ISO 19880-8:2024

International
Standard
ISO 19880-8
Second edition
Gaseous hydrogen — Fuelling
2024-12
stations —
Part 8:
Fuel quality control
Hydrogène gazeux — Stations de remplissage —
Partie 8: Contrôle qualité du carburant
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 3
5 Hydrogen specifications . 4
6 Quality control approaches . 4
6.1 General .4
6.2 Sampling .4
6.3 Monitoring .4
7 Potential sources of impurities . 4
8 Hydrogen quality assurance methodology . 4
8.1 General .4
8.2 Prescriptive methodology .5
8.3 Risk assessment methodology .5
8.4 Impact of impurities on fuel cell powertrain .7
9 Routine quality control . 8
10 Non-routine quality control . 8
11 Remedial measures and reporting . 9
Annex A (informative) Example of risk assessment . 10
Annex B (informative) Example of Japanese hydrogen quality guidelines .20
Annex C (informative) Typical hydrogen fuelling station supply chain .30
Annex D (informative) Routine hydrogen quality analysis .34
Bibliography .36

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
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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)
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Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee TC 197, Hydrogen technologies.
This second edition cancels and replaces the first edition (ISO 19880-8:2019), which has been technically
revised. It also incorporates the Amendment ISO 19880-8:2019/AMD 1:2021.
The main changes are as follows:
— aligned with the revision of ISO 14687, in particular the change in the specifications of Grade D, the
indicators required for risk assessment have been mainly changed;
— due to the change in the document structure of ISO 14687, the rationale for each of the ISO 14687, Grade
D specifications has been moved to ISO 14687.
A list of all parts in the ISO 19880 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
This document was developed to specify how the quality of gaseous hydrogen fuel for road vehicles which
use proton exchange membrane (PEM) fuel cells can be assured to meet the impurity levels in Grade D of
ISO 14687. The document discusses hydrogen quality control approaches for routine and non-routine
conditions, as well as quality assurance plans. It is based upon best practices and experience from the
gaseous fuels and automotive industry. ISO 21087 describes the requirements for analytical methods to
[1]
measure the level of contaminants in ISO 14687, Grade D. ISO 19880-9 outlines requirements for sampling
from hydrogen refuelling stations for samples taken at the dispenser.

v
International Standard ISO 19880-8:2024(en)
Gaseous hydrogen — Fuelling stations —
Part 8:
Fuel quality control
1 Scope
This document specifies the protocol for ensuring the quality of the gaseous hydrogen at hydrogen
distribution facilities and hydrogen fuelling stations for proton exchange membrane (PEM) fuel cells for
road vehicles.
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 19880-9, Gaseous hydrogen — Fuelling stations — Part 9: Sampling for fuel quality analysis
ISO 14687, Hydrogen fuel quality — Product specification
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
constituent
component (or compound) found within a hydrogen fuel mixture
3.2
contaminant
impurity (3.7) that adversely affects the components within the fuel cell powertrain (3.4) or the hydrogen
storage system
Note 1 to entry: An adverse effect can be reversible or irreversible.
3.3
filter
equipment to remove undesired particulates (3.14) from the hydrogen
3.4
fuel cell powertrain
power system used for the generation of electricity on a fuel cell vehicle (3.5)
Note 1 to entry: The fuel cell powertrain typically contains the following subsystems: fuel cell stack, air processing,
fuel processing, thermal management, and water management

3.5
fuel cell vehicle
FCV
vehicle which stores hydrogen on-board and uses a fuel cell powertrain (3.4) to generate electricity for
propulsion
3.6
fuelling station
facility for the dispensing of compressed hydrogen vehicle fuel, including the supply of hydrogen, and
hydrogen compression, storage, and dispensing systems
Note 1 to entry: Fuelling station is often referred to as hydrogen fuelling station or hydrogen filling station.
