Chapter FC:
Safety of applications, including coverage by
standards: stationary fuel cells and indoor
systems
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1.1
Stationary fuel cells
Fuel cells convert the chemical energy from a fuel (such as hydrogen or natural gas)
and from oxygen into electricity. This electricity can be used to power stationary,
mobile applications, etc.
1.1.1
Description
Fuel cells generate water from a fuel (such as hydrogen or natural gas) and from
oxygen in the air, while producing electricity and heat. This reaction is carried out in
each of the basic cells of the fuel cell.
Each fuel cell consists of an anode, a cathode, and an electrolyte allowing the
charges to move from one side to the other side of the fuel cell. As described in Figure
1, electrons move from the anode to the cathode through an external circuit, producing
an electrical current - and thus powering the load.
Figure 1: Block diagram of a fuel cell (Source: Wikipedia)
Such cells are placed in series, to reach an adequate voltage output. When
assembled together, the cells constitute an energy module of the required power
known as the stack.
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Ventilation
opening
Ventilation grille
at the front of the system
:
Fuel cells
Storage of
hydrogen:
6 cylinders
B50 max.
Figure 2: Example of a stationary fuel cell: the
Comm PacTM system, developed by Axane (Source: Axane)
Note: pressure of the gas feeding the fuel cell:10 bar (reduced to 250 mbar upstream
the fuel cell)
Different types of fuel cells exist. The main types of fuel cells are1: Proton Exchange
Membrane Fuel Cells (PEMFC), Solid Oxide Fuel Cells (SOFC) and Molten
Carbonate Fuel Cells (MCFC). These fuel cells are classified according to the type of
electrolyte they use.

In Proton Exchange Membrane Fuel Cells, a proton-conducting membrane
is used as an electrolyte.
In pure hydrogen PEMFC, hydrogen is dissociated into protons H+ and
electrons on the anode. Protons are conducted through the proton-conducting
membrane to the cathode. As the membrane is electrically insulated, electrons
move from the anode to the cathode through an external circuit, producing an
electrical current. On the cathode, oxygen reacts with the electrons and
protons to form water.
Such fuel cells operate at temperatures between 50 and 220°C, typically
80°C.
Other types of PEMFC also exist: some are fed with a mixture of CO 2 and H2.

In Solid Oxide Fuel Cells, a ceramic material called yttria-stabilized zirconia
(YSZ) is most commonly used as an electrolyte. In SOFC, oxygen gas reacts
on the cathode with electrons, to form negatively charged oxygen ions. These
oxygen ions move through the electrolyte from the cathode to the anode,
where they react with hydrogen gas, producing electricity and water.
1
Other types of fuel cells exist, such as: alkaline fuel cells, phosphoric acid fuel cells, etc.
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SOFC operates at high temperatures (between 800 and 1000°C). They can
be fed with fuels other than hydrogen gas, such as natural gas for instance.
Natural gas is then reformed (i.e. converted to hydrogen) internally.

In Molten Carbonate Fuel Cells, lithium potassium carbonate salt is used as
an electrolyte. At high temperatures (about 650°C), this salt melts and allows
for the movement of the negative carbonate ions from the electrolyte. On the
anode, hydrogen reacts with carbonate ions to produce mainly water, carbon
dioxide and electrons. The electrons move from the anode to the cathode,
producing an electrical current. On the cathode, carbon dioxide (from the
anode) and oxygen react with the electrons to form carbonate ions.
MCFC can be fed with fuels other than hydrogen gas, such as natural gas for
instance. As in SOFC, natural gas is reformed (i.e. converted to
hydrogen) internally.
Because of their high operating temperatures, Molten Carbonate Fuel Cells and Solid
Oxide Fuel Cells have slow start-up times. Therefore, they are not suitable for
mobile applications and are limited to stationary applications. Proton Exchange
Membrane Fuel Cells are preferred for mobile applications.
This section focuses on stationary fuel cells as the electrical safety of on-board
applications has already been explained in part 3.
Examples of stationary
applications are off-grid power supply and back-up power supply.
References:

