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