For methane detectors on explosion-protected LHD vehicles powered by a battery or internal combustion engine, which sequence of actions occurs as methane concentration increases?

• A. Alarm at 0.75%, trip ICE at 1.25%, trip power at 2%
• B. Alarm at 1%, trip internal combustion engine at 1.25%, trip power to electricity supply at 2%
• C. Alarm at 0.25%, trip at 0.5%, and hold
• D. Alarm at 2%, trip at 3%

Answer: (B)

A graduated response to rising methane levels is being tested here. As methane concentration increases, you want to warn first, then remove ignition sources in steps. Triggering an alarm at about 1% methane gives the operator a clear warning that gas is present and increasing, so actions can be taken promptly. If concentration climbs to roughly 1.25%, the system trips the internal combustion engine, removing a primary potential ignition source from the vehicle. If methane continues to rise to about 2%, the system then trips the electrical power supply, cutting off energy to further reduce the risk of sparks or electrical ignition. This sequence—alarm at 1%, engine shutdown at 1.25%, and power shutdown at 2%—provides a safe, escalating response that matches how ignition sources are progressively suppressed as gas levels become more hazardous.