1、Designation: E681 09Standard Test Method forConcentration Limits of Flammability of Chemicals (Vaporsand Gases)1This standard is issued under the fixed designation E681; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 chemicalshaving
3、 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 fla
4、mmabilitylimit (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 closelywhe
5、n 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), i
6、f 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 situ
7、ations 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 E2079 for measuring limiting oxygenconcentration
8、) 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). The
9、 maximumpractical operating temperature of this equipment is approxi-mately 150C.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.7 This test method should be used to measure and describethe properties of materials, product
10、s, 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 aselements of a fire risk
11、 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, associated with itsus
12、e. 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:2E171 Specification f
13、or Atmospheres for Conditioning andTesting Flexible Barrier MaterialsE582 Test Method for Minimum Ignition Energy andQuenching Distance in Gaseous MixturesE1445 Terminology Relating to Hazard Potential of Chemi-calsE1515 Test Method for Minimum Explosible Concentrationof Combustible DustsE2079 Test
14、Methods for Limiting Oxygen (Oxidant) Con-centration in Gases and Vapors2.2 NFPA Standard:NFPA 69 Standard on Explosion Prevention Systems33. Terminology3.1 Definitions:1This test method is under the jurisdiction of ASTM Committee E27 on HazardPotential of Chemicals and is the direct responsibility
15、of Subcommittee E27.04 onFlammability and Ignitability of Chemicals.Current edition approved Oct. 1, 2009. Published January 2010. Originallyapproved in 1979. Last previous edition approved in 2004 as E681 04. DOI:10.1520/E0681-09.2For referenced ASTM standards, visit the ASTM website, www.astm.org,
16、 orcontact ASTM 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 (NFPA), 1 BatterymarchPark, Quincy, MA 02169-7471, http:/www.nfpa.org.1Copyri
17、ght ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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 combu
18、stible and a gaseous 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 obse
19、rvation.By outward, 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 homogeneousmixtu
20、re of the combustible and a gaseous oxidizer under thespecified conditions of test.3.2 Additional terms can be found in Terminology E1445.4. 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 fr
21、om the ignition source is noted by visualobservation. The concentration of 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 co
22、ncentrations in air.5.2 This method measures the LFL and UFL for upward(and partially outward) flame propagation. The limits fordownward flame propagation are narrower.5.3 Limits of flammability may be used to determine guide-lines for the safe handling of volatile chemicals. They are usedparticular
23、ly in assessing ventilation requirements for the han-dling of gases and vapors. NFPA 69 provides guidance for thepractical use of flammability limit data, including the appro-priate safety margins to use.5.4 As discussed in Brandes and Ural4, there is a fundamen-tal difference between the ASTM and E
24、uropean methods forflammability determination. The ASTM methods aim to pro-duce the best representation of flammability parameters, andrely upon the safety margins imposed by the applicationstandards, such as NFPA 69. On the other hand, European testmethods aim to result in a conservative representa
25、tion offlammability parameters. For example, in this standard, LFL isthe calculated average of the lowest go and highest no-goconcentrations while the European test methods report the LFLas the minimum of the 5 highest no-go concentrations.NOTE 2For hydrocarbons, the break point between nonflammabil
26、ityand 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 may be difficult to ignite, such asammonia a
27、nd 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).6. Interferences6.1 This test method is not applicable to certain readilyoxidized chemicals. If si
28、gnificant oxidation takes place whenthe vapors are mixed with air, unreliable results may beobtained. Flow systems 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 vesselemplo
29、yed in this test method is of sufficient size to eliminatethe effects of the flame quenching for most materials (andconditions).NOTE 3There 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
30、or different ignition sources (seeAnnexA1,12-L flask) may show flame propagation that is not seen in the 5-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
31、 has an importanteffect on the UFL. Typically, room air is used. If cylinder air isused to simulate room air 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
32、. 1 is a schematic diagram of the apparatus; detailsand dimensions are presented in Appendix X1. The apparatusconsists 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
33、equipped with the necessary operating connections andcomponents.7.2 If tests are to be conducted at an elevated temperature,the test vessel may be heated as described inAppendix X1. Theheating system must be capable of controlling the gas tempera-ture inside the test vessel to within 63C both tempor
34、ally andspatially. An appropriate device such as a thermocouple mustbe used to monitor the gas temperature 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 heatin
35、g tapes must beemployed for heating components to the desired temperature.NOTE 4Certain bare wire thermocouples 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 empl
36、oyed.7.3 Pressure Transducer-A low-range pressure transducermay be used for the purpose of making partial pressureadditions of gases and vapors to the test vessel. The transducerand its signal conditioning/amplifying electronics should havean accuracy, precision and repeatability sufficient to accur
37、atelyresolve the required changes in the gas partial pressure for thecomponent used in lowest concentration at the appropriate testtemperature. The transducer should be protected from defla-gration pressures by means of an isolation valve. An error4Brandes, Elizabetg and Erdem A. Ural, 9Towards a Gl
38、obal Standard forFlammability Determination,9 42nd Annual Loss Prevention Symposium, NewOrleans, LA, April 2008.E681 092analysis must be performed to demonstrate that the internalvolume of the pressure gage and piping will not significantlyaffect the test mixture.8. Safety Precautions8.1 Tests shoul
39、d 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 compounds thatare potential oxi
40、dizers.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.8.2.1 Implosion of the test vessel at high vacuum levels ispossib
41、le; 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 with a lightlyheld or loose cov
42、er, 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 conducted at concen-trations less t
43、han 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, changes in sampleand air intr
44、oduction 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 conducted on thermally unstable
45、materials 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 ignition source does not cont
46、act 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-connects for all instrumentation line
47、s 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 clean, dry flask with all comp
48、onents 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 ofFIG. 1 Schematic Diagram of Test ApparatusE681 093the flask in cubic centimeters. (Slight error
49、s associated withwater 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 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/fl
