Jump to content

Flammability limit

(Redirected from Explosive limit)

Mixtures of dispersed combustible materials (such as gaseous or vaporised fuels, and some dusts) and oxygen in the 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 in 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

[edit]

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

[edit]

Lower flammability limit

[edit]

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 4.4%.[1] If the atmosphere has less than 4.4% 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.[2]

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 4.4%, or approximately 0.22% 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

[edit]

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

[edit]

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.

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 (except for gases that can energetically decompose even in the absence of an oxidizer, such as acetylene). 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

[edit]

Gas and vapor

[edit]

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

[edit]

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

[edit]

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.[3]

Examples

[edit]

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 73 °F (23 °C) and boiling point less than 100 °F (38 °C) have a NFPA 704 flammability rating of 4
  • Class IB liquids with a flash point less than 73 °F (23 °C) and a boiling point equal to or greater than 100 °F (38 °C) and class IC liquids with a flash point equal to or greater than 73 °F (23 °C), but less than 100 °F (38 °C) have a NFPA 704 flammability rating of 3
  • Class II liquids with a flash point equal to or greater than 100 °F (38 °C), but less than 140 °F (60 °C) and class IIIA liquids with a flash point equal to or greater than 140 °F (60 °C), but less than 200 °F (93 °C) have a NFPA 704 flammability rating of 2
  • Class IIIB liquids with a flash point equal to or greater than 200 °F (93 °C) have a NFPA 704 flammability rating of 1
SubstanceFlammability limit (%vol.)NFPA
class
Flash
point
Minimum ignition energy (mJ)
@ proportion in air at which achieved[a][4]
Autoignition
temperature
LowerUpper
Acetaldehyde4.057.0IA−39 °C0.37175 °C
Acetic acid (glacial)419.9II39–43 °C463 °C
Acetic anhydrideII54 °C
Acetone2.6–312.8–13IB−17 °C1.15 @ 4.5%465 °C, 485 °C[5]
AcetonitrileIB2 °C524 °C
Acetyl chloride7.319IB5 °C390 °C
Acetylene2.5100[6]IAFlammable gas0.017 @ 8.5%; 0.0002 @ 40%, in pure oxygen305 °C
Acrolein2.831IB−26 °C0.13
Acrylonitrile3.017.0IB0 °C0.16 @ 9.0%
Allyl chloride2.911.1IB−32 °C0.77
Ammonia1528IIIB11 °C680651 °C
Arsine4.5–5.1[7]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[5]8–15IB24 °C370 °C
2-Butanol1.79.829 °C405 °C
Isobutanol1.710.922–27 °C415 °C
n-Butanol1.4[5]11.2IC35 °C340 °C
n-Butyl chloride, 1-chlorobutane1.810.1IB−6 °C1.24
n-Butyl mercaptan1.4[8]10.2IB2 °C225 °C
Butyl methyl ketone, 2-hexanone1[9]8IC25 °C423 °C
Butylene, 1-butylene, 1-butene1.98[7]9.65IA−80 °C
Carbon disulfide1.050.0IB−30 °C0.009 @ 7.8%90 °C
Carbon monoxide12[7]75IA−191 °C Flammable gas609 °C
Chlorine monoxideIAFlammable gas
1-Chloro-1,1-difluoroethane6.217.9IA−65 °C Flammable gas
