How should a gas detector be set up when multiple gases are present?

Many our customers often ask the same question:
If there are several different combustible(flammable) gases leaking in one area, and their mixing ratios are not fixed, How many types of gas detectors need to be installed?
The answer is one.

Combustible gas detection is based on the Lower Explosive Limit (LEL) of gases. If multiple flammable gases are present at a site, we should first identify the LEL of each gas. The alarm should be set according to the gas with the lowest LEL value, because it is the most dangerous.
For example:
Assume the site contains the following combustible gases:
Methane (CH₄): LEL 5.0%
Ethylene (C₂H₄): LEL 2.8%
Propylene (C₃H₆): LEL 2.4%
Hydrogen (H₂): LEL 4.0%
Ethanol: LEL 3.4%
Among them, propylene has the lowest LEL (2.4%).
Therefore, the gas detector alarm should be set based on propylene. If propylene leaks and triggers the alarm, the concentrations of the other gases will still be within a safe range.
Why One Setting Is Enough?
The measuring range of a combustible gas detector is 0–100% LEL. This means the detector divides 2.4% (propylene LEL) into 100 equal parts.
Typical alarm settings are:
Low alarm: 25% LEL
High alarm: 50% LEL
When the high alarm (50% LEL) is triggered, the actual gas concentration is about 1.2%, which is still far below the explosive concentration of propylene. However, corrective action must be taken immediately, because continuous leakage may quickly lead to dangerous levels.

Requirements for Toxic and Combustible Gas Detection:
In areas with toxic gas production, use, storage, or transportation, gas detection alarms should be installed according to the following rules:
1.Combustible gas with toxic components
If leakage may cause combustible gas to reach 25% LEL, but toxic gas does not reach the maximum allowable concentration,
→ Install a combustible gas detector.
2.Toxic gas with combustible components
If leakage may cause toxic gas to reach the maximum allowable concentration, but combustible gas does not reach 25% LEL,
→ Install a toxic gas detector.
3.Gas that is both toxic and combustible
→ Only a toxic gas detector is required.
4.Areas where combustible gas and toxic gas exist at the same time
→ Install both combustible gas detectors and toxic gas detectors.

If you need our gas detection and analysis instruments or are looking to expand your business, please contact us. We’d be happy to discuss more product details with you:

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