A.1 General . 3
A.2 Time adjustment . 3
A.3 Choice of animal . 3
A.4 Adjustment for effects . 4
A.5 Read across . 4
A.6 Other routes of application . 4
A.7 Conclusion . 4
Annex B (informative) LC values for toxic gases and toxic vapours used in gas mixtures . 6
Bibliography . 11
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© ISO 2026 – All rights reserved
iii
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Foreword Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers
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 documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directiveswww.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.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.
This document was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 2, Cylinder
fittings, in collaboration with the European Committee for Standardization (CEN) Technical Committee
CEN/TC 23, Transportable gas cylinders, in accordance with the Agreement on technical cooperation between
Formatted: Font: Not Italic
ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 10298:2018), which has been technically
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revised. It also incorporates the Amendment ISO 10298:2018/Amd 1:2021.
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The main changes are as follows:
— — update of Annex BAnnex B to include new toxic gases which are being added to ISO 14456;
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— — some LC values have been updated;
— — incorporated Amendment 1 into 4.3.4.3.
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.htmlwww.iso.org/members.html.
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iv © ISO #### 2026 – All rights reserved
iv
ISO/DISFDIS 10298:2026(en)
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Introduction
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ISO 5145 specifies the dimensions of different valve outlets for different compatible gas groups. These
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compatible gas groups are determined according to practical criteria defined in ISO 14456.
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These criteria are based on certain physical, chemical, toxic and corrosive properties of the gases. In particular,
the tissue corrosiveness is considered in this document.
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The aim of this document is to assign for each gas a classification category that takes into account the toxicity
by inhalation of the gas. For gas mixtures containing toxic components, a calculation based on the method
specified in the Globally Harmonized System (GHS) is proposed.
Since the publication of the first edition of ISO 10298, this document has been used for other purposes than
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the selection of cylinder valve outlets, e.g. providing toxicity data for the classification of gas and gas mixtures
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according to the international transport regulations and according to the classification of dangerous
substances regulations, which, since 2003, is under the umbrella of the GHS.
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© ISO 2026 – All rights reserved
v
DRAFT International Standard ISO/DIS 10298:2026(en)

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single
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Gas cylinders — Gases and gas mixtures — Determination of toxicity
and Asian text, Adjust space between Asian text and
for the selection of cylinder valve outlets
numbers
1 Scope Formatted: Top: 1.4 cm, Bottom: 1 cm, Header
distance from edge: 1.27 cm, Footer distance from
edge: 0.5 cm
This document lists acute inhalation toxicity data for gases and gas mixtures to enable their classification for
the selection of cylinder valve outlets.
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 10286, Gas cylinders — Vocabulary
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3 Terms and definitions
Widow/Orphan control
For the purposes of this document, the terms and definitions given in ISO 10286 and the following apply.
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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
— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
3.1 3.1
lethal concentration 50
LC
concentration of a substance in air exposure to which, for a specified length of time, it is expected to cause the
death of 50 % of the entire defined experimental animal population after a defined time period
Note 1 to entry: See Annex AAnnex A for the selection of this LC value.
3.2 3.2
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toxicity level
quality, state, or relative degree of being poisonous of gases and gas mixtures
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Note 1 to entry: In ISO 14456, the toxicity level is divided into three groups:
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stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
— — subdivision 1: non-toxic [LC > 5 000 ppm (volume fraction)];
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
— — subdivision 2: toxic [200 ppm (volume fraction) < LC50 ≤ 5 000 ppm (volume fraction)];
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— — subdivision 3: very toxic [LC50 ≤ 200 ppm (volume fraction)].
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These subdivisions are sometimes used in transport regulations.
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where
between Asian text and numbers
Formatted Table
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LC values correspond to 1 h exposure to gas;
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ppm (volume fraction) indicates parts per million, by volume.
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Note 2 to entry: In the GHS, the inhalation toxicity levels are:
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Category 1: Fatal if inhaled 0 ppm < LC ≤ 100 ppm (volume fraction)
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Category 2: Fatal if inhaled 100 ppm (volume fraction) < LC50 ≤ 500 ppm (volume fraction)
between Asian text and numbers
Category 3: Toxic if inhaled 500 ppm (volume fraction) < LC ≤ 2 500 ppm (volume fraction)
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Category 4: Harmful if inhaled 2 500 ppm (volume fraction) < LC ≤ 20 000 ppm (volume fraction)
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Note 3 to entry: In GHS, the LC values correspond to 4-h exposure. Consequently, the LC50 values given in
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4 /1
Annex BAnnex B (see 4.2.2)4.2.2) are divided by 2 (i.e. ).�4⁄1). The reasoning behind the division by 2 is given in
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Clause A.2.Clause A.2.
