请输入您要查询的百科知识：

　

词条 Flammability limit
释义

  1. Violence of combustion

  2. Limits

     Lower flammability limit  Upper flammability limit  Influence of temperature, pressure and composition 

  3. Controlling explosive atmospheres

     Gas and vapor  Dusts  Volatile liquids 

  4. Examples

  5. See also

  6. References

  7. Further reading

Mixtures of dispersed combustible materials (such as gaseous or vaporised fuels, and some dusts) and air will burn only if the fuel concentration lies within well-defined lower and upper bounds determined experimentally, referred to as flammability limits or explosive limits. Combustion can range in violence from deflagration through detonation.

Limits vary with temperature and pressure, but are normally expressed in terms of volume percentage at 25 °C and atmospheric pressure. These limits are relevant both to producing and optimising explosion or combustion, as in an engine, or to preventing it, as in uncontrolled explosions of build-ups of combustible gas or dust. Attaining the best combustible or explosive mixture of a fuel and air (the stoichiometric proportion) is important in internal combustion engines such as gasoline or diesel engines.

The standard reference work is still that elaborated by Michael George Zabetakis, a fire safety engineering specialist, using an apparatus developed by the United States Bureau of Mines.

Violence of combustion

Combustion can vary in degree of violence. A deflagration is a propagation of a combustion zone at a velocity less than the speed of sound in the unreacted medium. A detonation is a propagation of a combustion zone at a velocity greater than the speed of sound in the unreacted medium. An explosion is the bursting or rupture of an enclosure or container due to the development of internal pressure from a deflagration or detonation as defined in NFPA 69.

Limits

Lower flammability limit

Lower flammability limit (LFL): The lowest concentration (percentage) of a gas or a vapor in air capable of producing a flash of fire in the presence of an ignition source (arc, flame, heat). The term is considered by many safety professionals to be the same as the lower explosive level (LEL). At a concentration in air lower than the LFL, gas mixtures are "too lean" to burn.

Methane gas has an LFL of 5.0%. If the atmosphere has less than 5.0% methane, an explosion cannot occur even if a source of ignition is present. From the health and safety perspective, the LEL concentration is considered to be Immediately Dangerous to Life or Health (IDLH), where a more stringent exposure limit does not exist for the flammable gas.[1]

Percentage reading on combustible air monitors should not be confused with the LFL concentrations. Explosimeters designed and calibrated to a specific gas may show the relative concentration of the atmosphere to the LFL—the LFL being 100%. A 5% displayed LFL reading for methane, for example, would be equivalent to 5% multiplied by 5.0%, or approximately 0.25% methane by volume at 20 degrees C. Control of the explosion hazard is usually achieved by sufficient natural or mechanical ventilation, to limit the concentration of flammable gases or vapors to a maximum level of 25% of their lower explosive or flammable limit.

Upper flammability limit

Upper flammability limit (UFL): Highest concentration (percentage) of a gas or a vapor in air capable of producing a flash of fire in the presence of an ignition source (arc, flame, heat). Concentrations higher than UFL or UEL are "too rich" to burn. Operating above the UFL is usually avoided for safety because air leaking in can bring the mixture into combustibility range.

Influence of temperature, pressure and composition

Flammability limits of mixtures of several combustible gases can be calculated using Le Chatelier's mixing rule for combustible volume fractions :

and similar for UFL.

Temperature, pressure, and the concentration of the oxidizer also influences flammability limits. Higher temperature or pressure, as well as higher concentration of the oxidizer (primarily oxygen in air), results in lower LFL and higher UFL, hence the gas mixture will be easier to explode. The effect of pressure is very small at pressures below 10 millibar and difficult to predict, since it has only been studied in internal combustion engines with a turbocharger.

Usually atmospheric air supplies the oxygen for combustion, and limits assume the normal concentration of oxygen in air. Oxygen-enriched atmospheres enhance combustion, lowering the LFL and increasing the UFL, and vice versa; an atmosphere devoid of an oxidizer is neither flammable nor explosive for any fuel concentration. Significantly increasing the fraction of inert gases in an air mixture, at the expense of oxygen, increases the LFL and decreases the UFL.