Website of Axane

Wikipedia
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1.1.2
Hazards and safety measures
Fuel cells are low-pressure systems: upstream the fuel cell, the hydrogen feed
pressure is reduced down to low pressures (e.g. 250 mbar at the cells’ inlet of Axane’s
fuel cell Comm PacTM). Therefore, stationary fuel cell systems are free from
hazards related with the handling of pressurized hydrogen.
But, since fuel cells consist of a stack of basic cells in which chemical reactions
involving hydrogen are carried out, there is a risk of leaks.
In order to avoid the formation of flammable mixtures, sensors able to detect
hydrogen leaks are used. Once sensors have detected the presence of hydrogen at
a concentration higher than a threshold value, isolation measures are taken.
1.1.3
Coverage by standards and certification
 IEC 62282-2
 Partially covered by IEC 62282-3-100
 IEC 62282-3-3
 NF M58-003 in development
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1.2
1.2.1
Indoor installations of hydrogen systems
Combination of means of prevention of explosion hazards
The accumulation of an explosive mixture due to a hydrogen leak is a particular
hazard to be addressed for indoor installations. This is prevented with a high degree of
reliability through a set of measures combining passive ventilation, avoidance of
ignition sources, hydrogen detection, safety ventilation, isolation and de-energization.
1.2.1.1
Natural ventilation; Permanent forced ventilation ; Triggered ventilation
Definitions
Hydrogen systems can either include a natural ventilation system in their design,
permanent forced ventilation or triggered ventilation.
Natural ventilation does not use any mechanical system; on the contrary,
permanent forced and triggered ventilation involve mechanical systems.
A permanent forced ventilation system is active permanently, preventing at all
times the formation of any explosive atmosphere which may result from a hydrogen
leak. A sensor is able to detect if the permanent forced ventilation system stops, and
then a process aiming at stopping the whole system is triggered.
Triggered ventilation is triggered after a sensor detects the presence of hydrogen at
a concentration higher than a threshold value. As there is always a risk of sensor
failure, permanent forced ventilation system is more reliable than triggered
ventilation.
Note: if triggered ventilation or permanent forced ventilation is used and if it is an
important part of the safety concept of the plant, a safety related monitoring system is
necessary to control the working operation of the ventilation system in case of an
emergency, e.g. hydrogen leak.
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Natural ventilation
Enclosures with two openings allow for better natural ventilation than enclosures with
only one opening (see section Error! Reference source not found.). The openings
should preferably be located on two different walls diametrically opposed of the
enclosure (one inlet opening is at the bottom of a wall and one outlet opening is at the
top of the opposed wall enclosure), so that a displacement ventilation can take place
(see section Error! Reference source not found.).
Attention must be given to preventing the potentially negative effect of wind as an
opposing wind might limit the selectiveness of natural ventilation (see section Error!
Reference source not found.).
Enclosure
with 2 openings
Wind
Figure 3: Small opposing wind
(Source: Air Liquide)
Measures to limit the effect of wind include:

Use of wind deflectors

Location of outlet on top surface rather than lateral surface

Use of wind activated extractors.
Triggered and permanent forced ventilations
For triggered ventilation, an ATEX certified mechanical ventilation system should be
used,
For permanent forced ventilation, a non-ATEX certified mechanical ventilation system
can be used. But this non-ATEX certified mechanical ventilation system should be
shut-off and replaced by an ATEX certified mechanical ventilation system as soon as
the hydrogen threshold concentration has been reached.
The mechanical ventilation system should preferably be installed in a high location.
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1.2.1.2
Hydrogen detection and isolation
When sensors detect the presence of hydrogen at a concentration higher than a
threshold value, whenever possible, the source of hydrogen shall be shut off and
an alarm triggered.
1.2.1.3
Use of classified equipment
Where a flammable atmosphere could occur due to foreseeable leaks, ignition risks
should be prevented by using classified equipment, i.e. equipment complying
with the ATEX directive (see section Error!
1.2.2
Reference source not found.).
Suitable combinations of means in function of hydrogen release
frequency and severity
Guidelines for the indoor installation of hydrogen systems have been the focus of a
recent project of standard NF M58-003. This standard shows whether the following
items are compatible: a hydrogen system and its risk management system, and
the room where the hydrogen system is to be installed.
These guidelines consist in four steps:

Step 1: characterize the installation within the room where the hydrogen
system is to be installed (characterization of the hydrogen system AND of the
equipments of the room)

Step 2: rate the risk management system concerning hydrogen accumulation
and ignition

Step 3: check the compatibility of the room where the hydrogen system is to
be installed with the hydrogen system and its associated risk management
system

Step 4: check to see whether the installation prescriptions for the room where
the hydrogen system is to be installed complies with the established
standards.
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Step 1: characterize the installation within the room where the hydrogen system
is to be installed (characterization of the hydrogen system AND of the
equipments of the room)

The main characteristics of the hydrogen system are identified: its power
(in kW), its operating pressure (in bar) and the quantity of hydrogen stored
in the system.

