prEN ISO 13734 rev

• Abstract:

  ISO 13734;2013 specifies requirements and test methods for organic compounds suitable for odorization of natural gas and natural gas substitutes for public gas supply, hereafter referred to as odorants.

• Status: Not Published
• Publication Date: 15-Nov-2027
• ICS: 75.060 - Natural gas
• Technical Committee: CEN/TC 238 - Test gases, test pressures and categories of appliances
• Current Stage: 4060 - Closure of enquiry - Enquiry
• Start Date: 13-Jul-2026
• Completion Date: 13-Jul-2026
• Ref Project: oSIST prEN ISO 13734:2026 - Natural gas - Organic components used as odorants for fuel gases - Requirements and test methods (ISO/DIS 13734:2026)

• Revises: EN ISO 13734:2013 - Natural gas - Organic components used as odorants - Requirements and test methods (ISO 13734:2013)
• Effective Date: 21-Feb-2024

Overview

prEN ISO 13734 rev specifies the requirements and test methods for organic components used as odorants in natural gas and natural gas substitutes, including biomethane and mixtures containing up to 20% hydrogen by volume. Developed under ISO/TC 193 and adopted by CEN, this standard ensures that fuel gases for public supply are safely detectable by smell at low concentrations, significantly mitigating the risk of undetected gas leaks. The document provides comprehensive guidance for selecting, testing, and applying suitable odorizing chemicals, as well as for verifying their stability, compatibility, and handling in diverse transmission and distribution environments.

Key Topics

• Odorant Effectiveness: The standard outlines essential criteria for odorants, including strong, distinctive, and unpleasant odors that are not easily confused with common smells. Effective odorants enable early detection of gas leaks, well before reaching hazardous concentrations.
• Physical and Chemical Properties: Requirements for boiling point, vapor pressure, cloud point, solubility in water, and absence of insoluble matter are specified to ensure odorant performance under varying operational conditions.
• Compatibility and Stability: Guidelines address the odorant's interaction with gas system materials (e.g., metals, elastomers) and its long-term endurance in storage, pipelines, soil, and water.
• Test Methods: Standardized procedures, such as gas chromatography for composition analysis and adherence to OECD and ISO methodologies for physical property tests, provide quality assurance.
• Handling and Transport: Emphasis is placed on proper documentation, labelling, and adherence to safety regulations, including requirements for Safety Data Sheets (SDS).
• Stability in the Environment: Detailed evaluation of odorant degradation in soil, the role of moisture, microbial activity, and soil types ensures reliability of odorization even in leak scenarios.

Applications

This standard is critical to the natural gas industry and is applicable to:

• Gas Transmission and Distribution: Ensures detectable odorization across network systems, covering both traditional natural gas and emerging gas mixtures, such as biomethane and hydrogen blends.
• Odorant Manufacturers and Distributors: Provides a framework for producing and supplying compliant odorant blends with documented quality control.
• Testing Laboratories: Offers precise requirements for laboratory testing and certification of odorant properties, ensuring consistency and regulatory compliance.
• Safety and Compliance: Essential reference for operators, safety managers, and regulatory authorities overseeing public safety in gas supply.

Related Standards

Several relevant standards and technical specifications complement prEN ISO 13734 rev:

• ISO 3015:2019: Petroleum and related products - Cloud point determination.
• ISO 6142-1:2015: Gas analysis - Preparation of calibration gas mixtures.
• ISO 14532: Natural gas vocabulary – definitions of key terms.
• ISO/TS 16922: Natural gas odorization - industry best practices for odorant selection and application.
• ISO/TS 18222: Correlation between odorant concentration and odour intensity.

Practical Value

Implementation of prEN ISO 13734 rev delivers measurable safety benefits by standardizing the odorization process for natural gas and its substitutes. It supports process engineers, quality managers, and compliance officers in:

• Selecting and testing effective and safe odorants.
• Ensuring the early detection of gas leaks under all operational and environmental conditions.
• Meeting regulatory requirements for public safety and environmental protection.
• Supporting the introduction of alternative gas mixtures, such as biomethane and hydrogen-enriched fuels, into existing natural gas infrastructures.

Keywords: natural gas odorants, fuel gas safety, gas odorization, CEN standards, biomethane, hydrogen blends, gas pipeline safety, odorant test methods, ISO 13734, gas leak detection.

