SIST-TP CEN/TR 17238:2018

SLOVENSKI STANDARD
SIST-TP CEN/TR 17238:2018
01-december-2018
Predlagane mejne vrednosti za onesnaževala v biometanu na podlagi meril
zdravstvene presoje
Proposed limit values for contaminants in biomethane based on health assessment
criteria
Vorgeschlagene Grenzwerte für Verunreinigungen in Biomethan auf Grundlage von
Gesundheitsgefährdungskriterien
Valeurs limites proposées pour les contaminants dans le biométhane sur la base de
critères d'évaluation de la santé
Ta slovenski standard je istoveten z: CEN/TR 17238:2018
ICS:
27.190 Biološki viri in drugi Biological sources and
alternativni viri energije alternative sources of energy
75.060 Zemeljski plin Natural gas
SIST-TP CEN/TR 17238:2018 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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CEN/TR 17238
TECHNICAL REPORT

RAPPORT TECHNIQUE

April 2018
TECHNISCHER BERICHT
ICS 75.160.30; 27.190
English Version

Proposed limit values for contaminants in biomethane
based on health assessment criteria
Valeurs limites proposées pour les contaminants dans Vorgeschlagene Grenzwerte für Verunreinigungen in
le biométhane sur la base de critères d'évaluation de la Biomethan auf Grundlage von
santé Gesundheitsgefährdungskriterien


This Technical Report was approved by CEN on 9 April 2018. It has been drawn up by the Technical Committee CEN/TC 408.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 17238:2018 E
worldwide for CEN national Members.

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Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Symbols, units and abbreviated terms . 8
3
4.1 Cg: maximum acceptable concentration in biomethane (mg/m ) . 8
4.2 Cexp: exposure concentration . 8
4.3 M: multiplier in the exposure model . 8
4.4 CAS number: Unique numerical identifier assigned by Chemical Abstracts Service . 8
5 Global Approach for assessment of limit values . 8
5.1 General . 8
5.2 Definition of the database for gas composition and HCVs . 9
5.3 Definition of the exposure model . 10
5.4 Part III: Determination of COPCs . 10
6 Assessment and selection of Health Criteria Values: general guidance on assessment
and selection of HCVs . 10
7 Application of the methodology: Biomethane injection into gas networks . 11
Annex A (Informative) Example of different sources of HCVs . 12
Annex B (Informative) Example of the application of the methodology . 13
B.1 General . 13
B.2 Conceptual Model . 13
B.3 Chemicals of Potential Concern (COPCs) . 14
B.4 Mathematical Exposure Model . 14
B.4.1 General . 14
B.4.2 Modelling exposure concentrations – domestic cooking situation. 15
B.5 Selection of HCVs . 18
B.6 Determination of the maximum tolerable concentration of each contaminant . 19
Annex C (Informative) Details of the exposure model . 21
C.1 Introduction . 21
C.2 Nomenclature . 21
C.3 Continuous releases . 22
C.4 Decay in concentration following cessation of release . 22
C.5 Average concentrations . 23
C.6 Use of multipliers . 26
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C.7 Exposure model spreadsheet . 26
Bibliography . 27

