ASTM G125-00(2023)
(Test Method)Standard Test Method for Measuring Liquid and Solid Material Fire Limits in Gaseous Oxidants
Standard Test Method for Measuring Liquid and Solid Material Fire Limits in Gaseous Oxidants
SIGNIFICANCE AND USE
5.1 This test method provides for measuring of the minimum conditions of a range of parameters (concentration of oxidant in a flowing mixture of oxidant and diluent, pressure, temperature) that will just support sustained propagation of combustion. For materials that exhibit flaming combustion, this is a flammability limit similar to the lower flammability limit, upper flammability limit, and minimum oxidant for combustion of gases (1).4 However, unlike flammability limits for gases, in two-phase systems, the concept of upper and lower flame limits is not meaningful. However, limits can typically be determined for variations in other parameters such as the minimum oxidant for combustion (the oxidant index), the pressure limit, the temperature limit, and others. Measurement and use of these data are analogous to the measurement and use of the corresponding data for gaseous systems. That is, the limits apply to systems likely to experience complete propagations (equilibrium combustion). Successful ignition and combustion below the measured limits at other conditions or of a transient nature are not precluded below the threshold. Flammability limits measured at one set of conditions are not necessarily the lowest thresholds at which combustion can occur. Therefore direct correlation of these data with the burning characteristics under actual use conditions is not implied.
SCOPE
1.1 This test method covers a procedure for measuring the threshold-limit conditions to allow equilibrium of combustion of materials in various oxidant gases under specific test conditions of pressure, temperature, flow condition, fire-propagation directions, and various other geometrical features of common systems.
1.2 This test method is patterned after Test Method D2863-95 and incorporates its procedure for measuring the limit as a function of oxidant concentration for the most commonly used test conditions. Sections 8, 9, 10, 11, 13, and for the basic oxidant limit (oxygen index) procedure are quoted directly from Test Method D2863-95. Oxygen index data reported in accordance with Test Method D2863-95 are acceptable substitutes for data collected with this standard under similar conditions.
1.3 This test method has been found applicable to testing and ranking various forms of materials. It has also found limited usefulness for surmising the prospect that materials will prove “oxygen compatible” in actual systems. However, its results do not necessarily apply to any condition that does not faithfully reproduce the conditions during test. The fire limit is a measurement of a behavioral property and not a physical property. Uses of these data are addressed in Guides G63 and G94.
Note 1: Although this test method has been found applicable for testing a range of materials in a range of oxidants with a range of diluents, the accuracy has not been determined for many of these combinations and conditions of specimen geometry, outside those of the basic procedure as applied to plastics.
Note 2: Test Method D2863-95 has been revised and the revised Test Method has been issued as D2863-97. The major changes involve sample dimensions, burning criteria and the method for determining the oxygen index. The aim of the revisions was to align Test Method D2863 with ISO 4589-2. Six laboratories conducted comparison round robin testing on self-supporting plastics and cellular materials using D2863-95 and D2863-97. The results indicate that there is no difference between the means provided y the two methods at the 95 % confidence level. No comparison tests were conducted on thin films. The majority of ASTM Committee G4 favors maintaining the D2863-95 as the backbone of G125 until comprehensive comparison data become available.
1.4 One very specific set of test conditions for measuring the fire limits of metals in oxygen has been codified in Test Method G124. Test Method G124 measures the minimum pressure limit in oxygen fo...
General Information
- Status
- Published
- Publication Date
- 28-Feb-2023
- Drafting Committee
- G04.01 - Test Methods
Relations
- Effective Date
- 01-Oct-2023
- Effective Date
- 29-Sep-2023
- Effective Date
- 01-Oct-2019
- Effective Date
- 01-Nov-2018
- Effective Date
- 01-Dec-2017
- Effective Date
- 15-Nov-2017
- Effective Date
- 15-Aug-2017
- Effective Date
- 01-Apr-2017
- Effective Date
- 01-Sep-2013
- Effective Date
- 01-Apr-2012
- Effective Date
- 01-Apr-2012
- Effective Date
- 01-Nov-2010
- Effective Date
- 01-Aug-2010
- Effective Date
- 01-Sep-2009
- Effective Date
- 01-Sep-2009
Overview
ASTM G125-00(2023), titled "Standard Test Method for Measuring Liquid and Solid Material Fire Limits in Gaseous Oxidants," defines a reliable laboratory procedure for determining the threshold conditions under which materials transition from non-combustion to sustained combustion in gaseous oxidant environments. Developed by ASTM International, this standard provides essential data on flammability characteristics of materials-especially liquids and solids-when exposed to specific oxidants (such as oxygen, nitrous oxide, and fluorine) under controlled conditions of temperature, pressure, flow, and geometry.
