If there has been a fire in a closed unventilated compartment it may be unsafe to enter because of __________.

Correct Answer: Option D — a lack of oxygen

Fires consume oxygen rapidly in enclosed, unventilated spaces. Even after the flames are extinguished, the atmosphere may remain oxygen-deficient, posing a severe asphyxiation hazard. Personnel must never enter such a compartment without self-contained breathing apparatus and proper testing to ensure the oxygen content is at safe levels.