What methane concentration prohibits equipment operation?

• A. 0.5% or above
• B. 0.1% or above
• C. 1.0% or above
• D. 2.0% or above

Answer: (C)

In gassy underground mining, there is a specific safety threshold for when equipment must be shut down due to methane in the air. Methane can ignite from sparks, hot surfaces, or electrical arcing, so rules set a clear stop point to protect workers. The common standard used is that once methane reaches 1.0% by volume in the mine atmosphere, equipment operation must stop and the area must be ventilated and gas levels reduced. This 1.0% figure balances safety with practical operations. The other options are not the standard prohibiting limit: lower thresholds would be unnecessarily conservative, and while 2.0% is also dangerous, the recognized limit to stop equipment is 1.0% or higher.