ISO/FDIS 13984

ISO/DIS FDIS 13984:2025(en)
ISO /TC 197/WG 35
Secretariat: SCC
Date: 2025-12-2810-29
Liquid Hydrogen hydrogen — Land vehicle fuellingfueling protocol
FDIS stage
ISO /FDIS 13984:####(X:2025(en)
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ii © ISO #### 2025 – All rights reserved
ii
ISO/DIS FDIS 13984:2025(en)
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Requirements. 9
5 Fuelling protocols requirements . 18
6 Single hose – target pressure based fuelling protocols . 22
7 Security and safety . 35
8 Maintenance . 38
9 Verification of the conformance to the fuelling protocol and validation of the dispenser 39
Annex A (informative) Guidance for piping, components and PRDs design and installation . 40
Annex B (informative) Testing and inspection methods . 44
Annex C (informative) Fuelling protocols scope rationale . 47
Annex D (normative) Pressure nomenclature . 63
Annex E (informative) Sub-procedures for single hose – target pressure-based fuelling
protocols . 69
Annex F (normative) Fuelling protocol conformance verification . 90
Annex G (informative) Risk assessment report and recommendations . 92
Bibliography . 115

Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Requirements. 8
4.1 Hydrogen and cryogenic temperatures compatibility . 8
4.2 Material specifications . 8
4.3 Piping . 8
4.4 Pressure relief devices . 9
4.5 Dispensing system . 10
4.5.1 General requirements . 10
4.5.2 Vehicle fuelling connectors . 11
4.5.3 Dispenser fuelling assembly . 12
4.6 Installation, assembly and operation of equipment . 14
4.7 Earthing and equipotential bonding . 14
4.8 Remote system control . 15
4.9 Vehicle fuel system . 15
5 Fuelling protocols requirements . 16
© ISO 2025 – All rights reserved
iii
ISO /FDIS 13984:####(X:2025(en)
5.1 General requirements . 16
5.2 Single hose – target pressure based protocols . 17
5.3 Alternative protocols . 18
5.4 Manual control of dispensing . 19
5.5 Hydrogen specification . 19
5.5.1 Hydrogen quality . 19
5.5.2 Hydrogen supply condition . 19
5.5.3 Hydrogen phase fraction. 19
6 Single hose – target pressure based fuelling protocols . 19
6.1 Introduction . 19
6.1.1 Pressure control . 20
6.1.2 Temperature control . 20
6.1.3 Fuelling rates control . 20
6.1.4 Tolerances . 21
6.2 Pre-fuelling . 21
6.3 Main fuelling . 23
6.3.1 Start of fuelling . 24
6.3.2 Steady state fuelling . 25
6.3.3 End of fuelling . 25
6.4 Post-fuelling . 26
7 Security and safety . 27
7.1 Risk assessment . 27
7.2 General . 28
7.3 Warning signs . 28
7.4 Dispenser operational instructions . 29
7.5 Training . 30
7.6 Emergency response plan (ERP). 30
7.7 Emergency contact information . 30
8 Maintenance . 30
9 Verification of the compliance to the fuelling protocol and validation of the dispenser . 31
9.1 Fuelling protocol test . 31
9.2 Test procedure . 31
9.3 Station inspection and tests following modifications . 32
Annex A (informative) Guidance for piping, components and PRDs design and installation . 33
Annex B (informative) Testing and inspection methods . 37
Annex C (informative) Fuelling protocols scope rationale . 40
Annex D (normative) Pressure nomenclature . 50
Annex E (informative) Sub-procedures for single hose – target pressure based fuelling protocols54
Annex F (normative) Fuelling protocol compliance verification . 69
Annex G (informative) Risk assessment report and recommendations . 72

iv © ISO #### 2025 – All rights reserved
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ISO/DIS FDIS 13984:2025(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.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 197, Hydrogen technologies.
This second edition cancels and replaces the first edition (ISO 13984:1999), which has been technically
revised.
The main changes are as follows:
— — updated scope;
— — updated normative references and definitions updated;
— — alignment with common ISO 19880-1 requirements;
— — technical requirements moved to annexes;
— — introduction of fuelling process and protocol details;
— — addition of supporting annexes.
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.
