ASTM E2079-19

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2079 − 07 (Reapproved 2013) E2079 − 19
Standard Test Methods for
Limiting Oxygen (Oxidant) Concentration in Gases and
Vapors
This standard is issued under the fixed designation E2079; 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 (´) indicates an editorial change since the last revision or reapproval.
1. 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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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.
1.6 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E1445 Terminology Relating to Hazard Potential of Chemicals
2.2 CGA Publication:
CGA P-23 Standard for Categorizing Gas Mixtures Containing Flammable and Nonflammable Components, 2015
2.3 ISO Publication:
ISO 10156 Gases and Gas Mixtures — Determination of Fire Potential and Oxidizing Ability for the Selection of Cylinder Valve
Outlets, 2010
2.4 NFPA Publication:Publications:
NFPA 69 Standard on Explosion Prevention Systems
NFPA 86 Standard for Ovens and Furnaces
These test methods are under the jurisdiction of ASTM Committee E27 on Hazard Potential of Chemicals and are the direct responsibility of Subcommittee E27.04 on
Flammability and Ignitability of Chemicals.
Current edition approved Oct. 1, 2013July 1, 2019. Published October 2013July 2019. Originally approved in 2000. Last previous edition approved in 20072013 as
E2079 – 07.E2079 – 07 (2013). DOI: 10.1520/E2079-07R13.10.1520/E2079-19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from Compressed Gas Association (CGA), 14501 George Carter Way, Suite 103, Chantilly, VA 20151, http://www.cganet.com.
Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Switzerland, http://www.iso.org.
Available from National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA 02169-7471, http://www.nfpa.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2079 − 19
2.3 NTIS Publications:
Bulletin 503 Coward, H.F., and Jones, G.W., Bureau of Mines, “Limits of Flammability of Gases and Vapors,” NTIS AD701575,
Bulletin 627 Zabetakis, M.G., Bureau of Mines, “Flammability Characteristics of Combustible Gases and Vapors,” NTIS
AD701576, 1965
Bulletin 680 Kuchta, J.M., Bureau of Mines, “Investigation of Fire and Explosion Accidents in the Chemical, Mining, and
Fuel-Related Industries — A Manual,” NTIS PB87113940, 1985
3. Terminology
3.1 Definitions—See also Terminology E1445.
3.2 Definitions of Terms Specific to This Standard:—See also Terminology E1445.
3.2.1 flammable—flammable, n—capable of propagating a flame.
3.2.2 ignition—ignition, n—the initiation of combustion.
3.2.3 limit of flammability—flammability, n—the boundary in composition space dividing flammable and nonflammable regions.
3.2.4 limiting oxygen (oxidant) concentration (LOC) of a fuel-oxidant-inert system—system, n—the oxygen (oxidant)
concentration at the limit of flammability for the worst case (most flammable) fuel concentration.
3.2.4.1 Discussion—
Limiting oxygen (oxidant) concentration is also known as minimum oxygen (oxidant) concentration or as critical oxygen (oxidant)
concentration.
4. Summary of Test Method
4.1 A mixture containing one or more flammable components (fuel), oxygen (oxidant) and inert gas(es) (such as nitrogen,
carbon dioxide, argon, etc.) is prepared in a suitable test vessel at a controlled initial temperature and made to the specified initial
pressure. Proportions of the components are determined by a suitable means. Ignition of the mixture is attempted and flammability
is determined from the pressure rise produced. The criterion for flammability is a pressure rise of ≥7 % above the initial absolute
test pressure. Fuel, oxygen (oxidant), and inert gas proportions are varied between trials until:
4.1.1 L—The lowest oxygen (oxidant) concentration for which flame propagation is possible for at least one combination of fuel
and inert gas (the “worst case” or most flammable fuel concentration range), and
4.1.2 H—The highest oxygen (oxidant) concentration for which flame propagation is not possible for the same worst case fuel
concentration range, are identified.
NOTE 1—The 7 % pressure criterion may not be appropriate for certain fuel and oxidant mixtures. This is also the case if the test enclosure volume
is small, or when the ignition energy is substantially larger than 10 J. It is therefore a prudent practice to perform exploratory tests in the vicinity of limit
mixtures to evaluate the validity of the selected pressure rise criterion. See, for example criterion (1, 2).
