NFPA 921 COMPREHENSIVE EXAM 2025 QUESTIONS AND
ANSWERS RATED A+
✔✔3.3.27 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
✔✔3.3.28 Ceiling Layer. - ✔✔A buoyant layer of hot gases and smoke
produced by a fire in a compartment.
✔✔3.3.29 Char. - ✔✔Carbonaceous material that has been burned or
pyrolyzed and has a blackened appearance.
✔✔3.3.30 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.
✔✔3.3.31 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.
✔✔3.3.32* Combustible. - ✔✔Capable of undergoing combustion.
✔✔3.3.33* Combustible Gas Indicator. - ✔✔An instrument that samples air and
indicates whether there are ignitible vapors or gases present.
✔✔3.3.35 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.
✔✔3.3.36 Combustion Products. - ✔✔The heat, gases, volatilized liquids and solids,
particulate matter, and ash generated by combustion.
✔✔3.3.37 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.
✔✔3.3.38 Conduction. - ✔✔Heat transfer to another body or within a
body by direct contact.
✔✔3.3.39 Convection. - ✔✔Heat transfer by circulation within a medium such as a gas
or a liquid.
, ✔✔3.3.40 Creep. - ✔✔The tendency of a material to move or deform
permanently to relieve stresses.
✔✔3.3.41 Current. - ✔✔A flow of electric charge.
✔✔3.3.42 Deductive Reasoning. - ✔✔The process by which conclusions are drawn by
logical inference from given premises.
✔✔3.3.43 Deflagration. - ✔✔Propagation of a combustion zone at a
velocity that is less than the speed of sound in the unreacted
medium. [68, 2013]
✔✔3.3.44 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.
✔✔3.3.45 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.
✔✔3.3.46 Detonation. - ✔✔Propagation of a combustion zone at a
velocity greater than the speed of sound in the unreacted medium. [68, 2013
✔✔3.3.47 Diffuse Fuel. - ✔✔A gas, vapor, dust, particulate, aerosol,
mist, fog, or hybrid mixture of these, suspended in the atmosphere, which is capable of
being ignited and propagating a flame front.
✔✔3.3.48 Diffusion Flame. - ✔✔A flame in which fuel and air mix or diffuse together at
the region of combustion.
✔✔3.3.49 Drop Down. - ✔✔The spread of fire by the dropping or falling
of burning materials. Synonymous with "fall down."
✔✔3.3.50 Effective Fire Temperatures. - ✔✔Temperatures reached in fires that produce
physical effects that can be related to specific
temperature ranges.
✔✔3.3.51 Electric Spark. - ✔✔A small, incandescent particle created
by some arcs.
✔✔3.3.52* Empirical Data. - ✔✔Factual data that is based on actual
measurement, observation or direct sensory experience rather than on theory.
ANSWERS RATED A+
✔✔3.3.27 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
✔✔3.3.28 Ceiling Layer. - ✔✔A buoyant layer of hot gases and smoke
produced by a fire in a compartment.
✔✔3.3.29 Char. - ✔✔Carbonaceous material that has been burned or
pyrolyzed and has a blackened appearance.
✔✔3.3.30 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.
✔✔3.3.31 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.
✔✔3.3.32* Combustible. - ✔✔Capable of undergoing combustion.
✔✔3.3.33* Combustible Gas Indicator. - ✔✔An instrument that samples air and
indicates whether there are ignitible vapors or gases present.
✔✔3.3.35 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.
✔✔3.3.36 Combustion Products. - ✔✔The heat, gases, volatilized liquids and solids,
particulate matter, and ash generated by combustion.
✔✔3.3.37 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.
✔✔3.3.38 Conduction. - ✔✔Heat transfer to another body or within a
body by direct contact.
✔✔3.3.39 Convection. - ✔✔Heat transfer by circulation within a medium such as a gas
or a liquid.
, ✔✔3.3.40 Creep. - ✔✔The tendency of a material to move or deform
permanently to relieve stresses.
✔✔3.3.41 Current. - ✔✔A flow of electric charge.
✔✔3.3.42 Deductive Reasoning. - ✔✔The process by which conclusions are drawn by
logical inference from given premises.
✔✔3.3.43 Deflagration. - ✔✔Propagation of a combustion zone at a
velocity that is less than the speed of sound in the unreacted
medium. [68, 2013]
✔✔3.3.44 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.
✔✔3.3.45 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.
✔✔3.3.46 Detonation. - ✔✔Propagation of a combustion zone at a
velocity greater than the speed of sound in the unreacted medium. [68, 2013
✔✔3.3.47 Diffuse Fuel. - ✔✔A gas, vapor, dust, particulate, aerosol,
mist, fog, or hybrid mixture of these, suspended in the atmosphere, which is capable of
being ignited and propagating a flame front.
✔✔3.3.48 Diffusion Flame. - ✔✔A flame in which fuel and air mix or diffuse together at
the region of combustion.
✔✔3.3.49 Drop Down. - ✔✔The spread of fire by the dropping or falling
of burning materials. Synonymous with "fall down."
✔✔3.3.50 Effective Fire Temperatures. - ✔✔Temperatures reached in fires that produce
physical effects that can be related to specific
temperature ranges.
✔✔3.3.51 Electric Spark. - ✔✔A small, incandescent particle created
by some arcs.
✔✔3.3.52* Empirical Data. - ✔✔Factual data that is based on actual
measurement, observation or direct sensory experience rather than on theory.
