Gases and gas mixtures -- Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets

Gaz et mélanges de gaz -- Détermination du potentiel d'inflammabilité et d'oxydation pour le choix des raccords de sortie de robinets

Plini in plinske mešanice - Določanje gorilne in oksidacijske sposobnosti za izbor izhodnih odprtin ventilov cilindrov

General Information

Status
Withdrawn
Publication Date
30-Apr-1996
Withdrawal Date
31-Oct-2005
Current Stage
9900 - Withdrawal (Adopted Project)
Start Date
01-Nov-2005
Due Date
01-Nov-2005
Completion Date
01-Nov-2005

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IS0
1 O1 56
First edition
1990-1 2-1 5
Gases and gas mixtures - Determination of fire
potential and oxidizing ability for the selection
of cylinder valve outlets
Gaz et mélanges de gaz - Détermination du potentiel d'inflammabilité
et d'oxydation pour le choix des raccords de sortie de robinets
Reference number
IS0 1 O1 56: 1990( E)
---------------------- Page: 1 ----------------------
IS0 1 O1 56:1990(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for
which a technical committee has been established has the right to be
represented on that committee. International organizations, govern-
mental and non-governmental, in liaison with ISO, also take pari in the
work. IS0 collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Drafi International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an Interna-
tional Standard requires approval by at least 75 % of the member bodies
casting a vote.
International Standard IS0 10156 was prepared by Technical Committee
ISO/TC 58, Gas cylinders.
Annex A forms an integral part of this International Standard.
8 IS0 1990

Ail rights reserved. No part of this publication may be reproduced or utilized in any form

or by any means, electronic or mechanical, including photocopying and microfilm, without

permission in writing from the publisher.
International Organlzation for Standardization
Case Postale 56 CH-I21 1 Geneve 20 Switzerland
Printed In Switzerland
---------------------- Page: 2 ----------------------
IS0 I O1 561 990(E)
I nt roduct ion
The purpose of IS0 5145 is to establish practical criteria for the deter-
mination of outlet connections of gas cylinders of water capacity 150 li-
tres or less. These criteria are based on certain physical and chemical
properties of the gases, In particular, the flammability in air and the
oxidizing potential (with air as the reference) are considered.
One of the difficulties in the application of IS0 5145 resides in the fact
that it is at times difficult to know if a gas or gas mixture is flammable
in air or more oxidizing than air.
In fact,
in the case of pure gases, there is abundant data in the literature,
although conflicting results are to be found, depending upon the test
methods employed;
but, above all,
in the case of gas mixtures, data in the literature is often incomplete
or even non-existent.
With standardized test methods, it will be possible
to eliminate the ambiguities in the case of conflicting results in the
literature:
and, above all,
to supplement existing data (mainly in the case of gas mixtures).
In particular, the application of standardized test methods will eliminate
the ambiguities concerning mixtures in groups 1, 3, 4, 6, 7, 8, 9, 12, 13
and 15, such as they are defined in IS0 5145, since it is necessary to
know, in the case of those mixtures, whether or not they are flammable
in air and/or more or less oxidizing than air.
---------------------- Page: 3 ----------------------
___ __ - ~
IS0 1 O1 56:1990(E)
INTERNATIONAL STANDARD
Gases and gas mixtures - Determination of fire potential and
oxidizing ability for the selection of cylinder valve outlets
3 Definitions and symbols
1 Scope
This International Standard specifies two test meth-
3.1 Definitions
ods for determining whether or not a gas is
flammable in air and whether a gas is more or less
For the purposes of this International Standard, the
oxidizing than air, respectively, with the aim of
following definitions apply:
eliminating difficulties entailed in the application of
IS0 5145.
3.1.1 gas or gas mixture flammable in air: A gas or
gas mixture which will ignite in air at atmospheric
NOTE 1 For certain special applications, such as special
pressure and a temperature of 20 OC.
gas mixtures produced to order (in small quantities), it
might prove relatively complex to apply the method

specified and to perform the special tests necessary to 3.1.2 lower flammability limit in air: The minimum

determine the flammability or oxidizing power of the gas
content of a gas or gas mixture in air at which the
mixture.
gas or gas mixture will ignite. This limit is deter-
mined at atmospheric pressure and 20 OC.
To avoid these difficulties, a simple method of calculation
is recommended to determine rapidly the type of con-

nection to be employed depending upon the character- 3.1.3 gas or gas mixture less oxidizing than air: A