Cyanogen6.0–6.6[10]32–42.6IAFlammable gas
Cyclobutane1.811.1IA−63.9 °C[11]426.7 °C
Cyclohexane1.37.8–8IB−18 – −20 °C[12]0.22 @ 3.8%245 °C
Cyclohexanol19IIIA68 °C300 °C
Cyclohexanone1–1.19–9.4II43.9–44 °C420 °C[13]
Cyclopentadiene[14]IB0 °C0.67640 °C
Cyclopentane1.5–29.4IB−37 – −38.9 °C[15][16]0.54361 °C
Cyclopropane2.410.4IA−94.4 °C[17]0.17 @ 6.3%498 °C
Decane0.85.4II46.1 °C210 °C
Diborane0.888IA−90 °C Flammable gas[18]38 °C
o-Dichlorobenzene, 1,2-dichlorobenzene2[19]9IIIA65 °C648 °C
1,1-Dichloroethane611IB14 °C
1,2-Dichloroethane616IB13 °C413 °C
1,1-Dichloroethene6.515.5IA−10 °C Flammable gas
Dichlorofluoromethane54.7Non flammable,[20] −36.1 °C[21]552 °C
Dichloromethane, methylene chloride1666Non flammable
Dichlorosilane4–4.796IA−28 °C0.015
Diesel fuel0.67.5IIIA>62 °C210 °C
Diethanolamine213IB169 °C
Diethylamine1.810.1IB−23 – −26 °C312 °C
Diethyl disulfide1.2II38.9 °C[22]
Diethyl ether1.9–236–48IA−45 °C0.19 @ 5.1%160–170 °C
Diethyl sulfideIB−10 °C[23]
1,1-Difluoroethane3.718IA−81.1 °C[24]
1,1-Difluoroethylene5.521.3−126.1 °C[25]
Difluoromethane14.4[26]
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[7]12–12.4IAFlammable gas, −135 °C515 °C
Ethanol, ethyl alcohol3–3.319IB12.8 °C365 °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[7]15.4IA−50 °C
Ethyl mercaptanIA
Fuel oil No.10.7[7]5
Furan214IA−36 °C
Gasoline (100 octane)1.47.6IB< −40 °C246–280 °C
Glycerol319199 °C
Heptane, n-heptane1.056.7−4 °C0.24 @ 3.4%204–215 °C
Hexane, n-hexane1.27.5−22 °C0.24 @ 3.8%225 °C, 233 °C[5]
Hydrogen4/18.3[27]75/59IAFlammable gas0.016 @ 28%; 0.0012, in pure oxygen500–571 °C
Hydrogen sulfide4.346IAFlammable gas0.068
Isobutane1.8[7]9.6IAFlammable gas462 °C
Isobutyl alcohol21128 °C
Isophorone1484 °C
Isopropyl alcohol, isopropanol2[7]12IB12 °C398–399 °C; 425 °C[5]
Isopropyl chlorideIA
Kerosene Jet A-10.6–0.74.9–5II>38 °C, as jet fuel210 °C
Lithium hydrideIA
2-MercaptoethanolIIIA
Methane (natural gas)ISO101565.014.3IAFlammable gas0.21 @ 8.5%580 °C
IEC60079-20-14.417
Methyl acetate316−10 °C
Methyl alcohol, methanol6–6.7[7]36IB11 °C385 °C; 455 °C[5]
MethylamineIA8 °C
Methyl chloride10.7[7]17.4IA−46 °C
Methyl etherIA−41 °C
Methyl ethyl etherIA
Methyl ethyl ketone1.8[7]10IB−6 °C505–515 °C[5]
Methyl formateIA
Methyl mercaptan3.921.8IA−53 °C
Mineral spirits0.7[5]6.538–43 °C258 °C
Morpholine1.810.8IC31–37.7 °C310 °C
Naphthalene0.9[7]5.9IIIA79–87 °C540 °C
Neohexane1.19[7]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 – −49 °C0.18 @ 4.4%, as 2-pentane260 °C
n-Pentane1.47.8IA0.28 @ 3.3%
iso-Pentane1.32[7]9.16IA420 °C
PhosphineIA
Propane2.19.5–10.1IAFlammable gas0.25 @ 5.2%; 0.0021, in pure oxygen480 °C
Propyl acetate2813 °C
Propylene2.011.1IA−108 °C0.28458 °C
Propylene oxide2.936IA
Pyridine21220 °C
Silane1.5[7]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[5]
Triethylborane−20 °C−20 °C
TrimethylamineIAFlammable gas
TrinitrobenzeneIA
Turpentine0.8[28]IC35 °C
Vegetable oilIIIB327 °C
Vinyl acetate2.613.4−8 °C
Vinyl chloride3.633
Xylenes0.9–1.06.7–7.0IC27–32 °C0.2
m-Xylene1.1[5]7IC25 °C525 °C
o-XyleneIC17 °C
p-Xylene1.06.0IC27.2 °C530 °C
  1. ^ Note that for many chemicals it takes the least amount of ignition energy halfway between the LEL and UEL.

