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LEL/UEL Lookup & Explosive Range Calculator

Look up Lower and Upper Explosive Limits for common gases and vapors, calculate mixture LEL, and convert between %LEL and %Volume

Free LEL/UEL reference and explosive range calculator for safety professionals, gas detection technicians, and industrial hygienists. Look up Lower Explosive Limit and Upper Explosive Limit for 80+ combustible gases and vapors from NFPA 497 and IEC 60079-20-1 reference data. Calculate the composite LEL for gas mixtures using Le Chatelier's rule. Convert between %LEL readings on a combustible gas detector and actual %Volume concentration. Includes flash point cross-reference and auto-ignition temperature for each substance.

Pro Tip: A combustible gas detector reading of 10% LEL means the gas concentration is at 10% of the Lower Explosive Limit, not 10% by volume. For methane (LEL = 5.0% volume), a 10% LEL reading means the actual concentration is only 0.5% by volume. Confusing these two scales is one of the most common errors in gas detection work.

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LEL/UEL Lookup & Explosive Range Calculator
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How It Works

  1. Look Up a Single Gas

    Search or browse the gas database to find the LEL, UEL, flash point, and auto-ignition temperature for any combustible substance. Data sourced from NFPA 497 and IEC 60079-20-1.

  2. Convert %LEL to %Volume

    Enter a combustible gas detector reading in %LEL and select the target gas. The calculator converts to actual %Volume concentration and shows where the reading falls relative to the explosive range.

  3. Calculate Mixture LEL

    For environments with multiple combustible gases, enter each component and its volume fraction. Le Chatelier's rule calculates the composite LEL for the mixture.

  4. Assess the Hazard Level

    Review the results against common action levels: 10% LEL (alarm setpoint per OSHA), 25% LEL (evacuation per many facility procedures), and 50% LEL (IDLH atmosphere for some gases).

Built For

  • Confined space entry teams verifying atmospheric conditions before and during entry per OSHA 1910.146
  • Gas detection technicians setting alarm thresholds and understanding instrument readings
  • Safety engineers conducting hot work permit atmospheric assessments
  • Industrial hygienists evaluating explosive atmospheres in NEC Class I hazardous locations
  • Plant operators monitoring LEL in process areas with combustible gas release potential
  • Fire investigators determining whether gas concentrations were within the explosive range

References

  • NFPA 497: Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations
  • IEC 60079-20-1: Explosive atmospheres - Material characteristics for gas and vapour classification
  • OSHA 29 CFR 1910.146: Permit-Required Confined Spaces
  • Le Chatelier, H. (1891): Estimation of firedamp by flammability limits, Annales des Mines

Frequently Asked Questions

They are the same thing. LEL (Lower Explosive Limit) and LFL (Lower Flammable Limit) are interchangeable terms. The NFPA uses "flammable" while OSHA and most gas detection manufacturers use "explosive." The numerical values are identical.
Expressing concentration as a percentage of the LEL normalizes the hazard across different gases. A reading of 50% LEL means the same level of explosion risk whether the gas is methane, propane, or hydrogen, even though the actual volume concentrations are very different. This makes it easier for workers to assess the hazard without memorizing LEL values for every gas.
Le Chatelier's rule provides a reasonable approximation for most simple hydrocarbon mixtures commonly encountered in industrial settings. It can be less accurate for mixtures containing hydrogen, carbon disulfide, or highly reactive species. For critical safety decisions involving unusual mixtures, consider laboratory testing of the specific mixture.
OSHA 1910.146 requires continuous atmospheric monitoring during confined space entry, with the atmosphere tested before entry. Most facility procedures set the first alarm at 10% LEL and require evacuation at 25% LEL. Some industries and permit conditions require lower thresholds. Always follow your facility's specific confined space program and hot work permit requirements.
Disclaimer: This tool provides reference data compiled from NFPA 497, IEC 60079-20-1, and other published sources. LEL/UEL values can vary with temperature, pressure, oxygen concentration, and measurement method. Always verify data against the primary source for critical safety decisions. This tool is not a substitute for professional atmospheric monitoring and hazard assessment.

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