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

Overview

ISO/FDIS 10298:2026 is an International Standard developed by the International Organization for Standardization (ISO) that specifies the methodology for determining the acute inhalation toxicity of gases and gas mixtures. The primary application of this standard is to enable the classification of gases and their mixtures for the selection of appropriate cylinder valve outlets, thereby ensuring safety in gas handling and storage. The standard provides a comprehensive listing of available toxicity data and offers guidance on classification based on toxicity, supporting compliance with global regulatory requirements.

Key Topics

• Acute Inhalation Toxicity Data: The standard compiles the best available toxicity data for a wide range of gases and gas mixtures, supported by a thorough review of current literature.
• Classification Criteria: Gases are classified by toxicity levels according to well-established thresholds, aligning with international regulations and the Globally Harmonized System (GHS) of classification and labelling of chemicals.
• Toxicity Levels:
  • Non-toxic: LC50 > 5000 ppm (volume fraction)
  • Toxic: 200 ppm < LC50 ≤ 5000 ppm
  • Very toxic: LC50 ≤ 200 ppm
• Test and Calculation Methods: ISO/FDIS 10298 describes both experimental testing (in accordance with internationally recognized guidelines) and calculation methods for determining the toxicity of gas mixtures when individual component data is available.
• Algorithm for Classification: An annex provides a logical step-by-step approach for selecting the appropriate LC50 value from available data, focusing on animal testing data and literature sources.

Applications

• Gas Cylinder Valve Selection: The core purpose of ISO/FDIS 10298 is to ensure that gases and gas mixtures are matched with compatible and safe cylinder valve outlets, according to their toxicity classification. This is critical for the safe transportation, storage, and handling of industrial, specialty, and medical gases.
• Regulatory Compliance: The standard is widely used by manufacturers, distributors, and regulators concerned with the classification of dangerous substances under international transport regulations and safety legislation following GHS guidelines.
• Safety Data Sheets (SDS): Toxicity values and classifications derived from this standard are frequently referenced in Safety Data Sheets used globally to communicate hazards associated with gaseous chemicals.
• Risk Assessment and Management: Laboratories, gas suppliers, and facilities using compressed gases utilize this standard to conduct risk assessments and inform appropriate mitigation measures for worker health and environmental protection.
• Cross-Referencing with Transport Regulations: The classification system within ISO/FDIS 10298 is consistent with UN transport recommendations for dangerous goods, providing harmonization across international safety protocols.

Related Standards

• ISO 5145: Details the dimensions and designations for cylinder valve outlets for different gas groups.
• ISO 14456: Specifies the grouping of gases according to properties such as flammability, oxidizing potential, and toxicity, forming the basis for compatible valve selection.
• ISO 10286: Provides the terminology and vocabulary relevant to gas cylinders and their fittings.
• Globally Harmonized System (GHS): Offers the overarching framework for classification and labelling of chemicals worldwide, which ISO/FDIS 10298 follows for toxicity classification.
• OECD TG 403: Defines internationally accepted procedures for acute inhalation toxicity testing, recognized in the test method section of this ISO standard.

Practical Value

ISO/FDIS 10298:2026 helps ensure the safety of operations involving compressed gases through scientifically validated toxicity data and robust classification methods. By standardizing how toxicity is assessed and applied to valve selection, this standard plays a critical role in minimizing inhalation hazards, supporting compliance with international transport and safety regulations, and facilitating global trade in industrial and specialty gases. Whether you are a gas producer, distributor, safety officer, or regulatory authority, adopting the practices set forth in ISO/FDIS 10298 promotes reliable safety management across the full gas supply chain.

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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Secretariat: AFNOR
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Date: 2026-03-0309-01
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Gas cylinders — Gases and gas mixtures — Determination of toxicity
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for the selection of cylinder valve outlets
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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
Formatted: French (France)
EmailE-mail: [e-mail]
Formatted: French (France)
Website: www.iso.orgwww.iso.org
Formatted: French (France)
Published in Switzerland
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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
Adjust space between Asian text and numbers
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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Formatted: HeaderCentered
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
Formatted: Default Paragraph Font
revised. It also incorporates the Amendment ISO 10298:2018/Amd 1:2021.
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
The main changes are as follows:
— — update of Annex BAnnex B to include new toxic gases which are being added to ISO 14456;
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
— — 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.
Formatted: Font: 10 pt
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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.
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
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.
Formatted: Default Paragraph Font
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
Formatted: Default Paragraph Font
the selection of cylinder valve outlets, e.g. providing toxicity data for the classification of gas and gas mixtures
Formatted: Default Paragraph Font
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
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for the selection of cylinder valve outlets
numbers
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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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— — 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
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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)
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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
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lethal dose 50
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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).
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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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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
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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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C is the mole fraction of the ith toxic component present in the gas mixture;
i
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LC50i is the lethal concentration of the ith toxic component [LC50 < 5 000 ppm (by volume)].
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After the LC50 of the gas mixture has been calculated, this mixture is classified in accordance with 3.2.3.2.
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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)
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where
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W is a constant which is specific for any given effect, e.g. the deaths of 50 % of the animals exposed;
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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
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is reasonably longer than the exposure time.
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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)
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0,5
When extrapolating from 4 h to 1 h, Formula (A.2) W = c ⋅ t (A.2) predicts lower LC values than does
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[73] [73]
Haber's rule. This principle was applied by the UN Transport Recommendations in adopting the
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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
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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.
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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.
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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.
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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
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physiological properties. Structure-activity relationships have been taken into consideration as far as possible.
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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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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),
...