istics (flammability, oxidizing power, etc.) of the gas
gas or gas mixture which is not able, at atmospheric
mixture and the characteristics of the pure substances
pressure, to support the combustion of substances
making up the mixture.
which are flammable in air.
3.2 Symbols
molar fraction of a flammable gas in a
mixture of gases
molar fraction of an inert gas in a mixture
2 Normative references
of gases
The following standards contain provisions which,
coefficient of oxygen equivalency
through reference in this text, constitute provisions
of this International Standard. At the time of publi-
ith flammable gas in a gas mixture
r;,
cation, the editions indicated were valid. All stan-
dards are subject to revision, and parties to
iih inert gas in a gas mixture
agreements based on this International Standard
n number of flammable gases in a gas
are encouraged to investigate the possibility of ap-
plying the most recent editions of the standards in- mixture
dicated below. Members of IEC and IS0 maintain
number of inert gases in a gas mixture
registers of currently valid International Standards.
of an inert gas
coefficient of equivalency
IS0 4589:1984, Plastics - Determination of
relative to nitrogen
flammability by oxygen index.
equivalent content of a flammable gas
A',
IS0 5145:1990, Cylinder valve outlets for gases and
gas mixtures - Selection and dimensioning. N2 nitrogen
---------------------- Page: 4 ----------------------
IS0 10156:1990(E)
maximum flammable-gas content for 4.2.2 Apparatus and materials
which a mixture of the flammable gas in
nitrogen is not flammable in air The apparatus (see figure 1) includes:
hydrogen
- a mixer;
carbon dioxide
- a tube in which the reaction takes place;
minimum concentration of an oxidizing
- an ignition system;
combustion gas, in a mixture with nitro-
gen, which will support combustion of a
- a system of analysis to determine the test-gas
test piece
composition.
helium
4.2.2.1 Preparation
argon
a) Test gas
neon
The test gas shall be prepared to represent the most
krypton
flammable composition that can occur in the normal
xenon
course of production. The criteria to be used in es-
tablishing the composition of the test gas are man-
sulfur dioxide
ufacturing tolerances, i.e. the test gas shall contain
the highest concentration of flammable gases en-
sulfur hexafluoride
countered in the normal manufacturing process and
the moisture content shall be less than or equal to
carbon tetrafluoride
10 ppm by volume. The test gas shall be thoroughly
octafluoropropane
mixed and carefully analysed to determine the exact
com position.
methane
b) Compressed air
nitrous oxide
The compressed air shall be analysed and shown to
lower flammability limit in air of a
be free of moisture.
flammable gas
oxygen
c) Test-gadair mixture
The compressed air and the gas to be tested are
mixed in a blender, controlling the flow rates, The
4 Flammability of gases and gas mixtures
air-flammable gas mixture shall be analysed using
in air
a chromatograph or a simple oxygen analyser.
4.2.2.2 Reaction tube
4.1 General
This tube shall be made of thick pyrex glass (e.g.
Gases and gas mixtures which are flammable shall
5 mm), with an inside diameter of at least 50 mm
be designated in accordance with IS0 5145:1990,
and a length at least five times the diameter.
annex A - category I - subdivision 2. Such gases
and gas mixtures have flammable limits in air. The
At one end of the tube, there shall be a cylindrical
following sub-clauses outline a test method and a
component designed to take:
calculation method for determining whether a gas
or gas mixture is flammable. In cases where the test
- an ignition spark plug, located about 50 mm from
result is different from that obtained by calculation,
the bottom of the tube;
the test result shall take precedence.
- an inlet for the gas mixture to be tested;
4.2 Test method
- a relief valve at the bottom of the pyrex tube
[see figure la)];
4.2.1 Principle
- two thermocouples, one located close to the ig-
nition system, the other located close to the top
The gas is mixed in the desired proportions with air.
of the tube, the purpose of these thermocouples
Then ignition energy is supplied in the form of an
being to allow easy detection of flame propa-
electric arc between two electrodes.
---------------------- Page: 5 ----------------------
IS0 10156:199O(E)

gation [see figure la)] (alternatively, gas ignition indicates that the flammability limit is close. In

may be observed by an experienced operator in this case, repeat the test at least five times. If, in

