CEN/TR 16793:2016

SLOVENSKI STANDARD
01-april-2016
Smernice za izbiro in uporabo plamenskih zapor
Guide for the selection, application and use of flame arresters
Richtlinie für die Auswahl, die Anwendung und den Einsatz von
Flammendurchschlagssicherungen
Guide pour la sélection, l'application et l'utilisation des arrête-flammes
Ta slovenski standard je istoveten z: CEN/TR 16793:2016
ICS:
13.220.99 Drugi standardi v zvezi z Other standards related to
varstvom pred požarom protection against fire
23.060.40 7ODþQLUHJXODWRUML Pressure regulators
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN/TR 16793
TECHNICAL REPORT
RAPPORT TECHNIQUE
January 2016
TECHNISCHER BERICHT
ICS 23.060.40; 13.220.99
English Version
Guide for the selection, application and use of flame
arresters
Guide pour la sélection, l'application et l'utilisation des Richtlinie für die Auswahl, die Anwendung und den
arrête-flammes Einsatz von Flammendurchschlagssicherungen

This Technical Report was approved by CEN on 22 December 2014. It has been drawn up by the Technical Committee CEN/TC
305.
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, 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: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16793:2016 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviated terms . 6
3.1 Terms and definitions . 6
3.2 Abbreviated terms . 8
4 Explosion risks . 9
5 Technical measures for explosion protection . 11
5.1 General . 11
5.2 Mitigation of the effects of explosion . 11
5.2.1 General . 11
5.2.2 Prevention of explosion propagation – explosion decoupling . 11
5.3 Safety concept . 11
6 Flame arresters . 13
6.1 General . 13
6.2 Principle of operation of flame arresters . 14
6.3 Types of flame arresters . 15
6.3.1 End-of-line deflagration flame arrester . 15
6.3.2 In-line deflagration flame arrester . 15
6.3.3 In-line detonation flame arrester . 15
6.3.4 Stabilized burning . 15
6.3.5 Pre-volume flame arresters . 16
6.4 Selection of flame arresters . 16
6.5 Application limits . 20
6.6 Installation limits . 21
6.6.1 General . 21
6.6.2 Arrangement of flame arresters at pipe branches [5] . 22
6.6.3 In-line deflagration flame arrester . 23
6.6.4 End-of-line deflagration flame arrester . 24
6.6.5 Liquid seal flame arrester . 25
6.6.6 Foot valve flame arrester . 26
6.6.7 Hydraulic flame arrester . 26
6.6.8 High velocity valves . 26
6.7 Insulation and heating . 26
7 Application of flame arresters . 27
7.1 General . 27
7.2 Protection of process units, containments and tanks [5] . 27
7.2.1 Necessity of flame arresters . 27
7.2.2 Protection against flame transmission during deflagration or detonation . 27
7.2.3 Protection against flame transmission during endurance burning . 28
7.2.4 Operating conditions [5] . 29
7.3 Changing the process . 29
8 Installation, operating and maintenance . 29
8.1 General . 29
8.2 Safety information . 30
8.3 Checking and installing . 30
8.4 Inspection and maintenance intervals . 31
8.5 Liquid seal flame arrester . 31
9 Commissioning checklist . 32
Bibliography . 33

European foreword
This document (CEN/TR 16793:2016) has been prepared by Technical Committee CEN/TC 305
“Potentially explosive atmospheres - Explosion prevention and protection”, the secretariat of which is
held by DIN.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
Introduction
The document provided is general in nature and for specific applications further expert advice should
be sought.
In addition to the content of operating manuals from manufacturers, the local accident prevention
regulations, environmental protection and general safety provisions for the devices’ area of use, as well
as relevant laws and national directives, this paper will support the user for a proper use of flame
arresters.
In Europe, the “Directive 2014/34/EU on equipment and protective systems intended for use in
potentially explosive atmospheres” (ATEX – Atmosphères Explosibles) is mandatory for the production
and test intended for use of products in potentially explosive atmospheres. Flame arresters are defined
as a Protective System.
Flame arresters should be tested according to EN ISO 16852, Flame arresters – Performance
requirements, test methods and limits for use, to fulfill the health and safety requirements of this
directive.
Flame arresters are subjected to an EC type examination and are designed for use in areas at risk from
explosion.