Controlling explosive atmospheres

Gas and vapor

Controlling gas and vapor concentrations outside the flammable limits is a major consideration in occupational safety and health. Methods used to control the concentration of a potentially explosive gas or vapor include use of sweep gas, an unreactive gas such as nitrogen or argon to dilute the explosive gas before coming in contact with air. Use of scrubbers or adsorption resins to remove explosive gases before release are also common. Gases can also be maintained safely at concentrations above the UEL, although a breach in the storage container can lead to explosive conditions or intense fires.

Dusts

Dusts also have upper and lower explosion limits, though the upper limits are hard to measure and of little practical importance. Lower flammability limits for many organic materials are in the range of 10–50 g/m³, which is much higher than the limits set for health reasons, as is the case for the LEL of many gases and vapours. Dust clouds of this concentration are hard to see through for more than a short distance, and normally only exist inside process equipment.

Flammability limits also depend on the particle size of the dust involved, and are not intrinsic properties of the material. In addition, a concentration above the LEL can be created suddenly from settled dust accumulations, so management by routine monitoring, as is done with gases and vapours, is of no value. The preferred method of managing combustible dust is by preventing accumulations of settled dust through process enclosure, ventilation, and surface cleaning. However, lower flammability limits may be relevant to plant design.

Volatile liquids

Situations caused by evaporation of flammable liquids into the air-filled void volume of a container may be limited by flexible container volume or by using an immiscible fluid to fill the void volume. Hydraulic tankers use displacement of water when filling a tank with petroleum.[2]

Examples

The flammable/explosive limits of some gases and vapors are given below. Concentrations are given in percent by volume of air.

  • Class IA liquids with a flash point less than {{convert|73|F|C}} and boiling point less than {{convert|100|°F|C}} have a NFPA 704 flammability rating of 4
  • Class IB liquids with a flash point less than {{convert|73|F|C}} and a boiling point equal to or greater than {{convert|100|°F|C}} and class IC liquids with a flash point equal to or greater than {{convert|73|F|C}}, but less than {{convert|100|°F|C}} have a NFPA 704 flammability rating of 3
  • Class II liquids with a flash point equal to or greater than {{convert|100|°F|C}}, but less than {{convert|140|F|C}} and class IIIA liquids with a flash point equal to or greater than {{convert|140|F|C}}, but less than {{convert|200|F|C}} have a NFPA 704 flammability rating of 2
  • Class IIIB liquids with a flash point equal to or greater than {{convert|200|F|C}} have a NFPA 704 flammability rating of 1
SubstanceLFL/LEL in %

by volume of air

UFL/UEL in %

by volume of air

NFPA ClassFlash pointMinimum ignition energy in mJ

expressed at percent by volume in air

(Note that for many chemicals it

takes the least amount of

ignition energy halfway between

the LEL and UEL.)[3]

