Structural Firefighting Flashcards
Explain the fire triangle
The fire triangle consists of:
Fuel.
Oxygen.
Heat.
If all are present this creates a self-sustained chain reaction. Which results in fire.
By manipulating the ‘fire triangle’ firefighters can more effectively control and extinguish structural fires.
What is pyrolysis
Pyrolysis is the decomposition of a substance caused by heat. When a substance is heated it gives of gases as it decomposes through the states of matter. At the right temperature and mixture the gases become flammable.
What is heat
Heat is a measurement of energy. Temperature is an expression of the relative amount of this energy that a body has. This gives us a means of comparing two objects.
Heat transfer terminology
Specific heat:
The specific heat required to raise the temperature of a body 1 degree. Varies on substance.
Latent heat:
The heat required to change a substance from one physical state to another.
Latent heat of vaporisation:
Is the amount of heat required to change a given mass of a substance from a liquid to vapour.
Why is water efficient for firefighting
Of all common substances water requires the greatest amount of latent heat to change it from a liquid to a vapour.
it is therefore extremely efficient for firefighting as it absorbs the greatest amount of heat energy from burning substances.
What is heat release rate
Heat release rate is the amount of heat energy releases over time.
Usually measured in watts (W).
1000 watts = 1 kilowatt (kW).
1000 kilowatts = 1 megawatt (MW).
Ignition sources
Piloted: Required a source. Such as electrical arc or independent flame.
Spontaneous: Auto ignition temperature (AIT) - enough heat is available that substance will ignite on its own, a localised energy source is not required.
Flame types
Diffused Flame:
When oxygen is drawn from the area surrounding the flame. This creates a slow, bright, lazy flame.
Premixed Flame:
When oxygen a fuel are mixed before ignition source. Greatly improves combustion efficiency and reduces unburnt fuel.
Ignition terminology
Flash point:
Is the lowest temperature at which a substance produces a flammable vapour.
Fire point:
Is the lowest temperature at which a substance produces a vapour that can sustain a continuous flame.
Auto ignition temperature:
Is the temperature at which a fuel will ignite on its own without any additional source of ignition.
Methods of heat transfer
Heat can be transferred through 3 methods:
Conduction.
Convection.
Radiation.
With fire all methods of heat transfer add to the overall heat of the room helping the fire progress.
Describe conduction heat transfer
Conduction is the heat transfer of heat energy through a material or any material in contact.
Describe convection heat transfer
Convection is heat transfer by fluid substances such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.
In fires, hot gaseous products of combustion (and air) expand and become lighter and move upward.
Describe radiation heat transfer
Radiation is heat transfer by the emission of electromagnetic waves which carry energy away from the emitting object.
Describe ideal mixture
Ideal mixture is the concentration of a gas or vapour (expressed as a volume percentage in air) that will burn with the maximum intensity and efficiency..
Describe the neutral plane
The neutral plane is a horizontal plane at which pressure at both sides of a vent (e.g. upper and lower) are equal.
For structural firefighting purposes, the neutral plane is the area between the under pressure (fresh air) and over pressure (hot fire gases) in a compartment.
Can be seen as the lowest level of smoke.
Describe gravity current
A gravity current occurs because the fresh air is denser than the hot gases existing within the compartment.
When an opening is made a gravity current is formed when the cooler fresh air (heavier) flows under the hot buoyant gases (lighter).
Thornton’s rule
Simply, as the fire accesses more oxygen, or a oxygen increases the heat release rate increases leading to potentially increased rates of extreme fire behaviour.
Charles’ law
Charles’s law states:
Gases expand when heated.
Gases become less dense and will rise when heated.
Gay-Lussac’s Law
Gay-Lussac’s Law states:
When gases are confined and heated, pressure increases.
Increased pressure indicates higher temperatures.
Gas laws on the fire ground
Understanding these laws helps fire fighters assess the stages of a fire progression and intensity. Fore example, with effective ‘gas cooling’ hose stream techniques we can cool the hot fire gases causing them to contract - maintaining visibility below the neutral plane.
What are the burning regimes
The two burning regimes are:
Fuel controlled.
Ventilation controlled.
Describe a fuel controlled burning regime
Fires with more than enough air (oxygen) for combustion are said to be fuel controlled. These fires can be compared to a free burning fire outside or a small fire in a kitchen pan. Signs include: Developing fire. High neutral plane. Better visibility. Bright yellow flames. Fire in decay stage.
Describe a ventilation controlled burning regime
Simply put, in a ventilation controlled fire, fire growth is limited by the available air supply. When a fire has used up all the available oxygen and needs more in order to grow. Signs include: Fully developed fire. Low neutral plane. Poor visibility. Air being drawn back into the fire. Smouldering fire. Smoke pulsations out of openings. Whistling sounds.
Describe the blow torch effect
Blow torch effect occurs when high winds enter an opening accelerating the combustion process resulting high energy release rate which looks like a blow torch exiting a seperate outlet. Signs of blow torch effect: Pulsing smoke Working fire Ventilation controlled, vented fire. Noticeable winds.
Describe salvage operations
Salvage describes the actions taken during and immediately after the fire to minimise the damage caused by fire and by the water used to extinguish it.
Describe overhaul operations
Overhaul involves the systematic checking, turning over and wetting down of structural materials and contents to ensure that no pockets of fire still exist.
Signs of structural collapse
Signs of structural collapse:
Falling plaster, mortar or brick from walls or ceilings.
Cancerous concrete spalling.
Walls leaning or bulging.
Ceilings sagging.
Floors spongey or springy.
Gaps appearing in between walls, beams or ceilings, or walls and floors.
Cracked or sagging arches over door or window openings.
Displacement of support pillars, joists or beams.
Fire classes
Class A : Solids Class B : Liquids Class C : Gases Class D : Metals Type E : Energised electrical equipment. Class F : Fats and oils.
Extinguisher types
Water - Red band - Class A Foam - Blue band - Class B Dry chemical - White band Classes C,D CO2 - Black band - Class E Wet chemical - Oatmeal band - Class F
Describe flammability range
The flammability range is the concentration range of a gas or vapour (expressed as a volume percentage in air) that will burn of explode if an ignition source is present.