Understanding and accurately evaluating fire limits and oxidant compatibility is critical for materials selection, fire risk assessment, and designing safety systems in industries where oxygen-enriched or otherwise oxidizing atmospheres are present.
Key Topics
- Threshold-limit conditions: ASTM G125 measures the minimum required oxidant concentration, pressure, and temperature that just support sustained combustion for a given material.
- Oxidant index: This value represents the lowest volume percent concentration of an oxidant (often oxygen) in a diluent (like nitrogen) required to maintain flaming or equilibrium combustion.
- Flammability assessment: Unlike gas flammability tests with distinct upper and lower limits, two-phase (solid/liquid) materials typically have a single measurable fire limit for variables such as oxidant concentration, pressure, or temperature.
- Controlled laboratory testing: Tests are conducted in specialized apparatuses with specified specimen sizes and flow rates, emphasizing repeatability and comparability.
- Variability and limitations: Results depend on replicating test conditions-including geometry, flow direction, and environmental factors. Flammability performance can differ significantly if the actual use deviates from test settings.
Applications
ASTM G125 is a valuable standard for a range of practical fire safety engineering and material compatibility tasks, including:
- Materials selection for oxygen service: Industries such as aerospace, healthcare, and chemical processing use this method to screen and rank materials for oxygen and other oxidizing environments.
- Fire risk assessment: Data produced aids in evaluating the probability that materials will sustain ignition and combustion under foreseeable accident scenarios in oxygen-enriched atmospheres.
- Product compliance and development: Manufacturers of plastics, composites, elastomers, and metallic parts can use fire limit data to certify products and improve formulations.
- Design of fire protection systems: Engineering teams rely on fire limit measurements to develop systems that minimize ignition and combustion risks wherever oxidizing gases are present.
- Safety justification for systems in oxidizing atmospheres: The method provides a standardized benchmark for determining whether a material is "oxidant compatible," supporting regulatory filings and hazard analyses.
Related Standards
ASTM G125 references and aligns with several related standards and guides for broader context and data interoperability:
- ASTM D2863: Test method for measuring the minimum oxygen concentration to support combustion of plastics (oxygen index), which G125 partly incorporates.
- ASTM G124: Standard for determining combustion behavior of metal materials in oxygen-enriched atmospheres.
- ASTM G63 & G94: Guides for evaluating nonmetallic and metallic materials for compatibility in oxygen service.
- ISO 4589-2: International standard for burning behavior of plastics (oxygen index).
- ASTM D618, D1071, D2444: Standards for specimen conditioning, volumetric gas measurement, and material impact resistance.
- ASTM G128: Guide for control of hazards and risks in oxygen-enriched systems.
By adhering to ASTM G125, manufacturers, researchers, and engineers enhance material fire safety and oxidant compatibility, fostering safer design and operation in oxygen-rich and other oxidizing environments. For more details, the complete standard and referenced documents are available from ASTM International.