3.7
impurity
non-hydrogen component in the gas stream
3.8
indicator species
one or more constituents (3.1) in the gas stream which can signal the presence of other chemical constituents
because it has the highest probability of presence in a fuel produced by a given process
3.9
monitoring
act of measuring the constituents (3.1) of a hydrogen stream or process controls of a hydrogen production
system on a continuous or semi-continuous basis by on-site equipment
3.10
non-routine
not in accordance with established procedures
3.11
on-site supply
hydrogen fuel supplying system with a hydrogen production system in the same site
3.12
off-site supply
hydrogen fuel supplying system without a hydrogen production system in the same site, receiving hydrogen
fuel which is produced out of the site
3.13
particulate
solid or liquid, such as oil mist, that can be entrained somewhere in the delivery, storage, or transfer of the
hydrogen fuel entering a fuel cell powertrain (3.4)
3.14
purifier
equipment to remove undesired constituents (3.1) from the hydrogen
Note 1 to entry: Hydrogen purifiers may comprise purification vessels, dryers, filters (3.3), and separators.
3.15
quality assurance
part of quality management focused on providing confidence that quality requirements will be fulfilled
3.16
quality control
part of quality management focused on fulfilling quality requirements
3.17
quality plan
documentation of quality management

3.18
reversible damage
reversible effect
effect, which results in a non-permanent degradation of the fuel cell power system performance that can be
restored by practical changes of operational conditions and/or gas composition
3.19
risk
combination of the probability of occurrence of harm and the severity (3.24) of that harm, encompassing
both the uncertainty about and severity of the harm
3.20
risk assessment
determination of quantitative or qualitative value of risk (3.19) related to a specific situation and a
recognized threat
Note 1 to entry: A recognized threat can also be referred to as a hazard.
3.21
risk level
assessed magnitude of the risk (3.19)
3.22
routine
in accordance with established procedures
3.23
sampling
act of capturing a measured amount of hydrogen for chemical analysis by external equipment
3.24
severity
measure of the possible consequences for fuel cell vehicles if filled with H containing a higher level of
impurities (3.7) than the threshold value
4 Abbreviated terms
Abbreviated term Definition
ATR autothermal reaction
Halogens halogenated compounds
HDS hydrodesulfurization
MS molecular sieve
OC occurrence class
PEM proton exchange membrane
Pox partial oxidation
PSA pressure swing adsorption
PSL process safety limit
SC severity class
SMR steam methane reforming
HC hydrocarbons
S sulfur compounds
TSA temperature swing adsorption
UD undetermined
5 Hydrogen specifications
The quality requirements of hydrogen fuel dispensed to PEM fuel cells for road vehicles shall comply with
Grade D of ISO 14687.
6 Quality control approaches
6.1 General
There are two common methods to control the quality of hydrogen at a fuelling station, by periodic sampling and
continuous monitoring. These methods can be used individually or together to ensure hydrogen quality levels.
6.2 Sampling
Periodic sampling at a fuelling station involves capturing a measured amount for chemical analysis. Sampling
is used to perform an accurate and comprehensive analysis of impurities which is done externally, typically
at a laboratory. Since the sampling process involves drawing a sample of gas, it is typically done on a periodic
basis and requires specialized sampling equipment and personnel to operate it. Sampling procedures shall
conform to ISO 19880-9. The advantage of periodic sampling is that a more detailed laboratory analysis can
be conducted on the sample. The disadvantage of periodic sampling is that it is not continuous and results in
a detailed analysis at a single point in time.
6.3 Monitoring
A fuelling station can have real time monitoring of the hydrogen gas stream for one or more impurities on
a continuous or semi-continuous basis. A critical impurity can be monitored to ensure it does not exceed
a critical level, or monitoring of an indicator species or control parameter can be used to alert of potential
issues with the hydrogen production or purification process. Monitoring equipment is installed in line
with the hydrogen gas stream and shall meet the process requirements of the fuelling station, as well as
be calibrated on a periodic basis. Continuous monitoring complements periodic sampling by offsetting the
disadvantages.
