ASTM E681-09(2023)

Standard Test Method for Concentration Limits of Flammability of Chemicals (Vapors and Gases)

SIGNIFICANCE AND USE
5.1 The LFL and UFL of gases and vapors define the range of flammable concentrations in air.  
5.2 This method measures the LFL and UFL for upward (and partially outward) flame propagation. The limits for downward flame propagation are narrower.  
5.3 Limits of flammability may be used to determine guidelines for the safe handling of volatile chemicals. They are used particularly in assessing ventilation requirements for the handling of gases and vapors. NFPA 69 provides guidance for the practical use of flammability limit data, including the appropriate safety margins to use.  
5.4 As discussed in Brandes and Ural,4 there is a fundamental difference between the ASTM and European methods for flammability determination. The ASTM methods aim to produce the best representation of flammability parameters, and rely upon the safety margins imposed by the application standards, such as NFPA 69. On the other hand, European test methods aim to result in a conservative representation of flammability parameters. For example, in this standard, LFL is the calculated average of the lowest go and highest no-go concentrations while the European test methods report the LFL as the minimum of the five highest no-go concentrations.
Note 2: For hydrocarbons, the break point between nonflammability and flammability occurs over a narrow concentration range at the lower flammability limit, but the break point is less distinct at the upper limit. For materials found to be non-reproducible per 13.1.1 that are likely to have large quenching distances and may be difficult to ignite, such as ammonia and certain halogenated hydrocarbon, the lower and upper limits of these materials may both be less distinct. That is, a wider range exists between flammable and nonflammable concentrations (see Annex A1).
SCOPE
1.1 This test method covers the determination of the lower and upper concentration limits of flammability of chemicals having sufficient vapor pressure to form flammable mixtures in air at atmospheric pressure at the test temperature. This test method may be used to determine these limits in the presence of inert dilution gases. No oxidant stronger than air should be used.  
Note 1: The lower flammability limit (LFL) and upper flammability limit (UFL) are sometimes referred to as the lower explosive limit (LEL) and the upper explosive limit (UEL), respectively. However, since the terms LEL and UEL are also used to denote concentrations other than the limits defined in this test method, one must examine the definitions closely when LEL and UEL values are reported or used.  
1.2 This test method is based on electrical ignition and visual observations of flame propagation. Users may experience problems if the flames are difficult to observe (for example, irregular propagation or insufficient luminescence in the visible spectrum), if the test material requires large ignition energy, or if the material has large quenching distances.  
1.3 Annex A1 provides a modified test method for materials (such as certain amines, halogenated materials, and the like) with large quenching distances which may be difficult to ignite.  
1.4 In other situations where strong ignition sources (such as direct flame ignition) is considered credible, the use of a test method employing higher energy ignition source in a sufficiently large pressure chamber (analogous, for example, to the methods in Test Method E2079 for measuring limiting oxygen concentration) may be more appropriate. In this case, expert advice may be necessary.  
1.5 The flammability limits depend on the test temperature and pressure. This test method is limited to an initial pressure of the local ambient or less, with a practical lower pressure limit of approximately 13 kPa (100 mm Hg). The maximum practical operating temperature of this equipment is approximately 150 °C.  
1.6 The values stated in SI units are to be regarded as standard. No other units of measuremen...

General Information

• Status: Published
• Publication Date: 30-Apr-2023
• ICS: 13.300 - Protection against dangerous goods
• Technical Committee: E27 - Hazard Potential of Chemicals
• Drafting Committee: E27.04 - Flammability and Ignitability of Chemicals

Standards Content (Sample)

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.
Designation: E681 − 09 (Reapproved 2023)
Standard Test Method for
Concentration Limits of Flammability of Chemicals (Vapors
1
and Gases)
This standard is issued under the fixed designation E681; 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 1.6 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.1 This test method covers the determination of the lower
standard.
and upper concentration limits of flammability of chemicals
having sufficient vapor pressure to form flammable mixtures in 1.7 This test method should be used to measure and describe
air at atmospheric pressure at the test temperature. This test the properties of materials, products, or assemblies in response
method may be used to determine these limits in the presence to heat and flame under controlled laboratory conditions and
of inert dilution gases. No oxidant stronger than air should be should not be used to describe or appraise the fire hazard or fire
used. risk of materials, products, or assemblies under actual fire
conditions. However, results of this test method may be used as
NOTE 1—The lower flammability limit (LFL) and upper flammability
elements of a fire risk assessment that takes into account all of
limit (UFL) are sometimes referred to as the lower explosive limit (LEL)
and the upper explosive limit (UEL), respectively. However, since the the factors pertinent to an assessment of the fire hazard of a
terms LEL and UEL are also used to denote concentrations other than the
particular end use.
limits defined in this test method, one must examine the definitions closely
1.8 This standard may involve hazardous materials,
when LEL and UEL values are reported or used.
operations, and equipment. This standard does not purport to
1.2 This test method is based on electrical ignition and
address all of the safety concerns, if any, associated with its
visual observations of flame propagation. Users may experi-
use. It is the responsibility of the user of this standard to
ence problems if the flames are difficult to observe (for
establish appropriate safety, health, and environmental prac-
example, irregular propagation or insufficient luminescence in
tices and determine the applicability of regulatory limitations
the visible spectrum), if the test material requires large ignition
prior to use. Specific precautionary statements are given in
energy, or if the material has large quenching distances.
Section 8.
1.3 Annex A1 provides a modified test method for materials
1.9 This international standard was developed in accor-
(such as certain amines, halogenated materials, and the like)
dance with internationally recognized principles on standard-
with large quenching distances which may be difficult to ignite.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.4 In other situations where strong ignition sources (such
mendations issued by the World Trade Organization Technical
as direct flame ignition) is considered credible, the use of a test
Barriers to Trade (TBT) Committee.
method employing higher energy ignition source in a suffi-
ciently large pressure chamber (analogous, for example, to the
2. Referenced Documents
methods in Test Method E2079 for measuring limiting oxygen
2
concentration) may be more appropriate. In this case, expert
2.1 ASTM Standards:
advice may be necessary.
E171 Practice for Conditioning and Testing Flexible Barrier
Packaging
1.5 The flammability limits depend on the test temperature
E582 Test Method for Minimum Ignition Energy and
and pressure. This test method is limited to an initial pressure
Quenching Distance in Gaseous Mixtures
of the local ambient or less, with a practical lower pressure
E1445 Terminology Relating to Hazard Potential of Chemi-
limit of approximately 13 kPa (100 mm Hg). The maximum
cals
practical operating temperature of this equipment is approxi-
E1515 Test Method for Minimum Explosible Concentration
mately 150 °C.
of Combustible Dusts
1
This test method is under the jurisdiction of ASTM Committee E27 on Hazard
Potential of Chemicals and is the direct responsibility of Subcommittee E27.04 on
2
Flammability and Ignitability of Chemicals. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2023. Published May 2023. Originally contact ASTM Customer Service at service@as
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