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Frequently Asked Questions
ASTM G125-00(2023) is a standard published by ASTM International. Its full title is "Standard Test Method for Measuring Liquid and Solid Material Fire Limits in Gaseous Oxidants". This standard covers: SIGNIFICANCE AND USE 5.1 This test method provides for measuring of the minimum conditions of a range of parameters (concentration of oxidant in a flowing mixture of oxidant and diluent, pressure, temperature) that will just support sustained propagation of combustion. For materials that exhibit flaming combustion, this is a flammability limit similar to the lower flammability limit, upper flammability limit, and minimum oxidant for combustion of gases (1).4 However, unlike flammability limits for gases, in two-phase systems, the concept of upper and lower flame limits is not meaningful. However, limits can typically be determined for variations in other parameters such as the minimum oxidant for combustion (the oxidant index), the pressure limit, the temperature limit, and others. Measurement and use of these data are analogous to the measurement and use of the corresponding data for gaseous systems. That is, the limits apply to systems likely to experience complete propagations (equilibrium combustion). Successful ignition and combustion below the measured limits at other conditions or of a transient nature are not precluded below the threshold. Flammability limits measured at one set of conditions are not necessarily the lowest thresholds at which combustion can occur. Therefore direct correlation of these data with the burning characteristics under actual use conditions is not implied. SCOPE 1.1 This test method covers a procedure for measuring the threshold-limit conditions to allow equilibrium of combustion of materials in various oxidant gases under specific test conditions of pressure, temperature, flow condition, fire-propagation directions, and various other geometrical features of common systems. 1.2 This test method is patterned after Test Method D2863-95 and incorporates its procedure for measuring the limit as a function of oxidant concentration for the most commonly used test conditions. Sections 8, 9, 10, 11, 13, and for the basic oxidant limit (oxygen index) procedure are quoted directly from Test Method D2863-95. Oxygen index data reported in accordance with Test Method D2863-95 are acceptable substitutes for data collected with this standard under similar conditions. 1.3 This test method has been found applicable to testing and ranking various forms of materials. It has also found limited usefulness for surmising the prospect that materials will prove “oxygen compatible” in actual systems. However, its results do not necessarily apply to any condition that does not faithfully reproduce the conditions during test. The fire limit is a measurement of a behavioral property and not a physical property. Uses of these data are addressed in Guides G63 and G94. Note 1: Although this test method has been found applicable for testing a range of materials in a range of oxidants with a range of diluents, the accuracy has not been determined for many of these combinations and conditions of specimen geometry, outside those of the basic procedure as applied to plastics. Note 2: Test Method D2863-95 has been revised and the revised Test Method has been issued as D2863-97. The major changes involve sample dimensions, burning criteria and the method for determining the oxygen index. The aim of the revisions was to align Test Method D2863 with ISO 4589-2. Six laboratories conducted comparison round robin testing on self-supporting plastics and cellular materials using D2863-95 and D2863-97. The results indicate that there is no difference between the means provided y the two methods at the 95 % confidence level. No comparison tests were conducted on thin films. The majority of ASTM Committee G4 favors maintaining the D2863-95 as the backbone of G125 until comprehensive comparison data become available. 1.4 One very specific set of test conditions for measuring the fire limits of metals in oxygen has been codified in Test Method G124. Test Method G124 measures the minimum pressure limit in oxygen fo...
SIGNIFICANCE AND USE 5.1 This test method provides for measuring of the minimum conditions of a range of parameters (concentration of oxidant in a flowing mixture of oxidant and diluent, pressure, temperature) that will just support sustained propagation of combustion. For materials that exhibit flaming combustion, this is a flammability limit similar to the lower flammability limit, upper flammability limit, and minimum oxidant for combustion of gases (1).4 However, unlike flammability limits for gases, in two-phase systems, the concept of upper and lower flame limits is not meaningful. However, limits can typically be determined for variations in other parameters such as the minimum oxidant for combustion (the oxidant index), the pressure limit, the temperature limit, and others. Measurement and use of these data are analogous to the measurement and use of the corresponding data for gaseous systems. That is, the limits apply to systems likely to experience complete propagations (equilibrium combustion). Successful ignition and combustion below the measured limits at other conditions or of a transient nature are not precluded below the threshold. Flammability limits measured at one set of conditions are not necessarily the lowest thresholds at which combustion can occur. Therefore direct correlation of these data with the burning characteristics under actual use conditions is not implied. SCOPE 1.1 This test method covers a procedure for measuring the threshold-limit conditions to allow equilibrium of combustion of materials in various oxidant gases under specific test conditions of pressure, temperature, flow condition, fire-propagation directions, and various other geometrical features of common systems. 