7 Potential sources of impurities
For a given fuelling station, the contaminants listed in the hydrogen specification referred to in Clause 5
may or may not be potentially present. There are several parts of the supply chain where impurities can be
introduced. The potential impurities in each step of the supply chain are described in Annex C.
When a contaminant is classified as potentially present, it shall be taken into account in the quality assurance
methodology (risk assessment or prescriptive approach) described in Clause 8.
8 Hydrogen quality assurance methodology
8.1 General
A quality assurance plan for the entire supply chain shall be created to ensure that the hydrogen quality
will meet the requirements described in Clause 5. The methodology used to develop the quality assurance
plan can vary but shall include one of the two approaches described in this document. A prescriptive
methodology may be used as described in 8.2 or a risk assessment methodology may be used (8.3). Examples
of these approaches: a) risk assessment and b) prescriptive approach for hydrogen quality, are presented in
Annexes A and B, respectively. The quality assurance plan for the fuelling station shall include the following
to ensure hydrogen quality is properly maintained:
— identification of potential impurities;
— methods to control and remove these impurities;

— sampling impurities and frequency;
— monitoring of impurities or process controls;
— description of solid and liquid particulate filters;
— cleanliness and maintenance procedures.
It is important to understand that quality should be maintained throughout the complete supply chain of
the product (from production source to fuelling station nozzle), such that the impurities that are given in the
specification remain below the threshold values.
Each component of the supply chain shall be investigated taking into account the already existing barriers
for a given contaminant.
NOTE An effective quality control approach can further ensure the quality of the hydrogen by providing
a proactive means to identify and control potential quality issues which can include sampling and monitoring.
Additionally, use of quality assurance can improve the decision making if a quality problem arises.
If a vehicle is found to have hydrogen with contamination that exceeds the specification in Clause 5 and the
source is unknown, the procedures in Clause 11 shall be followed.
8.2 Prescriptive methodology
The prescriptive approach to hydrogen quality assurance considers potential sources of contaminants and
establishes a fixed protocol for analysing and addressing potential contaminants. The prescriptive approach
can be applied for the clearly identified supply chain.
The prescriptive quality assurance plan shall be determined taking into account all hydrogen production
methods, hydrogen transportation methods and non-routine procedures which exists in the area where the
assurance plan is applicable.
NOTE Annex B presents Japanese hydrogen quality guidelines which is an example of a prescriptive quality
assurance plan.
8.3 Risk assessment methodology
The risk assessment approach determines the probability to have each impurity above the threshold values
of specifications given in Clause 5 and evaluates severity of each impurity for the fuel cell vehicle. As an aid
to clearly defining the risk(s) for risk assessment purposes, three fundamental questions are often helpful:
— What can go wrong: which event can cause the impurities to be above the threshold value?
— What is the likelihood (probability of occurrence expressed relative to the number of fuelling events)
that impurities can be above the threshold value?
— What are the consequences (severity) for the fuel cell vehicle?
In doing an effective risk assessment, the robustness of the data set is important because it determines
the quality of the output. Conservative values should be taken if the data is unknown or has a high level
of uncertainty. The risk analysis should be updated as the data is updated. Revealing assumptions and
reasonable sources of uncertainty will enhance confidence in this output and/or help identify its limitations.
The output of the risk assessment is a qualitative description of a range of risk. To determine the probability
of the occurrence that impurities in hydrogen exceed the threshold value, Table 1 defines the occurrence
classes.
Table 1 — Occurrence classes for an impurity
a
Occurrence class Class name Description Occurrence or frequency
Very unlikely Contaminant above threshold never
0 (Practically been observed for this source/sup- 1 per 10 000 000 fuellings
impossible) ply chain/station
Known to occur at least once for
1 Unlikely 1 per 1 000 000 fuellings
this source/supply chain/station
Has happened once a year for this
2 Possible 1 per 100 000 fuellings
source/supply chain/station
Has happened more than once a
3 Likely year for this type of source/supply 1 out of 10 000 fuellings
chain/station
Happens on a regular basis for this More than 1 out of 1 000 fuel-
4 Very likely
type of source/supply chain/station lings
a
Based on a fuelling station supplying 100 000 fuellings per year. In case the actual refuelling use of the subject HRS is known
at a yearly base, the occurrence corresponding to all the occurrence classes should be proportionally adjusted so that occurrence
class 2 reflects one occurrence per year
If the occurrence class is unknown, then the risk assessment shall assume the worst case. In addition, the
experience of the hydrogen supplier, station manufacturer/installer should be taken into account when
performing the risk analysis.
