ISO/FDIS 19723-1

Road vehicles — Liquefied natural gas (LNG) fuel systems — Part 1: Safety requirements

This document specifies the minimum safety requirements applicable to liquefied natural gas (LNG) on-board fuel system intended for use on the types of motor vehicles defined in ISO 3833. This document is applicable to vehicles (mono-fuel, bi-fuel or dual-fuel applications) using liquefied natural gas in accordance with the ISO 15403 series. It is not applicable to original-production and converted vehicles. All matters relating to the skills of installers and converters have been excluded from this document. This document is only applicable on the components in the "LNG system" meaning an assembly of components (tanks, valves, flexible fuel lines, etc., see Annex B) and connecting parts (fuel lines, fittings, etc.) fitted on motor vehicles using LNG in their propulsion system and related components up to and including the vaporizer. Other parts downstream from the vaporizer are considered as CNG components covered by ISO 15501.

Véhicules routiers — Systèmes à carburant gaz naturel liquéfié (GNL) — Partie 1: Exigences de sécurité

General Information

• Status: Not Published
• ICS: 43.060.40 - Fuel systems
• Technical Committee: ISO/TC 22/SC 41 - Specific aspects for gaseous fuels
• Drafting Committee: ISO/TC 22/SC 41 - Specific aspects for gaseous fuels
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 24-Sep-2025
• Completion Date: 24-Sep-2025

Relations

• Revises: ISO 19723-1:2018 - Road vehicles — Liquefied natural gas (LNG) fuel systems — Part 1: Safety requirements
• Effective Date: 18-Feb-2023

Standards Content (Sample)

FINAL DRAFT
International
Standard
ISO/TC 22/SC 41
Road vehicles — Liquefied natural
Secretariat: UNI
gas (LNG) fuel systems —
Voting begins on:
2025-09-24
Part 1:
Safety requirements
Voting terminates on:
2025-11-19
Véhicules routiers — Systèmes à carburant gaz naturel liquéfié
(GNL) —
Partie 1: Exigences de sécurité
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-
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 22/SC 41
Road vehicles — Liquefied natural
Secretariat: UNI
gas (LNG) fuel systems —
Voting begins on:
Part 1:
Safety requirements
Voting terminates on:
Véhicules routiers — Systèmes à carburant gaz naturel
liquéfié (GNL) —
Partie 1: Exigences de sécurité
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 2025
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-
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 . 2
4 Requirements . 4
4.1 Design .4
4.1.1 General .4
4.1.2 Components .5
4.2 Refuelling .8
4.2.1 General .8
4.2.2 Receptacle location .8
4.2.3 Receptacle mounting .8
4.2.4 Minimum receptacle clearance .8
4.3 Leakage control .8
4.4 Mounting of the tank(s) .9
4.5 Heat protection .9
4.6 Minimizing risk of gas ignition .9
4.7 Venting system .10
4.7.1 General .10
4.7.2 Ventilation lines for PRVs .10
4.7.3 Vent line closures .11
4.8 Gas temperature sensor .11
5 Instructions for use . .11
6 Marking . .11
Annex A (informative) Technical solutions to functional requirements .12
Annex B (informative) Liquefied natural gas (LNG) on-board fuel systems .13
Bibliography . 14

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 document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 41, Specific
aspects for gaseous fuels.
This second edition cancels and replaces the first edition (ISO 19723-1:2018), which has been technically
revised. It also incorporates the Amendment ISO 19723-1:2018/Amd 1:2021.
The main changes are as follows:
— updated Clause 2, Normative references;
— added requirements for the electronic control unit (ECU);
— updated requirements for minimum receptacle clearance;
— added requirements for vent line closures.
A list of all parts in the ISO 19723 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
All fuel system components in contact with liquid natural gas have been considered suitable for natural gas
as defined in the ISO 15403 series.
A safety device to prevent overfilling the vehicle's fuel system is part of the refuelling station. The pressure
gauge has not been considered as a safety component.
Technical solutions regarding functional requirements are given in Annex A.