1.2 This test method is patterned after Test Method D2863-95 and incorporates its procedure for measuring the limit as a function of oxidant concentration for the most commonly used test conditions. Sections 8, 9, 10, 11, 13, and for the basic oxidant limit (oxygen index) procedure are quoted directly from Test Method D2863-95. Oxygen index data reported in accordance with Test Method D2863-95 are acceptable substitutes for data collected with this standard under similar conditions. 1.3 This test method has been found applicable to testing and ranking various forms of materials. It has also found limited usefulness for surmising the prospect that materials will prove “oxygen compatible” in actual systems. However, its results do not necessarily apply to any condition that does not faithfully reproduce the conditions during test. The fire limit is a measurement of a behavioral property and not a physical property. Uses of these data are addressed in Guides G63 and G94. Note 1: Although this test method has been found applicable for testing a range of materials in a range of oxidants with a range of diluents, the accuracy has not been determined for many of these combinations and conditions of specimen geometry, outside those of the basic procedure as applied to plastics. Note 2: Test Method D2863-95 has been revised and the revised Test Method has been issued as D2863-97. The major changes involve sample dimensions, burning criteria and the method for determining the oxygen index. The aim of the revisions was to align Test Method D2863 with ISO 4589-2. Six laboratories conducted comparison round robin testing on self-supporting plastics and cellular materials using D2863-95 and D2863-97. The results indicate that there is no difference between the means provided y the two methods at the 95 % confidence level. No comparison tests were conducted on thin films. The majority of ASTM Committee G4 favors maintaining the D2863-95 as the backbone of G125 until comprehensive comparison data become available. 1.4 One very specific set of test conditions for measuring the fire limits of metals in oxygen has been codified in Test Method G124. Test Method G124 measures the minimum pressure limit in oxygen fo...
ASTM G125-00(2023) is classified under the following ICS (International Classification for Standards) categories: 13.300 - Protection against dangerous goods. The ICS classification helps identify the subject area and facilitates finding related standards.
ASTM G125-00(2023) has the following relationships with other standards: It is inter standard links to ASTM D2863-23, ASTM D2863-95, ASTM D2863-19, ASTM G124-18, ASTM D2863-17a, ASTM D2444-17, ASTM D2863-17, ASTM D1071-17, ASTM D2863-13, ASTM D2863-12e1, ASTM D2863-12, ASTM G124-10, ASTM D2444-99(2010), ASTM D2863-09, ASTM D2863-10. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
ASTM G125-00(2023) is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
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: G125 − 00 (Reapproved 2023)
Standard Test Method for
Measuring Liquid and Solid Material Fire Limits in Gaseous
Oxidants
This standard is issued under the fixed designation G125; 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.
self-supporting plastics and cellular materials using D2863-95 and D2863-
1. Scope
97. The results indicate that there is no difference between the means
1.1 This test method covers a procedure for measuring the
provided y the two methods at the 95 % confidence level. No comparison
threshold-limit conditions to allow equilibrium of combustion tests were conducted on thin films. The majority of ASTM Committee G4
favors maintaining the D2863-95 as the backbone of G125 until compre-
of materials in various oxidant gases under specific test
hensive comparison data become available.
conditions of pressure, temperature, flow condition, fire-
propagation directions, and various other geometrical features
1.4 One very specific set of test conditions for measuring
of common systems.
the fire limits of metals in oxygen has been codified in Test
Method G124. Test Method G124 measures the minimum
1.2 This test method is patterned after Test Method
pressure limit in oxygen for its own set of test conditions. Its
D2863-95 and incorporates its procedure for measuring the
details are not reproduced in this standard. A substantial
limit as a function of oxidant concentration for the most
database is available for this procedure, although it is much
commonly used test conditions. Sections 8, 9, 10, 11, 13, and
smaller than the database for Test Method D2863-95.
for the basic oxidant limit (oxygen index) procedure are quoted
(Warning—During the course of combustion, gases, vapors,
directly from Test Method D2863-95. Oxygen index data
aerosols, fumes or any combination of these are evolved which
reported in accordance with Test Method D2863-95 are accept-
may be hazardous.) (Warning—Adequate precautions should
able substitutes for data collected with this standard under
be taken to protect the operator.)
similar conditions.