The range of severity classes (level of damage for vehicle) is defined in Table 2.
Table 2 — Severity classes for an impurity
Impact categories
Severity
Performance Hardware Hardware
FCV performance impact or damage
class
impact impact impact
temporary permanent
0 — No impact No No No
— Minor impact Yes No No
— Temporary loss of power
— No impact on hardware
— Vehicle still operates
— Reversible damage Yes or No Yes No
— Requires specific light maintenance
procedure
— Vehicle still operates
— Reversible damage Yes Yes No
— Requires specific immediate maintenance
3 procedure
— Gradual power loss that does not
compromise safety
— Power loss or vehicle stop that
compromises safety
a
4 Yes No
Yes
— Irreversible damage
— Requires major repair procedure (e.g., stack
No Yes
change)
a
Any damage, whether permanent or temporary, which compromises safety will be categorized as SC 4, otherwise temporary
damage will be categorized as SC 1, 2 or 3.

The final risk is defined by the acceptability Table 3 which combines results from Tables 1 and 2:
Table 3 — Combined risk assessment
Severity
Occurrence class name Occurrence class
0 1 2 3 4
Very likely 4 + o * * *
Likely 3 + o o * *
Possible 2 + + o o *
Unlikely 1 + + + o o
Very unlikely
0 + + + + +
(Practically Impossible)
+ o *
Acceptable risk area: Existing Further investigations are Unacceptable risk;
Key
controls sufficient needed to ensure the risks additional control or
is reduced to as low as rea- barriers required
sonably practicable
NOTE 1 It is possible that contamination of a vehicle at severity class 1 or 2 is not noticeable immediately, thereby
making it difficult to identify the source of the contamination.
For each impurity of the specification and for a given fuelling station (including the supply chain of hydrogen),
a risk assessment shall be applied to define the global risk.
NOTE 2 Risk control includes decision making to reduce and/or accept risks. The purpose of risk control is to
reduce the risk to an acceptable level.
The amount of effort used for risk control should be proportional to the significance of the risk. Decision
makers can use different processes, including benefit-cost analysis, for understanding the optimal level of
risk control. Risk control can focus on the following questions:
— Is the risk above an acceptable level?
— What can be done to reduce or eliminate risks?
— What is the appropriate balance among benefits, risks and resources?
For each level of risk, a decision shall be taken in order to either refuse the risk and find mitigation or barriers
to reduce it, or accept the risk level as it is. Risk reduction focuses on processes for mitigation or avoidance of
quality risk when it exceeds an acceptable level (“o” or “*” zone in Table 3). Risk reduction typically includes
actions taken to mitigate the severity and/or probability of occurrence. However, this document only deals
with the mitigation of probability of occurrence.
In the “0” zone, the risk can be acceptable but redesign or other changes should be considered if reasonably
practicable.
Further investigation should be performed to give better estimate of the risk. When assessing the need of
remedial actions, the number of events of this risk level should be taken into consideration in order to be as
low as reasonably practicable.
8.4 Impact of impurities on fuel cell powertrain
It is necessary to evaluate the possible consequences on a fuel cell vehicle if any impurity exceeds the
threshold value in Clause 5. The impact for the vehicle will depend on the concentration of the contaminant.
Table 4 shows a summary of the concentration-based impact of the impurities on the fuel cell. The
contaminants and their chemical formulas are given in the first two columns of Table 4.
An estimation of the concentration above the ISO 14687 Grade D threshold values at which the severity
increases (if applicable) is named “Level 1” and is given in column 5 for each impurity where the “severity

class” is not already 4. According to this concentration a severity class is given in column 4 for each impurity.