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European foreword
This document (CEN/TR 17238:2018) has been prepared by Technical Committee CEN/TC 408
“Natural gas and biomethane for use in transport and biomethane for injection in the natural gas grid”,
the secretariat of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
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Introduction
This standard was prepared by CEN/TC 408 in response to the European Commission standardization
mandate M/475.
The Mandate asks for the development of a set of quality specifications for biomethane to be used as a
fuel for vehicle engines and to be injected in natural gas pipelines (network).
However, the scope of the standard was widened according to BT decision C109/2012 that redefined
the scope of CEN/TC 408: “Standardization of specifications for natural gas and biomethane as vehicle
fuel and of biomethane for injection in the natural gas grid, including any necessary related methods of
analysis and testing. Production process, source and the origin of the source are excluded”.
One of the aims of European policy in the field of energy is to increase the security of energy supply in
the EU as well as to contribute to reduce the emission of greenhouse gases accepted by the EU at Kyoto.
In this context a special focus is given to the development and use of energy from renewable sources.
Directive 2009/28/EC on the promotion of the use of energy from renewable sources and amending
and subsequently repealing Directives 2001/77/EC and 2003/30/EC stipulates clear aims regarding
the percentage of renewables in EU energy consumption and states the related need to support the
integration of energy from renewable sources into the energy networks including the establishment of
appropriate technical rules in line with Directive 2003/55/EC (Article 6) replaced by 2009/73/EC
(Article 8) for the realization of the competitive single European Gas Market and the technical
interoperability of gas networks, (network connection, gas quality, gas odorization and gas pressure
requirements).
Supporting the EU policy and therefore the maximization of the production and use of biomethane and
considering the absence of standards the European Commission DG ENER has included the injection of
biomethane in natural gas pipelines in Mandate M/475. Biomethane in this context can be produced
from biological (fermentation, digestion …) and thermochemical processes and it is essential that it is
appropriate to be used as a blending component to natural gas.
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1 Scope
This document explains an approach for assessment of limit values for contaminants that may be found
in biomethane. Limit values are generally required as an adjunct to a biomethane specification (such as
parts 1 and 2 of EN 16723, or an equivalent National specification) or as part of a Network Entry
Agreement for injection of biomethane into gas networks.
The methodology employed will permit derivation of limit values based solely on consideration of
potential for impact on human health and does not consider other impacts, such as integrity and
operation of plant and pipelines used to convey biomethane or appliances involved in its combustion or
other regulations like CLP regulation. Where consideration of such impacts would result in proposing
lower limit values than those based on health impacts, then the lowest limit values should generally be
proposed.
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.
EN 16723-1:2016, Natural gas and biomethane for use in transport and biomethane for injection in the
natural gas network — Part 1: Specifications for biomethane for injection in the natural gas network
EN 16723-2:2017, Natural gas and biomethane for use in transport and biomethane for injection in the
natural gas network — Part 2: Automotive fuels specification
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
biogas
gas, comprising principally methane and carbon dioxide, obtained from the anaerobic digestion of
biomass
3.2
biomass
biological material from living, or recently living organisms, typically this may be plants or plant-
derived materials
3.3
biomethane
gas comprising principally methane, obtained from either upgrading of biogas or methanation of bio-
syngas
3.4
bio-syngas
gas, comprising principally carbon monoxide and hydrogen, obtained from gasification of biomass
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3.5
contaminant
chemical with undesired properties which may be present in biomethane at a low concentration and for
which no maximum concentration is specified in EN 16723
3.6
Chemicals Of Potential Concern
(COPC)
chemicals that may present a risk to the environment directly or after combustion
3.7
Health Criteria Value
(HCV)
generic term to describe a benchmark level of exposure to a chemical derived from available toxicity
data for the purposes of safeguarding human health. They are defined for instance by US EPA (US),
3
ANSES (FR), Environment Agency (UK), RIVM (NL), ARPA (IT). The unit is mg/m
3.8
limit value
maximum concentration of a contaminant that is allowed in a gas quality specification
3.9
natural gas
complex gaseous mixture of hydrocarbons, primarily methane, but generally includes ethane, propane
and higher hydrocarbons, and some non-combustible gases such as nitrogen and carbon dioxide
Note 1 to entry: Natural gas can also contain components or contaminants such as sulphur compounds and/or
other chemical species.
3.10
natural gas network
transmission network or local distribution system
3.11
non-threshold effect chemical
chemical that may theoretically pose a risk at any level of exposure
3.12
(Health) Risk
possibility that a harmful event (death, injury or loss) arising from exposure to a chemical or physical
agent may occur under specific conditions
3.13
threshold effect chemical
chemical which might be present in such concentrations that it might initiate a health risk of concern
3.14
upgrading of biogas
removal of carbon dioxide and contaminants from biogas
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4 Symbols, units and abbreviated terms
3
4.1 Cg: maximum acceptable concentration in biomethane (mg/m )
4.2 Cexp: exposure concentration
4.3 M: multiplier in the exposure model
4.4 CAS number: Unique numerical identifier assigned by Chemical Abstracts Service
5 Global Approach for assessment of limit values
