Explosive And Flammable Atmospheres

Explosive or Flammable Atmospheres

Oxygen Enrichment

  • Proportionally increases the rate of many chemical reactions
  • Can cause normal combustible materials to turn out to be flammable or explosive
  • Many standards (which includes USA 29 CFR 1910.146) Specify 23.five % as oxygen enriched
    • Other codes (along with USA 29 CFR 1915 and NFPA guidelines) are extra stringent
    • More conservative technique is to apply 22.5 % as dangerous condition threshold

Lower Explosive Limit (L.E.L.)

  • Minimum concentration of a flamable gas or vapor in air for you to ignite if a supply of ignition is gift

Upper Explosive Limit (U.E.L.)

  • Most but now not all flamable gases have an explos info higher explosive restriction
    • Maximum concentration in air so as to support combustion
    • Concentrations which might be above the U.E.L. are too “wealthy” to burn

Flammability Range

  • The range among the L.E.L. and the U.E.L. of a combustible gasoline or liquid
  • Concentrations in the flammable variety will burn or explode if a source of ignition is present

Common Flammability Range

Fuel GasLEL (%VOL) UEL (%VOL)Acetylene2.2 85Ammonia15 28Benzene1.three 7.1Butane 1.eight 8.4Carbon Monoxide12 75Ethylene2.7 36Ethylene oxide3.zero 100Ethyl Alcohol3.3 19Fuel Oil #1 (Diesel)0.7 5Hydrogen 4 75Isobutylenel1.eight 9Isopropyl Alcohol2 12Gasoline1.4 7.6Kerosine0.7 5Methane5 15MEK1.8 10Hexane1.1 7.5Pentane1.five 7.8Propane2.1 10.1Toluene1.2 7.1p-Xylene 1.1 7.0The Lower Explosion Limit (LEL) awareness for methane is 5.zero% extent

Over-Limit Protection

  • LEL sensor most effective designed to locate zero-one hundred% LEL concentration of flammable fuel
  • If O2 attention much less than 10% O2, LEL sensor will not examine nicely
  • Also, sensor may be damaged through exposure to better than 100% LEL concentrations
  • To save you harm, sensor is switched OFF, the alarms are activated, and instrument indicates an “OL” message (Over Limit)
  • CSA 22.2 stipulates latched “OL” alarm can not be set higher than 60% LEL

According to Preamble to OSHA 1910.146

  • A combustible chance exists every time the flamable fuel awareness exceeds 10% LEL
  • This is the general dangerous circumstance threshold, NOT the concentration that have to usually be used for the LEL alarm set-point
  • According to the original preamble to 1910.146, if Alternate Entry Procedures are used, the danger condition threshold is 5% LEL
  • In some cases it can be necessary to apply an excellent decrease alarm placing to permit employees ok time to break out

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