Field Code Changed
© ISO 2025 – All rights reserved
v
ISO /FDIS 13984:####(X:2025(en)
Introduction
While the focus of this document is liquid hydrogen fuelling protocols, some technical requirements for the
dispensing system and the fuelling station are also included. This is done to ensure:
a) a) the fuelling protocols can be implemented safely and with adequate equipment;
b) b) the content of the previous edition of this document (ISO 13984:1999) has been reviewed and adapted
when relevant.
1 1)
This document has been prepared in coordination with the revision of ISO 13985 . . The fuelling protocols
described in this document and the liquid hydrogen storage systems built according to ISO 13985 are thus
intended to work together.
Stage at the time of publication: ISO/CD 13985:2025.
1)
Stage at the time of publication: ISO/DIS 13985:2025.
vi © ISO #### 2025 – All rights reserved
vi
Liquid Hydrogen -hydrogen — Land Vehicle Fuelling Protocolvehicle
fueling protocol
1 Scope
This document specifies fuelling protocols for liquid hydrogen (LH ), defining the minimum design,
installation and operation requirements for a safe, as well as fast, efficient and interoperable hydrogen
transfer from the fuelling station to the vehicle fuel system.
This document applies to land vehicles of all types equipped with a liquid hydrogen storage system in
accordance with ISO 13985. The protocols described in this document are currently limited to vehicles with
3 3
storage system total internal volume equal to or comprised between 0,6 m and 4 m . The requirements
specified in this document are also applicable to further hydrogen applications, however, further specific
requirements that can be necessary for the safe operation of such fuelling are not addressed in this document.
This document specifies the requirements for liquid hydrogen fuelling and dispensing systems, fuelling station
- vehicle interface and vehicle storage system in order to minimise the risk of fire, explosion or any other
hydrogen adverse effects to an acceptable level, especially during and after the fuelling process.
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 4126-1, Safety devices for protection against excessive pressure – Part 1: Safety valves
ISO 7369, Pipework — Metal hoses and hose assemblies — Vocabulary
ISO 10286, Gas cylinders — Vocabulary
ISO 10893--4, Non-destructive testing of steel tubes — Part 4: Liquid penetrant inspection of seamless and
welded steel tubes for the detection of surface imperfections
ISO 10893--6, Non-destructive testing of steel tubes — Part 6: Radiographic testing of the weld seam of welded
steel tubes for the detection of imperfections
ISO 10893--7, Non-destructive testing of steel tubes — Part 7: Digital radiographic testing of the weld seam of
welded steel tubes for the detection of imperfections
ISO 10893--8, Non-destructive testing of steel tubes — Part 8: Automated ultrasonic testing of seamless and
welded steel tubes for the detection of laminar imperfections
ISO 10893--10, Non-destructive testing of steel tubes — Part 10: Automated full peripheral ultrasonic testing of
seamless and welded (except submerged arc-welded) steel tubes for the detection of longitudinal and/or
transverse imperfections
ISO 11484, Steel products — Employer's qualification system for non-destructive testing (NDT) personnel
ISO/DIS 13985:2025, Liquid hydrogen — Land vehicle fuel tanks
ISO 14687, Hydrogen Fuel Qualityfuel quality — Product specification
ISO 17398, Safety colours and safety signs — Classification, performance and durability of safety signs
ISO 17636 (all parts), Non destructive testing of welds — Radiographic testing
ISO 19880--1:2020, Gaseous hydrogen — Fuelling stations — Part 1: General requirements
ISO 21013--1, Cryogenic vessels — Pressure-relief accessories for cryogenic service — Part 1: Reclosable
pressure-relief valves
ISO 21013--2, Cryogenic vessels –— Pressure-relief accessories for cryogenic service — Part 2: Non-reclosable
pressure-relief devices
ISO 21013--3, Cryogenic vessels – Pressure-relief accessories for cryogenic service — Part 3: Sizing and capacity
determination
IEC 60079--14, Explosive atmospheres - Part 14: Electrical installations design, selection and erection
IEC 60417, Graphical symbols for use on equipment - Overview and application
ECE/TRANS/180/Add.13/Amend.1 UN GTR No. 13, UN Global Technical Regulation on Hydrogen and
Fuel Cell Vehicles
63 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7369 and 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/obphttps://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
6.13.1 3.1
ambient temperature
unregulated temperature of the air
6.23.2 3.2
backgas
gaseous hydrogen flowing back from the vehicle to the fuelling station (3.19)(Error! Reference source not
found.) during the fuelling process (3.17)(Error! Reference source not found.)
