1、Designation: E 681 04Standard Test Method forConcentration Limits of Flammability of Chemicals (Vaporsand Gases)1This standard is issued under the fixed designation E 681; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the lowerand upper concentration limits of flammability of chemicalshav
3、ing sufficient vapor pressure to form flammable mixtures inair at atmospheric pressure at the test temperature. This testmethod may be used to determine these limits in the presenceof inert dilution gases. No oxidant stronger than air should beused.NOTE 1The lower flammability limit (LFL) and upper
4、flammabilitylimit (UFL) are sometimes referred to as the lower explosive limit (LEL)and the upper explosive limit (UEL), respectively. However, since theterms LEL and UEL are also used to denote concentrations other than thelimits defined in this test method, one must examine the definitions closely
5、when LEL and UEL values are reported or used.1.2 This test method is based on electrical ignition andvisual observations of flame propagation. Users may experi-ence problems if the flames are difficult to observe (forexample, irregular propagation or insufficient luminescence inthe visible spectrum)
6、, if the test material requires large ignitionenergy, 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 s
7、ituations where strong ignition sources (suchas direct flame ignition) is considered credible, the use of a testmethod employing higher energy ignition source in a suffi-ciently large pressure chamber (analogous, for example, to themethods in Test Method E 2079 for measuring limiting oxygenconcentra
8、tion) may be more appropriate. In this case, expertadvice may be necessary.1.5 The flammability limits depend on the test temperatureand pressure. This test method is limited to an initial pressureof the local ambient or less, with a practical lower pressurelimit of approximately 13 kPa (100 mm Hg).
9、 The maximumpractical operating temperature of this equipment is approxi-mately 150C (302F).1.6 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are provided forinformation only.1.7 This test method should be used to measure and describethe properties
10、of materials, products, or assemblies in responseto heat and flame under controlled laboratory conditions andshould not be used to describe or appraise the fire hazard or firerisk of materials, products, or assemblies under actual fireconditions. However, results of this test method may be used asel
11、ements of a fire risk assessment that takes into account all ofthe factors pertinent to an assessment of the fire hazard of aparticular end use.1.8 This standard may involve hazardous materials, opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any,
12、associated with itsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.Specific precautionary statements are given in Section 82. Referenced Documents2.1 ASTM Standards:
13、2E 171 Specification for Standard Atmospheres for Condi-tioning and Testing Flexible Barrier MaterialsE 582 Test Method for Minimum Ignition Energy andQuenching Distance in Gaseous MixturesE 1445 Terminology Relating to Hazardous Potential ofChemicalsE 1515 Test Method for Minimum Explosible Concent
14、ra-tion of Combustible DustsE 2079 Test Methods for Limiting Oxygen (Oxidant) Con-centration in Gases and Vapors2.2 NFPA Standard:NFPA 69 Standard on Explosion Prevention Systems31This test method is under the jurisdiction of ASTM Committee E27 on HazardPotential of Chemicals and is the direct respo
15、nsibility of Subcommittee E27.04 onFlammability and Ignitability of Chemicals.Current edition approved June 1, 2004. Published July 2004. Originally approvedin 1979. Last previous edition approved in 2001 as E 681 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact AST
16、M Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from National Fire Protection Association, Batterymarch Park,Quincy, MA 02269.1Copyright ASTM International, 100 Barr Harbor Drive, P
17、O Box C700, West Conshohocken, PA 19428-2959, United States.3. Terminology3.1 Definitions:3.1.1 lower limit of flammability or lower flammable limit(LFL)the minimum concentration of a combustible sub-stance that is capable of propagating a flame in a homogeneousmixture of the combustible and a gaseo
18、us oxidizer under thespecified conditions of test.3.1.2 propagation of flameas used in this test method, theupward and outward movement of the flame front from theignition source to the vessel walls or at least to within 13 mm(12 in.) of the wall, which is determined by visual observation.By outward