Autoignition
temperature
Acetaldehyde4.057.0IA −39 °C0.37175 °C
Acetic acid (glacial)419.9II39 °C to 43 °C463 °C
Acetic anhydrideII54 °C
Acetone 2.6–3 12.8–13IB −17 °C1.15 @ 4.5%465 °C, 485 °C[4]
AcetonitrileIB2 °C524 °C
Acetyl chloride7.319IB5 °C390 °C
Acetylene2.5100[5]IAFlammable gas0.017 @ 8.5% (in pure oxygen 0.0002 @ 40%)305 °C
Acrolein2.831IB −26 °C0.13
Acrylonitrile3.017.0IB 0 °C0.16 @ 9.0%
Allyl chloride2.911.1IB −32 °C0.77
Ammonia1528IIIB11 °C680651 °C
Arsine4.5–5.1[6]78IAFlammable gas
Benzene1.27.8IB −11 °C0.2 @ 4.7%560 °C
1,3-Butadiene2.012IA −85 °C0.13 @ 5.2%
Butane, n-butane1.68.4IA −60 °C0.25 @ 4.7%420–500 °C
n-Butyl acetate, butyl acetate1–1.7[4]8–15IB24 °C370 °C
Butyl alcohol, butanol111IC29 °C
n-Butanol1.4[4]11.2IC35 °C340 °C
n-Butyl chloride, 1-chlorobutane1.810.1IB −6 °C1.24
n-Butyl mercaptan1.4[7]10.2IB2 °C225 °C
Butyl methyl ketone, 2-hexanone1[8]8IC25 °C423 °C
Butylene, 1-butylene, 1-butene1.98[6]9.65IA −80 °C
Carbon disulfide1.050.0IB −30 °C0.009 @ 7.8%90 °C
Carbon monoxide12[6]75IA −191 °C Flammable gas609 °C
Chlorine monoxideIAFlammable gas
1-Chloro-1,1-difluoroethane6.217.9IA −65 °C Flammable gas
Cyanogen6.0–6.6[9]32–42.6IAFlammable gas
Cyclobutane1.811.1IA −63.9 °C[10]426.7 °C
Cyclohexane1.37.8–8IB −18 °C to -20 °C[11]0.22 @ 3.8%245 °C
Cyclohexanol19IIIA68 °C300 °C
Cyclohexanone1–1.19–9.4II43.9–44 °C420 °C[12]
Cyclopentadiene[13]IB0 °C0.67640 °C
Cyclopentane1.5–29.4IB −37 to −38.9 °C[14][15]0.54361 °C
Cyclopropane2.410.4IA −94.4 °C[16]0.17 @ 6.3%498 °C
Decane0.85.4II46.1 °C210 °C
Diborane0.888IA −90 °C Flammable gas[17]38 °C
o-Dichlorobenzene, 1,2-dichlorobenzene2[18]9IIIA65 °C648 °C
1,1-Dichloroethane611IB14 °C
1,2-Dichloroethane616IB13 °C413 °C
1,1-Dichloroethene6.515.5IA −10 °C Flammable gas
Dichlorofluoromethane54.7 Non flammable,[19] -36.1 °C[20]552 °C
Dichloromethane, methylene chloride1666Non flammable
Dichlorosilane4–4.796IA −28 °C0.015
Diesel fuel0.67.5IIIA>62 °C (143 °F)210 °C
Diethanolamine213IB169 °C
Diethylamine1.810.1IB −23 to −26 °C312 °C
Diethyl disulfide1.2II38.9 °C[21]
Diethyl ether1.9–236–48IA −45 °C0.19 @ 5.1%160–170 °C
Diethyl sulfideIB −10 °C[22]
1,1-Difluoroethane3.718IA −81.1 °C[23]
1,1-Difluoroethylene5.521.3 −126.1 °C[24]
Diisobutyl ketone1649 °C
Diisopropyl ether121IB −28 °C
Dimethylamine2.814.4IAFlammable gas
1,1-DimethylhydrazineIB
Dimethyl sulfideIA −49 °C
Dimethyl sulfoxide2.6–342IIIB88–95 °C215 °C
