ASTM E2079-00
(Test Method)Standard Test Methods for Limiting Oxygen (Oxidant) Concentration in Gases and Vapors
Standard Test Methods for Limiting Oxygen (Oxidant) Concentration in Gases and Vapors
SCOPE
1.1 These test methods cover the determination of the limiting oxygen (oxidant) concentration of mixtures of oxygen (oxidant) and inert gases with flammable gases and vapors at a specified initial pressure and initial temperature.
1.2 These test methods may also be used to determine the limiting concentration of oxidizers other than oxygen.
1.3 Differentiation among the different combustion regimes (such as the hot flames, cool flames and exothermic reactions) is beyond the scope of these test methods.
1.4 These test methods should be used to measure and describe the properties of materials, products, or assemblies in response to heat and flame under controlled laboratory conditions and should not be used to describe or appraise the fire hazard or fire risk of materials, products, or assemblies under actual fire conditions. However, results of this test may be used as elements of a fire risk assessment which takes into account all of the factors which are pertinent to an assessment of the fire hazard of a particular end use.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E 2079 – 00
Standard Test Methods for
Limiting Oxygen (Oxidant) Concentration in Gases and
Vapors
This standard is issued under the fixed designation E 2079; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope Mines, “Limits of Flammability of Gases and Vapors,”
NTIS AD701575, 1952
1.1 These test methods cover the determination of the
Zabetakis, M.G., Bulletin 627, Bureau of Mines, “Flamma-
limiting oxygen (oxidant) concentration of mixtures of oxygen
bility Characteristics of Combustible Gases and Vapors,”
(oxidant) and inert gases with flammable gases and vapors at a
NTIS AD701576, 1965
specified initial pressure and initial temperature.
Kuchta, J.M., Bulletin 680, Bureau of Mines, “Investigation
1.2 These test methods may also be used to determine the
of Fire and Explosion Accidents in the Chemical, Mining,
limiting concentration of oxidizers other than oxygen.
and Fuel-Related Industries - A Manual,” NTIS
1.3 Differentiation among the different combustion regimes
4,5,6
PB87113940, 1985
(such as the hot flames, cool flames and exothermic reactions)
is beyond the scope of these test methods.
3. Terminology
1.4 These test methods should be used to measure and
3.1 Definitions:
describe the properties of materials, products, or assemblies in
3.1.1 flammable—capable of propagating a flame.
response to heat and flame under controlled laboratory con-
3.1.2 ignition—the initiation of combustion.
ditions and should not be used to describe or appraise the fire
3.1.3 limit of flammability—the boundary in composition
hazard or fire risk of materials, products, or assemblies under
space dividing flammable and nonflammable regions.
actual fire conditions. However, results of this test may be used
3.1.4 limiting oxygen (oxidant) concentration (LOC) of a
as elements of a fire risk assessment which takes into account
fuel-oxidant-inert system—the oxygen (oxidant) concentration
all of the factors which are pertinent to an assessment of the
at the limit of flammability for the worst case (most flammable)
fire hazard of a particular end use.
fuel concentration.
1.5 This standard does not purport to address all of the
3.1.4.1 Discussion—Limiting oxygen (oxidant) concentra-
safety concerns, if any, associated with its use. It is the
tion is also known as minimum oxygen (oxidant) concentration
responsibility of the user of this standard to establish appro-
or as critical oxygen (oxidant) concentration.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
4. Summary of Test Method
4.1 A mixture containing one or more flammable compo-
2. Referenced Documents
nents (fuel), oxygen (oxidant) and inert gas(es) (such as
2.1 ASTM Standards:
nitrogen, carbon dioxide, argon, etc.) is prepared in a suitable
E 681 Test Method for Limits of Flammability of Chemi-
2 test vessel at a controlled initial temperature and made to the
cals
specified initial pressure. Proportions of the components are
E 918 Practice for Determining the Limits of Flammability
2 determined by a suitable means. Ignition of the mixture is
of Chemicals at Elevated Temperature and Pressure
attempted and flammability is determined from the pressure
2.2 NFPA Publication
3 rise produced. The criterion for flammability is a pressure rise
NFPA 69, Standard on Explosion Prevention Systems
of $ 7 % above the initial absolute test pressure. Fuel, oxygen
2.3 NTIS Publications
Coward, H.F. and Jones, G.W., Bulletin 503, Bureau of
National Technical Information Service, 5285 Port Royal Road, Springfield VA
These test methods are under the jurisdiction of ASTM Committee E-27 on 22161.
Hazard Potential of Chemicals and are the direct responsibility of Subcommittee Subramaniam, T.K. and Cangelosi, J.N., “Predict Safe Oxygen in Combustible
E27.04 on Flammability and Ignitability of Chemicals. Gases,” Chem. Eng. Prog., Dec. 1989, pp. 108-113.
