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FLASHOVER
July-Newsletter by Vincent Dunn-Flashover
Flashover! It is the most dangerous time of a fire. When the room bursts into flame, flashover has occurred. The
scientific definition of flashover states it is caused by the radiation feedback of heat. Heat from the growing fire is
absorbed into the upper walls and contents of the room, heating up the combustible gases and furnishings to
their auto-ignition temperature. This build up of heat in the room triggers flashover. Flashover signals several
major changes in a fire and is the end of an effective search and rescue in a room; It means the death of any
person trapped in the blazing room - either civilians or firefighters. It signals the end of using a portable
extinguisher to extinguish the fire; an attack hose-line is required after flashover occurs. It signals the end of the
growth stage and that the fire is in the second stage of combustion - the fully developed stage. Finally, flashover
signals the change from a contents to a structure fire. This is the beginning of the collapse danger. When
operating at a fire, Chiefs and firefighters want to delay flashover inside a burning room. By delaying flashover you
can "buy" several minutes which may be critical. For example, you may want to delay flashover to make a search
and rescue of the burning room or allow a firefighter to go above a fire to make a rescue of a trapped victim. Or,
you may want to delay flashover to gain several minutes when there is a delay in the placement of the first attack
hose-line. Three ways to delay flashover:venting: By venting windows of a burning room you release the build up
of heat in the room. This slows down flashover in addition to improving visibility in a smoke-filled room. not
venting- by not venting and instead closing the door to the burning room, you can also delay flashover. By not
venting, you starve the fire of oxygen, which slows down the combustion rate, which slows down the build up of
heat in the room. (See chart for when to vent and when not to vent.) This may be done when there is a delay in
stretching a hose-line and all persons are out of the burning room. portable extinguisher: The discharge of a
portable extinguisher can cool the heat down in a burning room temporarily and delay flashover. To avoid getting
trapped by flashover, firefighters must know the warning signs of flashover.
Warning signs of flashover There are two warning signs, which may signal the danger of flashover: heat mixed
with smoke and "rollover."
Heat: When heat mixes with smoke, it forces a firefighter to crouch down on hands and knees to enter a room to
perform search and rescue. This must be considered a warning sign that flashover may occur. Heat is the
triggering event for flashover. If the heat in the smoke filled room causes us to crouch down near the floor, we
must consider the danger of flashover.
Rollover: Rollover is defined, as sporadic flashes of flame mixed with smoke at ceiling level. Rollover is caused
by heated combustible gases in smoke, which ignites into flashes of flame when mixed with oxygen in the air.
Rollover precedes flashover. Rollover is another warning sign of flashover, which may be seen in the smoke
coming out of the tops of doorways or window openings of burning rooms before flashover occurs. When
searching for the location of a fire and there is no discernible heat in the smoke or signs of rollover, firefighters
may enter and proceed for some distance into a fire area. However, If one of these warning signs is discovered
and a flashover danger exists, defensive search procedures must be used by firefighters. Standard tactics and
procedures must be curtailed and defensive search and rescue procedures substituted when there is a danger of
flashover.
Defensive search procedures:There are two defensive search procedures that can reduce the risk of death
and injury from flashover: At a doorway: A firefighter should check behind the door for the victim, then enter the
hallway or room not more than five feet, sweep the floor, look for unconscious persons, call out and listen for a
response. If no response is forthcoming, close the door and wait for the hose-line. As the attack hose-line
advances, conduct a search and rescue behind the line, searching room and space outward from the hose-line.
At a window: When climbing a ladder placed at a window and the window breaks from either the heat of the fire or
because it is opened by the firefighters at the top of the ladder, and smoke and signs of rollover are seen in the
smoke, the firefighter should not enter the burning window. Instead the firefighter should crouch down below the
heat and sweep the area below the windowsill with a tool. In some instances a person may collapse at the
window and fall right below the sill. If a victim is found, a firefighter on the ladder might be able to crouch below
the heated smoke and flashes of flames mixed with smoke coming out the window and pull the victim to safety
on the ladder.
Point of no return
After a flashover occurs, firefighters may have past the point of no return. The point of no return is a distance
inside a burning room beyond which a searching firefighter will not escape and will not reach the door or window
entered. How far inside a burning room can a firefighter be and still escape back out the door alive and not suffer
serious bums after a flashover occurs? How far into the burning room that appears about to flashover should a
firefighter go? Five feet is the point of no return after the room explodes into a flashover. We can figure this
distance out by putting together several facts. For example, tests conducted in 1960 in California discovered that
fire temperatures of 280'-320' F cause intense pain and damage to exposed skin. Also the average temperature
in a room that flashes over is 1000' to 1500' F. And, time and motion tests in the Handbook of Fire Protection
reveal that the average person moves 2-1/2-feet per second when walking. Now, the question is how long can a
firefighter take 1000'-1500' F on the neck, ears, wrists and any other exposed portion of the body? I say two
seconds. If there is 1000' F flame in a burning room that has just flashed over and a firefighter is five feet inside
the room, and crawls back to the doorway at 2-1/2-feet per second, he will feel 1000'-1500' F on exposed
portions of skin not covered by fire gear for two seconds. If you say you can enter 10 feet into a room about to
flashover and it does, and you try to escape you will experience 1000' -1500' F on the exposed portions of your
body for four seconds. Think about it.
Lessons learned Firefighters should know the definition of flashover. They should know the warning signs of this
danger heat in smoke and rollover. Also firefighters must know how to delay flashover - a room bursting into
flames. And most important for firefighters' safety and survival, they must know defensive firefighting procedures
- how to search and stay alive.
Firefighting questions
True or False
1. Flashover is the most dangerous phase of fire growth.
Answer_______
2. According to fire protection engineers flashover is caused by which one of the following?
A. Radiation heat
B. Radiation feedback heat
C. Conduction heat
D. None of the above
Answer_______
3. Flashover signals major changes at a fire, which one of the following is not one of them?
A. The end of the search and entry
B. The end of using a portable extinguisher to fully extinguish the blaze
C. The end of the growth stage of fire
D. The end of the collapse danger
Answer_______
4. Which one of the following is not a method used by firefighters to delay flashover?
A. Venting to release heat
B. Not venting to starve the fire of oxygen and thus slow down heat generation
C. Use a portable extinguisher on the fire to cool it down
D. Remove combustible from the fire area
Answer_______
5. Which one of the following is not a warning sign of flashover?
A. Heat in smoke
B. Rollover-flashes of flame mixed with smoke
C. Black smoke
Answer_______
Answers: 1-True; 2-B; 3-D; 4-D; 5-C.