Signs of room flashover include:
- High heat conditions or flaming combustion overhead
- The existence of ghosting tongues of flame
- A lack of water droplets falling back to the floor following a short burst fog pattern being directed at the ceiling
- A sudden lowering of the smoke layer (previously referred to as the neutral plane)
- The sound of breaking glass as windows or glazing begin to fail from exposure to heat, possibly causing a visible rise in the smoke layer (previously referred to as the neutral plane)
- A change in smoke issuing from a window (seen from the exterior), with increasing velocity, as if issuing under pressure, and a darkening of smoke colour towards black
- The sudden appearance of light-coloured smoke (pyrolysis) from low-level items being subjected to high heat flux from the hot gas layer
This video demonstrates the phenomenon of flashover.
Where it is necessary to use a combination of direct and indirect firefighting techniques and gas cooling, firefighters should take care at all times to ensure that direct firefighting jets/sprays do not impact negatively on the conditions or on firefighting teams as they move through a structure when deployed for internal firefighting operations.
Summary of key fire behaviour indicators
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|
Fire behaviour indicator |
Hazard information |
|
1 |
Slow-moving light-coloured smoke issuing from an opening |
Early-stage fire development or smoke issuing some distance from the fire compartment |
|
2 |
Fast-moving darkening smoke issuing from an opening |
Impending flashover |
|
3 |
Heavily darkened or heat-crazed windows |
Under-ventilated fire conditions threatening backdraught or smoke explosion |
|
4 |
Pulsing (in and out) darkened smoke movements around closed doors and windows |
Fire development heading towards backdraught |
|
5 |
Very hot doors or windows (feel with back of the hand) |
Under-ventilated fire conditions threatening backdraught, smoke explosion or thermal runaway (flashover) |
|
6 |
Sudden reversal of smoke issuing from an opening, causing smoke to head back into the compartment/building |
The fire is rapidly developing and in need of more oxygen (impending flashover or backdraught), or a gusting wind-driven fire event is occurring |
|
7 |
A rapid lowering of the smoke layer (previously referred to as the neutral plane) |
Impending flashover |
|
8 |
A rising of the smoke layer (previously referred to as the neutral plane) |
A vent opening may have occurred at another location in the compartment/building |
|
9 |
Turbulence or rising and falling (bouncing) in the smoke layer (previously referred to as the neutral plane) |
Rapid fire development may be occurring |
|
10 |
Heat radiating down from the smoke layer (previously referred to as the neutral plane) |
Impending flashover |
|
11 |
Detached ‘ghosting’ tongues of flame moving around the fire compartment |
Impending flashover |
|
12 |
Flaming combustion seen near the ceiling or at the smoke interface |
Impending flashover |
|
13 |
Smoke seen issuing from closed windows, doors or roof eaves, as if under pressure |
Under-ventilated fire and impending backdraught |