1.5 The values stated in SI units are to be regarded as the
1.3 This test method has been found applicable to testing
standard. No other units of measurement are included in this
and ranking various forms of materials. It has also found
standard.
limited usefulness for surmising the prospect that materials will
prove “oxygen compatible” in actual systems. However, its
1.6 This basic standard should be used to measure and
results do not necessarily apply to any condition that does not
describe the properties of materials, products, or assemblies in
faithfully reproduce the conditions during test. The fire limit is
response to heat and flame under controlled laboratory con-
a measurement of a behavioral property and not a physical
ditions and should not be used to directly describe or appraise
property. Uses of these data are addressed in Guides G63 and
the fire hazard or fire risk of materials, products or assemblies
G94.
under actual fire conditions. However, results of this test may
be used as elements of a fire risk assessment which takes into
NOTE 1—Although this test method has been found applicable for
testing a range of materials in a range of oxidants with a range of diluents,
account all of the factors which are pertinent to an assessment
the accuracy has not been determined for many of these combinations and
of the fire hazard of a particular end use. The standard has
conditions of specimen geometry, outside those of the basic procedure as
more applicability in this regard at predicting the fire behavior
applied to plastics.
of materials and components that are close in size to the test
NOTE 2—Test Method D2863-95 has been revised and the revised Test
condition, than for systems that are much different (for ex-
Method has been issued as D2863-97. The major changes involve sample
dimensions, burning criteria and the method for determining the oxygen
ample: comparing a test rod to a valve seat rather than
index. The aim of the revisions was to align Test Method D2863 with ISO
comparing a test rod to a house or a particle).
4589-2. Six laboratories conducted comparison round robin testing on
1.7 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
This test method is under the jurisdiction of ASTM Committee G04 on
responsibility of the user of this standard to establish appro-
Compatibility and Sensitivity of Materials in Oxygen Enriched Atmospheres and is
priate safety, health, and environmental practices and deter-
the direct responsibility of Subcommittee G04.01 on Test Methods. Portions have
been adopted from Test Method D2863-95, which is under the jurisdiction of ASTM mine the applicability of regulatory limitations prior to use.
Committee D20 on Plastics.
1.8 This international standard was developed in accor-
Current edition approved March 1, 2023. Published March 2023. Originally
dance with internationally recognized principles on standard-
approved in 1994. Last previous edition approved in 2015 as G125 – 00 (2015).
DOI: 10.1520/G0125-00R23. ization established in the Decision on Principles for the
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G125 − 00 (2023)
Development of International Standards, Guides and Recom- 3.2.2 oxidant compatibility, n—the ability of a substance to
mendations issued by the World Trade Organization Technical coexist with both an oxidant and a potential source(s) of
Barriers to Trade (TBT) Committee. ignition within the acceptable risk parameter of the user (at an
expected pressure and temperature).
2. Referenced Documents
3.2.3 oxidant index, n—the minimum concentration of an
2.1 ASTM Standards:
oxidant such as oxygen, nitrous oxide, fluorine, etc., expressed
D618 Practice for Conditioning Plastics for Testing
as a volume percent, in a mixture of the oxidant with a diluent
D1071 Test Methods for Volumetric Measurement of Gas-
such as nitrogen, helium, carbon dioxide, etc., that will just
eous Fuel Samples
support sustained combustion of a material initially at given
D2444 Practice for Determination of the Impact Resistance
conditions of temperature, pressure, flow conditions, propaga-
of Thermoplastic Pipe and Fittings by Means of a Tup
tion direction, etc. (See also, oxygen index.)
(Falling Weight)
3.2.3.1 Discussion—The oxidant index may be more spe-
D2863 Test Method for Measuring the Minimum Oxygen
cifically identified by naming the oxidant: oxygen limit (or
Concentration to Support Candle-Like Combustion of
index), nitrous oxide limit (or index), fluorine limit (or index),
Plastics (Oxygen Index)
etc. Unless specified otherwise, the typical oxidant is taken to
D2863-95 Test Method for Measuring the Minimum Oxygen
be oxygen, the typical diluent is taken to be nitrogen, and the
Concentration to Support Candle-Like Combustion of
typical temperature is taken as room temperature.
Plastics (Oxygen Index)
3.2.4 pressure limit—the minimum pressure of an oxidant
D2863-97 Test Method for Measuring the Minimum Oxygen
(or mixture) that will just support sustained combustion of a
Concentration to Support Candle-Like Combustion of
material initially at given conditions of oxidant concentration,
Plastics (Oxygen Index)
temperature, flow condition, propagation direction, etc.
G63 Guide for Evaluating Nonmetallic Materials for Oxy-
3.2.4.1 Discussion—The pressure limit may be more spe-
gen Service
G94 Guide for Evaluating Metals for Oxygen Service cifically identified by naming the oxidant: oxygen pressure
limit, nitrous oxide pressure limit, fluorine pressure limit, etc.