5. Significance and Use
5.1 Knowledge of the limiting oxygen (oxidant) concentration is needed for safe operation of some chemical processes. This
information may be needed in order to start up or operate a reactor while avoiding the creation of flammable gas compositions
therein, or to store or ship materials safely. NFPA 69 provides guidance for the practical use of LOC data, including the appropriate
safety margin to use.
5.2 Examples of LOC data applications can be found in references (2-3-45).
NOTE 2—The LOC values reported in references (5-6-78), and relied upon by a number of modern safety standards (such as NFPA 69 and NFPA 86)
were obtained mostly in a 5-cm diameter flammability tube. This diameter may be too small to mitigate the flame quenching influence impeding accurate
determination of the LOC of most fuels. The 4-L minimum volume specified in Section 7 would correspond to a diameter of at least 20 cm. As a result,
some LOC values determined using this standard these test methods are approximately 1.5 vol % lower than the previous values measured in the
flammability tube, and are more appropriate for use in fire and explosion hazard assessment studies.
5.3 Much of the previous literature LOC data (5-6-78) were measured in the flammability tube.
5.4 Accepted LOC values (when nitrogen is the inert gas) determined for the five reference gases using these test methods in
20-L and 120-L test enclosures have been reported in Zlochower (9), and are summarized below:
Hydrogen—4.6 % in 120-L, 4.7 % in 20-L
Carbon Monoxide—5.1 % in 120-L
Methane—11.1 % in 120-L, 10.7 % in 20-L
Ethylene—8.5 % in 120-L, 8.6 % in 20-L
Propane—10.7 % in 120-L, 10.5 % in 20-L
The boldface numbers in parentheses refer to the list of references at the end of this standard.
E2079 − 19
NOTE 3—For carbon monoxide, results are sensitive to the humidity of the test mixture in the enclosure. Presence of a small concentration of water
vapor facilitates combustion and promotes flame propagation by supplying the hydrogen (H) and hydroxyl (OH) free radicals for the chain branching
reactions. For conservative results, provisions are made to humidify the test air to near saturation.
5.5 These test methods are often used to determine the LFL (lower flammability limit) and UFL (upper flammability limit) of
gases and vapors initially at or near atmospheric pressure. Accepted LFL and UFL values determined for the five reference gases
using these test methods have been reported in Zlochower (9).
5.6 These test methods are also used to determine the maximum content of flammable gas which, when mixed with specified
inert gas, is not flammable in air (ISO 10156, CGA P-23).
5.7 A minimum purity of 99 % is recommended for the standard reference gases used for the commissioning (qualification) of
the test apparatus and for the periodic verification of data quality.
6. Limitations
6.1 These test methods are not applicable to mixtures which undergo spontaneous reaction before ignition is attempted.
6.2 These test methods are limited to mixtures which have maximum deflagration pressures less than the maximum working
pressure of the test apparatus.
6.3 These test methods may be used up to the temperature limit of the test system.
6.4 Measurements of flammability are influenced by flame-quenching effects of the test vessel walls. Further surface effects due
to deposits of carbon or other materials can significantly affect limits of flammability, especially in the fuel-rich region. Refer to
Bureau of Mines Bulletin 503 (6) and Bulletin 627.Bulletin 627 (7). For certain chemicals (for example, ammonia, halogenated
materials, and certain amines) which have large ignition-quenching distances, tests may need to be conducted in vessels larger than
that specified below.
7. Apparatus
7.1 The test vessel must have a volume of at least 4 L.
NOTE 4—A survey of practitioners of this method these test methods indicates that test vessels in the size range of 4 to 35120 L are used.
7.2 Test vessels must be nearly spherical. The maximum aspect ratio of the test vessel (the ratio of largest to smallest internal
dimension) must be smaller than or equal to two.
7.3 Test vessel may be equipped with a means of mechanical agitation to ensure uniform mixing of components before an
ignition attempt.
7.4 If tests are to be conducted at an elevated temperature, the test vessel may be heated using a heating jacket, heating mantle
or placed inside a heated chamber. The heating system must be capable of controlling the gas temperature inside the test vessel
to within 63°C both temporally and spatially. An appropriate device such as a thermocouple should be used to monitor the gas
temperature within the test vessel.
