Why should you wear a self－contained breathing apparatus before entering the engine room a

Why should you wear a self-contained breathing apparatus before entering the engine room after the fixed CO2 system has been discharged to combat a major fire？

A.Because carbon dioxide dilutes the oxygen concentration in the atmosphere and may cause asphyxiation

B.Because carbon dioxide breaks down in a fire into carbon monoxide which may cause blood poisoning in the person breathing this gas

C.Because carbon dioxide is a colorless and odorless gas that becomes highly toxic in the presence of high temperatures and will quickly incapacitate a person exposed to this gas

D.This action is unnecessary as carbon dioxide is not poisonous nor toxic but is a relatively harmless gas

请帮忙给出正确答案和分析，谢谢！