G124 Test Method for Determining the Combustion Behav-
ior of Metallic Materials in Oxygen-Enriched Atmo-
3.2.5 temperature limit—the minimum temperature of an
spheres
oxidant (or mixture) that will just support sustained combus-
G128 Guide for Control of Hazards and Risks in Oxygen
tion of a material initially at given conditions of oxidant
Enriched Systems
concentration, temperature, flow condition, propagation
2.2 Other Standards:
direction, etc.
ISO 4589-2 Plastics—Determination of burning behavior by
3.2.5.1 Discussion—The temperature limit may be more
oxygen index—Part 2: Ambient temperature test
specifically identified by naming the oxidant: oxygen tempera-
ture limit, nitrous oxide temperature limit, fluorine temperature
3. Terminology
limit, etc.
3.1 Definitions:
3.1.1 oxygen compatibility, n—the ability of a substance to
4. Summary of Test Method
coexist with both oxygen and a potential source(s) of ignition
4.1 The threshold limit condition (minimum oxidant
within the acceptable risk parameter of the user (at an expected
concentration, minimum pressure, minimum temperature, etc.)
pressure and temperature). (See Guide G128.)
that will just support sustained combustion under equilibrium
3.1.2 oxygen index, n—the minimum concentration of
conditions is measured in a test apparatus. The equilibrium is
oxygen, expressed as a volume percent, in a mixture of oxygen
established by the relation between the heat generated from the
and nitrogen that will just support flaming combustion of a
combustion of the specimen (that may be augmented by the
material initially at room temperature under the conditions of
heat of decomposition of some oxidants) and the heat lost to
Test Method D2863. (See Test Method D2863.)
the surroundings as measured by one or the other of two
3.2 Definitions of Terms Specific to This Standard:
arbitrary criteria, namely, a time of burning or a length of
3.2.1 fire limit, n—the threshold limit conditions that will
specimen burned. This point is approached from both sides of
just support sustained combustion of a material under a
the critical threshold condition in order to establish the fire
combination of specified conditions and at least one variable
limit.
parameter (typically oxidant concentration, diluent nature,
pressure, temperature, geometry, flow or flame parameters,
5. Significance and Use
etc.).
5.1 This test method provides for measuring of the mini-
mum conditions of a range of parameters (concentration of
oxidant in a flowing mixture of oxidant and diluent, pressure,
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
temperature) that will just support sustained propagation of
Standards volume information, refer to the standard’s Document Summary page on
combustion. For materials that exhibit flaming combustion,
the ASTM website.
this is a flammability limit similar to the lower flammability
ISO 4589-2 First edition 1996-07-15, International Organization for
Standardization, Geneve, Switzerland, 1996. limit, upper flammability limit, and minimum oxidant for
G125 − 00 (2023)
combustion of gases (1). However, unlike flammability limits Oxidants behave dramatically different, because their basic
for gases, in two-phase systems, the concept of upper and chemistry with differing materials is different. For example,
lower flame limits is not meaningful. However, limits can even though nitrous oxide is a combination of nitrogen and
typically be determined for variations in other parameters such oxygen, it behaves much differently than a similar oxygen/
as the minimum oxidant for combustion (the oxidant index), nitrogen mixture. During combustion, nitrous oxide decom-
the pressure limit, the temperature limit, and others. Measure- poses to release heat that renders it more able to support
ment and use of these data are analogous to the measurement combustion than a simple mixture. Fluorine is very reactive
and use of the corresponding data for gaseous systems. That is, and produces more gaseous product species which changes its
the limits apply to systems likely to experience complete behavior in higher purity oxidant. There are data available in
propagations (equilibrium combustion). Successful ignition varying amounts for the oxidants: oxygen, nitrous oxide,
and combustion below the measured limits at other conditions fluorine, nitrogen trifluoride, and nitrogen (nitrogen is an
or of a transient nature are not precluded below the threshold. oxidant in some cases, a diluent in others).