Current edition approved March 10, 2000. Published June 2000. Britton, L.G., “Flammability Hazards of Lower Aliphatic Aldehydes at El-
Annual Book of ASTM Standards, Vol 14.02. evated Pressure and Temperature,” Process Safety Progress, Vol 17, No. 2, 1998, pp.
National Fire Protection Association, P.O. Box 9101, Quincy MA 02269-9101. 138-148.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 2079
(oxidant), and inert gas proportions are varied between trials 7.7 The maximum allowable working pressure (MAWP) of
until: the test vessel at the maximum test temperature must exceed
4.1.1 L—The lowest oxygen (oxidant) concentration for the maximum expected deflagration pressure.
which flame propagation is possible for at least one combina-
7.8 Pressure Transducers:
tion of fuel and inert gas (the “worst case” or most flammable
7.8.1 Low-Range Transducer—A low-range pressure trans-
fuel concentration range), and
ducer may be used for the purpose of making partial pressure
4.1.2 H—The highest oxygen (oxidant) concentration for
additions of gases and vapors to the test vessel. The transducer
which flame propagation is not possible for the same worst
and its signal conditioning/amplifying electronics should have
case fuel concentration range, are identified.
an accuracy, precision and repeatability sufficient to accurately
resolve the required changes in the gas partial pressure for the
5. Significance and Use
component used in lowest concentration. The transducer
5.1 Knowledge of the limiting oxygen (oxidant) concentra-
should be protected from deflagration pressures by means of an
tion is needed for safe operation of some chemical processes.
isolation valve. A pressure gage may be used if an error
This information may be needed in order to start up or operate
analysis is performed to demonstrate that the internal volume
a reactor while avoiding the creation of flammable gas com-
of the pressure gage and piping will not significantly affect the
positions therein, or to store or ship materials safely. NFPA 69
test mixture.
provides guidance for the practical use of LOC data, including
7.8.2 High-Range Transducer—This transducer has the pur-
the appropriate safety margin to use.
pose of measuring the pressure rise on ignition of the gas
6. Limitations mixture. It should have sufficient range to withstand the highest
pressure it is expected to experience while also having suffi-
6.1 These test methods are not applicable to mixtures which
cient accuracy and resolution to measure small pressure rises of
undergo spontaneous reaction before ignition is attempted.
the order of 7 % of the initial absolute test pressure.
6.2 These test methods are limited to mixtures which have
7.8.3 The pressure transducer and recording equipment
maximum deflagration pressures less than the maximum work-
must have adequate time resolution to capture the maximum
ing pressure of the test apparatus.
rate of pressure rise developed by the combustion event.
6.3 These test methods may be used up to the temperature
7.8.4 Calibration of the pressure transducer and data acqui-
limit of the test system.
sition system must be verified over the range of pressures at
6.4 Measurements of flammability are influenced by flame-
which the system is expected to operate.
quenching effects of the test vessel walls. Further surface
effects due to deposits of carbon or other materials can
7.9 Ignition Source—Several possible means of ignition
significantly affect limits of flammability, especially in the may be used which include those described below. The means
fuel-rich region. Refer to Bureau of Mines Bulletins 503 and of ignition used must be described in the test report.
627. For certain chemicals (for example, ammonia, haloge-
7.9.1 Fuse Wire—A fuse wire igniter can be constructed, for
nated materials, and certain amines) which have large ignition-
example from a piece of No. 40 (0.076 mm diameter) copper,
quenching distances, tests may need to be conducted in vessels
nichrome or platinum wire fastened to power supply terminals
larger than that specified below.
in such manner as to leave a filament of wire between the
terminals approximately 10 mm long. A 500 VA/115 V
7. Apparatus
isolating transformer, or a properly sized discrete discharge
7.1 The test vessel must have a volume of at least 4 L.
capacitor circuit will serve as an adequate igniter energy
supply.
NOTE 1—A survey of practitioners of this method indicates that test
vessels in the size range of 4 to 35 L are used.
7.9.2 Carbon Spark—Four 2 mm diameter graphite rods
wrapped by the leads coming from an electrical pulse genera-
7.2 Test vessels must be nearly spherical. The maximum
tor. The two electrical leads are separated bya6to10mm
aspect ratio of the test vessel (the ratio of largest to smallest
distance. The resulting discrete spark is in the form of a surface
internal dimension) must be smaller than or equal to two.
discharge over the graphite rods.