1,4-Dioxane222IB12 °C
Epichlorohydrin42131 °C
Ethane3[6]12–12.4IAFlammable gas -135 °C515 °C
Ethanol, ethyl alcohol3–3.319IB12.8 °C (55 °F)365 °C
2-Ethoxyethanol31843 °C
2-Ethoxyethyl acetate2856 °C
Ethyl acetate212IA −4 °C460 °C
Ethylamine3.514IA −17 °C
Ethylbenzene1.07.115–20 °C
Ethylene2.736IA0.07490 °C
Ethylene glycol322111 °C
Ethylene oxide3100IA −20 °C
Ethyl chloride3.8[6]15.4IA−50 °C
Ethyl mercaptanIA
Fuel oil No.10.7[6]5
Furan214IA −36 °C
Gasoline (100 octane)1.47.6IB< −40 °C (−40 °F)246–280 °C
Glycerol319199 °C
Heptane, n-heptane1.056.7 −4 °C0.24 @ 3.4%204–215 °C
Hexane, n-hexane1.17.5 −22 °C0.24 @ 3.8%225 °C, 233 °C[4]
Hydrogen4/18.3[25]75/59IAFlammable gas0.016 @ 28% (in pure oxygen 0.0012)500–571 °C
Hydrogen sulfide4.346IAFlammable gas0.068
Isobutane1.8[6]9.6IAFlammable gas462 °C
Isobutyl alcohol21128 °C
Isophorone1484 °C
Isopropyl alcohol, isopropanol2[6]12IB12 °C398–399 °C; 425 °C[4]
Isopropyl chlorideIA
Kerosene Jet A-10.6–0.74.9–5II>38 °C (100 °F) as jet fuel210 °C
Lithium hydrideIA
2-MercaptoethanolIIIA
Methane (natural gas)5.015IAFlammable gas0.21 @ 8.5%580 °C
Methyl acetate316 −10 °C
Methyl alcohol, methanol6–6.7[6]36IB11 °C385 °C; 455 °C[4]
MethylamineIA8 °C
Methyl chloride10.7[6]17.4IA −46 °C
Methyl etherIA −41 °C
Methyl ethyl etherIA
Methyl ethyl ketone1.8[6]10IB −6 °C505–515 °C[4]
Methyl formateIA
Methyl mercaptan3.921.8IA −53 °C
Mineral spirits0.7[4]6.538–43 °C258 °C
Morpholine1.810.8IC31–37.7 °C310 °C
Naphthalene0.9[6]5.9IIIA79–87 °C540 °C
Neohexane1.19[6]7.58−29 °C425 °C
Nickel tetracarbonyl2344 °C60 °C
Nitrobenzene29IIIA88 °C
Nitromethane7.322.235 °C379 °C
Octane1713 °C
iso-Octane0.795.94
Pentane1.57.8IA −40 to −49 °Cas 2-Pentane 0.18 @ 4.4%260 °C
n-Pentane1.47.8IA0.28 @ 3.3%
iso-Pentane1.32[6]9.16IA420 °C
PhosphineIA
Propane2.19.5–10.1IAFlammable gas0.25 @ 5.2% (in pure oxygen 0.0021)480 °C
Propyl acetate2813 °C
Propylene2.011.1IA −108 °C0.28458 °C
Propylene oxide2.936IA
Pyridine21220 °C
Silane1.5[6]98IA<21 °C
Styrene1.16.1IB31–32.2 °C490 °C
TetrafluoroethyleneIA
Tetrahydrofuran212IB −14 °C321 °C
Toluene1.2–1.276.75–7.1IB4.4 °C0.24 @ 4.1%480 °C; 535 °C[4]
Triethylborane −20 °C −20 °C
TrimethylamineIAFlammable gas
TrinitrobenzeneIA
Turpentine0.8[26]IC35 °C
Vegetable oilIIIB327 °C (620 °F)
Vinyl acetate2.613.4 −8 °C
Vinyl chloride3.633
Xylenes0.9–1.06.7–7.0IC27–32 °C0.2
m-Xylene1.1[4]7IC25 °C525 °C
o-XyleneIC17 °C
p-Xylene1.06.0IC27.2 °C530 °C