19、, it is meant a flame front that has a horizontalcomponent to the movement away from the ignition source.3.1.3 upper limit of flammability or upper flammable limit(UFL)the maximum concentration of a combustible sub-stance that is capable of propagating a flame in a homogeneousmixture of the combusti
20、ble and a gaseous oxidizer under thespecified conditions of test.4. Summary of Test Method4.1 A uniform mixture of a gas or vapor with air is ignitedin a closed vessel, and the upward and outward propagation ofthe flame away from the ignition source is noted by visualobservation. The concentration o
21、f the flammable component isvaried between trials until the composition that will just sustainpropagation of the flame is determined.5. Significance and Use5.1 The LFL and UFL of gases and vapors define the rangeof flammable concentrations in air.5.2 Limits of flammability may be used to determine g
22、uide-lines for the safe handling of volatile chemicals. They are usedparticularly in assessing ventilation requirements for the han-dling of gases and vapors. NFPA 69provides guidance for thepractical use of flammability limit data, including the appro-priate safety margins to use.NOTE 2For hydrocar
23、bons, the break point between nonflammabilityand flammability occurs over a narrow concentration range at the lowerflammability 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 tohave large quenching distances and ma
24、y be difficult to ignite, such asammonia and certain halogenated hydrocarbon, the lower and upper limitsof these materials may both be less distinct. That is, a wider range existsbetween flammable and nonflammable concentrations (see Annex A1).NOTE 3This method measures the LFL and UFL for upward (a
25、ndpartially outward) flame propagation. the limits for downward flamepropagation are narrower.6. Interferences6.1 This test method is not applicable to certain readilyoxidized chemicals. If significant oxidation takes place whenthe vapors are mixed with air, unreliable results may beobtained. Flow s
26、ystems designed to minimize hold-up timemay be required for such materials.6.2 Measured flammable limits are influenced by flamequenching effects of the test vessel walls. The test vesselemployed in this test method is of sufficient size to eliminatethe effects of the flame quenching for most materi
27、als (andconditions).NOTE 4There may be quenching effects, particularly on tests run atsubambient pressures. For materials that may be difficult to ignite (seeNote 2), tests in a larger vessel or different ignition sources (see Annex A1,12-L flask) may show flame propagation that is not seen in the 5
28、-L flaskwith spark or exploding wire igniters. This test method is a small scale testand this possible limitation must be considered in hazard assessments.6.3 The oxygen concentration in the air has an importanteffect on the UFL. Typically, room air is used. If cylinder air isused to simulate room a
29、ir it must have an oxygen concentrationof 20.946 0.1 %. Reconstituted air in cylinders has variabilityin the oxygen concentration and must be verified for oxygenconcentration.7. Apparatus7.1 Fig. 1 is a schematic diagram of the apparatus; detailsand dimensions are presented in Appendix X1. The appar
30、atusconsists of a glass test vessel, an insulated chamber equippedwith a source of controlled-temperature air, an ignition devicewith an appropriate power supply, a magnetic stirrer, and acover equipped with the necessary operating connections andcomponents.7.2 If tests are to be conducted at an ele
31、vated temperature,the test vessel may be heated as described in Appendix X1. Theheating system must be capable of controlling the gas tempera-ture inside the test vessel to within 63C both temporally andspatially. An appropriate device such as a thermocouple mustbe used to monitor the gas temperatur
32、e within the test vessel.Active (connected) volumes beyond the test vessel itself shouldbe held above the condensation temperature of all componentsin the material being tested. Electrical heating tapes must beemployed for heating components to the desired temperature.NOTE 5Certain bare wire thermoc
33、ouples may cause catalytic oxida-tion of test vapors, as evidenced by a persistent high-temperatureexcursion of the temperature reading. If this occurs, other thermocouplematerials should be employed.7.3 Pressure Transducer-A low-range pressure transducermay be used for the purpose of making partial
34、 pressureadditions of gases and vapors to the test vessel. The transducerand its signal conditioning/amplifying electronics should havean accuracy, precision and repeatability sufficient to accuratelyresolve the required changes in the gas partial pressure for thecomponent used in lowest concentrati
