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LEL/UEL Planning Lookup

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

Field guide: LEL and UEL Source-Boundary Guide

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Free LEL/UEL planning lookup for safety professionals, gas detection technicians, and industrial hygienists. Browse supported local gas and vapor rows, convert between combustible-gas detector %LEL readings and simplified %Volume concentration, and screen a composite LEL for simple mixtures using Le Chatelier math. The rows are source-gap planning fixtures with source pointers; they are not a current NFPA/IEC table, detector calibration procedure, confined-space entry approval, hot-work permit, ventilation approval, emergency-response instruction, or regulatory compliance determination.

Pro Tip: A combustible gas detector reading of 10% LEL means the gas concentration is at 10% of that gas row's Lower Explosive Limit, not 10% by volume. For methane (local LEL row = 5.0% volume), a 10% LEL reading screens as 0.5% by volume before detector calibration, gas identity, cross-sensitivity, oxygen level, and site procedure are checked.

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How It Works

  1. Look Up a Single Gas

    Search or browse the supported local rows to screen vapor density, heavier/lighter behavior, listed LEL values, and source-warning notes. Treat every row as a source-gap fixture until it is reconciled against current primary data, SDS, manufacturer information, and site requirements.

  2. Convert %LEL to %Volume

    Enter a combustible-gas detector reading in %LEL and select the target gas row. The calculator converts to simplified %Volume concentration and shows the local zone boundary; it does not verify sensor type, calibration gas, correction factor, or alarm configuration.

  3. Calculate Mixture LEL

    For simple combustible mixtures, enter each component and volume fraction. Le Chatelier math provides an estimate only, and can be less reliable for hydrogen, carbon disulfide, reactive species, oxygen changes, aerosols, mists, dusts, or poorly characterized mixtures.

  4. Review Source Boundaries

    Use the local 10% LEL calculator, LEL boundary, UEL boundary, and above-UEL warning as prompts for qualified review. Actual alarm, evacuation, ventilation, entry, and hot-work decisions come from the detector manual, employer program, AHJ, and site procedure.

Built For

  • Confined space teams reviewing percent-LEL math before applying the written entry program and instrument procedure
  • Gas detection technicians checking how detector scale, calibration gas, and target gas affect a local reading calculator
  • Safety engineers preparing hot-work or ventilation questions for qualified site review
  • Industrial hygienists flagging when flammability, toxicity, oxygen, and detector-response issues overlap
  • Plant operators training on why above-UEL conditions can still become hazardous during dilution
  • Incident reviewers documenting assumptions before primary-source, instrument, and site records are checked

References

  1. NFPA 497 source pointer for flammable gas and vapor data context
  2. Industrial Scientific combustible-gas LEL tip sheet source pointer
  3. ISA12.13 combustible gas detector standards context
  4. MSA ALTAIR 4XR operating manual combustible cross-reference factor context
  5. NIOSH Pocket Guide to Chemical Hazards and Bureau of Mines Bulletin 627 flammability reference context

Frequently Asked Questions

LEL (Lower Explosive Limit) and LFL (Lower Flammable Limit) are commonly used for the same lower flammability boundary, with terminology varying by source and industry. Use the term and value required by the current source, SDS, detector manual, and site procedure.
Percent LEL expresses a detector display as a percentage of the selected gas row's lower limit. It is useful for relative screening, but it does not make different gases equally hazardous or bypass sensor technology, calibration gas, correction-factor, oxygen, toxicity, or site-response requirements.
Le Chatelier math is a planning approximation for some simple combustible mixtures. It can be less accurate for hydrogen-containing mixtures, carbon disulfide, reactive species, oxygen changes, inerting, aerosols, mists, dusts, and poorly characterized process streams. Critical safety decisions require current source data, instrument review, and qualified evaluation.
This app does not set evacuation, entry, hot-work, or alarm thresholds. Follow the employer program, permit conditions, detector manual, AHJ requirements, and qualified safety or industrial-hygiene direction for the specific space, gas, instrument, and task.
Disclaimer: This tool provides source-aware planning rows and source pointers only. LEL/UEL values can vary with source edition, test method, temperature, pressure, oxygen concentration, humidity, gas mixture, and measurement method. Always verify the exact substance, detector, calibration, alarm configuration, SDS, site procedure, and primary source before safety decisions. This tool is not a substitute for calibrated atmospheric monitoring, a written confined-space or hot-work program, emergency response planning, regulatory review, or professional hazard assessment.

Guides for this job

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LEL and UEL Source-Boundary Guide

What lower and upper explosive limits mean, how gas detectors use %LEL readings, and why current source data, detector calibration, and site procedures still control.

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Gas Detector Cross-Sensitivity Explained

How response factors and interfering gases affect detector readings, with source-boundary, calibration, and manufacturer-manual warnings.

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Vapor Density and Gas Accumulation

How vapor density determines where gases collect. Heavier-than-air gases in trenches and pits, lighter-than-air gases at ceilings, and ventilation.

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Multi-Gas Detector Selection Guide

How to choose the right 4-gas or 5-gas monitor. Sensor types, bump test vs calibration, battery life, and brand comparison for confined space entry.

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