6.33.3 3.3
breakaway device
device on the fuelling hose (3.15)(Error! Reference source not found.) that disconnects the hose from the
dispenser (3.7)(Error! Reference source not found.) or the vehicle when a tension, load, stress or
displacement limit is exceeded and blocks the flow of hydrogen from the dispenser, e.g. if the vehicle moves
away with the fuelling hose connected to the vehicle
2 © ISO #### 2025 – All rights reserved

ISO/DIS FDIS 13984:2025(en)
6.43.4 3.4
check-valve
valve which allows fluid to flow in only one direction
6.53.5 3.5
control valve
valve electronically or pneumatically controlled that enables and disables the hydrogen flow
Note 1 to entry: The control system provides necessary inputs and signals to the valve.
6.63.6 3.6
connector
matching parts (such as male and female parts) that can be put together to form a “connection” which permits
the transfer of fluids, electric power, or control signals
[SOURCE: ISO 19880-1:2020, 3.12, modified — Notes to entry have been removed.]
6.73.7 3.7
dispenser
equipment in the dispensing system (3.9),(Error! Reference source not found.), including the dispenser
cabinet(s) (3.8)(Error! Reference source not found.) and support structure, that is physically located in the
fuelling area
Note 1 to entry: The hydrogen dispenser typically includes, as a minimum, the fuelling assembly (3.14),(Error!
Reference source not found.), required temperature and pressure instrumentation, filters, and the user interface to
conduct vehicle fuelling.
Note 2 to entry: The manufacturer of the hydrogen dispenser can elect to include additional equipment in the dispenser,
including the possibility of all equipment in the dispensing system.
[SOURCE: ISO 19880-1:2020, 3.13]
6.83.8 3.8
dispenser cabinet
protective housing (3.23)(Error! Reference source not found.) that encloses process piping and can also
enclose measurement, control and ancillary dispenser (3.7)(Error! Reference source not found.) equipment
[SOURCE: ISO 19880-1:2020, 3.14]
6.93.9 3.9
dispensing system
system downstream of the hydrogen supply system comprising all equipment necessary to carry out the
vehicle fuelling operation, through which the liquid hydrogen is supplied to the vehicle and which transferred
quantity may be measured
Note 1 to entry:  The supply system includes the fuelling station storage tank (3.39)(Error! Reference source not
found.) and other associated equipment to bring the hydrogen to the appropriate pressure and temperature.
6.103.10 3.10
enclosure
structure, protective housing (3.22),(Error! Reference source not found.), container, machine cabinet, etc.
which encloses or partially encloses equipment of a station that may have access for maintenance but is not
intended to be occupied
[SOURCE: ISO 19880-1:2020, 3.18, modified — Notes to entry have been removed.]
© ISO 2025 – All rights reserved
6.113.11 3.11
factory acceptance testing
FAT
tests performed in the factory on fuelling station (3.19)(Error! Reference source not found.) equipment or
systems to verify functionality and/or integrity prior to shipment to the site, (or an appropriate alternative
type acceptance methodology)
[SOURCE: ISO 19880-1:2020, 3.21]
6.123.12 3.12
mass flowrate
flowrate measured in g/s unless otherwise stated
6.133.13 3.13
fuelling
transfer of hydrogen fuel from the fuelling station (3.19)(Error! Reference source not found.) to the LHSS
(3.23)(Error! Reference source not found.)
6.143.14 3.14
fuelling assembly
part of the dispenser (3.7)(Error! Reference source not found.) providing the interface between the fuelling
station (3.19)(Error! Reference source not found.) and the vehicle, comprising an assembly consisting of a
hose breakaway device (3.3),(Error! Reference source not found.), a hose(s) (3.15),(Error! Reference
source not found.), a nozzle (3.26)(Error! Reference source not found.) and connections between these
components
[SOURCE: ISO 19880-1:2020, 3.26, modified — Notes to entry have been removed and definition revised for
clarity.]
