Fire Behavior and Control (1)
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All matter can be divided into what three forms?
Solid, Liquid, Gas
What are the four components of the fire tetrahedron?
Heat, fuel, oxygen, and chemical chain reaction
When fighting fire what must a firefighter basically do?
A fire fighters role is to apply firefighting techniques to separate the fuel from the heat, exclude oxygen, break up the chemical chain reaction.
What are the four different ways that heat transfers?
Direct flame, conduction, conviction, radiation
What is the definition of heat?
Heat is defined as the total amount of vibration in a group of molecules and is measured relative to absobtion of heat energy.
What is the definition of British Thermal Unit (BTU)
The amount of heat required to raise the temperature of one pound of water by one degree fahrenheit.
What is the definition of temperature?
The measurement of how fast molecules are vibrating
What is specific heat?
Specific heat is the ratio between the amount of heat needed to raise the teperature of a material by one degree F and the amount of heat needed to raise the same weight of water by one degree F
What is latent?
- Amount of heat that a material absorbs when is changes physical form.
- (solid to liquid - latent heat of fusion)
- (liquid to gas - latent heat of vaporization)
What are the melting and boiling points?
- The physical structure of elements, molecules varies- causing them to melt or boil at different rates of vibration.
- Oxygen is a solid at temperatures less than -361F
- Oxygen is a liquid between -361F and -297F
- Oxygen is a gas above -297F
In order to burn, what state mut all fuels be in?
All matter burn in gaseous physical state.
What must happen to solids to enable them to burn?
Solids have to be heated enough to decompose the solid material into liquid and gases.
What is the definition of ignition temperature?
Ignition temperature is the mimimum temperature that is require to initiate or cause self sustained combustion of a material independent of the heat source.
To ignite a material, how hot must an ignition source be?
Any ignition source must be at least as hot as the ignition temperature of the material
What is the definition of flash point?
Flash point is the temperature of which a flamable liquid produces enough vapors to be ignited.
(Flash point is not to be confused with the much higher ignition temperature of the flamable liquid.)
What is the definition of flammable range?
- In terms of cars, it's a mixture of vapors and air below the lower flammable limit is too lean to burn.
- On the other hand, a mixture of vapor and air above the upper flammable limit is too rich to burn.
- (Specific to each individual liquid or gas)
What is the definition of specific gravity?
the wiehgt of a solid or liquid substance as compared to the weight of an equal volume of water is its specific gravity.
What is the definition of vapor density?
- The relative density of a vapor of gas is its vapor density.
- (Ratio of any vapor or gas to that of air)
How does oxygen support combustion?
Oxygen itself does not burn; it combines with molecules that are heated.
Describe the process of combustion
Combustion is rapid oxidation or chemical combination, Accompanied by the release of heat and light.
- 1- A heat source is applied to fuel.
- 2- Fuel begins to decomposed, relaeasing particals of carbon and molecules of hydrogen and oxygen.
- 3- These products mix with the air and form flames which represents excess hydrogen gas, and flammable carbon monoxide.
- 4- Unburned carbon particles create black smoke.
How does spontaneous combustion occur?
Any time natural oil molecules are exposed to the air, they are constantly being oxidizied; this creates heat energy.
What must occur in a chemical chain reaction in order for combustion to be maintained?
- Once ignition occurs, the process if combustion continues to repeats until:
- A- The entire fuel is consumed
- B- The fuel is cooled below it's ignition temperature
- C- Exposure to oxygen is mitigated (made less severe)
- D- An interuption of the chemical chain reaction takes place to stop the process.
What is the definition of heat of combustion?
Different fuels produce different levels of heat engergy due to the arrangement of their atoms.
What are the four stages of combustion?
- Incipiant or Ignition phase
- Growth phase
- decay stage
What is a flashover and when does it occur?
Simultaneous ignition of all contents in a confined space when they reach their ignition temperature. Flashover will most likely occur during the free-burning phase.
What is a backdraft and when does it occur?
It is characterised by the build-up of flammable fire gases that have been heated to their ignition temperature. Everything goes boom. Backdraft occurs during the decay stage of the fire.
What are the three classes of fire gases?
- Asphyxiants: disallow oxygen from getting to the cells
- Irritants: irritate respiratory tract
- Toxics: attack internal organs
How do extinguishing agents work?
- By interupting the combustion cycle. This is accomplished by:
- Smothering the fire by excluding oxygen
- Cooling the burning material and/or atmosphere Separating the fuel from the heat and/or oxygen
- Interupting the chmical chain reaction.
How can the physical properties of a material aid in its extinguishment?
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