The Directive 1999/92/EC of the European Parliament and of the Council of 16 December 1999 on
minimum requirements for improving the safety and health protection of workers potentially at risk
from explosive atmospheres - gives the minimum requirements for the improvement of health
protection and safety of employers who could be endangered by explosive atmospheres. The main
issues are assessment of explosion risk, zone classification and the explosion protection documents
(including requirements for personnel to do engineering, equipment selection, installation,
maintenance, repair, etc.).
National regulations and/or codes relating to specific industries or applications may exist which have to
followed.
Flame arresters are required to protect against many types of explosion events within equipment.
The safety obtained depends heavily upon correct choice, installation and maintenance of the flame
arrester. This cannot be achieved without responsible, informed management.
1 Scope
This Technical Report is aimed primarily at persons who are responsible for the safe design and
operation of installations and equipment using flammable liquids, vapours or gases.
This document applies to both industrial and mining applications
This document describes possible risks and gives proposals for the protection against these risks by the
use of flame arresters.
This document gives some guidance to choice of flame arresters according to EN ISO 16852 for different
common scenarios and it gives best practice for the installation and maintenance of these flame
arresters.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN 60079-20-1, Explosive atmospheres — Part 20-1: Material characteristics for gas and vapour
classification — Test methods and data (IEC 60079-20-1)
EN ISO 16852:2010, Flame arresters — Performance requirements, test methods and limits for use (ISO
16852:2008, including Cor 1:2008 and Cor 2:2009)
EN ISO 28300:2008, Petroleum, petrochemical and natural gas industries — Venting of atmospheric and
low-pressure storage tanks (ISO 28300:2008)
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
atmospheric condition
pressure ranging from 80 kPa to 110 kPa (0,8 bar to 1,1 bar); temperatures ranging from -20 °C to
+60 °C
3.1.2
end-of-line flame arrester
flame arrester that is fitted with one pipe connection only
3.1.3
explosion
abrupt oxidation or decomposition reaction producing an increase in temperature, pressure, or in both
simultaneously
3.1.4
explosion group
Ex.G
ranking of flammable gas-air mixtures with respect to the MESG
Note 1 to entry: See EN ISO 16852:2010, 3.12.2.
3.1.5
explosion-pressure-resistant
property of vessels and equipment designed to withstand the expected explosion pressure without
becoming permanently deformed
3.1.6
explosion-pressure-shock resistant
property of vessels and equipment designed to withstand the expected explosion pressure without
rupturing, but allowing permanent deformation
3.1.7
deflagration
explosion propagating at subsonic velocity
[SOURCE: EN ISO 16852:2010, 3.8]
3.1.8
detonation
explosion propagating at supersonic velocity and characterized by a shock wave
[SOURCE: EN ISO 16852:2010, 3.9]
3.1.9
stable detonation
detonation progressing through a confined system without significant variation of velocity and pressure
characteristics
Note 1 to entry: For the atmospheric conditions, test mixtures and test procedures of this International
Standard, typical velocities range between 1 600 m/s and 2 200 m/s.
[SOURCE: EN ISO 16852:2010, 3.10]
3.1.10
unstable detonation
detonation during the transition of a combustion process from a deflagration into a stable detonation
Note 1 to entry: The transition occurs in a limited spatial zone, where the velocity of the combustion wave is not
constant and where the explosion pressure is significantly higher than in a stable detonation. The position of this
transition zone depends, amongst other factors, on pipe diameter, pipe configuration, test gas and explosion
group.
[SOURCE: EN ISO 16852:2010, 3.11]
3.1.11
flame arrester
device fitted to the opening of an enclosure, or to the connecting pipe work of a system of enclosures,
and whose intended function is to allow flow but prevent the transmission of flame
[SOURCE: EN ISO 16852:2010, 3.1]
3.1.12
flame arrester element
part of a flame arrester whose principal function is to prevent flame transmission
[SOURCE: EN ISO 16852:2010, 3.3]
3.1.13
in-line flame arrester
flame arrester that is fitted with two pipe connections, one on each side of the flame arrester
[SOURCE: EN ISO 16852:2010, 3.22]
3.1.14
mixture
used to represent any mixtures of gas and/or product vapour/air
3.1.15
product
equipment, protective systems, safety devices, components and their combinations
3.1.16
protected side
side of the plant component to be protected
3.1.17
protective system
autonomous devices to stop an explosion immediately and/or limit the effects of explosion flames and
pressures
3.1.18
stabilized burning
steady burning of a flame stabilized at, or close to, the flame arrester element [short time (max. 30
minutes) or endurance burning (for unlimited time)
3.1.19
unprotected side
ignition source side
3.1.20
restriction
reduction of the diameter of the pipe on the protected side of a flame arrester
Note 1 to entry: For example, a restriction can be a not fully opened valve.
