Analytical · Glossary
What is Lower Explosive Limit?
Symbol: LEL% by volume in airAnalytical
Lower explosive limit is the lowest concentration of a flammable gas in air that can ignite; below it the mixture is too lean.
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Lower Explosive Limit Explained
Gas detectors show flammable gas as % LEL: 100 % LEL is the LEL concentration. The upper explosive limit (UEL) is the richest mixture that can burn.
IEC 60079-20-1 gives LEL values for many gases.
Lower Explosive Limit Formula
LELmix = 100 ÷ Σ (Ci ÷ LELi)
| Ci | % of each fuel in the fuel mixture |
| LELi | LEL of each fuel (% vol) |
Example: Equal methane (4.4 %) and propane (1.7 %): LELmix ≈ 2.45 % vol (Le Chatelier).
Lower Explosive Limit: Typical Values
| Methane | 4.4 % vol (IEC 60079-20-1) |
| Propane | 1.7 % vol |
| Hydrogen | 4.0 % vol |
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Calculators for Lower Explosive Limit
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Frequently Asked Questions
What is Lower Explosive Limit?
Lower explosive limit is the lowest concentration of a flammable gas in air that can ignite; below it the mixture is too lean.
Why do LEL values differ between sources?
Older data used 5 % for methane; IEC 60079-20-1 gives 4.4 %. Detectors must use the same basis.
What alarm levels are usual?
Often about 20 % LEL low and 40 % LEL high, set by the fire and gas philosophy.
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