This severity class covers the impact of this impurity above the threshold value up to this limit.
If higher concentrations that exceed Level 1 can be reached, the severity class is given in column 6.
Table 4 — Impact of impurities on fuel cell powertrain
Severity class
Severity class
ISO 14687 (from ISO 14687
(greater than
Impurity Grade D Grade D Level 1 value
Level 1
a
threshold value threshold value to
threshold)
Level 1)
[μmol/mol] [μmol/mol]
Total non-H gases 300 1 500 4
Helium He 300 1 500 4
Nitrogen N 300 1 500 4
Argon Ar 300 1 500 4
Oxygen O 5 1 50 4
Carbon dioxide CO 2 1 3 4
b
Carbon monoxide CO 0,2 2-3 1 4
Methane CH 100 1 300 4
Water H O 5 4 NA 4
H S
Sulfur
equiva- 0,004 4 NA 4
compounds
lent
Ammonia NH 0,1 4 NA 4
CH
Hydrocarbons except
b
equiva- 2 1-2 5 4
methane
lent
b
Formaldehyde HCHO 0,2 2-3 1 4
Halogens 0,05 4 NA 4
Maximum particulate
concentration (liquid 1 mg/kg 4 NA 4
c
and solid)
Key
NA: not applicable
a
The threshold value is according to hydrogen specification of Grade D of ISO 14687.
b
A higher value is to be considered for risk assessment approach until more specific data is available.
c
Particulates are based upon mass density mg/kg.
9 Routine quality control
Routine analysis is performed on a periodic basis once every specified time period or once for each specified
number of deliveries. The methodology selected in the hydrogen quality assurance plan determines the type
and frequency of the routine analysis. A prescriptive methodology may be used as described in 8.1 or a risk
assessment methodology may be used (8.2). Information on the routine analysis for each step of the supply
chain is provided in Annex D.
10 Non-routine quality control
The hydrogen quality plan shall:
a) include sampling and analysis when a new fuelling station is commissioned;

b) identify any other reasonably foreseeable non-routine conditions requiring subsequent sampling and
analysis actions.
Some common non-routine conditions include the following:
— a new production system is constructed at a production site or a new fuelling station is first commissioned;
— the production system at a production site or fuelling station is modified;
— a routine or non-routine open inspection, repair, catalyst exchange, or the like is performed on a
production system at the production site or fuelling station;
— any severe malfunctions of a transportation system of compressed hydrogen, liquid hydrogen, and
hydrogen pipeline occur;
— a question concerning quality is raised when, for example, there is a problem with a vehicle because of
hydrogen supplied at the production site or fuelling station, and a claim is received from a user directly
or indirectly;
— an issue concerning quality emerges when, for example, a voluntary audit raises the possibility that
quality control is not administered properly; or
— analysis is deemed necessary for testing, research, or any other purposes.
11 Remedial measures and reporting
If a fuelling station dispenses hydrogen which does not meet the requirements in Clause 5, the fuelling
station operator shall immediately prevent any further dispensing until repaired. The station operator shall
notify the station owner and authorities having jurisdiction, as soon as possible. The station operator and
owner shall also make an effort to notify those affected by the contamination, as soon as possible. This may
include providing notifications to:
— vehicle manufacturer or dealerships;
— users of the station;
— industry groups, station status databases, social media.
The fuelling station owner/operator shall also review and update quality assurance methodologies to
prevent future contamination.
Annex A
(informative)
Example of risk assessment
A.1 Centralized production, pipeline transportation
The different steps for elaborating the quality assurance plan of one fuelling station are illustrated using the
following case: one fuelling station delivered by pipeline from an off-site SMR.
The solutions selected in this example to decrease the risk when necessary are given as a possible solution
for this specific case. Other solutions may be chosen depending on each fuelling station.
Following the procedure described in Clause 8, the risk assessment is performed on the following.