Flammability limits measured at one set of conditions are not
7.3 Diluents—Varying diluents can have a significant effect
necessarily the lowest thresholds at which combustion can
although much less impressive than oxidant, pressure or even
occur. Therefore direct correlation of these data with the
flow direction (1-8). Diluent’s thermal conductivity and heat
burning characteristics under actual use conditions is not
capacity appear to be the most significant properties. Reactivity
implied.
is a second issue. For example, nitrogen does not participate in
most polymer combustions but can react with some metals and
6. Abstract
exhibit widely different diluent natures. Among the diluents
6.1 A well-established procedure for measuring an oxidant
used to date are nitrogen, helium, argon, carbon dioxide, neon,
limit, the oxygen index, of plastics (See Test Method D2863) is
and xenon.
reviewed, then variations commonly used to collect data for
7.4 Pressures—Pressure has a dramatic effect on the fire
oxidant compatibility purposes are described. In the test, a
limit (1, 4, 5, 8, 9, 10, 11). The role of pressure is complex, yet
series of specimens is placed in a preadjusted oxidant mixture
it is one of the most important variables because oxygen
and deliberately ignited. Specimens that do not “burn” are
systems employ a range of pressures to 82 MPa (12000 psig).
retested in higher concentrations. Specimens that do burn are
retested in lower concentrations. When the operator is confi-
7.5 Temperatures—The fole of temperature appears to be
dent that the threshold has been determined by a suitable
among the more straightforward higher temperatures appear to
number and spread of negative tests below the threshold, the
imply lower fire limits. The effect can be gradual or abrupt. For
lowest positive is reported as the oxidant index.
example PTFE will not burn in the oxygen index test at room
6.2 Similar test methods apply when the oxidant concentra- temperature, but burns nicely at just a few degrees above room
tion is held constant and the temperature, pressure or other key temperature (9, 12).
factor is varied. In some cases, apparatus modification or
7.6 Flow and Propagation Schemes:
replacement is necessary, such as a pressurized vessel is
7.6.1 Variations in the flow scheme and the direction of
required to complete some tests (see Test Method G124).
propagation have dramatic effect on the fire limit. The earliest
Relatively little work (1-18) has been done using oxidants
work on oxygen index (8) demonstrated that for polymers, a
other than oxygen, diluents other than nitrogen, pressure,
much lower index resulted if the flow carried the hot combus-
temperature, or other properties as the variable parameter.
tion products over the unburned portions of a specimen. Later
work confirms the observation (9, 13, 14) (Therefore in most
7. Variations
polymer testing, lower limits were measured if the specimens
7.1 A number of variations of the procedure have been used.
were bottom ignited with upward flow or top ignited with
The principle variables have been oxidant, diluent, pressure,
downward flow than with the standard top ignition with
temperature, flow condition and flow direction. Relatively little
upward flow. The effect is similar but less dramatic with metals
work has been done for most of these variables (1-18). There
combustion. Indeed, the standard top-ignition upward-flow
is some qualitative and even quantitative understanding of the
conditions of Test Method D2863 and bottom-ignition condi-
manner in which these variables affect the fire limits of
tions of Test Method G124 were chosen to facilitate the
materials, but the understanding is largely incomplete. Finally,
measurement and its precision rather than to obtain the
the database for most combinations of variables is small (only
lowest-possible limit measurement. Similarly, in stagnant
Test Method D2863-95 and Test Method G124 have significant
systems, a concentration of inert combustion products,
databases) and so the ability to draw strong conclusions is
diluents, and even impurities in the oxidant gases can yield
limited. Nonetheless, where data is obtained for two or more
higher limits than otherwise. Limited work has been done with
materials, these data are useful to the evaluation of those
most of the combinations of vertical (upward or downward)
materials. Care is necessary in comparing materials that have
flow and vertical directions of propagation.
not been tested in similar procedures.
7.6.2 Variations in the flow scheme have been used (3, 6, 7)
7.2 Oxidants—Changing the oxidant may cause the greatest
in which a fire was established in the bore (intraluminal flame)
changes in results for other constant conditions (1, 2, 3).
of a flowing horizontal tube. These demonstrated that the effect
of diluents can be inverted at high flow rates and that there can
be an optimum velocity that yields a minimum fire limit.
