ASTM E918-83(1999)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:E918–83(Reapproved1999)
Standard Practice for
Determining Limits of Flammability of Chemicals at Elevated
Temperature and Pressure
This standard is issued under the fixed designation E918; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 lower limit of flammability or lower flammable limit
(LFL)—the minimum concentration of a combustible sub-
1.1 This practice covers the determination of the lower and
stance that is capable of propagating a flame through a
upper concentration limits of flammability of combustible
homogeneous mixture of the combustible and a gaseous
vapor-oxidant mixtures at temperatures up to 200°C and initial
oxidizer under the specified conditions of test.
pressures up to as much as 1.38 MPa (200 psia). This practice
3.1.2 upper limit of flammability or upper flammable limit
is limited to mixtures which would have explosion pressures
(UFL)—the maximum concentration of a combustible sub-
less than 13.79 MPa (2000 psia).
stance that is capable of propagating a flame through a
1.2 This practice should be used to measure and describe
homogeneous mixture of the combustible and a gaseous
the properties of materials, products, or assemblies in response
oxidizer under the specified conditions of test.
to heat and flame under controlled laboratory conditions and
3.2 Definitions of Terms Specific to This Standard:
should not be used to describe or appraise the fire hazard or
3.2.1 propagation of flames— as used in this practice,a
fire risk of materials, products, or assemblies under actual fire
combustion reaction that produces at least a 7% rise of the
conditions. However, results of this test may be used as
initial absolute pressure,
elements of a fire risk assessment which takes into account all
of the factors which are pertinent to an assessment of the fire P
^1.07.
P
hazard of a particular end use.
1.3 This standard may involve hazardous materials, opera-
NOTE 1—This 7% rise in pressure corresponds to 1 psia (0.007 MPa)
tions, and equipment. This standard does not purport to
per atmosphere of initial pressure.
address all of the safety problems associated with its use. It is
4. Summary of Practice
the responsibility of the user of this standard to establish
appropriate safety and health practices and determine the
4.1 A mixture of gaseous or vaporized fuel with a gaseous
applicability of regulatory limitations prior to use.
oxidizerispreparedinasteelorotherappropriatemetalvessel
at a controlled temperature and pressure. Proportions of the
2. Referenced Documents
components are determined by measurement of partial pres-
2.1 ASTM Standards:
sures during filling of the vessel. Ignition of the mixture is
E681 Test Method for Limits of Flammability of Chemi-
attempted with a fuse wire, and flammability is deduced from
cals
the pressure rise produced. Fuel concentration is varied be-
2.2 Other Documents:
tween trials until the limits of flammability have been deter-
Bulletin 503, Bureau of Mines, “Limits of Flammability of
mined. Composition of the mixtures which fix the flammable
Gases and Vapors,” NTIS AD701575
limits are confirmed by appropriate analysis.
Bulletin 627, Bureau of Mines, “Flammability Characteris-
5. Significance and Use
tics of Combustible Gases and Vapors,” NTISAD701576
5.1 Knowledgeofflammablelimitsatelevatedtemperatures
3. Terminology
and pressures is needed for safe and economical operation of
3.1 Definitions:
some chemical processes. This information may be needed in
ordertostartupareactorwithoutpassingthroughaflammable
range, to operate the reactor safely and economically, or to
This practice is under the jurisdiction of ASTM Committee E-27 on Hazard
store or ship the product safely.
Potential of Chemicalsand is the direct responsibility of Subcommittee E27.04on
5.2 Limits of flammability data obtained in relatively clean
Flammability and Ignition of Chemicals.
vessels must be carefully interpreted and may not always be
Current edition approved Feb. 25, 1982. Published April 1983.
Annual Book of ASTM Standards, Vol 14.02. applicable to industrial conditions. Surface effects due to
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E918
carbon deposits and other materials can significantly affect power supply, remotely controlled valves, pressure measuring
limits of flammability, especially in the fuel-rich region. Refer equipment, and a venting system for handling overpressuring.
to Bulletin 503 and 627.
8. Safety Precautions
6. Limitations
8.1 Adequate shielding must be provided to prevent injury
6.1 This practice is not applicable to mixtures which un-
in the event of equipment rupture. The apparatus is set up so
dergo spontaneous reaction before ignition is attempted.
that the operator is isolated by a blast-proof wall from the test
6.2 Measured limits of flammability are influenced by
vesselwhilethevesselcontainsachargeofreactants,including
flame-quenching effects of the test vessel walls. The vessel
the time while the vessel is being filled. The test apparatus
describedinthispracticeissuitableforusewithmostmixtures
should be equipped with interlocks so that the ignition source
at elevated temperatures and pressures. For certain amines,
cannot be activated unless the operator has taken necessary
halogenated materials etc., which have large ignition-
steps to protect personnel and equipment. Activation of the
quenching distances, tests may need to be conducted in larger
ignition source should be possible only from a position
diameter vessels.
shielded from the test vessel.