— The identification of the probability to have each impurity above the threshold values of specifications
but always below or equal to the level one defined in Table 4 or this document
— The evaluation of severity for the fuel cell vehicle, assuming values of impurities between the specification
and the level 1, also given in Table 4. For the impurities for which the severity is at level 4 whatever is the
concentration above the threshold, level 1 is not applicable in Table 4.
— This risk assessment is done for each part of the supply chain: SMR, pipeline distribution and fuelling
station itself (see Table A.1, Table A.2, and Table A.3).
A.2 Steam methane reforming
A.2.1 General
In this process, methane from natural gas and steam reacts at a high temperature to produce synthesis gas
(or syngas). Syngas is a mixture consisting mainly of hydrogen and carbon monoxide.
In order to achieve the reaction between natural gas and steam, catalysts and a high temperature are
required. These catalysts are poisoned by any trace of sulfur or chlorinated compounds. It is then necessary
to remove all sulfur components from natural gas before the SMR reaction. The purification system, named
hydrodesulfurisation is a two steps process: first transformation of all sulfur species in H S and then
adsorption of H S in specific adsorbents. At the outlet of this purification step, the natural gas contains less
than 0,05 µmol/mol of H S by design and less than 0,01 µmol/mol in normal conditions.
After the reforming reaction, the carbon monoxide is further reacted with steam in a water gas shift reaction.
It produces carbon dioxide and hydrogen and it increases the hydrogen yield. An additional separation step
is mandatory to provide hydrogen with a purity suitable for FCV application.
A.2.2 Purification by pressure swing adsorption
Pressure swing adsorption is a non-cryogenic gas separation process which uses adsorbent technology to
purify hydrogen from a gas mixture. PSA principle is based on preferential adsorption of some gaseous
components to others on highly porous materials. The PSA ability to trap impurities depends on the affinity
between the adsorbent and the gas molecule. Typically, a PSA column is filled with multiple adsorbents
with very high surface area to volume ratios. Typical adsorbents include silica, alumina, molecular sieves,
and activated carbons, which have different relative strength of adsorption depending on the gaseous
compounds.
Table A.1 — Probability of occurrence for off-site SMR
Im- Possible causes sources of
a
puri- Threshold contamination Typical barriers employed in this process Level 1 OC
ty SMR + PSA
μmol/mol μmol/mol
Inert
— PSA
Present in natural gas and
gas 300 500 2
syngas PSA malfunction
— Double analysis PSA outlet <400 μmol/mol with 3 levels of alarms
N
Inert Only ATR and POx present in
— PSA. Not sized to remove Ar. Ar content may be higher if H comes from ATR,
gas 300 O typical 0,6 % (mole frac- 500 1
POX or feeds with high Ar content
Ar tion) in syngas from ATR
Not present in syngas. O is
unstable in the condition of
O 5 — PSA cannot be used with significant O content for safety reasons 50 0
2 2
reforming and shift reactions.
Combines with H , CO, and CH
2 4
— PSA adsorption strength of MS, activated carbon, silicagel higher for CO than
Present in syngas (% (mole
CO 2 CO. A CO content lower than 10 μmol/mol insures a CO content lower than 3 0
2 2
fraction))
2 μmol/mol
Normal operation below
CO 0,2 threshold. Occasional peaks at — Double analysis at the PSA outlet + trip if the CO>1-10 μmol/mol at PSA outlet 1 4
μmol/mol level
— In most cases CO is sizing the PSA, therefore CO<10 μmol/mol ==>
Present in syngas at % (mole
CH 100 CH < 100 μmol/mol depending on users' specification (Europe pipeline 300 2
4 4
fraction) level
2 μmol/mol).
— PSA adsorbed in alumina and MS adsorption strength higher than CO .
H O 5 Syngas saturated in H O A CO content lower than 10 μmol/mol insures a H O content lower than 5 μmol/ NA 0
2 2 2
mol.
Key
NA: Not applicable because the severity is 4 above the threshold value.
a: Occurrence class for impurity between threshold limit and Level 1.