one of these repeat tests, the flame rises up the
a dark room);
tube, it shall be considered that the flammability
limit has been reached, i.e. the test gas is
- a safety device to minimize the risk of de-
struction of the tube in the event of an explosion flammable.
(preferably located close to the ignition system).
c) The flame rises slowly up the tube at 10 cm/s to
The tube and its accessories shall always be very
50 cm/s. In this case, it shall be considered that
clean in order to avoid any impurities, and partic-
the limit has been reached, i.e. the test gas is
ularly moisture resulting from a preceding test or
flammable.
from exposure to the atmosphere, from affecting the
determination.
d) The flame rises up the tube very rapidly. In this
case, the test gas is flammable.
The gas mixture is vented at the top of the reaction
tube by a tube fitted with a shut-off valve.
NOTES
This apparatus is located inside a ventilated metal
2 Instead of flowmeters, other appropriate devices, such

chamber, one side of which has a window made of as metering pumps, etc., can be used.

high-strength transparent material.
3 With mixtures containing hydrogen, the flame is almost
colourless. In order to confirm the presence of such
Prior to ignition, the composition of the mixture shall
flames, the use of temperature-measuring probes is re-
be tested by analysing the gas leaving the reaction
commended (see 4.2.2.2).
tube [see figurela), analysis at point 21 to ensure
that the tube has been properly purged.
4 Although it is beyond the scope of this International
Standard, if a precise value is required for the lower
4.2.2.3 Ignition system
flammability limit of the test gas, then repeated tests must
be carried out, varying the flammable-gas content until
A spark generator (e.g. 15 kV) shall be used which
the threshold point is reached between ignition and no

can supply sparks (across a 5 mm electrode gap, for ignition of the flammable gas.

instance) with an energy of 10 J per spark.
4.4 Key points concerning safety
4.3 Procedure
Tests shall be carried out by trained and competent
Care shall be taken when carrying out flammability
personnel working in accordance with authorized
tests to ensure that the explosive range is avoided.
procedures (see also 4.3). The reaction tube and
This can be done by commencing the experimental
flowmeter shall be adequately screened to protect
work at “safe” concentrations of flammable gas in
the personnel in the event of an explosion. Person-
air (“safe” = below the expected lower flammable
nel shall wear safety glasses. During the ignition
limit). Subsequently, the initial gas concentration
sequence, the reaction tube shall be open to the at-
can be slowly increased until ignition occurs.
mosphere and isolated frorn the gas supply. Care
shall also be taken during the analysis of the test
Blend the desired mixture using the flowmeter (the
gas or mixture.
efficiency of this step shall be checked by analysis).
Close the gas inlets simultaneously. Just prior to
ignition, ensure that the outlet valve (if there is one)
4.5 Results for pure gases
is opened, to bring the mixture to atmospheric
pressure.
A list of flammable gases is given in annex A to-
gether with some lower flammability limits. These
There are several possible results:
values have been obtained using similar test equip-
ment to that described in 4.2.2.
a) No combustion: the test-gas mixture is not
flammable in air at this concentration. In this
case, repeat the test at a slightly higher concen- 4.6 Calculation method
tration.
This method is limited to gas mixtures produced in
small quantities in cylinders to indicate if flammable
b) Partial combustion: a flame begins to burn
around the spark plug, and then goes out. This in air.
---------------------- Page: 6 ----------------------
IS0 10156:1990(E)
4.6.1 Mixtures containing n flammable gases and p A,F, + ... +Ail$+ ... + A,&+
inert gases
+ (KlB, + ... + KiBi + ... + K,B,)N,
The composition of a mixture of this kind can be ex-
Taking the sum of all the component gas fractions
pressed as follows:
to be equal to 1, the expression for the composition
A $, + . . . + A& + . . . + AnFn + B,I, + ... + Biii +
becomes:
+ ... + Bp$
where
Ai and Bi are the molar fractions of the ith
where
flammable gas and the ith inert gas,
respectively:
designates the ith flammable gas;
designates the ith inert gas;
is the equivalent flammable-gas content.
n is the number of flammable gases;
Table2 gives values for the maximum content Tci of
flammable gas which, in a mixture with nitrogen,
is the number of inert gases.
gives a composition which is not flammable in air.
Expressed mathematically, this condition for the
The composition of the mixture is re-expressed in
mixture not being flammable in air is
terms of an equivalent composition in which all the
inert-gas fractions are converted into their nitrogen
equivalent, using
...

