ASTM E918-83(2005)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:E918–83(Reapproved2005)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope Bulletin627 Bureau of Mines, “Flammability Characteris-
tics of Combustible Gases and Vapors,” NTISAD701576
1.1 This practice covers the determination of the lower and
upper concentration limits of flammability of combustible
3. Terminology
vapor-oxidant mixtures at temperatures up to 200°C and initial
3.1 Definitions:
pressures up to as much as 1.38 MPa (200 psia). This practice
3.1.1 lower limit of flammability or lower flammable limit
is limited to mixtures which would have explosion pressures
(LFL)—the minimum 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
3.1.2 upper limit of flammability or upper flammable limit
should not be used to describe or appraise the fire hazard or
(UFL)—the maximum concentration of a combustible sub-
fire risk of materials, products, or assemblies under actual fire
stance that is capable of propagating a flame through a
conditions. However, results of this test may be used as
homogeneous mixture of the combustible and a gaseous
elements of a fire risk assessment which takes into account all
oxidizer under the specified conditions of test.
of the factors which are pertinent to an assessment of the fire
3.2 Definitions of Terms Specific to This Standard:
hazard of a particular end use.
3.2.1 propagation of flames—as used in this practice,a
1.3 This standard may involve hazardous materials, opera-
combustion reaction that produces at least a 7% rise of the
tions, and equipment. This standard does not purport to
initial absolute pressure,
address all of the safety problems associated with its use. It is
P
the responsibility of the user of this standard to establish
^1.07.
P
appropriate safety and health practices and determine the
applicability of regulatory limitations prior to use.
NOTE 1—This 7% rise in pressure corresponds to 1 psia (0.007 MPa)
per atmosphere of initial pressure.
2. Referenced Documents
4. Summary of Practice
2.1 ASTM Standards:
E681 Test Method for Concentration Limits of Flammabil-
4.1 A mixture of gaseous or vaporized fuel with a gaseous
ity of Chemicals (Vapors and Gases)
oxidizerispreparedinasteelorotherappropriatemetalvessel
2.2 Other Documents:
at a controlled temperature and pressure. Proportions of the
Bulletin503 Bureau of Mines, “Limits of Flammability of
components are determined by measurement of partial pres-
Gases and Vapors,” NTIS AD701575
sures during filling of the vessel. Ignition of the mixture is
attempted with a fuse wire, and flammability is deduced from
the pressure rise produced. Fuel concentration is varied be-
This practice is under the jurisdiction of ASTM Committee E27 on Hazard
tween trials until the limits of flammability have been deter-
Potential of Chemicals and is the direct responsibility of Subcommittee E27.04 on
mined. Composition of the mixtures which fix the flammable
Flammability and Ignitability of Chemicals.
limits are confirmed by appropriate analysis.
Current edition approved Sept. 15, 2005. Published December 2005. Originally
approved in 1983. Last previous edition approved in 1999 as E918–83(1999).
5. Significance and Use
DOI: 10.1520/E0918-83R05.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.1 Knowledgeofflammablelimitsatelevatedtemperatures
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
and pressures is needed for safe and economical operation of
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. some chemical processes. This information may be needed in
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E918–83 (2005)
ordertostartupareactorwithoutpassingthroughaflammable and dimensions are presented in Annex A1. The apparatus
range, to operate the reactor safely and economically, or to consists of a metal pressure vessel with a minimum volume of
store or ship the product safely. 1 L and a minimum inside diameter of 76 mm (3 in.), an
5.2 Limits of flammability data obtained in relatively clean insulated chamber equipped with a source of controlled-
vessels must be carefully interpreted and may not always be temperature inert gas, an ignition device with appropriate
applicable to industrial conditions. Surface effects due to power supply, remotely controlled valves, pressure measuring
carbon deposits and other materials can significantly affect equipment, and a venting system for handling overpressuring.
limits of flammability, especially in the fuel-rich region. Refer
8. Safety Precautions
to Bulletin503 and Bulletin627.