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3.3 3.3
between Asian text and numbers
lethal dose 50
Formatted
LD .
amount of a material, given all at once, which causes the death of 50 % of a group of test animals
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...
3.4 3.4
lethal concentration low value Formatted Table
LC
LO
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lowest concentration of a substance in air, other than the LC , which was reported in the original reference
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paper as having caused death in humans or animals
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4 Determination of toxicity
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4.1 General
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Toxicity may be determined through a test method (see 4.2)4.2) for gas mixtures where the data for the
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components exist, or through a calculation method (see 4.3).4.3).
Formatted
...
For reasons of animal welfare, inhalation toxicity tests geared only for the classification of gas mixtures should
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be avoided if the toxicity of each of the components is available. In this case, toxicity is determined in
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accordance with 4.3.4.3.
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4.2 Test method
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Formatted
4.2.1 Test procedure .
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When new toxicity data are being considered for inclusion in this document, an internationally recognized test
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[43] [43]
method such as OECD TG 403 should be used.
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NOTE For this document, LC50 is equivalent to 1-h exposure to albino rats.
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4.2.2 Results for pure gases Formatted
...
Formatted
...
The toxicity of pure gases is listed in Annex B,Annex B, in which LC50 values correspond to 1-h exposure. Some
of these values have been estimated. See Annex A.Annex A.
4.3 Calculation method
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The LC value of a gas mixture is calculated using Formula (1):Formula (1):
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2 © ISO #### 2026 – All rights reserved
ISO/DISFDIS 10298:2026(en)
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LC = (1)
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C
i
∑
i
LC
50i
𝐿𝐿𝐶𝐶 = (1)
𝐶𝐶
𝑖𝑖
�
𝐿𝐿𝐶𝐶
50𝑖𝑖
𝑖𝑖
where
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between Latin and Asian text, Adjust space between
C is the mole fraction of the ith toxic component present in the gas mixture;
i
Asian text and numbers
LC50i is the lethal concentration of the ith toxic component [LC50 < 5 000 ppm (by volume)].
Formatted: Adjust space between Latin and Asian text,
After the LC50 of the gas mixture has been calculated, this mixture is classified in accordance with 3.2.3.2.
Adjust space between Asian text and numbers, Tab
stops: Not at 0.7 cm + 1.4 cm + 2.8 cm + 3.5 cm +
NOTE Potential synergistic effects are not considered in Formula (1). (1).
4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
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© ISO 2026 – All rights reserved
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Annex A
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Selection of an LC value for a particular gas
A.1 General
When collecting data from the open literature on the acute inhalation toxicity of gases, some difficulties are
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experienced. For example, taking into account that in the very early years after the publication of toxicity data,
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results of standardized tests cannot be expected to be obtained. Moreover, data from reporting sources have
to be validated with respect to their details in handling and summarizing information. Furthermore, there is
a lack of information on inhalation toxicity for several gases. Thus, particular attention is needed to
incorporate all the available facts to complete the toxicological characteristics of gases.
A.2 Time adjustment
In inhalation toxicity tests, the dose-response relationship can be described by Formula (A.1):Formula (A.1):
W = c ⋅ t (A.1)
Formatted: label
where
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between Latin and Asian text, Adjust space between
W is a constant which is specific for any given effect, e.g. the deaths of 50 % of the animals exposed;
Asian text and numbers
c ⋅ t is the applied dose expressed as the product of concentration and exposure time.
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This equation, called Haber's rule, is applicable as long as the biological half-life of the substance in question
Adjust space between Asian text and numbers, Tab
is reasonably longer than the exposure time.
stops: Not at 0.7 cm + 1.4 cm + 2.8 cm + 3.5 cm +
4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
For gases and vapours with appreciable rates of detoxification or excretion over the time in question, it was
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found that the relationship between concentration and time is better described by
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Formula (A.2).Formula (A.2).