3.2 Abbreviated terms
DN nominal size of the connection of a device or pipe fitting
LEL lower explosion limit of the explosion range
L pipe length between flame arrester and restriction
r
L pipe length on the unprotected side, maximum allowable run-up length for installation
u
p0 maximum operational pressure
T maximum operational temperature
MESG maximum experimental safe gap – safe gap measured in accordance with EN 60079-20-1
p/v valve pressure and vacuum relief vent valve
UEL upper explosion limit of the explosion range
NPSH net positive suction head
Z minimum operational water seal immersion depth when the mixture flow displaces the water
0min
from the immersion tubes, where Z > Z
0min Rmin
Z operational immersion depth, corresponding to Z plus the manufacturer's recommended safety
0 0min
margin
Z minimum water seal immersion depth at rest above the outlet openings of the immersion tubes
Rmin
Z immersion depth at rest, corresponding to Z plus the manufacturer's recommended safety
R Rmin
margin
safe volume flow rate

V
max
safe volume flow rate including a safety margin

V
s
4 Explosion risks
The following content is a summary of the non-binding guide to good practice for implementing the
European Parliament and Council Directive 1999/92/EC [1].
Three components are necessary at the same time for an explosion to occur. These are visualized in the
so-called explosion triangle (see Figure 1).
1) Air (oxidizer)
2) Fuel (flammable gas)
3) Ignition Source (e.g. spark, hot surface, etc.)

Figure 1 — Explosion triangle
Fuel mixed with air in a suitable ratio (above LEL and below UEL) is called explosive atmosphere.
Assessment of explosion risks is focused on:
— the likelihood that an explosive atmosphere will occur,
and subsequently on
— the likelihood that sources of ignition will be present and become effective.
Suitable methods for assessing the explosion risks associated with work processes or plant are those
which lend themselves to a systematic approach to checking plant and process safety. An analysis is
made of the existing sources of hazardous explosive atmospheres and the effective sources of ignition
which could occur at the same time. Explosion risks can in practice be assessed by means of
seven questions:
1) Are flammable substances present?
2) Can sufficient dispersal in air give rise to an explosive atmosphere?
3) Where can explosive atmospheres occur?
4) Is the formation of a hazardous explosive atmosphere possible?
5) Is the formation of hazardous explosive atmospheres reliably prevented?
6) To what zones can the places with hazardous explosive atmospheres be assigned?
7) Is the ignition of hazardous explosive atmospheres reliably prevented?
Depending on the answers of these questions, it could be necessary to apply adequate explosion
protection measures. "Explosion protection measures" mean all measures that prevent the formation of
hazardous explosive atmospheres, avoid the ignition of hazardous explosive atmospheres or mitigate
the effects of explosions. One of the possible measures is to use flame arresters.
An idealized representation of the flame acceleration process is presented in Figure 2.

Key
X pipe L/D 3 deflagration IIB - IIC
-1
Y1 flame speed in m ∙ s 4 deflagration IIA – IIB3
Y2 pressure in bar 5 deflagration to detonation transition
1 flame speed 6 stable detonation
2 pressure
Figure 2 — Development of an explosion in a pipeline
5 Technical measures for explosion protection
5.1 General
Priority shall be given to the prevention of the formation of hazardous explosive atmospheres. This can
be done by avoiding or reducing the use or by limiting the concentration of flammable substances.
Preventing of hazardous explosive atmospheres can also be realized by inerting.
If it is not possible to prevent the formation of a hazardous explosive atmosphere, its ignition shall be
avoided. This can be achieved by protective measures which avoid or reduce the probability of ignition
sources.
The probability that a hazardous explosive atmosphere and a source of ignition will be present at the
same place and time is estimated and the extent of the measures required is determined accordingly.
This is done on the basis of the zone concept, from which the necessary precautions are derived.
