LEL (Lower Explosive Limit)
LEL is the lowest concentration of flammable gas in air that can ignite. In confined space work, gas levels must stay below 5% LEL for safe entry.
Ask Chalkline about this →LEL stands for Lower Explosive Limit (also called Lower Flammable Limit or LFL). It is the lowest concentration of a flammable gas or vapour in air at which ignition can occur. Below the LEL, the mixture is too lean to ignite; above the LEL, ignition is possible.
In confined space work on residential sites, the atmospheric monitoring threshold for safe entry is that flammable gas concentrations must remain below 5% of the LEL. At 5% LEL, workers must evacuate immediately. The thresholds are set by AS/NZS 2865:2009 and the model WHS Regulations. Common flammable gases encountered in residential confined spaces include methane (from decomposing organic matter under sub-floor voids) and natural gas (from leaks in service chambers).
Atmospheric monitors used before and during confined space entry measure multiple gases simultaneously: oxygen content, LEL for flammable gases, hydrogen sulfide (H2S), and carbon monoxide (CO) are the standard four-gas configuration.
Also known as: lower flammable limit (LFL)
Category: WHS / confined space
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Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.