What two factors most often determine occupant tenability during a fire?

• A. Heat/temperature and toxic gas concentration in the smoke.
• B. Humidity and outside wind speed.
• C. Time of day and occupancy density.
• D. Exterior wind speed only.

Answer: (A)

Tenability in a fire is determined primarily by the heat exposure and the concentration of toxic gases in the smoke. Heat controls how quickly the skin and airways burn and how much heat stress the body can tolerate, while toxic gases like carbon monoxide and hydrogen cyanide impair oxygen delivery and can cause unconsciousness or death even before extreme heat is reached. These two factors together set whether occupants can survive long enough to evacuate or stay safe in place.

Other factors like humidity and outside wind speed can influence how smoke moves and how comfortable it feels, but they don’t define the immediate physiological limits of survival. Time of day and how many people are present affect evacuation dynamics, not the core conditions inside that determine tenability. Exterior wind speed alone doesn’t establish tenability since it doesn’t reflect the actual heat and gas levels occupants are exposed to.