NOTE It is, however, recognized that there can be sources of ignition that cannot be determined with a high
degree of accuracy (e.g. an electrostatic discharge within a pipe or a lightning strike).
5.2 Mitigation of the effects of explosion
5.2.1 General
In many cases, it is not possible to avoid explosive atmospheres and sources of ignition with a sufficient
degree of certainty. Measures shall then be taken to limit the effects of an explosion to an acceptable
extent. Such measures are:
— explosion-resistant design;
— explosion relief;
— explosion suppression;
— prevention of flame and explosion propagation.
These explosion protection measures generally relate to mitigation of the hazardous effects of
explosions.
5.2.2 Prevention of explosion propagation – explosion decoupling
An explosion occurring in one part of a plant can propagate to upstream and downstream parts, where
it may cause further explosions. Acceleration caused by plant fittings or propagation in pipes may
intensify the explosion effects. The explosion pressures can be much higher than the maximum
explosion pressure under normal conditions and may destroy items of plant even if they are of
explosion pressure resistant or explosion pressure shock resistant design. It is therefore important to
limit possible explosions to single parts of the plant. This is achieved by explosion decoupling. Explosion
decoupling can be performed, e.g. by isolation valves or flame arresters.
5.3 Safety concept
Hazardous areas are classified in zones by the operator of a facility according to the frequency and
duration of the explosive atmosphere as given in Table 1.
Table 1 — Hazardous areas
Definition Explosive atmosphere Example
zone 0 constantly, for a long period or frequently interior of a tank, pipe, device containing
present an explosive mixture
zone 1 sometimes present the immediate vicinity of zone 0, the
surrounding area of loading and unloading
stations, the immediate vicinity of the
outlet openings of vent pipes
zone 2 rare and during a short time of period areas which surround zone 0 and zone 1
present areas, the immediate vicinity of detachable
pipe connections
Openings of explosion-pressure-resistant or explosion-pressure-shock resistant plant components
where explosions can occur internally have to be equipped with pre-volume deflagration flame
arresters to prevent an explosion transmission from the inside to the outside if they are connected to
other plants which are not explosion-pressure-resistant or explosion-pressure-shock resistant.
The safety concept depends on the likelihood of adverse events (e.g. flame transmission from ignition
source), and the extent of the consequences (e.g. range of devastating explosion pressures).
The number of independent measures against flame transmission when facing high-level consequences
is shown in Table 2.
Table 2 — Number of independent measures – zone concept
Number of independent measures
Explosive atmosphere
Ignition source
permanent sometimes rare never
zone 0 zone 1 zone 2 (non-hazardous
area)
permanent 3 2 1 0
sometimes 2 1 0 0
rare 1 0 0 0
never 0 0 0 0
Depending on the hazardous area classification and the likelihood of ignition sources, flame arresters in
series can be used, as well as measures for concentration control and for ignition source control.
If flame arresters are to be used in series it has to be ensured that they function as independent
measures and are not subject to common mode failure, for example deflagration flame arresters in
series may not be independent measures.
If flammable mixtures are emitted or processed during operation in relatively large volumes and over a
relatively long period (e.g. when filling a tank or vapour processed to a vapour destruction unit), it shall
be anticipated that after any ignition there may be stabilized burning at the flame arrester element. In
such cases, suitable additional measures need to be taken to protect the plants, if the installed flame
arrester is not designed / approved for stabilized burning.
6 Flame arresters
6.1 General
The purpose of a flame arrester is to allow gas to pass through but stop a flame in order to prevent an
explosion or fire propagation. There are many different situations in which flame arresters are applied.
Flame arresters are designed to meet specific requirements of applications.
The severity of explosion depends on the operating conditions, the physical piping conditions, and
environmental factors. Flame arresters are designed for specific applications. Therefore, a wide variety
of flame arrester types are available.
The user shall ensure that a flame arrester has been tested for conditions that match or exceed the
intended application.
Figure 3 shows possible and typical locations of flame arresters, for example:
— tanks;
— processing systems;
— vapour combustion systems, incinerators, flares;
— ships, offshore platforms, vehicles and loading systems;
— vapour recovery units;
— as integrated components of pumps, blowers and other rotating machines.
Figure 3 — Typical locations for flame arresters
6.2 Principle of operation of flame arresters
Depending on the selected technical solution to prevent flame transmission flame arrester types
according to Table 3 are available.