8.1 Adequate shielding must be provided to prevent injury
6. Limitations
in the event of equipment rupture. The apparatus is set up so
6.1 This practice is not applicable to mixtures which un-
that the operator is isolated by a blast-proof wall from the test
dergo spontaneous reaction before ignition is attempted. vesselwhilethevesselcontainsachargeofreactants,including
6.2 Measured limits of flammability are influenced by
the time while the vessel is being filled. The test apparatus
flame-quenching effects of the test vessel walls. The vessel should be equipped with interlocks so that the ignition source
describedinthispracticeissuitableforusewithmostmixtures
cannot be activated unless the operator has taken necessary
at elevated temperatures and pressures. For certain amines, steps to protect personnel and equipment. Activation of the
halogenated materials etc., which have large ignition-
ignition source should be possible only from a position
quenching distances, tests may need to be conducted in larger
shielded from the test vessel.
diameter vessels.
8.2 The test vessel shall be fitted with a rupture disk vented
outside any enclosed area. Fuel may inadvertently be vented
7. Apparatus
inside the heated chamber or inside the enclosed area, so the
7.1 Fig. 1 is a schematic diagram of the apparatus; details heatedchambershouldbefittedwithaninertgaspurgeandthe
FIG. 1 Schematic Diagram of Test Apparatus
E918–83 (2005)
area should be adequately ventilated to prevent buildup of an 10.6 Earlyinthetestseries,useanappropriatemethodsuch
explosive mixture in the large space. asgaschromatographytoconfirmcompositionofgasmixtures
8.3 Undesirably energetic explosions may be produced if
made ready for explosion test. Make any changes in technique
tests are made at high initial pressures with mixtures well necessary to ensure homogeneous mixture. These mixtures
within the flammable range. Very strong oxidizers greatly
may not have the composition expected, due to nonideal gas
increase explosion severity and also greatly increase the
behavior. Errors will vary with the order of mixing, tempera-
fuel-rich limit. To help in avoiding testing highly energetic
ture,pressure,andtheparticularmaterials.Also,thegreaterthe
mixtures, limits of flammability should first be determined at
dead volume in tubing etc., not involved in mixing with the
atmospheric pressure. These limits are covered in Method
charge in the cylinder, the greater will be the difference from
E681. With this knowledge, the operator should proceed in
expected composition. If the composition is wrong make
cautious steps of initial pressure increase to work at higher
adjustments in partial pressure to get desired composition.
pressures and temperatures.
10.7 Record the temperature and pressure of the test gas.
10.8 Activate the pressure recording equipment.
9. Preparation of Apparatus
10.9 Attempt ignition of the gas mixture by applying 115V
9.1 Clean and dry the test vessel and other gas-handling
across the fuse wire.
equipment. Make sure that no oil, grease, or other combustible
10.10 Record the maximum pressure.
is left inside the parts.
10.11 Vent the test vessel through the exhaust valve. Purge
9.2 Assemble the equipment as shown in Fig. 1. Purge the
vessel with inert gas and then evacuate the system. the vessel with inert gas from the manifold.
9.3 Set the zero and gain on the pressure transducers so that
10.12 Install another spark plug fitted with a fuse wire.
their output represents true pressure after the test vessel is at
NOTE 5—By having the spark plug positioned in front of a socket
the working temperature.
wrench-sized hole in the wall of the heated chamber, the plug can be
changed without appreciably cooling off the chamber. Use a deep socket
METHOD A—SAMPLE COMPONENTS WHICH
wrench which fits the bushing, not the spark plug.
HAVE ADEQUATE VAPOR PRESSURE AT ROOM
TEMPERATURE 10.13 Vary fuel concentration (percent of the total vapor
pressure) as required to find the minimum concentration, L ,
10. Procedure that gives flame propagation and the maximum concentration,
L , below L , that does not give flame propagation. Flame
10.1 Attach pressure regulators to the supply cylinders of 2 1
propagation by this method is defined as a pressure ratio
gases to be used in the tests. Connect the regulators to the
manifold of remotely-controlled metering valves.
P
10.2 Flush each line from the supply cylinder to the meter- P
ing valve. Evacuate the test vessel and manifold. By use of the
of 1.07 or more. Record values for L and L measured by
1 2
remotely controlled valves, add to the test vessel the compo-
pressure during filling of the test vessel and by analysis of the
nentmostappropriatelyaddedfirst;usually,thisisthesmallest
mixtures. Repeat the analysis and test on composition L to
component. Close the ball valve next to the test vessel and
confirm its non-flammability.
evacuate or purge the manifold.