8.2 The test vessel shall be fitted with a rupture disk vented
7. Apparatus
outside any enclosed area. Fuel may inadvertently be vented
inside the heated chamber or inside the enclosed area, so the
7.1 Fig. 1 is a schematic diagram of the apparatus; details
heatedchambershouldbefittedwithaninertgaspurgeandthe
and dimensions are presented in Annex A1. The apparatus
area should be adequately ventilated to prevent buildup of an
consists of a metal pressure vessel with a minimum volume of
explosive mixture in the large space.
1 L and a minimum inside diameter of 76 mm (3 in.), an
insulated chamber equipped with a source of controlled- 8.3 Undesirably energetic explosions may be produced if
temperature inert gas, an ignition device with appropriate tests are made at high initial pressures with mixtures well
FIG. 1 Schematic Diagram of Test Apparatus
E918
within the flammable range. Very strong oxidizers greatly 10.6 Earlyinthetestseries,useanappropriatemethodsuch
increase explosion severity and also greatly increase the asgaschromatographytoconfirmcompositionofgasmixtures
fuel-rich limit. To help in avoiding testing highly energetic
made ready for explosion test. Make any changes in technique
mixtures, limits of flammability should first be determined at necessary to ensure homogeneous mixture. These mixtures
atmospheric pressure. These limits are covered in Method
may not have the composition expected, due to nonideal gas
E681. With this knowledge, the operator should proceed in
behavior. Errors will vary with the order of mixing, tempera-
cautious steps of initial pressure increase to work at higher
ture,pressure,andtheparticularmaterials.Also,thegreaterthe
pressures and temperatures.
dead volume in tubing etc., not involved in mixing with the
charge in the cylinder, the greater will be the difference from
9. Preparation of Apparatus
expected composition. If the composition is wrong make
9.1 Clean and dry the test vessel and other gas-handling
adjustments in partial pressure to get desired composition.
equipment. Make sure that no oil, grease, or other combustible
10.7 Record the temperature and pressure of the test gas.
is left inside the parts.
10.8 Activate the pressure recording equipment.
9.2 Assemble the equipment as shown in Fig. 1. Purge the
10.9 Attempt ignition of the gas mixture by applying 115V
vessel with inert gas and then evacuate the system.
across the fuse wire.
9.3 Set the zero and gain on the pressure transducers so that
their output represents true pressure after the test vessel is at 10.10 Record the maximum pressure.
the working temperature.
10.11 Vent the test vessel through the exhaust valve. Purge
the vessel with inert gas from the manifold.
METHOD A—SAMPLE COMPONENTS WHICH
10.12 Install another spark plug fitted with a fuse wire.
HAVE ADEQUATE VAPOR PRESSURE AT ROOM
TEMPERATURE
NOTE 5—By having the spark plug positioned in front of a socket
wrench-sized hole in the wall of the heated chamber, the plug can be
10. Procedure
changed without appreciably cooling off the chamber. Use a deep socket
10.1 Attach pressure regulators to the supply cylinders of wrench which fits the bushing, not the spark plug.
gases to be used in the tests. Connect the regulators to the
10.13 Vary fuel concentration (percent of the total vapor
manifold of remotely-controlled metering valves.
pressure) as required to find the minimum concentration, L ,
10.2 Flush each line from the supply cylinder to the meter-
that gives flame propagation and the maximum concentration,
ing valve. Evacuate the test vessel and manifold. By use of the
L , below L , that does not give flame propagation. Flame
2 1
remotely controlled valves, add to the test vessel the compo-
propagation by this method is defined as a pressure ratio
nentmostappropriatelyaddedfirst;usually,thisisthesmallest
P
component. Close the ball valve next to the test vessel and
P
evacuate or purge the manifold.
10.3 Add the second component up to the desired pressure,
of 1.07 or more. Record values for L and L measured by
1 2
as measured by the transducer. Repeat the clearing of the
pressure during filling of the test vessel and by analysis of the
manifoldandaddcomponentsuntilthedesiredpartialpressure
mixtures. Repeat the analysis and test on composition L to
of each component has been added to the test vessel. Obtain
confirm its non-flammability.
mixing of gas in the test vessel by adding the largest compo-
10.14 Commence upper limit tests in the nonflammable
nent last and at high velocity.
region at a concentration greater than the anticipated U . (See
NOTE 2—Bothfastadditionofthelastcomponenta
...