Large volumes of carbon dioxide are safe and effective for fighting fires in enclosed spaces, such as in a pump room, provided that the __________.

Correct Answer: Option D — ventilation system is secured and all persons leave the space

CO2 is an asphyxiant that works by oxygen displacement. To be effective, the space must be sealed to maintain the required concentration, and all personnel must evacuate to prevent suffocation. Ventilation must be secured to prevent the agent from escaping and to stop the supply of oxygen to the fire.