SLOVENSKI STANDARD
01-junij-2026
Zemeljski plin - Organske sestavine, uporabljene kot odoranti - Zahteve in
preskusne metode (ISO/DIS 13734:2026)
Natural gas - Organic components used as odorants for fuel gases - Requirements and
test methods (ISO/DIS 13734:2026)
Erdgas - Organische Verbindungen zur Verwendung als Odoriermittel - Anforderungen
und Prüfverfahren (ISO/DIS 13734:2026)
Gaz naturel - Composés organiques utilisés comme odorisants pour les gaz
combustibles - Prescriptions et méthodes d'essai (ISO/DIS 13734:2026)
Ta slovenski standard je istoveten z: prEN ISO 13734 rev
ICS:
75.060 Zemeljski plin Natural gas
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 13734
ISO/TC 193
Natural gas — Organic components
Secretariat: NEN
used as odorants for fuel gases —
Voting begins on:
Requirements and test methods
2026-04-20
ICS: 75.060
Voting terminates on:
2026-07-13
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
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BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
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Reference number
ISO/DIS 13734:2026(en)
DRAFT
ISO/DIS 13734:2026(en)
International
Standard
ISO/DIS 13734
ISO/TC 193
Natural gas — Organic components
Secretariat: NEN
used as odorants for fuel gases —
Voting begins on:
Requirements and test methods
ICS: 75.060
Voting terminates on:
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2026
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
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POTENTIAL TO BECOME STANDARDS TO
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Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 13734:2026(en)
ii
ISO/DIS 13734:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
4.1 Requirements for an effective odorant .2
4.2 Composition of odorants.3
4.3 Physical and chemical properties .3
4.3.1 General .3
4.3.2 Cloud point .3
4.3.3 Boiling point .3
4.3.4 Vapour pressure curve.4
4.3.5 Evaporation residue .4
4.3.6 Insoluble matter .4
4.3.7 Solubility in water .4
4.4 Compatibility of the odorant with the system .4
5 Handling and transport . 4
6 Tests . 4
6.1 General .4
6.2 Test sample .5
6.3 Test documentation .5
6.4 Determination of composition . .5
6.5 Determination of cloud point .5
6.6 Determination of phase properties .5
6.7 Determination of evaporation residue .6
6.8 Visual examination for solids or suspended matter .6
6.9 Determination of solubility in water .6
6.10 Odorant stability under pipeline conditions .6
6.11 Odorant stability in the ground and with water .7
6.11.1 Degradation of gas odorants in soil .7
6.11.2 Microbial mechanisms .7
6.11.3 Environmental factors .7
6.11.4 Soil factors testing .8
7 Labelling and documentation . 8
7.1 Labelling .8
7.2 Documentation .8
Annex A (informative) Properties of odorants . 10
Bibliography .13

iii
ISO/DIS 13734:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2. 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/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 193Natural Gas.
This third edition cancels and replaces the second edition (ISO 13734:2013), which has been technically
revised.
The main changes are as follows:
— Biomethane and mixtures of natural gas with a volume fraction of hydrogen up to 20 % have been
explicitly introduced in the scope of the standard
— Technical update, for the existing test method, in particular for determining the solubility in water
(clause 6.9)
— Addition of new clauses:
— 4.4 Compatibility of the odorant with the system;
— 6.10 Odorant stability under pipeline conditions;
— 6.11 Odorant stability in the ground and with water;
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO/DIS 13734:2026(en)
Introduction
Distributed fuel gases normally have little or no odour. For safety reasons, these gases are therefore odorized
to permit the detection, by smell, of the gas at very low concentrations in air.
Addition of hydrogen to natural gas at volume fraction less than 20 % doesn’t seem to affect the odorization
process.
Odorization of biomethane can be affected by the possible presence of odorous substances deriving from the
biogas production. In this case, odorization practices (choice and concentration of odorant) must be checked
[1][2]
for their effectiveness (no relevant masking shown) .
NOTE For odorization practices, refer to ISO 16922. It is commonly considered acceptable that fuel gas in air is
readily detectable by smell at a concentration of 20 % of the lower flammability limit (LFL).

v
DRAFT International Standard ISO/DIS 13734:2026(en)
Natural gas — Organic components used as odorants for fuel
gases — Requirements and test methods
1 Scope
This International Standard specifies requirements and test methods for organic compounds suitable for
odorization of fuel gases hereafter referred to as odorants.
This International Standard applies to fuel gases: natural gas, natural gas substitutes such as biomethane,
mixtures of natural gas with a volume fraction of hydrogen up to 20 %.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 3015:2019, Petroleum and related products from natural or synthetic sources — Determination of cloud
point
ISO 6142-1:2015, Gas analysis — Preparation of calibration gas mixtures — Part 1: Gravimetric method for
Class I mixtures
ISO 14532, Natural gas — Vocabulary
ISO/TS 16922, Natural gas — Odorization
ISO/TS 18222, Natural gas — Correlation between odorant concentration in air and odour intensity
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14532 and the following apply.
3.1
odorant
intensively smelling organic chemical or combination of chemicals added to fuel gases (normally odourless)
at low concentration and capable of imparting a warning odour, that is distinctive, unpleasant, and
not confusable with other frequently occurring odours, so gas leaks can be detected before hazardous
concentration is reached.
3.2
odorization
addition of odorants (3.1) to allow the recognition of gas leaks by smell at very low concentration (before a
build up to a dangerous concentration of fuel gas in air can occur)
3.3
odour character
distinctive and identifiable features of an odour or a flavour
[SOURCE: ISO 14532]
Note 1 to entry: Odour character is a qualitative parameter.