0,5
W = c ⋅ t (A.2)
Formatted: label
Formatted: Adjust space between Latin and Asian text,
0,5
When extrapolating from 4 h to 1 h, Formula (A.2) W = c ⋅ t (A.2) predicts lower LC values than does
Adjust space between Asian text and numbers, Tab
[73] [73]
Haber's rule. This principle was applied by the UN Transport Recommendations in adopting the
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
conversion factor 2 (i.e. 4 /1 ) 4⁄1) to allow classification of materials on the basis of 1-h LC50 data. On the
�
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
other hand, Haber's rule predicts a lower LC when going from a 1-h to a 4-h LC . To make use of all the
50 50
Formatted: Default Paragraph Font
available data on acute inhalation toxicity under the different exposure schemes, a more generalized version
was applied.
Using 1 h as the point of reference,
— — going up from shorter periods, linear extrapolation was preferred;
— — coming down from longer periods, the conversion factor x h /1 h 𝑥𝑥 h/1 h was used.
�
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However, test results for a period less than 0,5 h were not used, as this was deemed unreliable.
Adjust space between Asian text and numbers
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4 © ISO #### 2026 – All rights reserved
ISO/DISFDIS 10298:2026(en)
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A.3 Choice of animal
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Since data on humans, if available, are usually not sufficient to derive any dose-response relationship,
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laboratory animals are used to investigate the toxicity of substances on warm-blooded animals.
Adjust space between Asian text and numbers
Unless there are counter indications, such as extraordinarily high or low susceptibility of the rat compared to
other animals or humans, the rat is the preferred species in the most common toxicity tests. Therefore, LC
data in rats are the most likely to be found. If they are missing, data from animals close to the rat in body
weight are evaluated.
A.4 Adjustment for effects
Instead of LC , often the term LC is found in the reporting literature and in databases.
50 LO Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers
Unfortunately, the use of this term is not consistent enough to make any assumptions as to whether the LC
is below or above that value. Nevertheless, it seems reasonable to make the same use of the LC as if it were
LO
information about an approximate lethal concentration (ALC). For the classification of gases, no higher
precision is required, but the calculation formula for gas mixtures requires a definite LC value to be set.
Another LC value has been taken as LC when additional information proved it plausible to do so.
A.5 Read across
Some substances had to be characterized as analogous to chemically related structures with known
Formatted: Adjust space between Latin and Asian text,
physiological properties. Structure-activity relationships have been taken into consideration as far as possible.
Adjust space between Asian text and numbers
Moreover, in several instances, the toxicological impact on the respiratory tract is based on fundamental
reactions such as the hydrolysis of different gases in the presence of moisture leading to the same reactive
principle.
A.6 Other routes of application
This route should only be used as a very last option.
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Adjust space between Asian text and numbers
Sometimes the inhalation toxicity of volatile liquids has to be assessed on the basis of other parenteral,
especially intraperitoneal (i.p.), LD50 values. There is a good correlation between the LC50 and LD50 i.p. as far
as systemically active substances are concerned. Taking toxic pesticides as an example, it can be shown that
an LD50 i.p. corresponds in aerosol studies by far and large with the same body weight-related dose inhaled by
rats during a 4-h period. For instance, an LD i.p. of 100 mg/kg can be assumed to be equivalent to a 4 h-LC
50 50
of about 1 mg/l air.
A.7 Conclusion
The selection of an LC value for a particular gas follows the logic algorithm shown in Figure A.1.Figure A.1.
The preferred measurement standard is LC RAT for 1 h. Lacking good data for these exact parameters,
LC50 RAT values for times different from, but closest to, 1 h were selected, eliminating all data for exposures
less than 0,5 h. If no reliable LC data from RAT were available, the next animal of choice was MUS (mouse),
...

PROJET FINAL
Norme
internationale
ISO/TC 58/SC 2
Bouteilles à gaz — Gaz et mélanges
Secrétariat: AFNOR
de gaz — Détermination de la
Début de vote:
toxicité pour le choix des raccords
2026-09-16
de sortie de robinets
Vote clos le:
2026-11-11
Gas cylinders — Gases and gas mixtures — Determination of
toxicity for the selection of cylinder valve outlets
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.
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NATIONALE.
Numéro de référence
PROJET FINAL
Norme
internationale
ISO/TC 58/SC 2
Bouteilles à gaz — Gaz et mélanges
Secrétariat: AFNOR
de gaz — Détermination de la
Début de vote:
toxicité pour le choix des raccords
2026-09-16
de sortie de robinets
Vote clos le:
2026-11-11
Gas cylinders — Gases and gas mixtures — Determination of
toxicity for the selection of cylinder valve outlets
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2026
LES DESTINATAIRES DU PRÉSENT PROJET SONT
Tous droits réservés.
INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS,
NOTIFICATION DES DROITS DE PROPRIÉTÉ DONT ILS
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Publié en Suisse
Numéro de référence
ii
Sommaire Page
Avant-propos .iv
Introduction .v
1 Domaine d'application . 1
2 Références normatives . 1
3 Termes et définitions . 1
4 Détermination de la toxicité . . 2
4.1 Généralités .2
4.2 Méthode d'essai . .2
4.2.1 Mode opératoire d'essai .2
4.2.2 Résultats pour les gaz purs .2
4.3 Méthode de calcul .3
Annexe A (informative) Choix d’une valeur de LC pour un gaz particulier . 4
Annexe B (informative) Valeurs de LC pour les gaz et vapeurs toxiques utilisés dans les
mélanges de gaz . 7
Bibliographie .12

iii
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 (IEC) 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 brevet 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.
Le présent document a été élaboré par le comité technique ISO/TC 58, Bouteilles à gaz, sous-comité SC 2,
Accessoires de bouteilles, en collaboration avec le comité technique CEN/TC 23, Bouteilles à gaz transportables
du Comité européen de normalisation (CEN), conformément à l’Accord de coopération technique entre l’ISO
et le CEN (Accord de Vienne).
Cette quatrième édition annule et remplace la troisième édition (ISO 10298:2018), qui a fait l’objet d’une
révision technique. Elle intègre également l’Amendement ISO 10298:2018/Amd 1:2021.
Les principales modifications sont les suivantes:
— mise à jour de l’Annexe B afin d'inclure les nouveaux gaz toxiques ajoutés à l'ISO 14456;
— certaines valeurs de LC ont été mises à jour;
— intégration de l'Amendement 1 dans le 4.3.
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/members.html.

iv
Introduction
L’ISO 5145 spécifie les dimensions de différents raccords de sortie de robinets pour différents groupes de
gaz compatibles. Ces groupes de gaz compatibles sont déterminés selon les critères pratiques définis dans
l’ISO 14456.
Ces critères reposent sur certaines propriétés physiques, chimiques, toxiques et corrosives des gaz. La
corrosivité sur les tissus fait l’objet d’une considération particulière dans le présent document.
L’objectif du présent document est d’affecter à chaque gaz une catégorie de classification tenant compte de la
toxicité par inhalation du gaz. Pour les mélanges de gaz contenant des composants toxiques, une méthode de
calcul reposant sur la méthode spécifiée dans le système général harmonisé (SGH) est proposée.
Depuis la publication de la première édition de l'ISO 10298, ce document a été utilisé à d’autres fins que
le choix des raccords de sortie de robinets de bouteilles à gaz, par exemple en fournissant des données de
toxicité pour la classification des gaz et mélanges de gaz conformément à la réglementation internationale
sur les transports et à la réglementation sur la classification des substances dangereuses qui, depuis 2003,
est sous l’égide du SGH.
v
PROJET FINAL Norme internationale ISO/FDIS 10298:2026(fr)
Bouteilles à gaz — Gaz et mélanges de gaz — Détermination
de la toxicité pour le choix des raccords de sortie de robinets
1 Domaine d'application
Le présent document répertorie les données de toxicité aiguë par inhalation pour les gaz et les mélanges de
gaz afin de permettre leur classification pour le choix des raccords de sortie de robinets.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu'ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l'édition citée s'applique. Pour
les références non datées, la dernière édition du document de référence s'applique (y compris les éventuels
amendements).
ISO 10286, Bouteilles à gaz — Vocabulaire
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions de l'ISO 10286 ainsi que les suivants
s’appliquent.
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
concentration létale 50
LC
concentration d’une substance dans l’air, pour laquelle une exposition pendant une durée spécifiée, est
présumée entraîner la mort de 50 % de l'ensemble de la population définie d’animaux expérimentaux après
une durée définie
Note 1 à l'article: Voir l’Annexe A pour le choix de cette valeur de LC .
