TICKLING THE DRAGON’S TAIL
Submitted by Captain Bill Moure
Flashover is defined as radiant heating of the contents of a room to the point where everything in the room ignites simultaneously. Training firefighters to recognize flashover conditions is very important; but also very dangerous.
While most fire victims die from smoke inhalation long before the fire reaches them, firefighters wear self contained breathing apparatus (SCBA) which allows them to work in such conditions. However, with the temperatures involved in flashover, survival time in full bunker gear is only seconds.
We start a pile of pallets on fire and wake up the dragon. He opens his eyes, looking towards the ceiling.
Training involves starting a fire in the room and allowing the temperature to rise to the point where the temperature at the ceiling reaches the ignition temperature of the fire gasses (or smoke, which contains particles of carbon as well as carbon monoxide gas both of which are flammable). As the temperature at the ceiling approaches the ignition temperature of the smoke (approximately 600 C) it begins to ignite, resulting in visible flames that appear to roll across the ceiling (called “rollover”). This releases a large amount of radiant heat which rapidly raises the temperature of everything in the room (the “convective” heat from the fire stays at the ceiling, the “radiant” heat goes in all directions and is absorbed by the walls, floor, firefighters and anything else in the room).
Waking a little more, he sits up; his heat still going to the ceiling. We toy with him; stand up and look him in the eye. Feel his heat.
He is now wide awake and looking at us. A few puffs out his nostrils roll across the ceiling.
A slap in the face and he recoils.
At this point a small amount of water is directed at the ceiling to cool the burning smoke below its ignition temperature thus controlling the flashover. Too much cooling and the smoke drops to the floor where it will kill any “victims” there. We want to keep fire going enough to keep the smoke off the floor, but ensure a flashover does not occur. It is a balancing act…we are truly “tickling the dragon’s tail”.
He is getting mad but it takes a few minutes to get his breath back.
Every time he gets puffing, we slap him in the face. Now he is really mad and ready to let loose.
We have only two choices, kill him or get out of his way. Today is his day; this is his house. We scramble out.
The firefighters have now all seen the demonstration. While the fire is being controlled, the radiant heat from the “rollovers” has continued to elevate the temperature of the walls and floor. A sure sign that the room temperature is getting too hot is when the lead instructor’s helmet visor begins to melt. The demonstration is terminated and everyone leaves the structure.
He now rampages through the house. Disappointed he cannot get to us, he looks out the front door.
Less than a minute from exiting the structure, flashover has occurred and the structure is fully involved.