ISO/TS 15916

FINAL DRAFT
Technical
Specification
ISO/DTS 15916
ISO/TC 197
Hydrogen technologies — Basic
Secretariat: SCC
considerations for the safety of
Voting begins on:
hydrogen systems
2025-09-18
Voting terminates on:
2025-12-11
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Reference number
ISO/DTS 15916:2025(en) © ISO 2025

FINAL DRAFT
ISO/DTS 15916:2025(en)
Technical
Specification
ISO/DTS 15916
ISO/TC 197
Hydrogen technologies — Basic
Secretariat: SCC
considerations for the safety of
Voting begins on:
hydrogen systems
Voting terminates on:
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
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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
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Published in Switzerland Reference number
ISO/DTS 15916:2025(en) © ISO 2025

ii
ISO/DTS 15916:2025(en)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Overview of hydrogen applications .13
4.1 Basic hydrogen infrastructure . 13
4.1.1 Categories of infrastructure . 13
4.1.2 Production . 13
4.1.3 Storage and transport. 13
4.1.4 Hydrogen end use applications .14
4.2 Typical hydrogen system components . 15
4.2.1 General . 15
4.2.2 Storage vessels . 15
4.2.3 Fluid delivery lines, piping, joints, and seals . 15
4.2.4 Flow controls . 15
4.2.5 Pressure-relief systems .16
4.2.6 Detection methods .16
4.2.7 Other components .16
4.2.8 Considerations for conditions external to the system .16
4.3 Hydrogen fuel .17
4.4 Environmental effects .17
5 Basic properties of hydrogen . 17
5.1 General properties .17
5.1.1 Atomic and molecular properties .17
5.1.2 Appearance and general characteristics .18
5.2 Selected thermophysical properties .18
5.2.1 General .18
5.2.2 Selected thermophysical properties of gaseous hydrogen .18
5.2.3 Selected thermophysical properties of cryogenic liquid hydrogen .19
5.3 Basic combustion properties .19
5.3.1 General remark on safety characteristics .19
5.3.2 Selected combustion properties of hydrogen . 20
5.3.3 Deflagration . 20
5.3.4 Detonation .21
5.3.5 Explosions .21
5.3.6 Flammability limits . 22
5.3.7 Ignition energy and minimum ignition energy as applied to deflagration . 22
6 Safety considerations for the use of gaseous and liquid hydrogen .23
6.1 General . 23
6.2 Hazards involved as a consequence of the properties of hydrogen .24
6.2.1 General .24
6.2.2 Gaseous hydrogen .24
6.2.3 Liquid hydrogen .24
6.3 Factors involved in combustion hazards . 25
6.3.1 Aspects of combustion . 25
6.3.2 Non-premixed combustion processes . 25
6.3.3 Explosions . 26
6.4 Factors involved in pressure hazards .27
6.4.1 General .27
6.4.2 Gaseous storage .27
6.4.3 Liquid hydrogen .27
6.5 Factors involved in low temperature hazards .27

