ASTM E918-83(2011)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E918 − 83 (Reapproved 2011)
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. 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 3. Terminology
1.1 This practice covers the determination of the lower and 3.1 Definitions:
upper concentration limits of flammability of combustible 3.1.1 lower limit of flammability or lower flammable limit
vapor-oxidant mixtures at temperatures up to 200°C and initial (LFL)—the minimum concentration of a combustible sub-
pressures up to as much as 1.38 MPa (200 psia). This practice stance that is capable of propagating a flame through a
is limited to mixtures which would have explosion pressures homogeneous mixture of the combustible and a gaseous
less than 13.79 MPa (2000 psia). oxidizer under the specified conditions of test.
3.1.2 upper limit of flammability or upper flammable limit
1.2 This practice should be used to measure and describe
(UFL)—the maximum concentration of a combustible sub-
the properties of materials, products, or assemblies in response
stance that is capable of propagating a flame through a
to heat and flame under controlled laboratory conditions and
homogeneous mixture of the combustible and a gaseous
should not be used to describe or appraise the fire hazard or
oxidizer under the specified conditions of test.
fire risk of materials, products, or assemblies under actual fire
conditions. However, results of this test may be used as
3.2 Definitions of Terms Specific to This Standard:
elements of a fire risk assessment which takes into account all
3.2.1 propagation of flames—as used in this practice,a
of the factors which are pertinent to an assessment of the fire
combustion reaction that produces at least a 7 % rise of the
hazard of a particular end use.
initial absolute pressure,
1.3 This standard may involve hazardous materials,
P
^1.07.
operations, and equipment. This standard does not purport to
P
address all of the safety problems associated with its use. It is
NOTE 1—This 7 % rise in pressure corresponds to 1 psia (0.007 MPa)
the responsibility of the user of this standard to establish
per atmosphere of initial pressure.
appropriate safety and health practices and determine the
4. Summary of Practice
applicability of regulatory limitations prior to use.
4.1 A mixture of gaseous or vaporized fuel with a gaseous
2. Referenced Documents oxidizer is prepared in a steel or other appropriate metal vessel
at a controlled temperature and pressure. Proportions of the
2.1 ASTM Standards:
components are determined by measurement of partial pres-
E681 Test Method for Concentration Limits of Flammability
sures during filling of the vessel. Ignition of the mixture is
of Chemicals (Vapors and Gases)
attempted with a fuse wire, and flammability is deduced from
2.2 Other Documents:
the pressure rise produced. Fuel concentration is varied be-
Bulletin 503 Bureau of Mines, “Limits of Flammability of
tween trials until the limits of flammability have been deter-
Gases and Vapors,” NTIS AD701575
mined. Composition of the mixtures which fix the flammable
Bulletin 627 Bureau of Mines, “Flammability Characteris-
limits are confirmed by appropriate analysis.
tics of Combustible Gases and Vapors,” NTIS AD701576
5. Significance and Use
5.1 Knowledgeofflammablelimitsatelevatedtemperatures
This practice is under the jurisdiction of ASTM Committee E27 on Hazard
Potential of Chemicals and is the direct responsibility of Subcommittee E27.04 on and pressures is needed for safe and economical operation of
Flammability and Ignitability of Chemicals.
some chemical processes. This information may be needed in
Current edition approved Aug. 1, 2011. Published August 2011. Originally
order to start up a reactor without passing through a flammable
approved in 1983. Last previous edition approved in 2005 as E918 – 83 (2005).
range, to operate the reactor safely and economically, or to
DOI: 10.1520/E0918-83R11.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
store or ship the product safely.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5.2 Limits of flammability data obtained in relatively clean
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. vessels must be carefully interpreted and may not always be
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E918 − 83 (2011)
applicable to industrial conditions. Surface effects due to temperature inert gas, an ignition device with appropriate
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 Bulletin 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
described in this practice is suitable for use with most mixtures
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.
7. Apparatus
8.2 The test vessel shall be fitted with a rupture disk vented
outside any enclosed area. Fuel may inadvertently be vented
7.1 Fig. 1 is a schematic diagram of the apparatus; details
inside the heated chamber or inside the enclosed area, so the
and dimensions are presented in Annex A1. The apparatus
consists of a metal pressure vessel with a minimum volume of heated chamber should be fitted with an inert gas purge and the
area should be adequately ventilated to prevent buildup of an
1 L and a minimum inside diameter of 76 mm (3 in.), an
insulated chamber equipped with a source of controlled- explosive mixture in the large space.
FIG. 1 Schematic Diagram of Test Apparatus
E918 − 83 (2011)
8.3 Undesirably energetic explosions may be produced if 10.6 Early in the test series, use an appropriate method such
tests are made at high initial pressures with mixtures well as gas chromatography to confirm composition of gas mixtures
within the flammable range. Very strong oxidizers greatly made ready for explosion test. Make any changes in technique
increase explosion severity and also greatly increase the necessary to ensure homogeneous mixture. These mixtures
fuel-rich limit. To help in avoiding testing highly energetic may not have the composition expected, due to nonideal gas
mixtures, limits of flammability should first be determined at behavior. Errors will vary with the order of mixing,
atmospheric pressure. These limits are covered in Method temperature, pressure, and the particular materials. Also, the
E681. With this knowledge, the operator should proceed in greater the dead volume in tubing etc., not involved in mixing
cautious steps of initial pressure increase to work at higher with the charge in the cylinder, the greater will be the
pressures and temperatures. difference from expected composition. If the composition is
wrong make adjustments in partial pressure to get desired
9. Preparation of Apparatus composition.
9.1 Clean and dry the test vessel and other gas-handling 10.7 Record the temperature and pressure of the test gas.
equipment. Make sure that no oil, grease, or other combustible
10.8 Activate the pressure recording equipment.
is left inside the parts.