7.5 Ignition point must be positioned near the center of the vessel and away from any surfaces or obstacles inside the test vessel.
7.6 One design of an acceptable test vessel is described in Appendix X1.
7.7 The maximum allowable working pressure (MAWP) of the test vessel at the maximum test temperature must exceed the
maximum expected deflagration pressure.
7.8 Pressure Transducers:
7.8.1 Low-Range Transducer—A low-range pressure transducer may be used for the purpose of making partial pressure
additions of gases and vapors to the test vessel. The transducer and its signal conditioning/amplifying electronics should have an
accuracy, precision and repeatability sufficient to accurately resolve the required changes in the gas partial pressure for the
component used in lowest concentration. The transducer should be protected from deflagration pressures by means of an isolation
valve. A pressure gage may be used if an error analysis is performed to demonstrate that the internal volume of the pressure gage
and piping will not significantly affect the test mixture.
7.8.2 High-Range Transducer—This transducer has the purpose of measuring the pressure rise on ignition of the gas mixture.
It should have sufficient range to withstand the highest pressure it is expected to experience while also having sufficient accuracy
and resolution to measure small pressure rises of the order of 7 % of the initial absolute test pressure.
7.8.3 The pressure transducer and recording equipment must have adequate time resolution to capture the maximum rate of
pressure rise developed by the combustion event.
7.8.4 Calibration of the pressure transducer and data acquisition system must be verified over the range of pressures at which
the system is expected to operate.
7.9 Ignition Source—Several possible means of ignition may be used which include those described below. The means of
ignition used must be described in the test report.
E2079 − 19
7.9.1 Fuse Wire—A fuse wire igniter can be constructed, for example from a piece of No. 40 (0.076-mm diameter) copper,
nichrome, or platinum wire fastened to power supply terminals in such manner as to leave a filament of wire between the terminals
approximately 10 mm long. A 500 VA/115 V isolating transformer, or a properly sized discrete discharge capacitor circuit will
serve as an adequate igniter energy supply.
7.9.2 Carbon Spark—Four 2-mm diameter graphite rods wrapped by the leads coming from an electrical pulse generator. The
two electrical leads are separated by a 6 to 10-mm distance. The resulting discrete spark is in the form of a surface discharge over
the graphite rods.
7.9.3 Continuous Electric Arc—An electric arc igniter may consist of a pair of electrodes (steel or graphite) spaced
approximately 6 mm apart across which a 30 mA arc of typically less than 1 s duration can be supplied from a 115/15 000 volt
transformer (so-called luminous tube transformer).
7.9.4 Discrete Electric Spark—An electric spark igniter may consist of a pair of electrodes (steel or graphite) spaced
approximately 6 mm apart across which a short duration spark (lasting for typically 1 ms or less) is caused to occur upon a single
discharge of a capacitor. The electrical energy stored on or discharged from the capacitor, or both, should be measured and
reported. The energy dissipated in the spark gap may also be measured by appropriate means. Use of at least 10 Joules of nominal
(stored) spark energy is recommended.
NOTE 5—Electric arcs and sparks listed in 7.9.3 and 7.9.4 may fail to discharge when testing fuels with high dielectric strength and during tests
conducted at a high initial pressure.
7.9.5 Chemical Igniter—Some materials (such as chloro-fluoro-carbons) require a higher ignition energy than that can be
provided by the electrical means described above. In that case, tests with chemical igniters (for example, electric matches,
electrically activated kitchen match heads, or Sobbe igniters) may be necessary to determine the true limiting oxidant concentration
(or the flammability limit) as opposed to an “ignitability limit.” If tests are conducted in a sufficiently large vessel, electric matches
or Sobbe igniters may be used. However, it should be kept in mind that these igniters produce significantly larger and sometimes
multiple ignition kernels than the electrical ignition sources. Chemical igniters are likely to overdrive combustion events in small
test vessels, and in that case, measured LOC values are expected to be lower than the actual LOC values. If a chemical igniter is
used, the pressure rise from the igniter, by itself, must be determined. During a test, there is also an additional pressure generated
by the combustion of the fuel gas within the igniter flame, even though there is no propagation. One way to partially correct for
these igniter effects is to use a more stringent ignition criterion than the standard 7 % pressure rise. Appropriate ignition criterion
may be determined from a series of baseline tests conducted on actual fuel-oxidant-diluent mixtures chosen near the
non-flammable vicinity of the composition H defined in Section 4.