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ISO/DTS 15916:2025(en)
6.6 Factors involved in hydrogen embrittlement hazards . 28
6.6.1 Hydrogen embrittlement . 28
6.6.2 Hydrogen attack . . 28
6.7 Health hazards. 28
6.7.1 Cold burns . 28
6.7.2 High temperature burns . 28
6.7.3 Asphyxiation . 28
6.7.4 Combustion by-products . 29
7 Mitigation and control of hazards and risks .29
7.1 General mitigation and control of hazards and risk . 29
7.1.1 General . 29
7.1.2 Lessons learned from past experience . 29
7.1.3 Addressing hazards . 30
7.1.4 Minimizing the severity of the consequences of hazards . 30
7.2 Mitigation of design hazards and risks.31
7.2.1 Inherently safer design .31
7.2.2 Considerations in the selection of suitable construction material .31
7.2.3 Considerations for vessels and components . 33
7.2.4 Prevention of overpressure . 33
7.2.5 Considerations for piping, joints, and connections. 33
7.2.6 Cleaning considerations . 34
7.2.7 Component considerations . 35
7.3 Prevention and mitigation of fire and explosion hazards and risks . 36
7.3.1 General . 36
7.3.2 Prevention of unwanted hydrogen/oxidizer mixtures . 36
7.3.3 Identification of hazardous areas . 36
7.3.4 Ignition .37
7.3.5 Deflagration and detonation. 38
7.3.6 Oxygen enrichment . 38
7.4 Detection considerations . 39
7.4.1 Hydrogen release detection. 39
7.4.2 Fire detection . 40
7.5 Considerations for facilities . 40
7.5.1 General . 40
7.5.2 Locations . 40
7.5.3 Exclusion areas .41
7.5.4 Protecting barricades .41
7.5.5 Safety control equipment .41
7.5.6 Disposal of hydrogen .42
7.5.7 Ground material .43
7.5.8 Buildings .43
7.5.9 Ventilation . 44
7.5.10 Electrical components . 44
7.5.11 Alarms and warning devices .45
7.5.12 Fire protection and fire fighting .45
7.6 Considerations for operations . 46
7.6.1 General . 46
7.6.2 Operating procedures . 46
7.6.3 Personal protective equipment . 46
7.6.4 Cool-down .47
7.6.5 Transportation .47
7.6.6 Storage and transfer operations.47
7.6.7 Safety procedures . 48
7.7 Recommended practices for organizations . 49
7.7.1 General . 49
7.7.2 Control through organizational policies and procedures . 50
7.7.3 Use of approved procedures and checklists. 50
7.7.4 Conduct appropriate reviews. 50

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7.7.5 Approved maintenance and quality control programmes . 50
7.7.6 Personnel education/training . 50
7.7.7 Hazard and operability assessment .51
Annex A (informative) Hydrogen properties .52
Annex B (informative) Hydrogen combustion data .56
Annex C (informative) Material data.59
Annex D (informative) Other storage options .64
Bibliography .65

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ISO/DTS 15916:2025(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 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 197, Hydrogen technologies, in collaboration
with the European Committee for Standardization (CEN) Technical Committee CEN/CLC/JTC 6, Hydrogen in
energy systems, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This first edition of ISO/TS 15916 cancels and replaces ISO/TR 15916:2015, which has been technically
revised.
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.

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ISO/DTS 15916:2025(en)
Introduction
The focus of this document is on relatively new hydrogen energy applications. The intent is to provide, those
unfamiliar with the technology, a basis upon which to understand the safety issues. This document concerns
itself with applications that derive their utility from the chemical reactions of hydrogen and does not apply
to applications based on nuclear processes.
Traditionally, hydrogen has been used extensively in the petrochemical and chemical industries and in
smaller quantities in the electronics, steel-producing, glass-making, and food hydrogenation industries.
Given the promise that hydrogen brings as an efficient energy carrier and a fuel with minimal environmental
impact, systems are being developed that produce hydrogen using variety of energy sources and feedstocks
such as sunlight, wind, biomass, hydro power and fossil fuels, for use in energy applications for home and
office heating, generation of electricity and transportation.
The safe use of hydrogen as a fuel is a primary goal to facilitate the rapid emergence of these hydrogen
technologies. A key element in the safe use of hydrogen is to understand its unique safety-related properties
and related phenomena, and that there are acceptable engineering approaches to controlling the hazards
and risks associated with the use of hydrogen. This document describes the hazards associated with the use
and presence of hydrogen, discusses the properties of hydrogen relevant to safety, and provides a general
discussion of approaches taken to mitigate hydrogen hazards. The aim of this document is to promote the
acceptance of hydrogen technologies by providing key information to regulators and by educating people
involved with hydrogen safety issues.
The development of International Standards to eliminate barriers to international trade and to simplify the
arduous regulatory process by providing hydrogen-specific standards to allow implementation for rapidly
emerging technologies was among the needs identified by the ISO/TC 197. This document is one of many that
have been developed, or are in the process of being developed. Detailed safety requirements associated with
specific hydrogen applications are treated in separate International Standards. This document provides
an informative reference for those separate standards as a common, consistent source of safety-related
hydrogen information. This is expected to result in a reduction in duplication and possible inconsistencies in
these separate standards.
The considerations presented in this document are broad, general, and attempt to address most aspects of
hydrogen safety. The degree to which these guidelines are applied will vary according to the specifics of the
application (such as the conditions and quantity of hydrogen involved, and the way in which the hydrogen
is used). Industrial users may find large portions of the guidelines, presented herein, applicable for their
operations. It is not expected that the general public will be required to apply this degree of knowledge to
safely operate a hydrogen appliance. It is anticipated that good appliance design, coupled with appropriate
care in installation, will reduce the degree of safety considerations to levels that are deemed acceptable by
the public for common appliances. The manufacturers of hydrogen appliances will need to consider these
guidelines to tailor sufficient specific information for the operation of their appliances, in the environment
in which they are to be used, and for the audience that will use them. Readers are encouraged to keep these
points in mind as they consider the information presented in this document. Hydrogen has been safely used
in many different applications over many years. Adherence to the principles presented in this document can
lead to a continuation of the safe and sustainable use of hydrogen.

