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What is a fire?
A fire is a chemical reaction involving rapid oxidation (combustion) of fuel
What is usually the oxidizer and reducing agent in a fire?
The oxidizer (gives electrons away to become reduced) is usually oxygen, and the reducing agent (which becomes oxidized) is the fuel.
What are the elements of of a fire triangle?
- - Fuel (reducer)
- - Oxygen (the oxidizer)
- - Heat (needs to approprate temperature to ignite fuel)
What are the four classes of fire?
- - A - Ordinary combustibles (paper, clothing)
- - B - Flammable liquids (petroleum oil)
- - C - Electrical Fires
- - D - fire in combustible metals.
What percentage of the air is oxygen?
Which of the following requires the the lowest time to ignite? gas, vapour or solid.
Gas and vapour may be ignited with a spark, where as a solid may require longer heat source.
What does vapor density tell us?
A vapor density greater than air, the vapor will settle at ground level, and vapor density less than air would move upwards.
What is a flash point?
The minimum temperature at which the vapor above a liquid will first support a combustion transient (or "flash")
What are the two types of flash points usually given? Which is usually higher?
Usually, open cup and a closed cup flash point is given relating to how the flash point was found. Usually the open cup is a few degrees higher than the closed cup.
What does the term flammable mean?
Flammable is used for liquids with flash point below 100 degree F or 37.8 C
What does the term combustible mean?
The term combustible is used for liquids with a flash point above 100 degree F or 37.8 C
What is the fire point?
It is the temperature at where the flash becomes self sustaining.
What is the lower flammable limit (LFL) or lower explosive limit (LEL)?
The lowest concentration of a chemical (by volume of partial pressure) in air that will support combustible (fuel)
What is the upper flammable limit (UFL) or the upper explosive limit (UEL)?
The upper flammable limit is the maximum concentration of a chemical (by volume or partial pressure) in air that would be combustible.
What is the autoignition temperature?
Autoignition temperature at which the solid, liquid or vapour will spotaneously ignite resulting in a self sustaining fire.
What is minimum ignition energy?
Minimum ignition energy is the lowest energy that would be required to ignite a flammable mixture via electrical discharge
What is burning velocity?
Burning velocity is the speed at which the smooth flame moves into a stationary mixture of reactants.
What is the stoichiometric ratio?
- Stoichiometric ratio is the optimal ratio between fuel and oxidizer that will result in the optimal combustion and heat release.
- "lean" means not enough fuel
- "rich" means enough fuel or too much
What are the three methods of heat transfer?
What is conduction?
- Conduction is heat transfer through a solid
- can be through molecular motion or movement of free electrons
What is convection?
- Convection is heat transfer through a fluid
- Forced convection and natural convection
What is radiation heat transfer?
- Radiation does not require a medium to transfer heat (i.e. thermal radiation)
- Reflected, absorbed or transmitted
The tw oeffects of confined fires are
- confining the flame and combustion products
- restricting the ventilation supply of fresh air to the fire
For a liquid to ignite, three conditions must be satisfied:
- liquid must vaporize
- vapor must mix with air
- ignition source to obtain self-propagation of the flame must be available
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