5.1 General
The approach described in this technical report is similar to that commonly employed in environmental
health risk assessment, an example of which can be seen at the US Dept. of Energy’s Risk Assessment
Information System (RAIS) website [9].
Conventional health risk assessments aims to assess and quantify the health risk presented by a
particular activity. If the risk exceeds a maximum acceptable value, then mitigation actions are assessed
and implemented. In conventional risk assessment, therefore, the output is a (quantified) level of risk
associated with the process. However, in the context of specifying limit values for contaminants in
biomethane the INVERSE of this risk assessment procedure is followed: an acceptable level of risk is
agreed and the activity (in this instance injection of biomethane into natural gas grids) is modified by
implementing an appropriate gas quality specification. In this situation, the acceptable level of risk is an
input to the risk assessment procedure and the output is a gas quality specification. Such a specification
will contain limit values for content of those contaminants that are likely to be present.
NOTE The contaminants that are likely to be present that can present a risk to the environment are
commonly called “Chemicals of Potential Concern” (COPCs).
Similar approaches have been previously employed for development of gas quality specifications for
biomethane: in 2008 in France (Afsset [1]) and in 2012 in the UK (UK Environment Agency [7]). This
approach may be used whenever compounds of interest are added in the list of data. In addition, several
realistic scenarios should be assessed in order to identify the worst case that will lead to the most
appropriate limit value.
These scenarios depend at least on these elements:
• The national laws and regulations,
• The conceptual model designed,
• The national practices,
• Specific assumptions.
The procedure for assessing limit values in this Technical Report can be summarized in following
scheme (Figure 1):
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Figure 1 — Description of the methodology to apply to each contaminant
5.2 Definition of the database for gas composition and HCVs
When assessing limit values for contaminants present in biomethane, the point at which COPCs are
identified will depend on the context, i.e. whether a site-specific or generic assessment is being carried
out and whether a detailed chemical analysis of biogas/biomethane is available or not.
Trace compounds will strongly be influenced by its production process. Production processes for
biomethane vary significantly. For example:
• Anaerobic digestion of a wide range of biomass feedstocks, followed by upgrading (carbon dioxide
removal) and purification (removal of contaminants).
• Gasification of a wide range of biomass feedstocks to a bio-syngas, followed by purification and
upgrading (water gas shift and methanation).
It means that the database of the target compounds is defined using gas analysis and literature. Each
target compound should be described with its CAS number. C (concentration to be expected in
exp
biomethane) will be estimated also and included in the database.
Health Criteria Values (HCVs) are obtained for each contaminant, based on expert assessment
reported in the literature and the scenario considered. At the end of the process, one HCV will be
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obtained for each compound and each scenario. This methodology should be applied when HCV for the
target compound is available. Assessment and choice of HCVs are discussed in Clause 6.
5.3 Definition of the exposure model
The exposure model is usually dependant on national practices.
For each scenario, A “Source-Pathway-Receptor” conceptual model of exposure is agreed. The
conceptual model clarifies the assumptions about the Source (i.e. how a particular contaminant arises),
the Receptor (i.e. the environment/entity that is exposed to the contaminant and for which impact is
assessed) and the Pathway (i.e. how the contaminant is transported from the Source to the Receptor).
Based on the stated assumptions and boundaries of the conceptual model, a mathematical
exposure model is derived. The exposure model permits assessment of the ratio of concentration of a
given contaminant in the Source to the average concentration to which the Receptor is likely to be
exposed. This ratio is designated the “multiplier” (symbol M) and defined as in Formula (1).
Formula 1: multiplier
[1]
Because the exposure model is based on the conceptual model and its assumptions, then it too will
usually be specific to a particular country or national situation.
For each scenario, a specific Cg is established from its exposure model and selected HCV. The maximum
acceptable concentration is taken to be the lowest Cg value of these scenarios.
5.4 Part III: Determination of COPCs
The maximum acceptable concentration of each contaminant at the Source is assessed from the product
of the HCV and the Multiplier (Formula (2):
Formula 2: Maximum acceptable concentration at the source
[2]
3
Cg is usually expressed in mg/m .
When assessing combustion product of a contaminant, then the HCV of the combustion product and not
the contaminant itself is employed. In this situation, the relationship between the quantity of the
combustion product and the quantity of the contaminant in biomethane is required.
Cg is compared to Cexp to estimate if this chemical should be targeted as a COPC.
In the approach used in the “Risk Assessment Information System” (RAIS) of the US Department of
1
Energy , identification of COPCs is carried out at an early stage so as to limit the number of chemicals
for which risk assessment is carried out. Generally speaking, it is impractical to specify limit values for
large numbers of contaminants and so some form of reduction in the number of COPCs to be covered is
required if limit values are to be specified in a gas quality specification.
6 Assessment and selection of Health Criteria Values: general guidance on
assessment and selection of HCVs
Detailed guidance on assessment and selection of HCVs is available in a number of sources ((8)(6)) and
so only general advice is provided in this Technical Report. The basic toxicological approaches to
deriving HCVs for environmental chemicals are similar throughout the international scientific

