Question 637 Deck Safety

The correct answer is D) incapable of supporting combustion because the hydrocarbon vapor content makes the atmosphere above the UFL (Upper Flammable Limit). The atmosphere in a tank is considered "too rich" when the hydrocarbon vapor content is above the upper flammable limit (UFL), making the atmosphere incapable of supporting combustion. When the vapor concentration is above the UFL, there is not enough oxygen present to sustain a fire or explosion, even if an ignition source is introduced. The other options are incorrect because A) a noncombustible state does not indicate a "too rich" atmosphere, B) an atmosphere capable of supporting combustion is not considered "too rich," and C) an atmosphere below the lower flammable limit (LFL) is not "too rich" but rather "too lean" to support combustion.