Question 18Safety & Environmental - 1st Asst/Chief

The correct answer is D) Carbon monoxide. Carbon monoxide is the poisonous gas most likely to be found in a closed compartment involved in a fire. This is because carbon monoxide is a byproduct of incomplete combustion, which often occurs in fires with limited oxygen supply, such as in a closed compartment. Carbon monoxide is an odorless, colorless gas that can be fatal in high concentrations. The other options are incorrect because nitrogen and hydrogen are not inherently poisonous, and carbon dioxide, while potentially dangerous in high concentrations, is not as immediately toxic as carbon monoxide in a fire scenario.