SLOVENSKI STANDARD
SIST ISO 10156:1996
01-maj-1996

3OLQLLQSOLQVNHPHãDQLFH'RORþDQMHJRULOQHLQRNVLGDFLMVNHVSRVREQRVWL]DL]ERU

L]KRGQLKRGSUWLQYHQWLORYFLOLQGURY

Gases and gas mixtures -- Determination of fire potential and oxidizing ability for the

selection of cylinder valve outlets

Gaz et mélanges de gaz -- Détermination du potentiel d'inflammabilité et d'oxydation

pour le choix des raccords de sortie de robinets
Ta slovenski standard je istoveten z: ISO 10156:1990
ICS:
23.020.30 7ODþQHSRVRGHSOLQVNH Pressure vessels, gas
MHNOHQNH cylinders
71.100.20 Industrijski plini Gases for industrial
application
SIST ISO 10156:1996 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST ISO 10156:1996
---------------------- Page: 2 ----------------------
SIST ISO 10156:1996
IS0
1 O1 56
First edition
1990-1 2-1 5
Gases and gas mixtures - Determination of fire
potential and oxidizing ability for the selection
of cylinder valve outlets
Gaz et mélanges de gaz - Détermination du potentiel d'inflammabilité
et d'oxydation pour le choix des raccords de sortie de robinets
Reference number
IS0 1 O1 56: 1990( E)
---------------------- Page: 3 ----------------------
SIST ISO 10156:1996
IS0 1 O1 56:1990(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for
which a technical committee has been established has the right to be
represented on that committee. International organizations, govern-
mental and non-governmental, in liaison with ISO, also take pari in the
work. IS0 collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Drafi International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an Interna-
tional Standard requires approval by at least 75 % of the member bodies
casting a vote.
International Standard IS0 10156 was prepared by Technical Committee
ISO/TC 58, Gas cylinders.
Annex A forms an integral part of this International Standard.
8 IS0 1990

Ail rights reserved. No part of this publication may be reproduced or utilized in any form

or by any means, electronic or mechanical, including photocopying and microfilm, without

permission in writing from the publisher.
International Organlzation for Standardization
Case Postale 56 CH-I21 1 Geneve 20 Switzerland
Printed In Switzerland
---------------------- Page: 4 ----------------------
SIST ISO 10156:1996
IS0 I O1 561 990(E)
I nt roduct ion
The purpose of IS0 5145 is to establish practical criteria for the deter-
mination of outlet connections of gas cylinders of water capacity 150 li-
tres or less. These criteria are based on certain physical and chemical
properties of the gases, In particular, the flammability in air and the
oxidizing potential (with air as the reference) are considered.
One of the difficulties in the application of IS0 5145 resides in the fact
that it is at times difficult to know if a gas or gas mixture is flammable
in air or more oxidizing than air.
In fact,
in the case of pure gases, there is abundant data in the literature,
although conflicting results are to be found, depending upon the test
methods employed;
but, above all,
in the case of gas mixtures, data in the literature is often incomplete
or even non-existent.
With standardized test methods, it will be possible
to eliminate the ambiguities in the case of conflicting results in the
literature:
and, above all,
to supplement existing data (mainly in the case of gas mixtures).
In particular, the application of standardized test methods will eliminate
the ambiguities concerning mixtures in groups 1, 3, 4, 6, 7, 8, 9, 12, 13
and 15, such as they are defined in IS0 5145, since it is necessary to
know, in the case of those mixtures, whether or not they are flammable
in air and/or more or less oxidizing than air.
---------------------- Page: 5 ----------------------
SIST ISO 10156:1996
---------------------- Page: 6 ----------------------
SIST ISO 10156:1996
___ __ - ~
IS0 1 O1 56:1990(E)
INTERNATIONAL STANDARD
Gases and gas mixtures - Determination of fire potential and
oxidizing ability for the selection of cylinder valve outlets
3 Definitions and symbols
1 Scope
This International Standard specifies two test meth-
3.1 Definitions
ods for determining whether or not a gas is
flammable in air and whether a gas is more or less
For the purposes of this International Standard, the
oxidizing than air, respectively, with the aim of
following definitions apply:
eliminating difficulties entailed in the application of
IS0 5145.
3.1.1 gas or gas mixture flammable in air: A gas or
gas mixture which will ignite in air at atmospheric
NOTE 1 For certain special applications, such as special
pressure and a temperature of 20 OC.
gas mixtures produced to order (in small quantities), it
might prove relatively complex to apply the method