The potential leak rates of the hydrogen system are assessed. On this
basis, the system is attributed a qualification Q1, Q2, Q3 or “without
qualification” leaks, depending on the value of the expectable and foreseeable
leak rates. For being attributed a qualification, the two corresponding
conditions on expectable and foreseeable leaks need to be met.
Table 1: Classification of the leaks
(Source: « Atelier de présentation du projet de norme NF M58-003 Installation des
systèmes mettant en œuvre l’hydrogène », AFNOR, November 2011)
Kind of leak
Q1
Q2
Q3
Without qualification
Expectable
< 0,1 g/s
< 0,3 g/s
< 1 g/s
< 3 g/s
< 10 g/s
Expectable leak > 1 g/s
or
foreseeable leak > 10 g/s
Foreseeable

< 1 g/s
The equipments of the installation are classified according to their ATEX
qualifications. Equipments are either qualified for an ATEX zone 0, 1, 2, or
without any ATEX qualification2.
2
Definitions for ATEX zones:
Zone 0 - An atmosphere where a mixture of air and flammable substances in the form
of gas, vapor or mist is present frequently, continuously or for long periods.
Zone 1 - An atmosphere where a mixture of air and flammable substances in the form
of gas, vapor or mist is likely to occur in normal operation occasionally.
Zone 2 - An atmosphere where a mixture of air and flammable substances in the form
of gas, vapor or mist is not likely to occur in normal operation but, if it does occur, will
persist for only a short period.
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Step 2: rate the risk management system concerning hydrogen accumulation
and ignition
The safety measures enforced to reduce the risks of each type of leaks
(continuous hydrogen leak, expectable leak and conceivable leak) are reviewed.
These measures include passive ventilation, triggered ventilation, hydrogen
detection and isolation, etc.
Depending on the type of release and the ATEX qualification of the equipment,
these safety measures against hydrogen build-up have varying degrees of
reliability. Prevention of explosion hazards must be all the more reliable that a leak is
probable. In other words, reliability requirements with regards to prevention of
explosive atmosphere are more stringent measures for continuous gas leaks than for
accidental leaks.
For each type of leak, an assessment of the reliability of the safety measures to
prevent hydrogen an explosion hazard is performed. The outcome is the rating of the
explosion risk control system enforced for each type of leak, ranging from 1 to 4.
The rating attributed to the system as a whole is the lowest of these ratings.
An overall rating of 4 means that explosion hazards are very well controlled, and
hence installation in any room is allowed. If the overall rating is 1, the system may only
be installed in a dedicated building.
Table 2: Global rating of the risk management system
(Source: « Atelier de présentation du projet de norme NF M58-003 Installation des
systèmes mettant en œuvre l’hydrogène », AFNOR, November 2011)
Equipment qualification and safety
measures against H 2 build-up
Kind of leak
Without
qualification
Continuous gas
leaks
Expectable leaks
Conceivable leaks
Qualified
for zone 2
Qualified for
zone 1 or 0
Safety measures against H 2 build-up:
Rating of the
explosion
risks control
Example: 4
 Ventilation (passive, active,
triggered)
Ventilation and emergency control
Example: 3
Example: 4
Global rating
= minimum : 3
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Step 3: check of the compatibility of the room where the hydrogen system will
be installed with the hydrogen system and its associated risk control system
Depending on the characteristics of the system (mass of stored hydrogen and power),
on the class of potential leaks and on the rating of explosion risks control, the type of
room where the hydrogen system may be installed is identified, based on the most
stringent criterion for the particular case (see example on Table 3).
Table 3: Identification of the kind of place where the hydrogen system can be installed
(Source: « Atelier de présentation du projet de norme NF M58-003 Installation des
Risk level
-
+
System
characterization
Class of
potential leaks
Rating of
explosion risk
control
Type of indoor
location
<8 kg and P<30 kW
Q1
4
Common premises
<8 kg and P<70 kW
Q2
≥3
Technical premises
<35 kg and P<150 kW
Q3
≥2
Dedicated technical
premises
≥1
Dedicated buildings
>35 kg and P>150 kW
Outdoors
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-
+
Safety of the premise
systèmes mettant en œuvre l’hydrogène », AFNOR, November 2011)
Step 4: checking of the compliance of the installation prescriptions for the room
where the hydrogen system is to be installed.
Depending on the kind of room in which the hydrogen system may be installed
(common premises, technical premises, dedicated technical premises, dedicated
buildings, outdoors or on a flat roof), the specifications of the installation are
different: access to the installation, access to other premises from the installation,
separation distances, ventilation and isolation, fire resistance of the structures,
warning displays.
Table 4: Specifications of the installations
(Source: « Atelier de présentation du projet de norme NF M58-003 Installation des
systèmes mettant en œuvre l’hydrogène », AFNOR, November 2011)
Type of location
Specifications of the installation
 Not accessible to the public
 Adequate design of the ventilation
 At least one label indicating the presence of pressurized
hydrogen at the entrance and in the premises
 High floor
Technical
premises
 Walls made of M0 materials with a fire-resistance rating of
one hour
 One door with:
o fire resistance of 1/2h if the door opens in a room or
place accessible to the public
o otherwise: flame screen with resistance rating of 1/2h
o equipped with a self-closer (which opens toward the
exit and can be opened from the inside)
 Not accessible to the public
Dedicated
 Adequate design of the ventilation
technical
 At least one label indicating the presence of pressurized
premises
/
Dedicated
buildings
hydrogen at the entrance and in the premises
 Walls made of M0 materials with a fire-resistance rating of
two hours
 Communication facilities with other premises must have a fire
resistance rating of one hour (opening toward the exit) and
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doors must be equipped with self-closers (premises with
significant risks)
 No direct communication with premises and places
accessible to the public (premises with significant risks)
 Not accessible to the public
 Adequate design of the ventilation
 At least one label indicating the presence of pressurized
hydrogen at the entrance and in the premises
Outdoors
 Walls made of M0 materials
 Separation distances
 If separation distances cannot be observed, firewalls
(minimum height: 2m and fire resistance rating of 2h)
Reference:

