What is a 'flashover' and how might vertical ventilation influence its occurrence?

• A. Flashover is rapid, simultaneous ignition of fuels in a space; premature ventilation can introduce air and accelerate flashover if not timed with interior operations.
• B. Flashover is the cooling of fire; ventilation reduces that effect.
• C. Flashover is a type of water hiss; vertical ventilation causes it.
• D. Flashover is when the roof collapses due to heat; ventilation prevents.

Answer: (A)

Flashover is a rapid transition in a room or compartment where heat and flames cause everything capable of burning to ignite almost simultaneously, making the environment extremely dangerous in a very short time. Vertical ventilation can influence this by changing how much fresh air reaches the fire and how heat and gases escape. If ventilation is opened too early or without coordination with interior attack, the added oxygen can feed the fire and push it toward flashover faster. When ventilation is timed with suppression efforts and interior operations, it can help remove heat and smoke and reduce the likelihood of an uncontrolled ignition, but the key idea is that introducing air without coordination can accelerate flashover.