v
FINAL DRAFT International Standard ISO/FDIS 19723-1:2025(en)
Road vehicles — Liquefied natural gas (LNG) fuel systems —
Part 1:
Safety requirements
1 Scope
This document specifies the minimum safety requirements applicable to liquefied natural gas (LNG) on-
board fuel system intended for use on the types of motor vehicles defined in ISO 3833.
This document is applicable to vehicles (mono-fuel, bi-fuel or dual-fuel applications) using LNG according to
the ISO 15403 series. It is applicable to original-production and converted vehicles.
All matters relating to the skills of installers and converters have been excluded from this document.
This document is only applicable to the components in the LNG system which is an assembly of components
(tanks, valves, flexible fuel lines, etc., see Annex B) and connecting parts (fuel lines, fittings, etc.) fitted
on motor vehicles using LNG in their propulsion system and related components up to and including the
vaporizer. Other parts downstream from the vaporizer are considered as compressed natural gas (CNG)
components covered by the ISO 15501 series.
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 7637-1, Road vehicles — Electrical disturbances from conduction and coupling — Part 1: Vocabulary and
general considerations
ISO 7637-2, Road vehicles — Electrical disturbances from conduction and coupling — Part 2: Electrical transient
conduction along supply lines only
ISO 11451-1, Road vehicles — Vehicle test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 1: General principles and terminology
ISO 11451-2, Road vehicles — Vehicle test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 2: Off-vehicle radiation sources
ISO 11451-4, Road vehicles — Vehicle test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 4: Harness excitation methods
ISO 11452-1, Road vehicles — Component test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 1: General principles and terminology
ISO 11452-2, Road vehicles — Component test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 2: Absorber-lined shielded enclosure
ISO 11452-3, Road vehicles — Component test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 3: Transverse electromagnetic (TEM) cell
ISO 11452-4, Road vehicles — Component test methods for electri
...

2025-03-05
ISO/DISFDIS 19723-1:2024(en)
ISO/TC 22/SC 41/WG 7
Secretariat: UNI
Date:2025-09
Road vehicles — Liquefied natural gas (LNG) fuel systems —
Part 1:
Safety requirements
Véhicules routiers — Systèmes à carburant gaz naturel liquéfié (GNL) —
Partie 1: Exigences de sécurité
FDIS stage
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Fax: [phone]
EmailE-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved
ii
DRAFT INTERNATIONAL STANDARD ISO/DIS 19723-1:2024(en)

Contents Page
Foreword . 3
Introduction . 4
Part 1: Safety requirements . 5
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 7
4 Requirements . 9
4.1 Design . 9
4.1.1 General. 9
4.1.2 Components . 11
4.2 Refuelling . 14
4.2.1 General. 14
4.2.2 Receptacle location . 14
4.2.3 Receptacle mounting . 14
4.2.4 Minimum receptacle clearance . 14
4.3 Leakage control . 14
4.3.1 Pressurized gas systems shall be designed so that they withstand the stresses that can be
expected during operation without leakage. . 14
4.3.2 The tank or parts of the gas system, or both, shall be mounted in a position which
ensures that any leaking or venting gas from the fuel systems does not directly enter the
driver or passenger compartment, boot or other spaces not sufficiently ventilated.
Alternatively, it shall be ensured that any leaked gas is directed safely to the atmosphere
(see Annex A). . 14
4.3.3 Where a tank or vessel is located within the driver or passenger compartment or other
insufficiently ventilated space, the valves, connections and pipework shall be enclosed in
a gas-tight housing such that any gas leakage is vented and directed to the outside of the
vehicle. . 15
4.3.4 Any ventilation opening shall be positioned away from any openings into any vehicle
compartment, away from any ignition source, and in a location where it is not
susceptible to blockage. . 15
4.4 Mounting of the tank(s) . 15
4.4.1 The tank(s) shall be securely attached to the vehicle to prevent slipping, rotating and
dislodging. . 15
4.4.2 LNG tank and attachments for mounting on the vehicle shall be designed and constructed
to minimize wear, corrosion (field welding on tanks is not permitted) and fatigue during
the service life of the vehicle. . 15
4.4.3 When tested in accordance with ISO 19723-2, the tanks or vessels shall be mounted and
fixed so that the following accelerations (g is equal to 9,81 m/s ) can be absorbed
(without damage or distortion occurring) when the tanks are full. . 15
4.5 Heat protection . 15
4.6 Minimizing risk of gas ignition . 16
4.7 Venting system . 16
4.7.1 General. 16
4.7.2 Ventilation lines for PRVs . 17
4.7.3 Vent line closures . 17
4.8 Gas temperature sensor . 17
5 Instructions for use . 17
6 Marking . 18
Annex A (informative) Technical solutions to functional requirements . 19
Annex B (informative) Liquefied natural gas (LNG) on-board fuel systems . 20
Bibliography . 22

