Which concentration triggers the trip of the internal combustion engine on explosion-protected LHD vehicles?

• A. 1.25%
• B. 1.0%
• C. 0.5%
• D. 2.0%

Answer: (A)

Gas monitoring on explosion-protected LHDs is set to shut the engine automatically when methane in the surrounding air reaches a level that could ignite and cause an explosion. The trigger point is 1.25% methane by volume. This threshold sits well above normal background levels but still well below the methane’s lower explosive limit (5%), providing a safety buffer to stop the engine before ignition sources in the engine compartment could ignite a leak. Choosing 1.25% balances safety with practicality, avoiding unnecessary nuisance trips that would occur if the threshold were lower, while keeping ignition risk low if methane starts to accumulate. Higher thresholds (like 2.0%) would allow more methane to build up before stopping the engine, increasing the chance of ignition, whereas lower thresholds (like 1.0% or 0.5%) would lead to more frequent shutdowns without a proportional gain in protection.