6.153.15 3.15
fuelling hose
flexible tube designed for dispensing liquid hydrogen to vehicles through a fuelling nozzle (3.26)(Error!
Reference source not found.)
Note 1 to entry: ISO 7369, ISO 10380 and ISO 21012 provide example of hoses
6.163.16 3.16
fuelling pad
area with special construction requirements adjacent to the hydrogen dispensers (3.7),(Error! Reference
source not found.), where customers park their vehicles during fuelling
[SOURCE: ISO 19880-1:2020, 3.28]
6.173.17 3.17
fuelling process
procedure to implement vehicle fuelling according to parameters defined in the fuelling protocol
(3.18),(Error! Reference source not found.), including design, hardware, as well as control and operation
rules of hardware of the hydrogen fuelling station (3.19)(Error! Reference source not found.)
4 © ISO #### 2025 – All rights reserved

ISO/DIS FDIS 13984:2025(en)
6.183.18 3.18
fuelling protocol
specification of minimum safety and performance requirements of the fuelling process (3.17),(Error!
Reference source not found.), allowing interoperability between hydrogen fuelling station (3.19)(Error!
Reference source not found.) and vehicle
6.193.19 3.19
hydrogen fuelling station
fuelling station
facility for the dispensing of liquid hydrogen vehicle fuel, often referred to as a hydrogen refuelling station
(HRS) or hydrogen filling station, including the supply of hydrogen, and hydrogen pump, storage, and
dispensing systems (3.9)(Error! Reference source not found.)
6.203.20 3.20
fuelling station operator
person or organisation responsible for the safe operation, maintenance and housekeeping of the fuelling
station (3.19)(Error! Reference source not found.)
[SOURCE: ISO 19880-1:2020, 3.32]
6.213.21 3.21
guard
part of a machine specially used to provide protection by means of a physical barrier
Note 1 to entry: Depending on its construction, a guard can be called casing, cover, screen, door, enclosed guard, etc.
[SOURCE: ISO 19880-1:2020, 3.33]
6.223.22 3.22
housing
guard (3.21) or enclosure (3.10)guard (Error! Reference source not found.) or enclosure (Error! Reference
source not found.) for operating parts, control mechanisms, or other components, that need not be accessible
during normal operation
[SOURCE: ISO 19880-1:2020, 3.40]
6.233.23 3.23
liquefied hydrogen storage system
LHSS
system that stores the liquid hydrogen, allows its fuelling from a dispenser, allows its feeding to a hydrogen
conversion system and maintains integrity and safety
Note 1 to entry: The LHSS is composed of the liquefied hydrogen storage container(s), pressure relief devices, shut-off
devices, check-valves, boil-off valve and interconnection pipings and fittings between the above components, on-board
vehicle, as defined in ISO 13985.
6.243.24 3.24
liquid hydrogen
LH
hydrogen that has been liquefied, i.e. brought to a liquid state
6.253.25 3.25
subcooled liquid hydrogen
liquid hydrogen (3.24) (Error! Reference source not found.) at a pressure-temperature condition above the
saturation pressure for this temperature
© ISO 2025 – All rights reserved
Note 1 to entry: Variation of either pressure, temperature or both can bring a saturated liquid to a subcooled liquid
state.
Note 2 to entry: Figure 1 0 shows the saturation curve for hydrogen
1,0
0,1
0,01
5 10 15 20 25 30 35 40
X (K)
Key
X temperature
Y pressure
1 solid  X Temperature
2 liquid  Y Pressure
3 gaseous
4 supercritical
5 saturation curve
6 critical point
6 © ISO #### 2025 – All rights reserved

Y (MPa(g))
ISO/DIS FDIS 13984:2025(en)
Figure 1 — Phase diagram of hydrogen
6.263.26 3.26
nozzle
device connected to a fuel dispensing system (3.9),(Error! Reference source not found.), which permits the
quick connect and disconnect of fuel supply to the vehicle fuel system
[SOURCE: ISO 19880-1:2020, 3.53, modified — "vehicle storage system" changed to "vehicle fuel system".]