« Atelier de présentation du projet de norme NF M58-003 Installation des
systèmes mettant en œuvre l’hydrogène », AFNOR, November 2011
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1.2.3
Use of hydrogen detectors and hydrogen detection limits
Use of hydrogen detectors
When there is a reasonably foreseeable possibility of a hydrogen release or of leak
generating a hazardous explosive atmosphere despite the existing passive ventilation
means, the enclosed area shall be equipped with a hydrogen detection system.
Hydrogen detection limits
Hydrogen detectors are gas sensors that detect the presence of hydrogen. Under
normal room conditions, hydrogen concentrations should stay below 0,4 vol % (i.e.
10% Lower Flammability Limit LFL).
If the hydrogen content in the air exceeds the alarm threshold, an audible alarm will
be triggered. 1 vol % (25% LFL) is the maximum concentration for the alarm
threshold.
If the hydrogen concentration reaches 1.6 to 2.4 vol % (40 to 60 % LFL), hydrogen
sources are isolated and all activity and equipment having the potential to generate
an ignition source will be stopped/de-energized.
These hydrogen detection limits are given in the ISO 15916.
Location of the hydrogen detectors
Hydrogen detectors can be located above potential leak sources, or in high points
where hydrogen presence is not likely under normal conditions. The precise
location of the hydrogen detectors in high points is not important as hydrogen builds
up a homogeneous upper layer in enclosures.
Information about the selection, installation and use of hydrogen sensors is given in:
IEC 60079-1, IEC 60079-2, IEC 60079-7, IEC 60079-11, IEC 60079-15, IEC 6007918, IEC 60079-20-1, IEC 60079-29-1.
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1.2.4
Coverage by standards and certification

Partially covered by ISO 62282-3-3

ISO 15916

NF M58-003 in development

ISO 26142 (for hydrogen detectors)

IEC 60079-1, Explosive atmospheres — Part 1: Equipment protection by
flameproof enclosures “d”

[5] IEC 60079-2, Explosive atmospheres — Part 2: Equipment protection by
pressurized enclosures “p”

[6] IEC 60079-7, Explosive atmospheres — Part 7: Equipment protection by
increased safety “e”

[7] IEC 60079-11, Explosive atmospheres — Part 11: Equipment protection by
intrinsic safety “i”

[8] IEC 60079-15, Explosive atmospheres — Part 15: Equipment protection by
type of protection “n”

[9] IEC 60079-18, Explosive atmospheres — Part 18: Equipment protection by
encapsulation “m”

[10] IEC/TR 60079-20-1, Explosive atmospheres — Part 20-1: Material
characteristics for gas and vapor classification — Test methods and data

[11] IEC 60079-29-1, Explosive atmospheres — Part 29-1: Gas detectors —
Performance requirements of detectors for flammable gases
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