You are testing a tank that contained gasoline by using a combustible gas indicator. Under testing, the tank sample caused the needle to move rapidly to 100 on the dial then fall to zero. What is the concentration of flammable gas?

Correct Answer: Option D — Over the flammable range

When a combustible gas indicator needle rapidly peaks to 100 and drops to zero, the atmosphere exceeds the upper explosive limit. The extremely rich fuel concentration deprives the combustion chamber of sufficient oxygen, giving a false zero reading despite a dangerously over-rich explosive environment.