NFPA 921 STUDY GUIDE 2025 QUESTIONS AND ANSWERS
RATED A+
✔✔British Thermal Unit (Btu). - ✔✔The quantity of heat required to raise the
temperature of one pound of water 1°F at the pressure of 1 atmosphere and
temperature of 60°F; a British thermal unit is equal to 1055 joules, 1.055 kilojoules, and
252.15 calories.
✔✔Burning Rate. - ✔✔See 3.3.99, Heat Release Rate (HRR).
✔✔Calcination of Gypsum. - ✔✔A fire effect realized in gypsum products, including
wallboard, as a result of exposure to heat that drives off free and chemically bound
water.
✔✔Calorie. - ✔✔The amount of heat necessary to raise 1 gram of water 1°C at the
pressure of 1 atmosphere and temperature of 15°C; a calorie is 4.184 joules, and there
are 252.15 calories in a British thermal unit (Btu).
✔✔Cause. - ✔✔The circumstances, conditions, or agencies that brought about or
resulted in the fire or explosion incident, damage to property resulting from the fire or
explosion incident, or bodily injury or loss of life resulting from the fire or explosion
incident.
✔✔Ceiling Jet. - ✔✔A relatively thin layer of flowing hot gases that develops under a
horizontal surface (e.g., ceiling) as a result of plume impingement and the flowing gas
being forced to move horizontally.
✔✔Ceiling Layer. - ✔✔A buoyant layer of hot gases and smoke produced by a fire in a
compartment.
✔✔Char. - ✔✔Carbonaceous material that has been burned or pyrolyzed and has a
blackened appearance.
✔✔Char Blisters. - ✔✔Convex segments of carbonized material separated by cracks or
crevasses that form on the surface of char, forming on materials such as wood as the
result of pyrolysis or burning.
✔✔Clean Burn. - ✔✔A distinct and visible fire effect generally apparent on
noncombustible surfaces after combustible layer(s) (such as soot, paint, and paper)
have been burned away. The effect may also appear where soot has failed to be
deposited because of high surface temperatures.
✔✔Combustible. - ✔✔Capable of undergoing combustion.
, ✔✔Combustible Gas Indicator. - ✔✔An instrument that samples air and indicates
whether there are ignitible vapors or gases present.
✔✔Combustible Liquid. - ✔✔Any liquid that has a closed-cup flash point at or above
37.8°C (100°F). (See also 3.3.79, Flammable Liquid.)
✔✔Combustion. - ✔✔A chemical process of oxidation that occurs at a rate fast enough
to produce heat and usually light in the form of either a glow or flame.
✔✔Combustion Products. - ✔✔The heat, gases, volatilized liquids and solids,
particulate matter, and ash generated by combustion.
✔✔Competent Ignition Source. - ✔✔An ignition source that has sufficient energy and is
capable of transferring that energy to the fuel long enough to raise the fuel to its ignition
temperature. (See 19.4.2.)
✔✔Conduction. - ✔✔Heat transfer to another body or within a body by direct contact.
✔✔Convection. - ✔✔Heat transfer by circulation within a medium such as a gas or a
liquid.
✔✔Creep. - ✔✔The tendency of a material to move or deform permanently to relieve
stresses.
✔✔Current. - ✔✔A flow of electric charge.
✔✔Deductive Reasoning. - ✔✔The process by which conclusions are drawn by logical
inference from given premises.
✔✔Deflagration. - ✔✔Propagation of a combustion zone at a velocity that is less than
the speed of sound in the unreacted medium. [68, 2013]
✔✔Density. - ✔✔The mass of a substance per unit volume, usually specified at
standard temperature and pressure. The density of water is approximately one gram per
cubic centimeter. The density of air is approximately 1.275 grams per cubic meter.
✔✔Detection. - ✔✔(1) Sensing the existence of a fire, especially by a detector from one
or more products of the fire, such as smoke, heat, infrared radiation, and the like. (2)
The act or process of discovering and locating a fire.