ISO/DIS 13734:2026(en)
3.4
odour intensity
strength of odour perception
Note 1 to entry: According to the general law established by Weber, Fechner and Stevens, the odour intensity is
proportional to the logarithm of the odorant concentration
[SOURCE: ISO 14532]
3.5
threshold concentration
concentration at which an individual has a probability of 0,5 to perceive the odour
Note 1 to entry: To detect an odour does not imply that this odour may be identified.
3.6
Odour intensity curve
relationship between odour intensity and odorant concentration in air
Note 1 to entry: The odour intensity can only be determined by the human olfactory organ.
3.7
diluent
odourless organic liquid, normally consisting of paraffinic hydrocarbons, in which odorant is fully soluble
and used to reduce the concentration of an odorant to a suitable level at which the solution may be injected
into the gas
3.8
cloud point
temperature at which a cloud of icy crystals first appears in a liquid when it is cooled under specified
conditions
4 Requirements
4.1 Requirements for an effective odorant
Gas odorants shall meet the following general requirements:
a) The gas odorant shall have a strong odour at very low concentration.
b) The odour character of the odorant shall be distinctive, unpleasant, and not confusable with other
frequently occurring odours so that it is unmistakably associated with a gas leak.
Note 1 Odour character perception can be different due to regional or cultural variations
c) The odour character shall be the same at different dilutions of fuel gas with air.
d) The odorant shall be sufficiently stable during storage and when mixed with fuel gas.
e) The odorant shall not react significantly with any fuel gas components.
f) The volatility of the odorant shall be high enough so that the odorant does not appreciably condense
under the conditions (temperature and pressure) existing in the pipeline system.
g) Evaporation of the gas odorant shall not appreciably leave residues.
h) The odorant shall be useable at low temperatures, when required.
i) The combustion of the odorant shall not leave significant solid deposits.
j) The addition of the odorant to fuel gas shall not make the resulting gas harmful.

ISO/DIS 13734:2026(en)
These general requirements shall be assessed against the specific conditions of use of the odorant (conditions
of the fuel gas transportation grid, odorization installation, type of odorant, composition of the gas).
Experience in many countries has shown that these basic requirements are best met by organic sulfur
compounds - sulfides (thioethers) and mercaptans (thiols) - with boiling points below 130 °C. Since primary
mercaptans are easily oxidized to disulfides which have a much lower odour intensity, mercaptan-based
odorants need to predominantly contain secondary and tertiary mercaptans.
While it has been established that the above sulfur compounds fulfil the basic requirements listed above
under a) to j), other, non-sulfurous odorants have been developed and are available.
In some cases, odorization may impact the applications of the end users. In these cases, if necessary, the
odorant shall be replaced by an odorant with a less impacting formula or to remove the odorant before a
sensitive equipment.
NOTE The same requirements apply to a diluted odorant.
4.2 Composition of odorants
The mass fraction of the declared chemical products in the undiluted odorant or odorant blend shall be at
least 95 %. The composition of the odorant or odorant blend, and where applicable the dilution range, shall
be declared by the producer or distributor. The determination of the composition of odorants refers to 6.3. It
shall be stable over the maximum shelf time as declared by the manufacturer.
According to the chemical nature of the odorant components, care shall be taken to mitigate potential
reactivity e.g. by use of an appropriate additive to avoid polymerisation of odorants (i.e. acrylate-based
odorants).
NOTE Refer to ISO/TS 16922 for odorization process.
4.3 Physical and chemical properties
4.3.1 General
Some properties determine the suitability of a compound or mixture to be used as gas odorant. Other
characteristics are analyzed for each lot of odorant delivery to control critical quality parameters.
For example, properties such as boiling point, vapor pressure curve, solubility in water, evaporation
residue being directly linked to the composition guaranteed by specifications, may be supplied as “physical
characteristics” in separate documentation (Technical datasheet or specific brochures upon request).
Other properties being potentially impacted by low concentration contaminants (insoluble matter, cloud
point) may be assessed as per Certificate of Analysis or Certificate of Conformity.
Physical and chemical properties of odorant formulation should be evaluated and documented by a qualified
laboratory.
T
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