G125 − 00 (2023)
7.7 Geometries: propane, or other gas flame at the end that can be inserted into
7.7.1 The influence of geometry is not well understood, but the open end of the column to ignite the test specimen. A
work shows that specimen size (8) is not a particularly suitable flame may be from 6 mm to 25 mm long.
significant variant in polymer tests performed as in Sections 8,
8.6 Timer—A suitable timer capable of indicating at least 10
9, 10, 11, 13, and 14, but that the change from rod to tubing can
min and accurate at 5 s shall be used.
have a dramatic effect on the fire limit of stainless steel but may
8.7 Soot, Fumes, and Heat Removal—To ensure the removal
have a much smaller effect on carbon steel (5).
of toxic fumes, soot, heat, and other possible noxious products,
7.7.2 Powders and liquids have been tested (15, 16) with
the column shall be installed in a hood or other facilities
slight modification of Test Method D2863-95. Typically, pow-
providing adequate exhaust.
ders have had lower fire limits than their bulk counterparts.
Few materials can be tested as both liquid and solid. However,
NOTE 6—If soot-generating specimens are being tested, the glass
column becomes coated on the inside with soot and should be cleaned as
data suggest that if materials could be tested as solids or gases,
often as necessary for good visibility.
the gases would exhibit a lower fire limit (1).
9. Test Specimens
8. Apparatus
9.1 Cut a sufficient number of specimens (normally 5 to 10)
8.1 Test Column, consisting of a heat-resistant glass tube of
from the material to be tested. Use Table 1 to determine
75 mm minimum inside diameter and 450 mm minimum
specimen dimensions.
height. The bottom of the column or the base to which the tube
9.1.1 Test the specimens in the as-received condition unless
is attached shall contain noncombustible material to mix and
otherwise agreed upon.
distribute evenly the gas mixture entering at this base. Glass
9.1.2 Moisture content of some materials has been shown to
beads 3 mm to 5 mm in diameter in a bed 80 mm to 100 mm
affect the oxygen index. Where a material is suspected to be
deep have been found suitable (an example is shown in Fig. 1).
affected by retained moisture, condition the specimens in
NOTE 3—A column with a 95 mm inside diameter and 210 mm high
accordance with Procedure A of Test Methods D618.
with a restricted upper opening (diameter = 50 mm) has been found to
give equivalent results.
NOTE 7—If non-standard size specimens are used, a difference in
NOTE 4— It is helpful to place a wire screen above the noncombustible
oxygen index may result.
material to catch falling fragments and aid in keeping the base of the
9.1.3 For Type C specimens, make comparisons only be-
column clean.
tween materials of similar densities.
8.2 Specimen Holder—Any small holding device that will
support the specimen at its base and hold it vertically in the NOTE 8—For certain types of cellular plastics, the direction of anisot-
ropy may have an effect and should be evaluated unless a particular
center of the column is acceptable. For physically self-
direction has previously been agreed upon.
supporting specimens, a typical arrangement (See Fig. 1)
9.1.4 Test Type D materials in the as-received thickness, but
consists of a laboratory thermometer clamp inserted into the
make comparisons only between material of the same thick-
end of a glass tube held in place by glass beads or otherwise
ness.
firmly supported. For other forms, such as film and thin sheet,
9.1.5 The edges of the specimens shall be relatively smooth
the frame shown in Fig. 2 shall be used and held in place by the
and free from fuzz or burrs of material left from machining.
above tube. The test specimen must be held securely along both
upright edges by the frame, using clips or other means.
10. Procedure
8.3 Gas Supply—Commercial grade (or better) oxygen and
nitrogen shall be used. If an air supply is used with oxygen or 10.1 Calibrate the flow-measuring system using a water-
sealed rotating drum meter (wet test meter) in accordance with
nitrogen, it must be clean and dry.
Test Method D1071 or by equivalent calibration devices. It is
8.4 Flow Measurements and Control Devices—Suitable
recommended that this calibration be repeated at least every six
flow measurement and control devices shall be available in
months.
each line that will allow monitoring the volumetric flow of
each gas into the column with 1 % in the range being used.
NOTE 9—One step in the calibration should be to check carefully for
leaks at all joints.
After the flow is measured in each line, the lines should be
joined to allow the gases to mix before being fed into the
10.2 The test shall be conducted at room temperature
column.
conditions in accordance with Practice D618.
NOTE 5—One satisfactory flow control consists of calibrated jeweled
10.3 Clamp the specimen vertically in the approximate
orifice
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