Table A.1 (continued)
Im- Possible causes sources of
a
puri- Threshold contamination Typical barriers employed in this process Level 1 OC
ty SMR + PSA
μmol/mol μmol/mol
— Desulfuration upstream reformer (typical values: normal < 10 nmol/mol,
maximum < 20 nmol/mol, guarantee < 50 nmol/mol)
— Typical dilution factor 2,5 (1 mol natural gas produces 2,5 mole H )
— Pre-reformer catalyst poisoning by sulfur is irreversible. Sulfur trapped at this
stage.
In case of breakthrough, process condition cannot be achieved
S 0,004 Sulfur from natural gas — Reformer catalyst poisoning by sulfur is irreversible. Sulfur trapped at this NA 0
stage.
In case of breakthrough, process condition cannot be achieved
— Shift catalyst poisoning by sulfur is irreversible. Sulfur trapped at this stage.
In case of breakthrough, process condition cannot be achieved
— PSA adsorption of H S before CO, CO , species
2 2
— H S adsorption in pipe and vessels. Strong affinity with steel
— PSA adsorption strength of alumina and molecular sieve higher than CO. A CO
NH 0,1 Traces present in syngas NA 0
content lower than 10 μmol/mol insures a NH content lower than 0,1 μmol/mol
Traces of C2+ after reforming — PSA C2 C3, C4, C5+adsorbed by activated carbon layer. A CO content lower than
HC 2 5 0
reaction 10 μmol/mol insures a HC (CH excluded) content lower than 2 μmol/mol
Key
NA: Not applicable because the severity is 4 above the threshold value.
a: Occurrence class for impurity between threshold limit and Level 1.

Table A.1 (continued)
Im- Possible causes sources of
a
puri- Threshold contamination Typical barriers employed in this process Level 1 OC
ty SMR + PSA
μmol/mol μmol/mol
— PSA. Formaldehyde adsorption strength of alumina and molecular sieve
May be present in syngas. higher than CO. A CO content lower than 10 μmol/mol insures a HCHO content
HCHO 0,2 1 0
essentially liquid lower than 0,1 μmol/mol. To guarantee 0,01 μmol/mol would require more
experience of measuring at those levels
— Any Cl present in natural gas would be stopped by HDS
— Pre-reformer catalyst poisoning by Cl irreversible Cl trapped at this stage. If
breakthrough, process condition cannot be achieved
Halo- — Reformer catalyst poisoning by Cl irreversible. Cl trapped at this stage I break
0,05 Present in natural gas NA 0
gens through, process condition cannot be achieved
— Shift catalyst poisoning by Cl irreversible. Cl trapped at this stage. I break
through, process condition cannot be achieved
— PSA adsorption of Cl before CO, CO , species
Not present in natural gas in N
Europe (<10 μmol/mol). Passes
He 300 500 0
through the whole process.
Dilution factor 2,5
Key
NA: Not applicable because the severity is 4 above the threshold value.
a: Occurrence class for impurity between threshold limit and Level 1.

Table A.2 — Probability of occurrence for pipeline
Typical barriers Level 1
Possible source of contamination
a
Impurity Threshold employed in OC
pipeline
this process
μmol/mol μmol/mol
Air intake if some areas are at negative
Inert gas pressure Inlet pressure PSL trip on
300 500 1
N From seal gas or purge gas compressors
Wrong purging after maintenance
1 % (mole fraction Ar in
the air.
Inert gas 100 μmol/mol would
300 No potential 500 0
Ar mean 1 % (mole fraction)
air in the pipe
Never been observed
Air intake if some areas are at negative Inlet pressure PSL trip on
O 5 50 1
pressure compressors
2 μmol/mol of CO would
From Air: CO at 400 μmol/mol in the mean 0,5 % (mole frac-
CO 2 3 0
air tion) air in the pipe
Never been observed
CO 0,2 No potential 1 0
CH 100 No potential 300 0
H > 40 bar ==> leak
Wrong drying after pressure hydraulic
H O 5 from H O to H unlikely NA 1
2 2 2
test
during operation.