6.273.27 3.27
pressure
gauge pressure measured in MPa against atmospheric pressure unless otherwise stated
6.283.28 3.28
design pressure
pressure used for the calculation of the minimum characteristics for each component or sub-system in the
system
Note 1 to entry: The design pressure cannot be less than the pressure at the most severe condition of coincident internal
or external pressure and temperature (minimum or maximum) expected during service.
6.293.29 3.29
maximum allowable working pressure
MAWP
highest pressure to which a component, a pressure container or a storage system is permitted to operate
permanently under normal operating conditions
Note 1 to entry: Further guidance on pressure terminology is included in Annex D.Annex D.
6.303.30 3.30
maximum fuelling pressure
MFP
Maximummaximum dispensing system (3.9)(Error! Reference source not found.) pressure expected during
normal (fault-free) vehicle fuelling
Note 1 to entry: Further guidance on pressure terminology is included in Annex DAnnex D
[SOURCE: ISO 19880-1:2020, 3.46, modified —Note 1 to entry replaced.]

6.323.31 3.31
maximum operating pressure
MOP
highest pressure expected for a component or system during normal operation including anticipated
transients
Note 1 to entry: Further guidance on pressure terminology is included in Annex DAnnex D
[SOURCE: ISO 19880-1:2020, 3.47, modified —Note 1 to entry replaced.]
6.333.32 3.32
operating pressure
pressure at which the piping system operates
Note 1 to entry: Operating pressure can notcannot exceed the maximum operating pressure.
© ISO 2025 – All rights reserved
6.343.33 3.33
target pressure
P
target
dispenser (3.7)(Error! Reference source not found.) fuel pressure that the fuelling protocol (3.18)(Error!
Reference source not found.) targets for the end of fuelling
Note 1 to entry: The pressure measurement is as close as possible to the fuelling assembly (3.14).(Error! Reference
source not found.).
Note 2 to entry: Further guidance on pressure terminology is included in Annex D.Annex D.
6.353.34 3.34
pressure relief device
PRD
reclosable or non-reclosable safety device that releases gases or liquids above a specified pressure value in
cases of emergency or abnormal conditions
6.363.35 3.35
qualified personnel
personnel with knowledge or abilities, gained through training and/or experience as measured against
established requirements, standards or tests, that enable the individual to perform a required function
[SOURCE: ISO 10417:2004, 3.13, modified — The word "characteristics" has been replaced with "knowledge".]
6.373.36 3.36
receptacle
device from the vehicle fuel system (3.41)(Error! Reference source not found.) which receives the nozzle
(3.26)(Error! Reference source not found.)
[SOURCE: ISO 19880-1:2020, 3.64, modified — "vehicle storage system" changed to "vehicle fuel system".]
6.383.37 3.37
site acceptance testing
SAT
tests performed after installation of the fuelling station (3.19)(Error! Reference source not found.) at the
site to verify functionality and/or integrity
[SOURCE: ISO 19880-1:2020, 3.75]
6.393.38 3.38
standards development organisation
SDO
industry- or sector-based standards organisations that develop and publish industry specific standards
Note 1 to entry: In some cases, international industry-based SDOs can have direct liaisons with international standards
organisations. SDOs are differentiated from standards setting organisations (SSOs) in that SDOs can be accredited to
develop standards using open and transparent processes.
Note 2 to entry: In the European Union, only standards created by CEN, CENELEC, and ETSI are recognised as European
standards, and member states are required to notify the European Commission and each other about all the draft
technical regulations. These rules were laid down in Directive 2015/1535/EU with the goal of providing transparency
and control with regard to technical regulations.
8 © ISO #### 2025 – All rights reserved

ISO/DIS FDIS 13984:2025(en)
[SOURCE: ISO 19880-1:2020, 3.77]
6.403.39 3.39
fuelling station storage tank
liquid hydrogen reservoir, located at the fuelling station (3.19),(Error! Reference source not found.), to
contain liquid hydrogen, which is then transferred to the vehicle fuel system (3.41)(Error! Reference source
not found.)
6.413.40 3.40
temperature
temperature measured in K unless otherwise stated
6.423.41 3.41
vehicle fuel system
VFS
LHSS fuel system
assembly of components used to store or supply hydrogen fuel to a fuel cell (FC) or internal combustion engine
(ICE), according to UN GTR No.13
Note 1 to entry: The fuel system typically includes one or more LHSS (3.23),(Error! Reference source not found.),
receptacles, interconnecting lines, boil-off gas management system.