7.3 Test vessel may be equipped with a means of mechani-
7.9.3 Continuous Electric Arc—An electric arc igniter may
cal agitation to ensure uniform mixing of components before
consist of a pair of electrodes (steel or graphite) spaced
an ignition attempt.
approximately 6 mm apart across which a 30 mA arc of
7.4 If tests are to be conducted at an elevated temperature,
typically less than 1 s duration can be supplied from a
the test vessel may be heated using a heating jacket, heating
115/15 000 volt transformer (so-called luminous tube trans-
mantle or placed inside a heated chamber. The heating system
former).
must be capable of controlling the gas temperature inside the
test vessel to within 6 3°C both temporally and spatially. An 7.9.4 Discrete Electric Spark—An electric spark igniter
may consist of a pair of electrodes (steel or graphite) spaced
appropriate device such as a thermocouple should be used to
monitor the gas temperature within the test vessel. approximately 6 mm apart across which a short duration spark
7.5 Ignition point must be positioned near the center of the (lasting for typically 1 ms or less) is caused to occur upon a
vessel and away from any surfaces or obstacles inside the test single discharge of a capacitor. The electrical energy stored on
vessel. or discharged from the capacitor, or both, should be measured
7.6 One design of an acceptable test vessel is described in and reported. The energy dissipated in the spark gap may also
Appendix X1. be measured by appropriate means. Use of at least 10 Joules of
E 2079
nominal (stored) spark energy is recommended. necessary protection and mitigation measures must be imple-
mented.
NOTE 2—Electric arcs and sparks listed in 7.9.3 and 7.9.4 may fail to
8.3 If the fuel can inadvertently be vented inside the heated
discharge when testing fuels with high dielectric strength and during tests
chamber or inside the enclosed area, the heated chamber
conducted at a high initial pressure.
should be fitted with an inert gas purge or the area should be
7.9.5 Chemical Igniter—Some materials (such as chloro-
adequately ventilated to prevent buildup of an flammable
fluoro-carbons) require a higher ignition energy than that can
mixture in the large space.
be provided by the electrical means described above. In that
8.4 It is recommended that LOC evaluations be performed
case, tests with chemical igniters (for example, electric
at atmospheric pressure prior to conducting evaluations at
matches, electrically activated kitchen match heads, or Sobbe
elevated initial pressure. This measure should provide baseline
igniters) may be necessary to determine the true limiting
data which will help to avoid unexpectedly energetic explo-
oxidant concentration (or the flammability limit) as opposed to
sions at high initial pressure.
an “ignitability limit.” If tests are conducted in a sufficiently
8.5 Where the LOC is expected to exceed 21 %, testing
large vessel, electric matches or Sobbe igniters may be used.
should begin at 21 % oxygen and the oxygen concentration
However, it should be kept in mind that these igniters produce
should be increased in small increments.
significantly larger and sometimes multiple ignition kernels
NOTE 5—The maximum deflagration pressure that can be developed
than the electrical ignition sources. Chemical igniters are likely
during the test should be estimated by a suitable means, before testing.
to overdrive combustion events in small test vessels, and in that
case, measured LOC values are expected to be lower than the 8.6 Test matrix must be planned carefully to avoid testing of
actual LOC values. If a chemical igniter is used, the pressure detonable mixtures.
8.7 Compressed gas cylinders should be secured by means
rise from the igniter, by itself, must be determined. During a
test, there is also an additional pressure generated by the appropriate to the size of cylinder. Gas cylinder valves should
be closed when not in use. Gas cylinders should be fitted with
combustion of the fuel gas within the igniter flame, even
though there is no propagation. One way to partially correct for pressure regulators of the correct pressure range and type
these igniter effects is to use a more stringent ignition criterion suited for use with the gas contained therein. Regulator
than the standard 7 % pressure rise. Appropriate ignition delivery pressure should be set to the lowest value required for
criterion may be determined from a series of baseline tests efficient gas transfer. The use of check valves in gas supply
conducted on actual fuel-oxidant-diluent mixtures chosen near lines is recommended. All connections in gas transfer lines
the non-flammable vicinity of the composition H defined in should be checked for tightness.
Section 4.
9. Preparation of Apparatus
NOTE 3—Igniters dissipating large quantities of energy (especially
9.1 Clean and dry the test vessel and other gas-handling
chemical igniters) are capable of producing a finite pressure rise in the
equipment. Make sure that no oil, grease, or other combustible
smaller test vessels, even in the absence of flammable test mixtures. The
is left inside the parts.
pressure rise due to igniter must be quantified before the LOC testing, and
9.2 Assemble the test system components and check for
must be subtracted from the peak pressure rise measured at each test (see
10.1.11). If the pressure rise due to igniter is a non-negligible fraction of leak points.
the absolute pressure of the test mixture, the accompanying compressive
9.3 Verify that the test system is at the required ope
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