S 0,004 No potential NA 0
NH 0,1 No potential NA 0
HC 2 No potential 5 0
HCHO 0,2 No potential 1 0
From cleaning material after mainte- NA
Halogens 0,05 1
nance
He 300 No potential 500 0
Key
NA: Not applicable because the severity is 4 above the threshold value.
a: Occurrence class for impurity between threshold limit and Level 1.

Table A.3 — Probability of occurrence for fuelling station to be source of impurities
Causes possible Level 1
a
Impurity Threshold Existing barriers OC
For the source studied
μmol/mol μmol/mol
N purging operation, air intake
Inert gas
300 during normal operation or main- 500 3
N
tenance
1 % (mole fraction) Ar
in the air. 100 μmol/mol
Inert gas Air intake during normal operation would
300 500 0
Ar or maintenance mean 1 % (mole fraction)
air in the fuelling station
Never been observed
Air intake during normal operation
O 5 50 2
or maintenance
2 μmol/mol CO would
Air intake during normal operation mean 0,5 % (mole frac-
CO 2 3 0
or maintenance tion) air in the fuelling sta-
tion. Never been observed
CO 0,2 No potential at fuelling station level 1 0
CH 100 No potential at fuelling station level 300 0
Maintenance, leaks from compres-
sor exchangers, improper pressure
vessel drying after periodic inspec-
H O 5 tion, H O coming from the vent in NA 2
2 2
case of check valve malfunction,
depending on fuelling station/com-
pressor technology
Materials gaskets, valve seats and
S 0,004 Material specifications NA 1
tubing
NH 0,1 No potential NA 0
Oil carryover from compressor
HC 2 (depending on compressor technol- 5 2
ogy)
HCHO 0,2 No potential 1 0
Halogens 0,05 From degreasing material NA 1
If pure He is not used for 500
He 300 No potential at fuelling station level 0
maintenance
Key
NA: Not applicable because the severity is 4 above the threshold value.
a: Occurrence class for impurity between threshold limit and Level 1.
When the study has been conducted for each step within the supply chain (i.e., production, distribution, and
fuelling) the highest probability is selected as the compounded probability. Table A.4 gives an example.
To define the severity class of each impurity as it is presented in Table A.4, some assumptions are made
concerning the impurity levels above the threshold value. These impurity levels are assumed to be reached
for a short period of time.
Table A.4 — Combined risk assessment
ISO specification Supply chain probability  Residual
Produc- Pipeline Fuel- Compound-
Thresh- Sev- Criti- Additional risk Sever- Critical-
a
Impurity tion distribu- ling ed probabil- OC
old er-ity cal-ity reduction measures ity ity
SMR tion station ity
μmol/
mol
Systematic N analysis after shutdown before
Inert gas
300 2 1 3 3 1 o resuming operation or specific purging procedure 1 o
N
at HRS
Inert gas
300 1 0 0 1 1 + 1 1 +
Ar
O 5 0 1 2 2 1 + 2 1 +
CO 2 0 0 0 0 1 + 0 1 +
CO absorber at fuelling station design margin
100 % (mole fraction) + operation procedure for
CO 0,2 4 0 0 4 3 * 1 3 o
replacement when H quantity purified = 50 %
(mole fraction) of design capacity.
CH 100 2 0 0 2 1 + 2 1 +
At HRS check H O at commissioning and after
maintenance involving opening of vessels or
H O 5 0 1 2 2 4 * piping. Measurement shall be done at appropriate 1 4 +
location downstream of the considered vessel or
piping
At HRS check S at commissioning and after main-
tenance involving parts modification (piping,
S 0,004 0 0 1 1 4 o 0 4 +
valves, seals, gaskets). Not required for part
replaced by identical component
NH 0,1 0 0 0 0 4 + 0 4 +
Oil/grease cleaning at commissioning and after
maintenance. Compressor surveillance depending
HC 2 0 0 2 2 2 o 0 2 +
on compressor technology (coalescing filter) HC
analysis or commissioning and
...