3.2
niveau de toxicité
qualité, état ou degré relatif de toxicité des gaz et des mélanges de gaz
Note 1 à l'article: Dans l’ISO 14456, le niveau de toxicité est divisé en trois groupes:
— subdivision 1: non toxique [LC > 5 000 ppm (fraction volumique)];
— subdivision 2: toxique [200 ppm (fraction volumique) < LC ≤ 5 000 ppm (fraction volumique)];
— subdivision 3: très toxique [LC ≤ 200 ppm (fraction volumique)].
Ces subdivisions sont parfois utilisées dans la réglementation sur les transports.

où
valeurs de LC correspondent à une exposition de 1 h au gaz;
ppm (fraction volumique)indique des parties par million, en volume.
Note 2 à l'article: Dans le SGH, les niveaux de toxicité par inhalation sont:
Catégorie 1: Mortel par inhalation 0 ppm < LC ≤ 100 ppm (fraction volumique)
Catégorie 2: Mortel par inhalation 100 ppm (fraction volumique) < LC ≤ 500 ppm (fraction volumique)
Catégorie 3: Toxique par inhalation 500 ppm (fraction volumique) < LC ≤ 2 500 ppm (fraction volumique)
Catégorie 4: Nocif par inhalation 2 500 ppm (fraction volumique) < LC ≤ 20 000 ppm (fraction volu-
mique)
Note 3 à l'article: Dans le SGH, les valeurs de LC correspondent à une exposition de 4 heures. Par conséquent, les
valeurs de LC50 données en Annexe B (voir le 4.2.2) sont divisées par 2 (à savoir 41/ ). Le raisonnement justifiant la
division par 2 est donné à l’Article A.2.
3.3
dose létale 50
LD
quantité d’un matériau, donné en une seule fois, qui entraîne la mort de 50 % d’un groupe d’animaux d’essai
3.4
concentration létale basse
LC
LO
concentration la plus faible d’une substance dans l’air, autre que celle de la LC , ayant été signalée dans le
rapport pris en référence comme ayant provoqué la mort d’êtres humains ou d’animaux
4 Détermination de la toxicité
4.1 Généralités
La toxicité peut être déterminée par une méthode d’essai (voir le 4.2) pour des mélanges de gaz lorsque les
données existent pour les composants, ou par une méthode de calcul (voir le 4.3).
Pour des raisons de protection des animaux, il convient d’éviter les essais de toxicité par inhalation destinés
uniquement à la classification des mélanges gazeux si la toxicité de chacun des composants est connue. Dans
ce cas, la toxicité est déterminée conformément au 4.3.
4.2 Méthode d'essai
4.2.1 Mode opératoire d'essai
Lorsqu’il est envisagé d’inclure de nouvelles données de toxicité dans le présent document, il convient
d’employer une méthode d’essai reconnue au niveau international, comme par exemple l’essai OCDE n°
[43]
403 .
NOTE Pour ce document, LC équivaut à une exposition de rats albinos pendant 1 h.
4.2.2 Résultats pour les gaz purs
La toxicité des gaz purs est indiquée dans l’Annexe B. Les valeurs de LC correspondent à une exposition
de 1 h. Certaines de ces valeurs ont été estimées. Voir l’Annexe A.

4.3 Méthode de calcul
La valeur de LC d’un mélange de gaz est calculée à l’aide de la Formule (1).
LC  (1)
c
i

i
LC
50i
où
C est la fraction molaire du ième composé toxique présent dans le mélange de gaz;
i
LC est la concentration létale du ième composé toxique [LC < 5 000 ppm (en volume)].
50i 50
Après que la LC du mélange de gaz a été calculée, ce mélange est classé conformément au 3.2.
NOTE Les effets synergiques potentiels ne sont pas considérés dans la Formule (1).

Annexe A
(informative)
Choix d’une valeur de LC pour un gaz particulier
A.1 Généralités
Lors de la collecte de données issues d'ouvrages de référence accessibles au public sur la toxicité aiguë par
inhalation des gaz, certaines difficultés se présentent. Si l’on considère, par exemple, les toutes premières
années suivant la publication des données de toxicité, il ne faut pas s’attendre à y trouver les résultats d’essais
normalisés. En outre, les données concernant les manipulations et les conclusions des sources d’information
doivent être validées. De plus, les informations relatives à la toxicité par inhalation de plusieurs gaz sont
insuffisantes. Il faut donc veiller tout particulièrement à utiliser tous les faits disponibles afin de compléter
les caractéristiques toxicologiques des gaz.