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FINAL DRAFT Technical Specification ISO/DTS 15916:2025(en)
Hydrogen technologies — Basic considerations for the safety
of hydrogen systems
1 Scope
This document provides guidelines for the use of hydrogen in its gaseous and liquid forms as well as its storage
in either of these or other forms (hydrides). This document identifies the basic safety concerns, hazards and
risks, and describes the properties of hydrogen that are relevant to safety. Detailed safety requirements
associated with specific hydrogen applications are treated in separate International Standards.
“Hydrogen” in this document means protium (the most common isotope of hydrogen) ( H ), not deuterium
2 3
( H ) or tritium ( H ).
2 2
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
ambient conditions
local surrounding conditions characterized by the temperature and pressure at a particular location, such
as a city or facility
Note 1 to entry: See normal temperature and pressure (3.69).
3.2
annealing
heat treatment process used to soften hard steel so that it can be machined or cold-worked
3.3
arrested flame
combustion process that is stopped or flame that is put out
3.4
auto-ignition
ignition that does not require external ignition energy because the thermal energy of the molecules alone is
enough to overcome the activation threshold for combustion initiation
3.5
auto-ignition temperature
lowest temperature at which auto-ignition (3.4) occurs

ISO/DTS 15916:2025(en)
3.6
backfill
process by which a desired gas is used to replace an undesired gas in a system volume
Note 1 to entry: Typically, the undesired gas is first removed by evacuation with a vacuum pump, then the desired gas
is put in.
3.7
blast wave
intense pressure wave set in motion by the shock waves (3.91) and/or hot product gases of a fast deflagration
(3.20) or detonation (3.23) that impinges upon the surroundings, typically air
3.8
boiling liquid expanding vapour explosion
BLEVE
phenomenon that occurs when a vessel containing a pressurized liquid substantially above its (atmospheric)
boiling point is ruptured, releasing the content explosively
3.9
bourdon tube
thin-wall curved tube that is closed at one end and attached to a pressure source at the other end
Note 1 to entry: Pressure changes cause a change in the curvature of the Bourdon tube that is used to indicate the
pressure in the system.
3.10
buoyancy
vertical force exerted on a body of less dense gas by the surrounding heavier static gas, typically air
3.11
catalytic converter
catalyst that is used for converting ortho-hydrogen to para-hydrogen in a liquefaction process so that the
liquid hydrogen produced is mostly para-hydrogen
Note 1 to entry: Some commonly used catalysts in this conversion process are hydrous ferric oxide, chromic oxide on
alumina particles, and nickel-based compounds.
3.12
check valve
valve that operates on differential pressure and allows flow in one direction only
3.13
combustion
reaction process by which a flammable substance is oxidized, producing hot product gases, heat, radiation,
and possibly pressure waves
Note 1 to entry: An explosion (3.36) in the sense of this document is a combustion process.
3.14
component
any part of a complete item or system
3.15
confined space
area with limited access, as described in national regulations, which requires special considerations for entry
[SOURCE: ISO 16972:2020, 3.58]
3.16
confinement
physical restriction, sufficient to influence the combustion process or to facilitate the accumulation of
hydrogen
ISO/DTS 15916:2025(en)
3.17
convection current
motion or circulation of a fluid involving the transport of mass from one location to another driven by
temperature dependent density gradients
Note 1 to entry: See natural convection (3.66).
3.18
cryogenic fluid
refrigerated liquefied gas
gas that is partially liquid because of its low temperature
Note 1 to entry: This includes totally evaporated liquids and supercritical fluids.
Note 2 to entry: The 13th International Institute of Refrigeration's (IIR) International Congress of Refrigeration (held