74 Requirements
7.14.1 Hydrogen and cryogenic temperatures compatibility
All components of the fuelling system which come in contact with liquid hydrogen and cryogenic gaseous
hydrogen shall be compatible with and suitable for liquid hydrogen service and cryogenic gas flows, such as
those associated with the handling of cryogenic gaseous hydrogen returning from the LHSS fuel system. They
shall also be designed and qualified for the intended service life of the fuelling station.
Piping systems exposed to temperature fluctuations over the service temperature range shall be designed to
withstand thermal expansion and contraction.
Consideration shall also be given to the possible condensation of air. Where prevention is not possible,
countermeasures such as dripping pans shall be used.
NOTE Guidance for material under cryogenic service is given in ISO/TR 15916, ISO 21010 or ISO 21028-1.
7.24.2 Material specifications
Material used in the manufacture of components for liquid hydrogen service shall have proven performance
with hydrogen and cryogenic temperatures.
NOTE Guidance for material compatibility choices is given in ISO 21010 and ISO 11114-1.
7.34.3 Piping
Piping, valves, filters, fittings, gaskets and sealants shall be suitable for hydrogen service at the temperatures
and pressures involved.
Guidance on design, thickness definition, cyclic effects accommodation for piping are provided in A.1.1.A.1.
© ISO 2025 – All rights reserved
7.44.4 Pressure relief devices
Liquid hydrogen systems and equipment shall be protected from over-pressure, e.g. by use of one or more
PRD(s), or by other appropriate means.
Re-closing PRDs shall meet the requirements of ISO 21013-1 (equivalent national/regional standards can
exist).
Non re-closing safety devices shall meet the requirements of ISO 21013-2 (equivalent national/regional
standards can exist).
Sizing and capacity determination of liquid hydrogen system PRDs shall meet the requirements of ISO 21013-
3 (equivalent national/regional standards can exist). The different behaviour of gaseous and liquid phases
shall be taken in consideration. These pressure-relief devices shall be set to discharge at or below the design
pressure of the section of the pressure equipment they protect.
When fittings and piping are used on the upstream and/or downstream sides of pressure-relief systems, the
passages shall be designed so that the flow capacity of the pressure relief systems will not be reduced below
the capacity required for the pressure equipment on which the pressure-relief systems are installed. The
opening through all piping and fittings shall have at least the same flow area as the inlet of the pressure-relief
device to which it is connected. The nominal size of the discharge piping shall be at least as large as that of the
pressure-relief device outlet. Oversized pressure-relief devices may be used without requiring all openings in
their lines to have the same flow area, provided the required flow capacity is assured through the system.
Pressure relief devices shall be provided to prevent over-pressure, including overpressure by thermal
expansion where liquid can be trapped.
Pressure relief devices and vent piping shall be designed or located so that moisture cannot collect and freeze
in a manner which would interfere with proper operation of the pressure relief device.
Consideration should also be given in the design of the installation to facilitate the periodic inspection and
testing of the pressure relief devices. Pressure relief valves shall be inspected and set point tested according
to the manufacturer risk assessment and maintenance manual.
Further guidance on PRDs is provided in A.1.2A.2 as well as on pressure terminology in Annex D.Annex D.
7.54.5 Dispensing system
7.5.14.5.1 General requirements
An exemplary diagram of a fuelling station dispensing system is provided in Figure 2.0.
10 © ISO #### 2025 – All rights reserved

ISO/DIS FDIS 13984:2025(en)
16 16
2 6 8
3 4 5
10 11
Key
1 liquid hydrogen supply 9 hose breakaway device
2 pressure relief device supply 10 fuelling hose
3 flowmeter 11 nozzle
4 main fuelling valve 12 nozzle parking position
5 filter 13 purge gas supply
6 pressure relief device dispenser 14 purge gas inlet valve
7 pressure sensor 15 purge gas outlet valve
8 vent valve 16 vent
Key
1 liquid hydrogen supply  9 hose breakaway device

2 pressure relief device supply
3 flowmeter
4 main fuelling valve
5 filter
6 pressure relief device dispenser
7 pressure sensor
8 vent valve
9 hose breakaway device
10 fuelling hose
3 flowmeter  11 nozzle
4 main fuelling valve  12 nozzle parking position
5 filter   13 purge gas supply
6 pressure relief device dispenser 14 purge gas inlet valve
7 pressure sensor  15 purge gas outlet valve
8 vent valve  16 vent
© ISO 2025 – All rights reserved
Figure 2 — Exemplary illustration of a fuelling station dispensing system
The dispensing system shall be equipped with a main fuelling valve capable of starting and stopping the flow
of hydrogen transferred to the vehicle, according to the inputs of the control system. The main fuelling valve
may additionally control the flowrate.