ASTM E681

[edit]
Duration: 18 seconds.
Image of a flame of R-32 (Difluoromethane) near its LFL in a 12 L ASTM E-681 apparatus.[26]

In the U.S. the most common method of measuring LFLs and UFLs is ASTM E681.[26] This standard test is required for HAZMAT Class 2 Gases and for determining refrigerant flammability classifications. This standard uses visual observations of flame propagation in 5 or 12 L spherical glass vessels to measure the flammability limits. Flammable conditions are defined as those for which a flame propagates outside a 90° cone angle.

See also

[edit]

References

[edit]
  1. ^ "Gases - Explosion and Flammability Concentration Limits".
  2. ^ "Current Intelligence Bulletin #66: Derivation of Immediately Dangerous to Life or Health (IDLH) Values" (PDF). The National Institute for Occupational Safety and Health (NIOSH). November 2013. Retrieved 11 February 2018.
  3. ^ Morrell, Robert W. (1931). Oil Tankers (Second ed.). New York: Simmons-Boardman Publishing Company. pp. 305&306.
  4. ^ Britton, L. G "Using Material Data in Static Hazard Assessment." as found in NFPA 77 - 2007 Appendix B
  5. ^ Jump up to: a b c d e f g h i j Working with modern hydrocarbon and oxygenated solvents: a guide to flammability Archived June 1, 2009, at the Wayback Machine American Chemistry Council Solvents Industry Group, pg. 7, January 2008
  6. ^ Matheson Gas Products. Matheson Gas Data Book (PDF). p. 443. Archived from the original (PDF) on 30 September 2019. Retrieved 30 October 2013.
  7. ^ Jump up to: a b c d e f g h i j k l m n o "Gases - Explosive and Flammability Concentration Limits". Retrieved 9 September 2013.
  8. ^ "ICSC 0018 - n-BUTYL MERCAPTAN". www.inchem.org. Retrieved 18 March 2018.
  9. ^ "2-HEXANONE ICSC:0489". oit.org. Retrieved 18 March 2018.
  10. ^ "IPCS INTOX Site Closed". www.intox.org. Retrieved 18 March 2018.
  11. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 211
  12. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 216
  13. ^ "ICSC 0425 - CYCLOHEXANONE". www.inchem.org. Retrieved 18 March 2018.
  14. ^ "MSDS Cyclopentadiene". ox.ac.uk. Archived from the original on 7 December 2010. Retrieved 18 March 2018.
  15. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 221
  16. ^ "ICSC 0353 - CYCLOPENTANE". www.inchem.org. Retrieved 18 March 2018.
  17. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 226
  18. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 244
  19. ^ Walsh (1989) Chemical Safety Data Sheets, Roy. Soc. Chem., Cambridge.
  20. ^ "Encyclopedia.airliquide.com" (PDF). Archived from the original (PDF) on 26 May 2020. Retrieved 25 June 2023.
  21. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 266
  22. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 281
  23. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 286
  24. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 296
  25. ^ Yaws, Carl L.; Braker, William; Matheson Gas Data Book Published by McGraw-Hill Professional, 2001 pg. 301
  26. ^ Jump up to: a b c Kim, Dennis K.; Klieger, Alexandra E.; Lomax, Peter Q.; Mccoy, Conor G.; Reymann, Jonathan Y.; Sunderland, Peter B. (14 September 2018). "An improved test method for refrigerant flammability limits in a 12 L vessel". Science and Technology for the Built Environment. 24 (8): 861–866. Bibcode:2018STBE...24..861K. doi:10.1080/23744731.2018.1434381. ISSN 2374-4731. S2CID 139489210.
  27. ^ "Periodic Table of Elements: Hydrogen - H (EnvironmentalChemistry.com)". environmentalchemistry.com. Retrieved 18 March 2018.
  28. ^ "Combustibles" (PDF). afcintl.com. Archived from the original (PDF) on 3 March 2016. Retrieved 18 March 2018.

Further reading

[edit]
  • 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
Arc.Ask3.Ru: конец переведенного документа.
Arc.Ask3.Ru
Номер скриншота №: 3bb45fdbefdf60e9fd5f9c1eb836cfb1__1721392680
URL1:https://arc.ask3.ru/arc/aa/3b/b1/3bb45fdbefdf60e9fd5f9c1eb836cfb1.html
Заголовок, (Title) документа по адресу, URL1:
Flammability limit - Wikipedia
Данный printscreen веб страницы (снимок веб страницы, скриншот веб страницы), визуально-программная копия документа расположенного по адресу URL1 и сохраненная в файл, имеет: квалифицированную, усовершенствованную (подтверждены: метки времени, валидность сертификата), открепленную ЭЦП (приложена к данному файлу), что может быть использовано для подтверждения содержания и факта существования документа в этот момент времени. Права на данный скриншот принадлежат администрации Ask3.ru, использование в качестве доказательства только с письменного разрешения правообладателя скриншота. Администрация Ask3.ru не несет ответственности за информацию размещенную на данном скриншоте. Права на прочие зарегистрированные элементы любого права, изображенные на снимках принадлежат их владельцам. Качество перевода предоставляется как есть. Любые претензии, иски не могут быть предъявлены. Если вы не согласны с любым пунктом перечисленным выше, вы не можете использовать данный сайт и информация размещенную на нем (сайте/странице), немедленно покиньте данный сайт. В случае нарушения любого пункта перечисленного выше, штраф 55! (Пятьдесят пять факториал, Денежную единицу (имеющую самостоятельную стоимость) можете выбрать самостоятельно, выплаичвается товарами в течение 7 дней с момента нарушения.)