For combustible (LEL) sensors: calibrate on methane, then multiply the %LEL reading by the gas factor to get the true %LEL — or set the factor in the instrument. Calibrating on n-pentane instead? Divide each factor by 2.1.
| Gas / vapour | 100% LEL (vol%) | Factor (methane cal) |
|---|---|---|
| Methane (cal ref) | 4.4 | ×1.0 |
| Ethane | 2.5 | ×1.5 |
| n-Butane | 1.4 | ×2.3 |
| Isobutane | 1.3 | ×2.1 |
| n-Pentane | — | ×2.1 |
| n-Hexane | 1.0 | ×2.0 |
| n-Heptane | 1.1 | ×2.2 |
| Hydrogen | 4.0 | ×0.9 |
| Ethylene | 2.3 | ×1.3 |
| Acetylene | 2.3 | ×2.8 |
| Ethanol | 3.1 | ×1.7 |
| Methanol | 5.5 | ×1.5 |
| Isopropanol (IPA) | 2.0 | ×1.9 |
| Acetone | 2.5 | ×1.7 |
| Benzene | 1.2 | ×1.8 |
| Cyclohexane | 1.2 | ×1.8 |
| Ammonia | 15.0 | ×0.9 |
| Carbon monoxide | 10.9 | ×1.3 |
⚠️ Reference only — always verify against the instrument’s own documentation and your calibration gas before field use. Toxic (electrochemical) sensors use different cross-sensitivity data.
Source: RAE Systems by Honeywell — Technical Note TN-205, “Correction Factors for Combustible Gas (LEL) Sensors” (EMEA, per EN61779). View note ›
Official Crowcon manuals — opens the PDF. All links verified live.