What is a danger HVAC systems pose during a structure fire?

• A. They pull in fresh air to the fire zone
• B. Ducts can move heated air and products of combustion from involved compartments to other compartments within the structure
• C. They increase airflow to suppress the fire
• D. They filter air to remove contaminants

Answer: (B)

During a structure fire, HVAC systems can become a highway for fire and smoke. The ducts and fans can move heated air and products of combustion from the compartments where the fire is burning into other parts of the building, spreading heat, smoke, and toxic gases. This cross-ventilation through the ductwork can dramatically worsen conditions on floors and in rooms that weren’t initially involved, complicating suppression and rescue efforts.

The idea that HVAC merely pulls in fresh air to the fire zone is a real concern because it can feed the fire, but the sharper hazard described here is the movement of heat and combustion products through ducts to other areas. The notion that airflow is used to suppress the fire is incorrect, as increasing airflow often fuels the fire rather than suppressing it. Filtering air to remove contaminants isn’t the primary danger in this context, and filtration systems aren’t typically reliable enough to prevent the spread of smoke and heat during a structure fire.