✔✔Detonation. - ✔✔Propagation of a combustion zone at a velocity greater than the
speed of sound in the unreacted medium. [68, 2013]
RATED A+
✔✔British Thermal Unit (Btu). - ✔✔The quantity of heat required to raise the
temperature of one pound of water 1°F at the pressure of 1 atmosphere and
temperature of 60°F; a British thermal unit is equal to 1055 joules, 1.055 kilojoules, and
252.15 calories.
✔✔Burning Rate. - ✔✔See 3.3.99, Heat Release Rate (HRR).
✔✔Calcination of Gypsum. - ✔✔A fire effect realized in gypsum products, including
wallboard, as a result of exposure to heat that drives off free and chemically bound
water.
✔✔Calorie. - ✔✔The amount of heat necessary to raise 1 gram of water 1°C at the
pressure of 1 atmosphere and temperature of 15°C; a calorie is 4.184 joules, and there
are 252.15 calories in a British thermal unit (Btu).
✔✔Cause. - ✔✔The circumstances, conditions, or agencies that brought about or
resulted in the fire or explosion incident, damage to property resulting from the fire or
explosion incident, or bodily injury or loss of life resulting from the fire or explosion
incident.
✔✔Ceiling Jet. - ✔✔A relatively thin layer of flowing hot gases that develops under a
horizontal surface (e.g., ceiling) as a result of plume impingement and the flowing gas
being forced to move horizontally.
✔✔Ceiling Layer. - ✔✔A buoyant layer of hot gases and smoke produced by a fire in a
compartment.
✔✔Char. - ✔✔Carbonaceous material that has been burned or pyrolyzed and has a
blackened appearance.
✔✔Char Blisters. - ✔✔Convex segments of carbonized material separated by cracks or
crevasses that form on the surface of char, forming on materials such as wood as the
result of pyrolysis or burning.
✔✔Clean Burn. - ✔✔A distinct and visible fire effect generally apparent on
noncombustible surfaces after combustible layer(s) (such as soot, paint, and paper)
have been burned away. The effect may also appear where soot has failed to be
deposited because of high surface temperatures.
✔✔Combustible. - ✔✔Capable of undergoing combustion.
, ✔✔Combustible Gas Indicator. - ✔✔An instrument that samples air and indicates
whether there are ignitible vapors or gases present.
✔✔Combustible Liquid. - ✔✔Any liquid that has a closed-cup flash point at or above
37.8°C (100°F). (See also 3.3.79, Flammable Liquid.)
✔✔Combustion. - ✔✔A chemical process of oxidation that occurs at a rate fast enough
to produce heat and usually light in the form of either a glow or flame.
✔✔Combustion Products. - ✔✔The heat, gases, volatilized liquids and solids,
particulate matter, and ash generated by combustion.
✔✔Competent Ignition Source. - ✔✔An ignition source that has sufficient energy and is
capable of transferring that energy to the fuel long enough to raise the fuel to its ignition
temperature. (See 19.4.2.)
✔✔Conduction. - ✔✔Heat transfer to another body or within a body by direct contact.
✔✔Convection. - ✔✔Heat transfer by circulation within a medium such as a gas or a
liquid.
✔✔Creep. - ✔✔The tendency of a material to move or deform permanently to relieve
stresses.
✔✔Current. - ✔✔A flow of electric charge.
✔✔Deductive Reasoning. - ✔✔The process by which conclusions are drawn by logical
inference from given premises.
✔✔Deflagration. - ✔✔Propagation of a combustion zone at a velocity that is less than
the speed of sound in the unreacted medium. [68, 2013]
✔✔Density. - ✔✔The mass of a substance per unit volume, usually specified at
standard temperature and pressure. The density of water is approximately one gram per
cubic centimeter. The density of air is approximately 1.275 grams per cubic meter.
✔✔Detection. - ✔✔(1) Sensing the existence of a fire, especially by a detector from one
or more products of the fire, such as smoke, heat, infrared radiation, and the like. (2)
The act or process of discovering and locating a fire.
✔✔Detonation. - ✔✔Propagation of a combustion zone at a velocity greater than the
speed of sound in the unreacted medium. [68, 2013]