35、on at the appropriate testtemperature. The transducer should be protected from defla-gration pressures by means of an isolation valve. An erroranalysis must be performed to demonstrate that the internalvolume of the pressure gage and piping will not significantlyaffect the test mixture.8. Safety Pre
36、cautions8.1 Tests should not be conducted in this apparatus withoxidizers stronger than air, since explosion violence increasesas oxidizer strength increases. Do not use oxygen, nitrousoxide, nitrogen dioxide, chlorine, etc., in this glass apparatus.Extra care must be used when working with compound
37、s thatare potential oxidizers.8.2 Adequate shielding must be provided to prevent injuryin the event of equipment rupture due to both implosions andexplosions. A metal enclosure, such as that recommended inAppendix X1, is one method suitable for this purpose.E6810428.2.1 Implosion of the test vessel
38、at high vacuum levels ispossible; therefore, all evacuations must be made with therequired shielding to protect against flying fragments.8.2.2 Energetic explosions may be produced if tests aremade at concentrations within the flammable range, betweenthe LFL and UFL. The glass test vessel, equipped w
39、ith a lightlyheld or loose cover, vents most explosions adequately. Never-theless, shielding is required to protect against vessel rupture.Methods for estimating initial test concentrations, discussed inAppendix X2, Appendix X3, and Appendix X4, may beemployed to ensure that initial trials are condu
40、cted at concen-trations less than the LFL or greater than the UFL.8.2.3 In rare instances, particularly in the upper limit tests,self-ignition may be encountered when air is rapidly introducedinto the partially evacuated test vessel containing the vaporizedsample. Valves permitting remote operation,
41、 changes in sampleand air introduction sequences, simple shields, and othertechniques may be employed to ensure safe operations.8.2.4 The test area should be equipped with electricalinterlocks to prevent activation of the ignition source unlessadequate shielding is in place.8.3 Tests should not be c
42、onducted on thermally unstablematerials that might undergo explosive decomposition reac-tions.8.4 Tests should be conducted in a fume hood or otherventilated area to prevent personal exposure to toxic chemicalsor combustion products.8.5 Precautions must be taken to ensure that the high-voltage spark
43、 ignition source does not contact temperature orpressure-measuring devices or other conductive paths thatcould create an electrical hazard to personnel or instrumenta-tion outside the shielded area. Careful attention to electricalinsulation integrity can reduce the possibility of hazard. Dis-connect
44、s for all instrumentation lines will provide positiveprotection.9. Calibration9.1 Accurate determination of the flask volume is necessaryfor the calculation of flammable limits when the samplemeasurement is on a weight or volume basis.9.1.1 Determine the total volume of the flask as follows:Weigh a
45、clean, dry flask with all components installed. Fill theflask with distilled water. Reinsert the cover, allowing theexcess water to overflow, dry the outside of the flask, andreweigh. Record the difference in grams as the net volume ofthe flask in cubic centimeters. (Slight errors associated withwat
46、er density differences are beyond the accuracy of this testmethod.)9.2 Calibrate pressure-, temperature-, and liquid-measuringdevices against adequate standards.10. Procedure10.1 Assemble the equipment, as shown in Fig. 1, using anappropriate fume hood or other ventilated area, and secure thedoor of
47、 the metal enclosure. The test vessel and all componentsshould be clean and dry. Evacuate the system and flush with airto ensure removal of residual volatile materials that may bepresent as a result of cleaning or prior tests. As many as threeevacuation/flush cycles may be required to ensure complet
48、eremoval of combustion products between tests.FIG. 1 Schematic Diagram of Test ApparatusE68104310.2 Adjust the flask to the desired test temperature. Thistemperature must be above the vapor condensation temperatureof the mixture being tested.10.2.1 When working at elevated temperatures and withmater
49、ials that can condense at room temperature, it may benecessary to heat or insulate cover components and feed linesseparately to prevent vapor condensation.10.3 Record the actual barometric pressure at the testlocation.10.4 Double-check to make certain that all safety precau-tions have been taken.10.5 Procedure for Sample Introduction As a Liquid:10.5.1 Ensure that sample and any combustion productsfrom previous runs have been removed. This may be accom-plished by evacuating the flask to a pressure of less than 2.7kPa (20 mm Hg).10.5.2 Place the desired liquid volume in a
