Flashover and Backdraught

Question 1

What is flashover?

Answer 1

the stage of a fire where TOTAL THERMAL RADIATION form the
FIRE PLUME,
HOT GASES and
HOT COMPARTMENT BOUNDARIES
causes all
EXPOSED COMBUSTIBLE SURFACES to
PYROLYSE (release flammable gases) and
IGNITE when there is adequate ventilation.
It is the SUDDEN and SUSTAINED transition from a growing fire to a fully developed fire.

Question 2

What is BACKDRAUGHT?

Answer 2

Backdraught is where LIMITED VENTILATION can lead to a COMPARTMENT producing fire gases containing significant proportions of PARTIAL COMBUSTION PRODUCTS and UNBURNED PYROLYSATES. If these accumulate, the admission of air into the compartment when opened can lead to a SUDDEN DEFLAGRATION. which moves through the compartment and out of the opening.

Question 3

What is a FIRE GAS IGNITION?

Answer 3

Fire Gas Ingnition occurs when gases from a compartment fire have leaked into an adjacent compartment and mixed with air. This mix may then fall within the appropriate flammable limits, which if ignited will create an increase in pressure, either with or without an explosive force. It is not necessary for an opening to be made for this to occur. If an explosive force is experienced this is commonly termed a SMOKE EXPLOSION. An ignition with much less pressure the term FLASH FIRE is appropriate

Question 4

What are the 8 signs of flashover?

Answer 4

High heat conditions
Flaming combustion overhead
Ghosting tongues of flames
No water falling back after “gas cooling”
A sudden lowering of the smoke layer
The sound of breaking glass as windows fail
A change in smoke issueing (increased velocity and darkening in colour towards black)
The presence of light coloured smoke from pyrolysis

Question 5

What are the 9 signs of backdraught?

Answer 5

Fire in tightly closed compartments
Darkened windows
Windows, doors and door handles hot to touch (back of hand)
Rattling sound or pulsating smoke
smoke being drawn into back into openings
Ghosting tongues of flame in the compartment
Turbulance in the smoke layer
Whistling or roaring sounds
Change to fast moving smoke exiting at high velocity as if under pressure