Table 3 — Flame arrester principle
Types of flame arresters Remark Safeguard principle
Static flame arrester measurable type; flame arrester Flame quenching
element with quenching gaps that
can be drawn, measured and
controlled
non-measurable type; flame
arrester element with quenching
gaps that cannot be drawn,
measured or controlled
Liquid product detonation flame liquid seal flame arrester; Prevention of flame transmission at
arrester a barrier formed by the liquid
foot valve flame arrester
product
Hydraulic flame arrester — Prevention of flame transmission at
a barrier formed by water
Dynamic flame arrester high-velocity pressure relief valve Nominal flow velocity at the outlet
exceed flame velocity thus prevent
flame transmission
Flame arresters can be distinguished in several ways.
6.3 Types of flame arresters
6.3.1 End-of-line deflagration flame arrester
End of line deflagration flame arresters are used to stop flames coming from outside and avoid
explosion entering the pipe work or tank.
6.3.2 In-line deflagration flame arrester
In-line deflagration flame arresters are designed and tested for stopping deflagrations developing in a
pipeline. For use of in-line deflagration flame arresters there is a maximum allowable L / D ratio.
6.3.3 In-line detonation flame arrester
Unstable detonation flame arresters (Type 1 and Type 2) are designed and tested for stopping
deflagrations and stable and unstable detonations.
Stable detonation flame arresters (Type 3 and Type 4) are designed and tested for stopping
deflagrations and stable detonations.
6.3.4 Stabilized burning
6.3.4.1 Short time burning flame arresters
For operation conditions leading to stabilized burning of the mixtures directly on the flame arrester
element, there will be only limited safety against stabilized burning, i.e. flame transmission protection.
Then flame arresters can be fitted with temperature sensors to detect the flame and trigger measures to
suppress the stabilized burning (e.g. emergency functions such as switching the plant off/over, inerting,
etc.) within half the time for which the flame arrester is resistant to short time burning.
An explosion-proof temperature sensor shall be designed for measuring temperatures both in liquid
and gaseous media. A common design is a resistance thermometer with a PT100 measuring resistance.
The measuring probe can be installed in zone 0. The length of the probe depends on the flame arrester
design and its function should be tested with the flame arrester according to the standard for flame
arresters.
A temperature sensor shall respond within half of the time for which the flame arrester is safe against
short-time burning.
Check that the system for preventing stabilized burning activates after the trigger temperature (to be
set in each instance) is exceeded. Ensure adherence to the permitted response time for activation. The
trigger temperature may be no more than 60 K above the operating temperature for the flame arrester.
It is recommended a trigger temperature of 20 K above the maximum operating temperature. For
heated flame arresters it is recommend a trigger temperature of 30 K to 40 K above the maximum
operating temperature.
A fire with high temperatures can destroy the measuring resistance (PT100). Exchange the measuring
probe, if the flame temperature exceeded the operating temperature of the temperature sensor.
If the operating company installs any temperature sensors of their work standards, these shall comply
with the safety specifications of the temperature sensor tested with the flame arrester. It further has to
be proven that in the event of short time burning the same response times are met and (in the case of
in-line deflagration and detonation arresters) the mechanical strength matches that of the model
approved.
6.3.4.2 End-of-line endurance burning flame arrester
End-of-line endurance burning flame arresters are designed and tested for stopping both atmospheric
deflagrations and flame transmission in case of stabilized burning for unlimited time (endurance
burning).
The safe use of static flame arresters is limited to hydrocarbons. For flammable fluids that are not pure
hydrocarbons (e.g. alcohols, ketones, etc.) a separate testing is necessary.
6.3.5 Pre-volume flame arresters
Flame arrester that, after ignition by an internal ignition source, prevents flame transmission from
inside an explosion-pressure-resistant containment (e.g. a vessel or closed pipe work) to the outside, or
into the connecting pipe work.
6.4 Selection of flame arresters
Flame arresters should be selected for the intended use (see Figure 4). For the correct selection of a
flame arrester an assessment should be carried out to identify:
— what should be protected;
— where the potential ignition sources are;
— where an explosive atmosphere may arise;
— what kind of explosive atmosphere can occur;
— operating parameters (temperature, pressure, etc.) of the explosive atmosphere.
NOTE For additional information, see also EN ISO 16852:2010, Annex B.