NOTE 6—Igniters dissipating large quantities of energy (especially chemical igniters) are capable of producing a finite pressure rise in the smaller test
vessels, even in the absence of flammable test mixtures. The pressure rise due to igniter must be quantified before the LOC testing, and 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 the absolute pressure of
the test mixture, the accompanying compressive heating of the test mixture must be considered.
NOTE 7—Some igniters may not be capable of dissipating all or any of their rated energy at the extremes of pressure and temperature. If there is any
doubt, the reliability of the igniter function must be demonstrated at the test conditions.
8. Safety Precautions
8.1 Adequate shielding must be provided to prevent injury in the event of equipment rupture. The apparatus should be set up
so that the operator is isolated from the test vessel while the vessel contains a charge of reactants, including the time while the
vessel is being filled. The test apparatus should be equipped with interlocks so that the ignition source cannot be activated unless
the operator has taken necessary steps to protect personnel and equipment. Activation of the ignition source should be possible only
from a position shielded from the test vessel. The test vessel may be fitted with a rupture disk vented to a safe location.
8.2 In the selection of the safe location for the vessel discharge, whether it is through discharge piping or through a rupture disk,
full consideration should be given to the safety of the personnel, environment and property. The impact of both unburnt and burnt
test mixture venting must be considered, and necessary protection and mitigation measures must be implemented.
8.3 If the fuel can inadvertently be vented inside the heated chamber or inside the enclosed area, the heated chamber should
be fitted with an inert gas purge or the area should be adequately ventilated to prevent buildup of an flammable mixture in the large
space.
8.4 It is recommended that LOC evaluations be performed at atmospheric pressure prior to conducting evaluations at elevated
initial pressure. This measure should provide baseline data which will help to avoid unexpectedly energetic explosions at high
initial pressure.
8.5 Where the LOC is expected to exceed 21 %, testing should begin at 21 % oxygen and the oxygen concentration should be
increased in small increments.
NOTE 8—The maximum deflagration pressure that can be developed during the test should be estimated by a suitable means, before testing.
8.6 Test matrix must be planned carefully to avoid testing of detonable mixtures.
E2079 − 19
8.7 Compressed gas cylinders should be secured by means appropriate to the size of cylinder. Gas cylinder valves should be
closed when not in use. Gas cylinders should be fitted with pressure regulators of the correct pressure range and type suited for
use with the gas contained therein. Regulator delivery pressure should be set to the lowest value required for efficient gas transfer.
The use of check valves in gas supply lines is recommended. All connections in gas transfer lines should be checked for tightness.
8.8 Where oxidizers stronger than air are used, the potential safety consequences of enhanced reactivity must be addressed.
9. Preparation of Apparatus
9.1 Clean and dry the test vessel and other gas-handling equipment. Make sure that no oil, grease, or other combustible is left
inside the parts.
9.2 Assemble the test system components and check for leak points.
9.3 Verify that the test system is at the required operating temperature and check for leaks.
10. Procedure
10.1 Two different test methods are used depending on the state of the test mixture components at room temperature:
TEST METHOD A—WHERE SAMPLE COMPONENTS ARE GASES AT ROOM TEMPERATURE
10.1.1 Connect the gas supply lines to the manifold of metering valves and flush the lines.
10.1.2 Verify that the test vessel has been thoroughly purged of gases from prior tests.
10.1.3 Evacuate the test vessel and manifold, as required. By use of the valves, add to the test vessel the component most
appropriately added first; usually, this is the component to be used in the smallest amount. Record the partial pressure of this
component using the low range-transducer.
10.1.4 If the internal volume of the manifold or any piping system connected to the test vessel is appreciable compared to the
test vessel volume, purging, evacuation or other measures must be implemented to ensure the accuracy of the test mixture.
10.1.5 Add the second component up to the desired pressure, as measured by the transducer. Repeat the procedure to introduce
other components until the desired partial pressure of each component has been added to the test vessel. Obtain mixing of gas in
the test vessel by adding the largest component last and at high velocity. Where the vessel configura
...