Fire Investigation Flashcards
Fire Triangle
Oxygen Sources
Heat Sources
Fuel Sources
Fire Causes
Criminal
- Accelerants, points of entry, vandalism, delay devices, Suicide.
Accidental
- Electrical appliances, gas supply, chip pans, smoking materials
Main Types of Fire
Naked Flame
Smouldering Fire
- Before, after or during a naked flame fire
Explosions
- Condensed phase
- Dispersed phase
Flaming Fires
- Most common
Fire stages
- Incipient stage
- Growth Stage
- Growth to Flashover
- Post Flashover
- Decay
Incipient Fire Stage
First stage of fire development after ignition
Flames localised to fuel
Normal oxygen levels
Temperature not started to rise
Growth Fire Stage
Fire grows in intensity
More fuel
Flames move upward and outward from origin
Temperature begins to increase, bringing nearby fuels to ignition temperature
Lateral movement depends on distance of fuels
Hot gases form a layer under ceiling
Chemical releases and high temperatures start to provide conditions for flashover
Growth to flashover Fire Stage
Hot layer of gas reaches critical temperature of 600*C generating approx. 20kW/m^2 of radiant heat at floor level
sufficient to bring all fuels present to ignition temperatures
Post Flashover Fire Stage
All fuel is burning and the size of fire is based on the availability of oxygen
Determined by buoyant flows of hot gases and air in and out of a room if ventilated
Decay Fire Stage
Eventually all available fuel is exhausted and the open-flame which is burning will gradually lower and become less prevalent.
Smouldering Fire
Flameless combustion
Can proceed at low oxygen concentrations
Smoke/ fire products may be deposited
Can develop into a flaming fire
May produce considerable localized damage
Explosions
Condensed Phase
- High explosives (TNT, Semtex, RDX)
- May cause severe damage
Dispersed Phase
- Vapour phase Explosions
- Typically petrol/ gases
- Less damage than high explosives
- BLEVE
- Explosive limits of some gases and liquids
- Methane - 5%-15%
- Propane - 2.2%-9.5%
- Butane - 1.5%-7.8%
- Acetylene - 2.5%-80%
- Petrol - 1.1%-8.7%
Dispersed phase explosions
Propagate as a flame
Usually spherical and move away from point of ignition
Combustion raises temperature, expands the gas, increases the reaction speed, turbulence and mixing
Expanding gases create a pressure wave leading to an explosion when confined
Spontaneous Combustion
Industrial
- Driers
- Storage of hot materials
- Bulk storage
- Oil soaked rags
Agricultural
- Stored hay
Launderettes
- Tumble dried synthetic fabrics in a pile
General Fire Rules
Fires burn upwards and outwards
Fire spreads faster on vertical surfaces
Flame height varies with position of fire
Flashover
Fire spread Factors
- Conduction
- Convection
- Radiation
- Ventilation
- Fire load
- Structural collapse
- Fire-fighting operations
- Burning gases and liquids
- Electrical effects
- Accelerants
- Reduced fire resistance