10.9 Attempt ignition of the gas mixture by applying 115 V
9.2 Assemble the equipment as shown in Fig. 1. Purge the
across the fuse wire.
vessel with inert gas and then evacuate the system.
10.10 Record the maximum pressure.
9.3 Set the zero and gain on the pressure transducers so that
10.11 Vent the test vessel through the exhaust valve. Purge
their output represents true pressure after the test vessel is at
the vessel with inert gas from the manifold.
the working temperature.
10.12 Install another spark plug fitted with a fuse wire.
METHOD A—SAMPLE COMPONENTS WHICH
HAVE ADEQUATE VAPOR PRESSURE AT ROOM
NOTE 5—By having the spark plug positioned in front of a socket
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
wrench which fits the bushing, not the spark plug.
10. Procedure
10.13 Vary fuel concentration (percent of the total vapor
10.1 Attach pressure regulators to the supply cylinders of
pressure) as required to find the minimum concentration, L ,
gases to be used in the tests. Connect the regulators to the
that gives flame propagation and the maximum concentration,
manifold of remotely-controlled metering valves.
L , below L , that does not give flame propagation. Flame
2 1
10.2 Flush each line from the supply cylinder to the meter-
propagation by this method is defined as a pressure ratio
ing valve. Evacuate the test vessel and manifold. By use of the
P
remotely controlled valves, add to the test vessel the compo-
P
nent most appropriately added first; usually, this is the smallest
of 1.07 or more. Record values for L and L measured by
1 2
component. Close the ball valve next to the test vessel and
pressure during filling of the test vessel and by analysis of
evacuate or purge the manifold.
the mixtures. Repeat the analysis and test on composition L
to confirm its non-flammability.
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
manifold and add components until the desired partial pressure
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
NOTE 2—Both fast addition of the last component and restricting the tip
test vessel after a fuel-rich explosion.
of the dip tube are necessary to achieve homogeneity. One way to add gas
at high velocity with low risk of overshooting is to make use of a
NOTE 6—These deposits are likely to affect subsequent results. To
quick-opening dump valve on the pneumatic actuator system for the
remove the carbon insert through the spark plug hole an L-shaped piece of
metering valve. The last component should be added in less than 15 s.
6.4-mm ( ⁄4-in.) metal tubing attached by a flexible hose to an inert gas
NOTE3—Wherethevesselconfigurationwillpermit,aninternalmixing
supply. Blow inert gas vigorously around inside the test vessel until no
device may be used.
more carbon is displaced. Finish cleaning out the carbon by igniting, as if
NOTE 4—If the pressure and temperature do not hold steady after a
it were the next sample, a fuel-lean mixture such as 6 % methane in air.
component is added this may indicate reaction prior to ignition. Reaction
After trying this burn-out procedure, remove the spark plug, insert a light
of a halogen will probably cause a pressure drop. Reaction of oxygen will
bulb through the spark plug hole, and inspect the vessel for cleanliness.
probably cause a pressure rise.
Repeat the lean mixture explosion if necessary to clean the vessel.
10.4 Close the remotely controlled valve between the test
Mechanical means may also be used to remove unwanted carbon.
vesselandthelow-rangepressuretransducerinordertoprotect
10.16 Record the values for the highest fuel concentration,
this transducer from explosion pressure.
U , that will propagate a flame and the lowest concentration,
10.5 Allow the test gas mixture to equilibrate to test U , above U , that will not propagate a flame. Make duplicate
2 1
conditions. tests on U .
E918 − 83 (2011)
METHOD B—FUEL WHICH MUST BE HEATED TO difficult. Connect the needle valve to the section of fill line
REACH ITS LIMITS OF FLAMMABILITY holding the low range pressure transducer. This allows the ball
valve shown at the right side of this pressure transducer to be
11. Procedure used to 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,
for the introduction of fuel.Asmall cylinder of liquid fuel may
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
NOTE7—Thecylinderofliquidfuelmustbefittedwithapressure-relief
12.1 Calculate the lower limit of flammability (LFL) and
device which discharges outside the heated chamber and outside any other
upper limit of flammability (UFL) from the values recorded in
structure which would confine the material. Fuels which might undergo
hazardous reaction in the heated cylinder must not be tested by this 10.13 and 10.16.
procedure. If any uncertainty exists as to whether the sample may react in
LFL 5½ ~L 1L ! (1)
1 2
the heated chamber, thermal stability testing should be performed.
UFL 5½ U 1U (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. If the fuel will evaporate without fractionation, place the
percent. It is sometimes appropriate to report limits in terms of weight per
valve in contact with the vapor phase in the cylinder.
unit volume at the test conditions, part
...