specified and to perform the special tests necessary to 3.1.2 lower flammability limit in air: The minimum

determine the flammability or oxidizing power of the gas
content of a gas or gas mixture in air at which the
mixture.
gas or gas mixture will ignite. This limit is deter-
mined at atmospheric pressure and 20 OC.
To avoid these difficulties, a simple method of calculation
is recommended to determine rapidly the type of con-

nection to be employed depending upon the character- 3.1.3 gas or gas mixture less oxidizing than air: A

istics (flammability, oxidizing power, etc.) of the gas
gas or gas mixture which is not able, at atmospheric
mixture and the characteristics of the pure substances
pressure, to support the combustion of substances
making up the mixture.
which are flammable in air.
3.2 Symbols
molar fraction of a flammable gas in a
mixture of gases
molar fraction of an inert gas in a mixture
2 Normative references
of gases
The following standards contain provisions which,
coefficient of oxygen equivalency
through reference in this text, constitute provisions
of this International Standard. At the time of publi-
ith flammable gas in a gas mixture
r;,
cation, the editions indicated were valid. All stan-
dards are subject to revision, and parties to
iih inert gas in a gas mixture
agreements based on this International Standard
n number of flammable gases in a gas
are encouraged to investigate the possibility of ap-
plying the most recent editions of the standards in- mixture
dicated below. Members of IEC and IS0 maintain
number of inert gases in a gas mixture
registers of currently valid International Standards.
of an inert gas
coefficient of equivalency
IS0 4589:1984, Plastics - Determination of
relative to nitrogen
flammability by oxygen index.
equivalent content of a flammable gas
A',
IS0 5145:1990, Cylinder valve outlets for gases and
gas mixtures - Selection and dimensioning. N2 nitrogen
---------------------- Page: 7 ----------------------
SIST ISO 10156:1996
IS0 10156:1990(E)
maximum flammable-gas content for 4.2.2 Apparatus and materials
which a mixture of the flammable gas in
nitrogen is not flammable in air The apparatus (see figure 1) includes:
hydrogen
- a mixer;
carbon dioxide
- a tube in which the reaction takes place;
minimum concentration of an oxidizing
- an ignition system;
combustion gas, in a mixture with nitro-
gen, which will support combustion of a
- a system of analysis to determine the test-gas
test piece
composition.
helium
4.2.2.1 Preparation
argon
a) Test gas
neon
The test gas shall be prepared to represent the most
krypton
flammable composition that can occur in the normal
xenon
course of production. The criteria to be used in es-
tablishing the composition of the test gas are man-
sulfur dioxide
ufacturing tolerances, i.e. the test gas shall contain
the highest concentration of flammable gases en-
sulfur hexafluoride
countered in the normal manufacturing process and
the moisture content shall be less than or equal to
carbon tetrafluoride
10 ppm by volume. The test gas shall be thoroughly
octafluoropropane
mixed and carefully analysed to determine the exact
com position.
methane
b) Compressed air
nitrous oxide
The compressed air shall be analysed and shown to
lower flammability limit in air of a
be free of moisture.
flammable gas
oxygen
c) Test-gadair mixture
The compressed air and the gas to be tested are
mixed in a blender, controlling the flow rates, The
4 Flammability of gases and gas mixtures
air-flammable gas mixture shall be analysed using
in air
a chromatograph or a simple oxygen analyser.
4.2.2.2 Reaction tube
4.1 General
This tube shall be made of thick pyrex glass (e.g.
Gases and gas mixtures which are flammable shall
5 mm), with an inside diameter of at least 50 mm
be designated in accordance with IS0 5145:1990,
and a length at least five times the diameter.
annex A - category I - subdivision 2. Such gases
and gas mixtures have flammable limits in air. The
At one end of the tube, there shall be a cylindrical
following sub-clauses outline a test method and a
component designed to take:
calculation method for determining whether a gas
or gas mixture is flammable. In cases where the test
- an ignition spark plug, located about 50 mm from
result is different from that obtained by calculation,
the bottom of the tube;
the test result shall take precedence.
- an inlet for the gas mixture to be tested;
4.2 Test method
- a relief valve at the bottom of the pyrex tube
[see figure la)];
4.2.1 Principle
- two thermocouples, one located close to the ig-
nition system, the other located close to the top
The gas is mixed in the desired proportions with air.
of the tube, the purpose of these thermocouples
Then ignition energy is supplied in the form of an
being to allow easy detection of flame propa-
electric arc between two electrodes.
---------------------- Page: 8 ----------------------
SIST ISO 10156:1996
IS0 10156:199O(E)