2 © ISO 2018 – All rights reserved
ISO/DISFDIS 19723-1:20242025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO [had/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 22, Road vehicles, Subcommittee SC 41, Specific
aspects for gaseous fuels.
This second edition cancels and replaces the first edition (ISO 19723-1:2018), which has been technically
revised. It also incorporates the Amendment ISO 19723-1:2018/Amd 1:2021.
The main changes are as follows:
— updated 2update clause 2, Normative references;
— Addedadded requirements for Electronicthe electronic control unit (ECU);
— Updatedupdated requirements for Minimumminimum receptacle clearance;
— Addedadded requirements for Ventvent line closures.
A list of all parts in the ISO 19723 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
Introduction
All fuel system components in contact with liquid natural gas have been considered suitable for natural gas as
defined in the ISO 15403 series.
A safety device to prevent overfilling the vehicle's fuel system is part of the refuelling station. The pressure
gauge has not been considered as a safety component.
Technical solutions regarding functional requirements are given in Annex AAnnex A.

4 © ISO 2018 – All rights reserved
ISO/DISFDIS 19723-1:20242025(en)
Road vehicles — Liquefied natural gas (LNG) fuel systems —
Part 1:
Safety requirements
1 Scope
This document specifies the minimum safety requirements applicable to liquefied natural gas (LNG) on-board
fuel system intended for use on the types of motor vehicles defined in ISO 3833.
This document is applicable to vehicles (mono-fuel, bi-fuel or dual-fuel applications) using liquefied natural
gas in accordance withLNG according to the ISO 15403 series. It is applicable to original-production and
converted vehicles.
All matters relating to the skills of installers and converters have been excluded from this document.
This document is only applicable to the components in the LNG system which is an assembly of components
(tanks, valves, flexible fuel lines, etc., see Annex BAnnex B)) and connecting parts (fuel lines, fittings, etc.) fitted
on motor vehicles using LNG in their propulsion system and related components up to and including the
vaporizer. Other parts downstream from the vaporizer are considered as compressed natural gas (CNG)
components covered by the ISO 15501 series.
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 7637-1, Road vehicles — Electrical disturbances from conduction and coupling — Part 1: Vocabulary and
general considerations
ISO 7637-2, Road vehicles — Electrical disturbances from conduction and coupling — Part 2: Electrical transient
conduction along supply lines only
ISO 11451-1, Road vehicles — Vehicle test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 1: General principles and terminology
ISO 11451-2, Road vehicles — Vehicle test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 2: Off-vehicle radiation sources
ISO 11451-4, Road vehicles — Vehicle test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 4: Harness excitation methods
ISO 11452-1, Road vehicles — Component test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 1: General principles and terminology
ISO 11452-2, Road vehicles — Component test methods for electrical disturbances from narrowband radiated
electromagnetic energy — Part 2: Absorber-lined shiel
...