1
US Department of Energy. (2016, March). Risk Assessment Information System. https://rais.ornl.gov/
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community. However, with so many different organisations conducting risk assessments and regulatory
bodies each working to the unique wording of their national legislation, inevitable differences exist in
the precise methods followed and terminology used.
Whilst the approach employed in this Technical Report is consistent with that generally applied in most
countries, it is generally the case that no single set of common HCVs will be available and so values will
often need to be obtained from a variety of sources (see Annex A).
Generally HCVs are set by National or International expert panels and although there may often
be international agreement, for some chemicals conflicting values may exist. In such situations
users of this protocol are recommended to seek advice from appropriate National expert bodies, taking
into account the National regulatory situation covering biomethane injection into gas grids. HCVs could
also be subject to guidance or regulation from National Expert bodies.
7 Application of the methodology: Biomethane injection into gas networks
Annex B illustrates the application of the methodology outlined in this Technical Report by way of an
example that deals with injection of biomethane into a gas distribution network. The conceptual model
considers the pathway from Source to Receptor to be inhalation of biomethane and its combustion
products released during cooking operations in a domestic property. Because these are well understood
operations it can be modelled using a deterministic mathematical model, where the outcome (i.e.
quantification of exposure to contaminants) will always be the same for the same inputs.
This example is an illustration of the methodology and should not be taken to be representative of a
particular national situation.
An alternative conceptual model could consider inhalation of biomethane that is released as a result of
undetected leaks from pipework within a domestic property. However, estimating exposure to
contaminants would require a stochastic mathematical model because there are a number of processes
involved in the pathway that contain an element of randomness. For example:
• The minimum concentration of biomethane in a room that is detectable by the occupant. Although
all distributed gas is odorised, the lowest concentration at which biomethane is detectable will vary
from person to person.
• Not all residencies have leaking pipework and the distribution of numbers of leaks of a given size
will vary for all residencies.
• Occupancy varies, both in terms of fraction of the day that a residence is occupied and the number
and ages of occupants.
In principle a stochastic exposure model could be developed using probability density functions that
described each of the above processes and which would provide estimates of multipliers at a chosen
probability level. However, an example of such an approach is not provided in this Technical Report.
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Annex A
(Informative)

