Study Sheet 11 - Chapter 5
5. Air normally contains what percentage of oxygen?
21%
23. What is the extinguisher rating for a 2½ gallon pressurized water portable fire extinguisher?
2A A=equivalent to 1.25 gallons of water
28. Based on factors such as specific gravity, vapor density and flammable limits, what problem will flammable liquids present in a spill incident?
A liquid spill can cause several problems. Depending on specific gravity, it can float on water. Flammable vapors can either rise or sink in the air according to its vapor density. If the vapor is within its flammable range, it can ignite.
17. On what types of fires are dry chemicals effective?
B C
24. Which classes of fires have numerical ratings on fire extinguishers?
Class A and B
13. The factors of surface area, moisture content and flame spread are important characteristics when dealing with fires that involve fuels in what form of matter?
Class A fires
25. On which class of fire is a wet chemical fire extinguisher intended to be used?
Class K
2. Identify the products of complete combustion and the products of incomplete combustion.
Complete combustion =H20 and CO2 Incomplete combustion=H2O, CO, and H2
19. On what type of fires are dry powder extinguishers used?
D
21. With regard to flammable range and flammable limits, how do flash point and fire point differ?
Flash point cannot sustain combustion
30. Why would a hazardous material classified as a FLAMMABLE GAS (such as methane) have an ignition temperature, but no flash point?
Flash point is defined as the temperature a liquid needs to be heated to release enough vapors to ignite. A flammable gas is already primed for combustion.
b. Lower Explosive Limit (LEL)
Lowest concentration of vapor/gas to oxygen that is capable of producing a flash of fire in presence of an external ignition source.
d. Upper Explosive Limit (UEL)
Maximum concentration of vapor/gas to oxygen where it can ignite.
a. Flash point
Minimum temperature of a liquid at which it gives off vapors sufficient enough to ignite, but does not sustain combustion
22. Define ignition temperature.
Minimum temperature to which a substance must be raised before it will ignite.
26. How do ordinary base and multipurpose base dry chemical extinguishing agents differ?
Multipurpose can be used on different types of metal
a. Too lean to burn
Not enough vapor to oxygen ratio to ignite.
29. What is the correlation between a liquid's flash point and it's lower explosive limit?
Once it reaches its flash point, it will produce enough vapors to reach its lower explosive limit.
c. Flammable range / Flammable limit
Range of gas/vapor concentration to oxygen where it can ignite
8. What are the four methods of fire extinguishment?
Reduction of temperature, removal of fuel, exclusion of oxygen, and inhibition of chain reaction.
b. Fire point
Temperature at which a liquid gives sufficient vapors to ignite and support combustion.
c. Smoldering (Decay)
The fire begins to die out. The area is filled with superheated smoke and gases above ignition temperature. Oxygen=below 15%.
1. What is the fire tetrahedron and how can it be used in fire extinguishment and fire prevention?
The fire tetrahedron consists of fuel, heat, oxygen, and a chain chemical reaction. If any can be taken away, the fire will be extinguished.
c. Boiling point
The temperature where a liquid rapidly becomes a vapor. The rate of evaporation exceeds the rate of condensation.
b. Free-Burning (Flashover + Fully-Developed)
The transition between growth and fully developed. Flashover is where fuels in the compartment reach their ignition temperature and everything ignites. Fully developed is where all combustible fuels are burning. Oxygen=16%. Temperature=1300-2000 degrees F.
14. What is the difference between vapor density and specific gravity?
Vapor density determines if a vapor or gas will sink/rise in air. Specific gravity determines if a substance will float or sink in water.
e. Too rich to burn
Vapor/gas is too concentrated, not enough oxygen for it to ignite.
a. Incipient (Ignition + Growth)
Where the fire initially ignites either piloted or nonpiloted. The fire begins to grow into a fire plume. Oxygen=20-21%, Temperature=1,112 degrees F
class k
cooking oils/greases
class c
energized electrical equipment
class b fuel
liquids and gases
class d
metals
class a fuel
ordinary combustibles