A.2 Détermination du temps
Dans les essais de toxicité par inhalation, la relation dose-réponse peut être décrite par la Formule (A.1):
W = c ⋅ t (A.1)
où
W est une constante spécifique à un effet donné, par exemple la mort de 50 % des animaux
exposés;
c ⋅ t est la dose appliquée, exprimée sous la forme du produit de la concentration par la durée de
l’exposition.
Cette loi, appelée loi de Haber, n’est applicable que si la demi-vie biologique de la substance concernée est
sensiblement supérieure à la durée de l’exposition.
Lorsque les gaz ou les vapeurs présentent un taux de désintoxication ou d’excrétion non négligeable par
rapport à la durée d’exposition, la relation entre la concentration et la durée est décrite plus précisément par
la Formule (A.2):
0,5
W = c ⋅ t (A.2)
En extrapolant de 4 h à 1 h, la Formule (A.2) donne des valeurs de LC inférieures à celles obtenues avec la
[73]
loi de Haber. Ce principe a été adopté dans les recommandations des Nations Unies en matière de
transport pour retenir un facteur de conversion de 2 (c’est-à-dire 41/ ) afin de permettre une classification
des matériaux reposant sur des données 1 h-LC . D’un autre côté, la loi de Haber donne un facteur LC
50 50
inférieur lorsque l’on passe de 1 h à 4 h-LC . Dès lors, et pour pouvoir utiliser toutes les données de toxicité
aiguë par inhalation disponibles dans des schémas d’exposition différents, une relation plus générale a été
appliquée.
En prenant 1 h comme point de référence:
— l’extrapolation linéaire a été retenue en partant des durées d’exposition inférieures;
— pour des durées d’exposition plus longues, le facteur de conversion xhh/1 a été utilisé.
Toutefois, les résultats des essais pour des durées inférieures à 0,5 h n’ont pas été retenus, car ils ne
semblaient pas fiables.
A.3 Choix des animaux
Les données concernant les êtres humains, lorsqu’elles sont disponibles, étant généralement insuffisantes
pour en déduire une relation dose-réponse, on utilise des animaux de laboratoire pour étudier la toxicité des
substances sur des animaux à sang chaud.
À moins de contre-indications, telles que sensibilité excessivement élevée ou faible par rapport à celle des
autres animaux ou à celle des êtres humains, le rat reste l’espèce préférée pour la plupart des essais de
toxicité. Les données LC du rat sont donc celles qui sont les plus faciles à trouver. Dans le cas contraire, on
détermine celles se rapportant aux animaux qui, en poids, sont proches du rat.
A.4 Réglage des effets
On trouve souvent dans les rapports et bases de données des notations LC au lieu de LC .
LO 50
Malheureusement, l’utilisation de ce terme n’est pas assez cohérente pour permettre de supposer que la
valeur de LC lui est supérieure ou inférieure. Quoi qu’il en soit, il semble raisonnable de considérer le
terme LC comme une concentration létale approximative (ALC, approximate lethal concentration). La
LO
classification des gaz ne demande pas une meilleure précision, mais le calcul de la toxicité des mélanges
de gaz exige une valeur précise de LC . Une autre valeur de LC a été retenue comme LC lorsque des
50 50
informations complémentaires prouvaient qu’il était possible de le faire.
A.5 Analogie
Certaines substances doivent être caractérisées comme analogues à des structures chimiques apparentées
présentant des propriétés physiologiques connues. Les relations structure/activité ont été prises en
considération autant que possible. De plus, en de nombreuses occasions, l’impact toxicologique sur le
système respiratoire repose sur des réactions fondamentales, telles que l’hydrolyse des différents gaz en
présence d’humidité, donnant lieu à la même réaction.
A.6 Autres champs d’application
Il convient de n'utiliser cette option qu’en dernier ressort.
Dans certains cas, la toxicité par inhalation de liquides volatils doit être estimée à partir d'autres valeurs
de LD parentérales et, en particulier, intrapéritonéales. Il existe, pour des substances systématiquement
actives, une bonne corrélation entre les valeurs de LC et les valeurs intrapéritonéales LD . Si l’on considère
50 50
par exemple les pesticides toxiques, il peut être démontré qu’une quantité intrapéritonéale LD correspond
généralement, dans le domaine des aérosols, à la même dose rapportée au poids, inhalée par des rats pendant
une période de 4 h. En fait, par exemp
...