in Washington DC in 1971) endorsed a universal definition of "cryogenics" and "cryogenic" by accepting a threshold of
120 K (−153 °C) to distinguish these terms from conventional refrigeration.
[SOURCE: ISO 21009-1: 2022 clause 3.4, modified – removal of Note 2 to entry, and inclusion of a replacement
Note 2 to entry]
3.19
cryo-pumping
process that consists of cooling a surface to a temperature of less than 120 K so that gases and vapours
condense on the surface
Note 1 to entry: This process, though usually undesirable in the context here, is also used as a vacuum pump.
3.20
deflagration
combustion process in which a flame or chemical reaction moves through a flammable mixture at a rate less
than the speed of sound in the unburned mixture
Note 1 to entry: Fast deflagrations are characterized by velocities in the hundreds of metres per second, and their
effects do not differ much from those of a detonation (3.23).
Note 2 to entry: Laminar deflagration waves are characterized by velocities in the several metres per second and do
not cause significant over pressures in the open.
3.21
deflagration-to-detonation-transition
DDT
event, often caused by turbulence, in which a deflagration (3.20) initiates a detonation (3.23)
3.22
deluge system
water spray system that is used to keep equipment, especially hydrogen storage vessels, cool in the event of a fire
3.23
detonation
shock stabilized combustion process resulting in a combustion phenomenon propagating faster than the
speed of sound
Note 1 to entry: A detonation is an explosion, but the reverse is not true.
Note 2 to entry: The thermal energy of the reaction sustains the shock wave, and the shock wave compresses unreacted
material, producing the high temperatures necessary to drive the reaction.

ISO/DTS 15916:2025(en)
3.24
detonation cell
fundamental part of the mechanism for energy release within a detonation (3.23)
Note 1 to entry: The spatial arrangement of the shock front and acoustic waves moving behind and transverse to the
shock front defines a cellular region of combustion that is observed experimentally as a “fish-scale” shaped track on
sooted foils exposed to the detonation.
Note 2 to entry: The width of this diamond shape denotes the cell size, and its length can be empirically related to
the formulae that can predict the energy required to directly initiate detonation and the physical dimensions of the
structures that prohibit detonation.
3.25
detonation limits
maximum and minimum concentrations of a gas, vapour, mist, spray or dust, in air or oxygen, for stable
detonation (3.23) to occur
Note 1 to entry: The limits are in reality controlled not only by the concentration of the mixture but also by the size
and geometry of the environment as well as the means by which ignition occurs. There is no standard procedure for
their determination.
Note 2 to entry: See flammability limits (3.45)
3.26
deuterium
D
H
isotope of hydrogen with a nucleus containing one neutron and one proton and a mass number of two
3.27
diffusion
flux of a fluid through another fluid or material due to concentration gradient
EXAMPLE The motion of hydrogen gas through air, or the movement of hydrogen gas through the wall of a
rubber hose.
Note 1 to entry: The diffusion coefficient is the mass of material diffusing across a unit of area in a unit of time at a unit
concentration gradient.
3.28
diluent
inert component within a gas mixture that reduces the concentration of the remaining (active) materials
3.29
dual-fault tolerance
system design in which the failure of two elements to perform as intended does not cause an entire system
to function unpredictably or catastrophically
Note 1 to entry: The faults can be in two related areas or two areas that function completely independently, and the
system should continue to function as intended.
3.30
ductility
percentage elongation to failure or the reduction in cross-sectional area of a specimen in a
simple tensile test
Note 1 to entry: Materials can make a ductile-to-brittle transition at low temperatures.
3.31
electrolyser
device that performs electrolysis (3.32)

