What are the four stages of a compartment fire?
- Developing stage
- Flashover stage
- Fully developed stage
- Decay stage
What are the two key signs used to determine likely fire behavior?
- Height
- Turbulence
What are the signs of a flashover?
- Ventilated fire (an open door is sufficient)
- Painful radiant heat with crews forced low by high temperatures
- Lowering of the neutral plane with flames at ceiling height (‘fingers of flame’ in the smoke)
- Hot surfaces
- Increased rate of pyrolysis
- Increased turbulence of the neutral plane
- Flaming occurs throughout the volume of the compartment
- A ‘billowing effect’ from the gases may be seen
What is a backdraught?
The sudden introduction of air into a severely under ventilated fire resulting in an explosive like event.
What are the signs of a backdraught?
- Fire with limited or no ventilation
- Lack of visible flames
- Thick roiling black, yellow and white smoke
- Dirty brown smoke
- Smoke pulsating through small gaps & openings
- Air being drawn in (whistling noise)
- Blackened deposits on windows
What are the 3 extreme fire bahaviours?
- Flashover
- Backdraught
- Fire Gas Ignition
What is Fire Gas Ignition?
Flammable fire gases from one compartment can enter an adjacent compartment through convection process.
The addition of air is not always a requirement for ignition of these gases, which have already formed into an ideal pre-mixed state, simply awaiting an ignition source.
What 3 elements will contribute to Fire Gas Ignition?
- Conduction: heat can be conducted from the fire compartment to other compartments.
- Leakage: there can be leakage of fire gases from the compartment that is on fire through various voids, cavities, and ducting to other compartments.
- Construction: the construction of the premise will influence the possibility of a fire gas explosion.
What are the 3 things water does as an extinguishing agent?
- Reduces fuel
- Reduces heat
- Reduces oxygen
What is the expansion rate of water to steam?
- 1:1700 at 100°Celcius.
- 1:3500 at 450°Celcius.
What hose line would you use for a small residential fire?
38mm
Define pyrolysis.
Decomposition of a substance through the application of heat.
Define flashover.
The sudden and sustained transition from a developing fire to a fully developed fire.
Describe indirect extinguishment.
Applying water spray onto super-heated surfaces and/or overhead gases in a compartment, to create a mass of steam that displaces the oxygen to smother the fire.
Describe direct extinguishment.
The extinguishment agent is applied directly onto the burning fuel, using a jet or spray.
What are the effects of direct extinguishment?
- Cools the surface below the temperature at which combustion can occur.
- Can be used to stop pyrolysis.
- Care must be taken to avoid excessive water damage.
- Care should be taken not to disturb embers which can be ignition sources.
- Can draw/entrain air into the fire compartment.
What are the effects of indirect extinguishment?
- Cools and dilutes the fire gases
- Cools burning combustibles and structure of the compartment
- Large quantities of steam produced have a smothering effect on the fire
- Lowers neutral plane, reducing vision. Steam can have a debilitating effect on firefighters and any victims.
- Should be applied from outside of the compartment or from a distance.
Describe gas cooling.
A hose stream technique used to cool hot fire gases below their auto-ignition temperatures, preventing further fire spread and the potential for flashover.
To employ gas cooling, direct a water spray into the overhead hot gases to cool and dilute them, thereby reducing the potential to ignite.