Flame arresters are designed and tested to meet particular operating conditions. To ensure that an
effective flame arrester is selected, it is essential that the conditions in which it will be used are
specified carefully (see Figure 4).
A first selection is to decide whether to use an end-of line or an in-line flame arrester. In some special
applications, pre-volume flame arresters are used to prevent flame transmission from inside an
explosion-pressure-resistant containment (e.g. a vessel or closed pipe work) to the outside, or into the
connecting pipe work. End-of-line detonation flame arresters are devices in liquid product lines to
protect the filling and emptying line of a tank. End-of-line flame arresters are designed mainly to stop
atmospheric deflagrations. A typical application is the protection of storage tanks for flammable liquids
against atmospheric deflagrations initiated by lightning strikes or other external ignition sources.
Stabilized burning for out-breathing tanks is a risk. Depending on the duration of the steady flow out, an
endurance burning or a short time burning flame arrester shall be selected. The maximum time a short
time burning proof flame arrester will withstand a stabilized flame is less than 30 min and is marked on
the marking plate as burning time (t ). Note that the time needed to fill a tank can be many hours.
BT
The selection of in-line flame arresters depends on the distance between the identified ignition source
and the installation location of the flame arrester. Deflagration flame arresters are designed and tested
for limited distance in accordance with the IOM (Installation and Operating Manual) of the
manufacturer (maximum L /D = 50 for explosion groups IIA1, IIA, IIB1, IIB2 and IIB3 and L /D = 30 for
u u
explosion groups IIB and IIC). For applications with longer distances or where the location of the
ignition source is not identified, deflagration arresters shall not be used.
For stabilized burning of mixtures due to the operating conditions directly at the flame arrester element
a flashback can only be prevented for a limited period of time. Therefore, additional safety measures are
necessary. This time limited safety against stabilized burning generally applies to most in-line flame
arresters. If due to special operating conditions stabilized burning of mixtures is possible at the flame
arrester element – this includes for example the application within closed pipeline systems of process-
technical plants with operationally force-actuated volume flows – flame arresters with integrated
temperature sensors shall be used, in order to trigger an alarm to start measures to stop the stabilized
burning on the element (by a shut down or by-pass, inerting, etc.). For stabilized burning check the
likelihood on which side or on both sides it may burn and a temperature sensor(s) shall then be
installed accordingly – either on one side only or on both sides.
Figure 4 — Selection of flame arresters
After selection of the flame arrester type the explosive atmosphere should be checked (see Figure 5).
Vapour and gases are classified in Explosion Groups by means of the safety classification number
Maximum Experimental Safe Gap (MESG) [9], [10]. MESG is independent of the actual gap size (also
called gap width or gap height) of a static flame arrester’s element. EN ISO 16852 classifies into the
explosion groups according to Table 4.
Table 4 — Explosion groups and the corresponding MESG
Maximum experimental safe gap
Explosion group
mm
a
IIA1 ≥ 1,14
IIA > 0,90
IIB1 ≥ 0,85
IIB2 ≥ 0,75
IIB3 ≥ 0,65
IIB ≥ 0,5
IIC < 0,5
a
Group IIA1 was designated as Group I previously.
NOTE MESG is a safety characteristic of the material and depends on the measurement system. In this
document, the MESG is determined according to EN 60079-20-1; other methods may give different results. The
determination of the MESG of the process media is the responsibility of the user of a flame arrester. Flame
arresters are tested with vapours/gases of the respective explosion group and are marked accordingly. The
application is limited to mixtures with an MESG equal to or greater than that tested.
Be aware if you use flame arresters marked according to other standards e.g. American code NFPA 70
(NEC) because the explosion groups can differ from the international explosion groups of EN ISO 16852.
Mixtures which tend to self-decompose (e.g. acetylene or ethylene oxide), are chemically unstable, and
mixtures with higher oxygen concentration (chlorine as oxidant, etc.) are excluded from the standard
approval procedure according to EN ISO 16852. Carbon disulphide is also excluded. Flame arresters
intended for the mentioned gas mixtures have to be tested with the special mixture directly and be
marked accordingly.
Flame arresters according to EN ISO 16852 are designed and tested for gas/air or vapour/air mixtures,
not for oxygen enriched mixtures or self-decomposing substances. The explosion group shall be verified
depending on the components of the mixture. To be on the safe side, the explosion group of the
component with the smallest MESG value may be used. Other methods and models are available to
estimate the MESG of the worst case gas mixture composition. In case of any doubt, it is recommended
to contact the manufacturer of flame arrester.
