Fire Science 2 Flashcards
Two types of flames are ?
Diffused and premix
Qualities of a diffused flame?
8
Gases are not mixed prior to ignition
Unclean burn
Burn cooler
Flame colour: orange/red
Less noisy
Lower velocity of the deflagration
Defined outline to the flame
Less efficient burning
Premixed flame qualities?
8
Gases are mixed up prior to ignition
Burn cleaner
Burn hotter
Flame colour: Blue
More noisy
Higher velocity or the deflagration
More stable flame but harder to discern edges due to blurred flame
More efficient burning
If too little or too much fuel is present, combustion will not take place. The mixture is then described as too lean or too rich to burn.
What are these limits referred to as?
Lower explosive limit (LEL)
Upper explosive limit (UEL)
What is the lower explosive limit defined as?
The lowest concentration of a fuel that will just support a self-propagating flame
What is the upper explosive limit defined as?
The highest concentration of a fuel that will just support a self-propagating flame
The progression of a fire within a compartment can be divided into four phases which are?
Phase one: developing fire stage
Phase two: flashover stage
Phase three: fully developed fire stage
Phase four: decay stage
A number of factors can affect fire progression:
Insufficient fuel
Airtight compartment
Smouldering fire
Walls and ceilings
Three fire phenomena present a particular hazard to FF’s are?
Flashover
Backdraught
Fire gas ignition
The signs of flashover include
8
A ventilated fire with an adequate oxygen supply
Flames visible in the fire gases at ceiling level
Combustible material gassing off due to pyrolysis
High temperatures and an increasing rate of combustion
Neutral plane moving down
Sudden increase in fire development
Pyrolysis at floor level in the compartment
Increased turbulence of the neutral plane
Actions taken when the signs of flashovers are identified
6
Withdrawing and firefighting from the outside the compartment
Communicate hazard to other firefighters, ECO, sector commander or IC
Ventilate to remove gases, only on IC orders
Use thermal imaging camera (TIC) to assess the temperatures within the compartment
Teams should stay low in cooler air
Pulse spray in to the over pressure to cool gases to reduce the radiated heat
Backdraught can be defined as
Deflagration cause by air being introduced to a fire compartment that is oxygen starved, has limited ventilation and where there is a build up of unburnt fire gases
External signs of backdraught
5
Fire with limited or no ventilation
Fire has been burning for some time
Fire gases being pushed out under pressure from gaps
Windows blackened with no visible sign of flame
Fire gases pulsing out from gaps
Internal signs of backdraught
5
Low neutral plane
Darkening of fire gases
Inrush of air and fire gases forced out, through the opening
Pulsation of gases through an opening
Deflagration through an opening
FFs actions for backdraught at an incident
5
Communicate the hazard to other firefighters, ECO sector commander or IC
Consider ventilating the compartment prior to entry
Use the TIC to assess the temperatures within the compartment
Always use correct door procedures. This will include a min of 45mm jet and support team with a covering jet
Pulse spray the interior to cool and dilute fire gases