10.3 Add the second component up to the desired pressure, 10.14 Commence upper limit tests in the nonflammable
as measured by the transducer. Repeat the clearing of the region at a concentration greater than the anticipated U . (See
manifoldandaddcomponentsuntilthedesiredpartialpressure 10.16.) Fuel concentration at the upper limit may be substan-
of each component has been added to the test vessel. Obtain
tially greater at elevated temperature and pressure than it is at
mixing of gas in the test vessel by adding the largest compo- atmospheric conditions.
nent last and at high velocity.
10.15 Remove any carbon deposits that may be left in the
test vessel after a fuel-rich explosion.
NOTE 2—Bothfastadditionofthelastcomponentandrestrictingthetip
ofthediptubearenecessarytoachievehomogeneity.Onewaytoaddgas
NOTE 6—These deposits are likely to affect subsequent results. To
at high velocity with low risk of overshooting is to make use of a
removethecarboninsertthroughthesparkplugholeanL-shapedpieceof
quick-opening dump valve on the pneumatic actuator system for the
6.4-mm ( ⁄4-in.) metal tubing attached by a flexible hose to an inert gas
metering valve. The last component should be added in less than 15 s.
supply. Blow inert gas vigorously around inside the test vessel until no
NOTE 3—Wherethevesselconfigurationwillpermit,aninternalmixing
more carbon is displaced. Finish cleaning out the carbon by igniting, as if
device may be used.
it were the next sample, a fuel-lean mixture such as 6% methane in air.
NOTE 4—If the pressure and temperature do not hold steady after a
After trying this burn-out procedure, remove the spark plug, insert a light
component is added this may indicate reaction prior to ignition. Reaction
bulb through the spark plug hole, and inspect the vessel for cleanliness.
of a halogen will probably cause a pressure drop. Reaction of oxygen will
Repeat the lean mixture explosion if necessary to clean the vessel.
probably cause a pressure rise.
Mechanical means may also be used to remove unwanted carbon.
10.4 Close the remotely controlled valve between the test
10.16 Record the values for the highest fuel concentration,
vesselandthelow-rangepressuretransducerinordertoprotect
this transducer from explosion pressure. U , that will propagate a flame and the lowest concentration,
U , above U , that will not propagate a flame. Make duplicate
10.5 Allow the test gas mixture to equilibrate to test
2 1
conditions. tests on U .
E918–83 (2005)
METHOD B—FUEL WHICH MUST BE HEATED TO Connect the needle valve to the section of fill line holding the
REACH ITS LIMITS OF FLAMMABILITY low range pressure transducer. This allows the ball valve
shownattherightsideofthispressuretransducertobeusedto
11. Procedure keep fuel from condensing outside the heated chamber.
11.3 After the vessel is evacuated, add the fuel component
11.1 Set up the equipment as described in MethodAexcept
first.Withthedesiredamountoffuelpressureinthetestvessel,
fortheintroductionoffuel.Asmallcylinderofliquidfuelmay
proceed with the test starting with the last sentence of 10.2.
be placed in the heated chamber with the test vessel or heated
separately.
12. Calculations
NOTE 7—The cylinder of liquid fuel must be fitted with a pressure-
12.1 Calculate the lower limit of flammability (LFL) and
reliefdevicewhichdischargesoutsidetheheatedchamberandoutsideany
upper limit of flammability (UFL) from the values recorded in
other structure which would confine the material. Fuels which might
10.13 and 10.16.
undergo hazardous reaction in the heated cylinder must not be tested by
this procedure. If any uncertainty exists as to whether the sample may
LFL 5 ½ ~L 1 L ! (1)
1 2
reactintheheatedchamber,thermalstabilitytestingshouldbeperformed.
UFL 5 ½ ~ U 1 U ! (2)
1 2
11.2 Fit the fuel cylinder with a remotely controlled needle
NOTE 8—Limit concentrations are usually reported in terms of volume
valve.Ifthefuelwillevaporatewithoutfractionation,placethe
percent.Itissometimesappropriatetoreportlimitsintermsofweightper
valve in contact with the vapor phase in the cylinder. Other-
unit volume at the test conditions, particularly with multicomponent fuels
wise, place the needle valve in contact with the liquid phase
or materials exhibiting a high degree of nonideal vapor phase behavior.
even though th
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