Figure 5 — Flame atmosphere
6.5 Application limits
The marking of a flame arrester according to EN ISO 16852 contains, amongst others, application limits
as shown in Table 5. Ensure that this and the further data specified according to Table 6 conform to the
intended operating conditions. According to EN ISO 16852 the warning “flame arresters have
installation and application limits” has to be marked on the flame arrester.
Flame arresters for special purposes may have different application limits.
Table 5 —Application limits marked on the flame arrester according to EN ISO 16852
Protected side (for directional flame arresters)
Explosion group of the gas, starting with the sign

Maximum operating temperature T
Maximum operating pressure p
Type designation:
“DEF” for deflagration flame arresters in combination with maximum allowable L /D for in-line flame
u
arresters
“DET” for detonation flame arresters in combination with the type number “1” to “4” (see Figure 4)
“BC” for burn rating in combination with the burn classification “a”, “b” or “c”.
“a" – endurance burn (no time limit)
“b” – short time burn from 1 min to 30 min
“c” – not burn time
In case of class b the burn time t in minutes the flame arrester was tested for (from 1 min to max. 30 min)
BT
shall be given.
Maximum flow rate for hydraulic flame arresters
Table 6 — Further application limits
Application limits Remarks
Working direction for in-line flame arresters Directional (the protected side shall be marked)
or bi-directional
Oxygen concentration Flame arresters are tested for mixtures with air
normally. Air has approximate 21 vol. % oxygen (O ).
Flame arresters for oxygen-enriched mixtures have to
be tested and approved accordingly.
Housing test pressure (6.5 of EN ISO 16852:2010) Necessary for in-line flame arrester to know the
maximum test pressure for pipework
for deflagration flame arresters ≥ 1,1 ∙ 10 Pa
(10 Pa = 1 MPa = 10 bar)
for detonation flame arresters ≥ 10 x p
Endurance burning (static flame arresters) The safe use is limited to pure hydrocarbons,
admissible use for other chemicals (e.g. alcohols,
ketones, etc.) have to be explicitly tested.
Endurance burning is guaranteed for a specified
installation position only under atmospheric conditions
(p ≤ 0,11 MPa, T ≤ 60 °C) at the flame arresting
element.
Maximum suction rate for emptying Has to be observed for liquid product detonation flame
arresters
Surface temperature Limit the maximum surface temperature to 80 % of the
flammable mixture’s auto-ignition temperature
Material resistance When selecting the flame arrester the user shall ensure
that they are sufficiently resistant (e.g. against
corrosion) with regard to the substances present in the
system. This also applies to possible coatings.
Information in this matter the user can find in the
instruction for use.
6.6 Installation limits
6.6.1 General
6.6 includes information about specific types of flame arresters and specific installation based on
experience. Where limited knowledge is available guidance is not provided.
For information on use of inline stable detonation flame arresters, see EN ISO 16852:2010, Annex D.
Installation limits apply; these are summarized in Table 7.
Table 7 — Installation limits
Installation limits Remarks
Installation orientation Arresters may have limits on their installation orientation. The
worst case for in-line flame arresters under stabilized burn
condition is flow vertically downwards and potential ignition
source from below. The user shall take into account the
instructions for use given by the manufacturer.
Plugging Plugging, e.g. accumulation of condensate due to incorrect
installation can lead to uncertain operating conditions; the
plants operating pressure could be exceeded.
Max. permitted L /D ratio L /D is the ratio between pipeline length on the unprotected
u u
side and the nominal pipe size.
Nominal pipe sizes The nominal sizes of the pipelines connected on the side of the
ignition source (unprotected side) have to be less or equal to
the flame arresters’ nominal size.
The nominal sizes of the pipelines connected on the protected
side have to be equal to or larger than the nominal size on the
unprotected side.
6.6.2 Arrangement of flame arresters at pipe branches [5]
Installation of flame arresters at or near pipe branches may require special consideration, and advice
should be sought from the manufacturer. Specific proven examples are given below.
At pipe branches stable detonation flame arresters shall be placed in a way that any instability caused
by the propagation of a detonation through the pipe does not cause any unsafe stresses.
This is achieved by a certain distance fr
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