The dispensing system shall be equipped with a vent valve to handle hydrogen during the cool-down or purge
process of the dispenser. It shall be capable of receiving the backgas from the vehicle in case of initial
depressurisation of the vehicle fuel system. This valve should be of the normally open type, unless otherwise
defined by risk assessment. Venting shall be directed to vent pipe termination point assessed and determined
to be a safe location, i.e. accounting for ignition sources, as well as impact on persons, systems and structures.
Safety shut off valves in liquid hydrogen service shall be installed such that their actuators do not risk being
blocked by accumulation of ice.
The dispensing system shall be capable of depressurising an LHSS, if required by the fuelling protocol specific
starting pressure, while not exceeding its maximum operating pressure to initiate the fuelling process. The
corresponding procedure is described in Annex E.Annex E.
The dispensing system components shall have an MAWP sufficient to handle backgas from the VFS. The
associated PRD shall be set and designed accordingly. See Annex DSee Annex D for guidance on pressure
levels.
The flow length between pressure sensor or transmitter and the beginning of the fuelling assembly shall not
be greater than 1 m.
The dispensing system shall be equipped with a system capable of performing leak testing and purging of the
connector before and after fuelling. The leak test and purge system shall be designed and have safeguards to
prevent contamination or damage to the LHSS, e.g., appropriate pressure level. It is recommended to use
helium for this purpose, but other gases, including hydrogen may be used, if proper measures are taken against
freezing, contamination and build-up of dangerous flammable mixtures. The leak and purge system shall be
designed, validated and maintained with a sufficient safety level, defined by the manufacturer risk assessment.
The dispensing system should be capable of performing a cool down procedure in case of warm LHSS at the
beginning of the process. The corresponding procedure is described in Annex E.Annex E.
An emergency shutdown (ESD) system shall be provided that includes a shutoff valve for stopping liquid
supply and shutting down transfer equipment. An ESD actuator, distinctly marked for easy recognition with a
permanently affixed, legible sign, shall be provided near the dispenser and also at a safe, remote location.
The dispensing system shall be protected from vehicle collision damage in accordance with ISO 19880-1:2020,
5.3.7.4 and shall have means of detecting hydrogen leaks.
7.5.24.5.2 Vehicle fuelling connectors
The main function of the fuelling connector is to enable the flow of liquid hydrogen from the fuelling station
to the vehicle fuel system and in specific cases, allow the backgas flow from the vehicle fuel system to the
fuelling station.
A vehicle fuelling connector shall provide for the reliable and secure connection of the VFS to a source of liquid
hydrogen only. The connector shall be keyed, sized or located so that they cannot be cross-connected to
12 © ISO #### 2025 – All rights reserved

ISO/DIS FDIS 13984:2025(en)
compressed gaseous hydrogen, compressed natural gas, liquefied natural gas or any other fuel connectors,
thereby minimising the possibility of connecting incompatible gaseous fluids or pressure levels. Consideration
shall be given to pressure levels of other liquid hydrogen connectors.
The fuelling connector shall prevent escape of hydrogen, in either its gaseous or liquid form, when the
connector is not properly engaged or becomes separated.
Until an appropriate International Standard on LH₂LH connectors is available, the fuelling connector shall
have an MAWP suitable for the application and follow the recognized state of the art.
NOTE At the time of publication of this document, ISO standardisation activities for the connector were ongoing.
The fuelling connector shall at minimum provide the following features:
— — allow flow of hydrogen in both directions;
— — have an automatic valve controlled by the fuelling station to isolate the nozzle;
— — have the ability to open vehicle fuel system check-valves at the interface, with attention giv
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