ISO/DTS 15916:2025(en)
3.32
electrolysis
process in which electric current is used to promote a chemical reaction
Note 1 to entry: In the case of water, an example is the separation of hydrogen from oxygen.
3.33
emergency
unintended circumstance, bearing clear and present danger to personnel or property, which requires an
immediate response
3.34
enclosed space
space in which, by virtue of its enclosed, or partially enclosed nature, there arises a reasonably foreseeable
risk associated with the release of flammable fluid, not expected to be present for a release into an open,
naturally ventilated, space
Note 1 to entry: See confined space for the foreseeable risk to personnel in enclosed, or partially enclosed spaces
3.35
enthalpy
thermodynamic property of a material that is equivalent to the sum of the internal energy and the product
of the pressure and the volume
3.36
explosion
self-sustained combustion of a gas mixture releasing heat, and hot combustion products when the rate of
reaction in a reacting mixture increases with time until either the fuel or oxidizer is consumed
Note 1 to entry: This definition excludes pressure sources not related to chemical reactions (like burst of a pressure
vessel, BLEVE, etc.).
Note 2 to entry: There is neither a standard terminology nor another generally acknowledged definition for the term
“explosion”, but different sources give different definitions, some of them not even requiring that combustion takes place.
Note 3 to entry: When hydrogen and an oxidizer (air) are allowed to form a mixture prior to ignition (premixed
mixture), after ignition, the ensuing chemical reaction (combustion wave) will propagate through the flammable
region. The resulting combustion process releases heat. The resulting dilatation of the products, if fast enough, can
cause a pressure wave to propagate from the source. See References [9] and [11] for more information.
3.37
facility
group of buildings or equipment used for specific operations at one geographic location
3.38
fail-safe
ability to sustain a failure without causing loss of equipment, injury to personnel, or loss of operating time
3.39
fatigue
gradual deterioration of a material that is subjected to repeated loading and unloading
Note 1 to entry: See load cycle (3.60).
3.40
fire
sustained burning of a fuel jet as manifested by any or all of the following: light, flame, heat, and smoke
3.41
fire triangle
visual concept showing the requirements for combustion depicting a fuel, an oxidizer and an ignition source
as the three sides of a triangle, where combustion cannot occur if any one side is not present

ISO/DTS 15916:2025(en)
3.42
flame
zone of combustion of a gas or vapour from which light and heat are emitted
Note 1 to entry: A flame can be stationary with the flammable mixture fed into the reaction zone, or a flame can
propagate through the flammable mixture, as in a deflagration (3.20).
Note 2 to entry: Unlike hydrocarbon flames, hydrogen flames are weakly radiating. They radiate in the near UV (faint
blue) and in the near IR (reddish). Only if particles are entrained into the flow from the surroundings will the flame
thermally radiate producing a yellow colour. Because hydrogen flames radiate weakly in the near UV and IR, they are
often difficult to see in the daylight.
3.43
flame front
region of burning or chemical reaction (typically from fractions to several millimetres across) that separates
burned and unburned regions
3.44
flammability
degree to which a material is ignitable in an oxidizing atmosphere
3.45
flammability limits
lower flammable limit and upper flammable limit of gas in a gas-air mixture, between which a flammable
mixture is formed
Note 1 to entry: The term “explosive limits” is used especially in European standardization and regulations
interchangeably to describe these limits.
Note 2 to entry: The concentration can be expressed as either a volume fraction or a mass per unit volume.
Note 3 to entry: These limits are functions of temperature, pressure, diluents, fluid dynamics, and ignition energy.
Note 4 to entry: The value
...