gation [see figure la)] (alternatively, gas ignition indicates that the flammability limit is close. In

may be observed by an experienced operator in this case, repeat the test at least five times. If, in

one of these repeat tests, the flame rises up the
a dark room);
tube, it shall be considered that the flammability
limit has been reached, i.e. the test gas is
- a safety device to minimize the risk of de-
struction of the tube in the event of an explosion flammable.
(preferably located close to the ignition system).
c) The flame rises slowly up the tube at 10 cm/s to
The tube and its accessories shall always be very
50 cm/s. In this case, it shall be considered that
clean in order to avoid any impurities, and partic-
the limit has been reached, i.e. the test gas is
ularly moisture resulting from a preceding test or
flammable.
from exposure to the atmosphere, from affecting the
determination.
d) The flame rises up the tube very rapidly. In this
case, the test gas is flammable.
The gas mixture is vented at the top of the reaction
tube by a tube fitted with a shut-off valve.
NOTES
This apparatus is located inside a ventilated metal
2 Instead of flowmeters, other appropriate devices, such

chamber, one side of which has a window made of as metering pumps, etc., can be used.

high-strength transparent material.
3 With mixtures containing hydrogen, the flame is almost
colourless. In order to confirm the presence of such
Prior to ignition, the composition of the mixture shall
flames, the use of temperature-measuring probes is re-
be tested by analysing the gas leaving the reaction
commended (see 4.2.2.2).
tube [see figurela), analysis at point 21 to ensure
that the tube has been properly purged.
4 Although it is beyond the scope of this International
Standard, if a precise value is required for the lower
4.2.2.3 Ignition system
flammability limit of the test gas, then repeated tests must
be carried out, varying the flammable-gas content until
A spark generator (e.g. 15 kV) shall be used which
the threshold point is reached between ignition and no

can supply sparks (across a 5 mm electrode gap, for ignition of the flammable gas.

instance) with an energy of 10 J per spark.
4.4 Key points concerning safety
4.3 Procedure
Tests shall be carried out by trained and competent
Care shall be taken when carrying out flammability
personnel working in accordance with authorized
tests to ensure that the explosive range is avoided.
procedures (see also 4.3). The reaction tube and
This can be done by commencing the experimental
flowmeter shall be adequately screened to protect
work at “safe” concentrations of flammable gas in
the personnel in the event of an explosion. Person-
air (“safe” = below the expected lower flammable
nel shall wear safety glasses. During the ignition
limit). Subsequently, the initial gas concentration
sequence, the reaction tube shall be open to the at-
can be slowly increased until ignition occurs.
mosphere and isolated frorn the gas supply. Care
shall also be taken during the analysis of the test
Blend the desired mixture using the flowmeter (the
gas or mixture.
efficiency of this step shall be checked by analysis).
Close the gas inlets simultaneously. Just prior to
ignition, ensure that the outlet valve (if there is one)
4.5 Results for pure gases
is opened, to bring the mixture to atmospheric
pressure.
A list of flammable gases is given in annex A to-
gether with some lower flammability limits. These
There are several possible results:
values have been obtained using similar test equip-
ment to that described in 4.2.2.
a) No combustion: the test-gas mixture is not
flammable in air at this concentration. In this
case, repeat the test at a slightly higher concen- 4.6 Calculation method
tration.
This method is limited to gas mixtures produced in
small quantities in cylinders to indicate if flammable
b) Partial combustion: a flame begins to burn
around the spark plug, and then goes out. This in air.
---------------------- Page: 9 ----------------------
SIST ISO 10156:1996
IS0 10156:1990(E)
4.6.1 Mixtures containing n flammable gases and p A,F, + ... +Ail$+ ... + A,&+
inert gases
+ (KlB, + ... + KiBi + ... + K,B,)N,
The composition of a mixture of this kind can be ex-
Taking the sum of all the component gas fractions
pressed as follows:
to be equal to 1, the expression for the composition
A $, + . . . + A& + . . . + AnFn + B,I, + ... + Biii +
becomes:
+ ... + Bp$
where
Ai and Bi are the molar fractions of the ith
where
flammable gas and the ith inert gas,
respectively:
designates
...

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