Example of different sources of HCVs
These examples given in Table A.1 are extracted from a French study by INERIS. For a set of several
compounds, sources to define HCV come from several countries or National experts’ panel. They are
defined under specific conditions which are further explained in the references.
Table A.1 — examples of different sources of HCVs
HCV - Inhalation pathway -
CAS Substances
Threshold toxicity
  (mg/m3) References
75–01–4 Vinyl chloride 56 RIVM, 2001
156–59–2 cis-1,2-Dichloroethene 6 RIVM, 2007
71–55–6 1,1,1-trichloroethane (1,1,1-TCA) 1 OEHHA, 2008
79–01–6 Trichloroethylene (TCE) 2 US-EPA, 2011
127–18–4 Tetrachloroethylene (PCE) 4 US-EPA, 2011
75–09–2 Dichloromethane 4 OEHHA, 2000
67–66–3 Trichloromethane (chloroforme) 63 AFSSET, 2008
(TCM)
56–23–5 Tetrachloromethane (TCC) 38 AFSSET, 2008
75–25–2 Tribromomethane No value
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Annex B
(Informative)

Example of the application of the methodology
B.1 General
This example illustrates the procedure for setting limit values for contaminants in biomethane based on
health assessment criteria. The procedure follows the five-step approach described in clause 5.
Additional details of individual steps is provided in subsequent annex.
In general, different realistic situations in which human beings are exposed to unburned biomethane
and to flue gasses of biomethane are defined and the most severe one will be used to set the limit value.
In this example, biomethane is to be injected into a 2 barg pressure gas distribution network and is
combusted in a domestic cooking situation. The biomethane is produced by upgrading (removal of
carbon dioxide) and purification (removal of contaminants) of a biogas that is produced by anaerobic
digestion of sewage sludge. A chemical analysis of the biogas demonstrates that contaminants are
present at the following concentrations (Table B.1):
Table B.1 — Contaminants present and their concentration in the example biogas
Contaminant Units Concentration
3
Formaldehyde mg/m 0,05
3
D-limonene mg/m 2,53
3
Dichloromethane mg/m 1,5
3
Arsenic µg/m 5,4
B.2 Conceptual Model
The conceptual model is based on the injection of biomethane into a gas distribution network and
subsequent exposure to occupants of a domestic property to which gas is conveyed.
Table B.2 below sets out the main assumptions regarding a conceptual model of exposure to
contaminants contained in biomethane.
Table B.2 — Conceptual model of exposure to contaminants in biomethane
 Assumption Notes
Source: Biomethane injected into a gas grid Although typical biomethane production
for conveyance to a consumer’s and injection facilities are relatively

premises. small. Injection is commonly into low
pressure systems where demand may be
low. The gas conveyed within the gas
pipeline is therefore considered to be
100 % biomethane.
Pathway: Two pathways are considered: A gas cooker hob is assumed to be the
most common unflued gas appliance.
a) Inhalation of unburnt biomethane
released from a gas cooker hob
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 Assumption Notes
prior to its ignition.
b) Inhalation of contaminants or
products of combustion of
contaminants released whilst a
gas cooker hob is in use.
Receptor: Human acute and chronic exposure It is assumed in this example that
through inhalation during cooking cooking is carried out in a separate,
operations. typical domestic kitchen by adults. If
children and elderly people are expected
to be present in this kitchen, then an
additional factor can be applied.
B.3 Chemicals of Potential Concern (COPCs)
The chemical analysis of the biogas shown in Table B.1 suggests that the contaminants listed in
Table B.3 should be considered to be COPCs, since they are present in biogas and hence there is reliance
on the upgrading and purification process to remove them to an acceptable level.
Table B.3 — List of contaminants considered to be COPCs
Contaminant
Formaldehyde
D-limonene
Dichloromethane
Hydrogen Chloride
Arsen
...