Structural Firefighting (Fire Dynamics, Methods of Attack, Elements of Fire Behaviour) Flashcards
Define the three (3) states of matter:
- Solid - retains a fixed volume and shape. Particles are fixed in place, not easily compressible (wood, coal)
- Liquid - assumes the shape of the part of the container it occupies. Not easily compressible. Particles can move/slide past one another (petrol, oil, paints)
- Gas - assumes the shape and volume of its container. flows easily and particles can move past one another. Compressible (methane, nitrogen, oxygen)
What is Vapour Density?
The weight of pure vapour or gas, relative to the weight of an equal volume of dry air at the same temperature and pressure.
Note: Vapour density of air = 1
- VD greater than 1, the material is heavier than air
- VD less than 1, the material is lighter than air
What is Specific Gravity?
The weight of a solid or liquid material, compared with the weight of an equal volume of water at the same temperature and pressure.
Note: Specific gravity of water = 1
- SG is greater than 1, the material will sink in water
- SG is less than 1, the material will float in water
List and describe the four (4) stages of combustion
Incipient Stage:
Invisible products of combustion given off. NO visible smoke, flame or appreciable heat is present.
Smouldering Stage:
Combustion products now visible as smoke. Flame or appreciable heat is still not present.
Flame Stage:
Actual fire now exists. Appreciable heat is still not present, but follows almost instantaneously.
Heat Stage:
Uncontrolled heat and rapidly expanding air now complete the dangerous combination. The considerable heat is transferred to the atmosphere and nearby matter.
Define each of the following terms and explain how each contributes to fire growth within a structure: Convection Conduction Radiation Direct burning
Convection:
Heat transfer due to the mass movement of the heated molecules/gases within a liquid or gas. In a structure fire, the heated air and hot gases rise and expand, the cooler air is displaced downwards creating oxygen to sustain combustion (ie. stairwells and lift shafts)
Conduction:
The transfer of heat (or heat conduction) through a solid material. An example is a steel girder within a structure conducting heat and causing a fire spread beyond the wall.
Radiation:
Heat transfer by the emission of electromagnetic waves, which carry energy away from the emitting object. Large structural fires release a great deal of radiant heat, enough to blister paint on exposed surfaces.
Direct burning:
The physical contact of the flame with other available fuel. Fire may spread along a piece of wood and set fire to other pieces of wood that are in contact with it due to direct burning.
What is the expansion rate of steam?
- 1:1700 at 100°c
* 1:3500 at 450°c
List the six (6) Classes of Fire
A - Solids B - Liquids C - Gas D - Metals E - Electrical (hazard only) F - Cooking oils
Define a combustion
A chemical reaction that occurs between a fuel (eg. hydrocarbon) and an oxidising agent (eg. oxygen) that produces energy, usually in the form of heat and light/glow
Identify and describe the progression of the four (4) stages of a fire within a Compartment
Developing:
The initial growth of fire, which is dependent on nature and state of fuel. It is small in comparison to the size of the compartment.
Flashover:
The sudden and sustained transition from the developing stage to the fully developed stage of a fire within an enclosure.
Fully Developed:
The compartment has had adequate oxygen to achieve flashover and heat release rate has peaked. Everything combustible within the compartment is on fire.
Decay:
The fuel within a compartment becomes consumed an the rate of heat release declines, leading to a corresponding decrease in the compartments temperature.
Define the concepts of Flashover:
During the stages of fire development, materials are heated and undergo thermal decomposition which release flammable gases. Flashover occurs when these flammable gases are in an environment with adequate oxygen and are heated to their ignition temperature.
Define the concepts of Backdraught:
Backdraught occurs when there is a history of high temperature in a compartment. The fire has limited ventilation and is burning accumulated gaseous products of incomplete combustion (or unburnt pyrolysis products). If air is introduced into the heated and gaseous compartment and the ideal mixture is achieved, it can create an explosion of fire that moves through the compartment and out of the opening.
Define the concepts of Fire gas ignition:
Gases from a compartment fire leak into adjacent compartments and mix with the additional air within this area. The mixture of gas with air may fall within the appropriate flammable limits and when ignited, it will create a pressure increase either with or without and explosive force. You may also see it burn back into the compartment through the gas/smoke layers.
What are the two (2) burning regimes? Identify and describe:
Fuel controlled fire:
fuel controlled fires have enough air for complete combustion so are controlled by the amount of fuel added or removed.
Ventilation controlled fire:
fire that has adequate fuel to burn, but the fire development is determined by the available air or oxygen supply.
Describe the following types of hose line attacks:
Direct attack
Indirect attack
Gas cooling
Direct attack:
Used in early stages of the fire or decay stage to knock down the seat of the fire and for maximum penetration. The branch is set to a jet or spray setting and aimed directly at the fire.
Indirect attack:
When the fire has become fully developed or there is a risk of backdraught, the branch is controlled in circular motions with a fog or spray setting (Long pulse cone). Large quantities of steam are produced, which cools down and dilutes the fire gases and combustibles. Indirect attack reduces the likelihood of Flashover. Also used during hot door entries.
Gas cooling:
Used to maintain the level of the neutral plane by cooling a diluting overhead hot gases. By aiming short bursts of water spray directly overhead, the gases are cooled to below their auto ignition temperatures as the small water drops vaporise and dilute the flammable mixture. Used to control the fire when advancing and during search and rescue. Firefighters should be careful of steam burns when using this method of attack.
With regards to gas cooling explain the purpose when the following are used:
Short pulse techniques:
Used to cool and dilute the flammable gasses, which in turn will prevent the fire gases from reaching their auto ignition temperature. This technique is utilised as soon as there is hot gases above, or around a hose crew.
Long pulse techniques:
Long pulse gas cooling is critical at most fires and should always be used aggressively when there are large amounts of fire gases and/or the compartment size requires greater penetration.