See also

{{Portal|Chemistry}}
  • Flammability
  • Limiting oxygen concentration
  • Minimum ignition energy

References

1. ^{{Cite web|url=https://www.cdc.gov/niosh/docs/2014-100/pdfs/2014-100.pdf|title=Current Intelligence Bulletin #66: Derivation of Immediately Dangerous to Life or Health (IDLH) Values|last=|first=|date=November 2013|website=The National Institute for Occupational Safety and Health (NIOSH)|archive-url=|archive-date=|dead-url=|access-date=2018-02-11}}
2. ^{{cite book |last=Morrell |first=Robert W. |authorlink = |title =Oil Tankers |publisher =Simmons-Boardman Publishing Company |volume = |edition =Second |date =1931 |location =New York |pages =305&306 |isbn =}}
3. ^Britton, L. G “Using Material Data in Static Hazard Assessment.” as found in NFPA 77 - 2007 Appendix B
4. ^1 2 3 4 5 6 7 8 9 Working with modern hydrocarbon and oxygenated solvents: a guide to flammability {{webarchive |url=https://web.archive.org/web/20090601224141/http://www.americanchemistry.com/s_acc/sec_solvents.asp?CID=1488&DID=5735 |date=June 1, 2009 }} American Chemistry Council Solvents Industry Group, pg. 7, January 2008
5. ^{{cite book | last1 = Matheson Gas Products | title = Matheson Gas Data Book | pages = 443 | url = http://www.mathesongas.com/pdfs/products/Lower-(LEL)-&-Upper-(UEL)-Explosive-Limits-.pdf | accessdate = 2013-10-30}}
6. ^1 2 3 4 5 6 7 8 9 10 11 12 13 14 {{cite web | url = http://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html | title = Gases - Explosive and Flammability Concentration Limits | accessdate = 2013-09-09}}
7. ^{{cite web|url=http://www.inchem.org/documents/icsc/icsc/eics0018.htm|title=ICSC 0018 - n-BUTYL MERCAPTAN|author=|date=|website=www.inchem.org|accessdate=18 March 2018}}
8. ^{{cite web|url=http://www.oit.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc04/icsc0489.htm|title=2-HEXANONE ICSC:0489|author=|date=|website=oit.org|accessdate=18 March 2018}}
9. ^{{cite web|url=http://www.intox.org/databank/documents/chemical/cyanogen/cie430.htm|title=IPCS INTOX Site Closed|author=|date=|website=www.intox.org|accessdate=18 March 2018}}
10. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 211
11. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 216
12. ^{{cite web|url=http://www.inchem.org/documents/icsc/icsc/eics0425.htm|title=ICSC 0425 - CYCLOHEXANONE|author=|date=|website=www.inchem.org|accessdate=18 March 2018}}
13. ^{{cite web|url=http://msds.chem.ox.ac.uk/CY/cyclopentadiene.html|title=MSDS Cyclopentadiene|author=|date=|website=ox.ac.uk|accessdate=18 March 2018}}
14. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 221
15. ^{{cite web|url=http://www.inchem.org/documents/icsc/icsc/eics0353.htm|title=ICSC 0353 - CYCLOPENTANE|author=|date=|website=www.inchem.org|accessdate=18 March 2018}}
16. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 226
17. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 244
18. ^Walsh (1989) Chemical Safety Data Sheets, Roy. Soc. Chem., Cambridge.
19. ^Encyclopedia.airliquide.com{{dead link|date=October 2017 |bot=InternetArchiveBot |fix-attempted=yes }}
20. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 266
21. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 281
22. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 286
23. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 296
24. ^Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 301
25. ^{{cite web|url=http://environmentalchemistry.com/yogi/periodic/H.html|title=Periodic Table of Elements: Hydrogen - H (EnvironmentalChemistry.com)|author=|date=|website=environmentalchemistry.com|accessdate=18 March 2018}}
26. ^{{cite web|url=http://www.afcintl.com/pdf/combustibles.pdf|title=Combustibles|author=|date=|website=afcintl.com|accessdate=18 March 2018}}

Further reading

  • David R. Lide, Editor-in-Chief; CRC Handbook of Chemistry and Physics, 72nd edition; CRC Press; Boca Raton, Florida; 1991; {{ISBN|0-8493-0565-9}}

4 : Combustion|Explosion protection|Fire|Natural gas safety
随便看

　

开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。

　

Copyright © 2023 OENC.NET All Rights Reserved
京ICP备2021023879号 更新时间：2024/11/10 17:04:24