NFPA 921 Highlights Exam 2025
Questions and Answers
3.3.9 Arc Mapping - ANSWER✔✔-The systematic evaluation of the electrical circuit configuration,
spatial relationship of the circuit components, and identification of electrical arc sites to assist in the
identification of the area of origin and analysis of the fire's spread.
3.3.12 Area of Origin - ANSWER✔✔-A structure, part of a structure, or general geographic
location within a fire scene, in which the "point of origin" of a fire or explosion is reasonably
believed to be located.
3.3.13 Arrow Pattern. - ANSWER✔✔-A fire pattern displayed on the crosssection of a burned
wooden structural member.
3.3.16 Autoignition Temperature - ANSWER✔✔-The lowest temperature at which a combustible
material ignites in air without a spark or flame.
3.3.17 Backdraft - ANSWER✔✔-A deflagration resulting from the sudden introduction of air into a
confined space containing oxygendeficient products of incomplete combustion.
3.3.19 Blast Pressure Front - ANSWER✔✔-The expanding leading edge of an explosion reaction
that separates a major difference in pressure between normal ambient pressure ahead of the front
and potentially damaging high pressure at and behind the front.
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, 3.3.22 British Thermal Unit (Btu) - ANSWER✔✔-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.
3.3.25 Calorie - ANSWER✔✔-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).
3.3.26 Cause. - ANSWER✔✔-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.
3.3.27 Ceiling Jet - ANSWER✔✔-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.
3.3.30 Char Blisters. - ANSWER✔✔-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 - ANSWER✔✔-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.
3.3.35 Combustion - ANSWER✔✔-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.
FOR STUDY PURPOSES ONLY COPYRIGHT © 2025 ALL RIGHTS RESERVED 2
Questions and Answers
3.3.9 Arc Mapping - ANSWER✔✔-The systematic evaluation of the electrical circuit configuration,
spatial relationship of the circuit components, and identification of electrical arc sites to assist in the
identification of the area of origin and analysis of the fire's spread.
3.3.12 Area of Origin - ANSWER✔✔-A structure, part of a structure, or general geographic
location within a fire scene, in which the "point of origin" of a fire or explosion is reasonably
believed to be located.
3.3.13 Arrow Pattern. - ANSWER✔✔-A fire pattern displayed on the crosssection of a burned
wooden structural member.
3.3.16 Autoignition Temperature - ANSWER✔✔-The lowest temperature at which a combustible
material ignites in air without a spark or flame.
3.3.17 Backdraft - ANSWER✔✔-A deflagration resulting from the sudden introduction of air into a
confined space containing oxygendeficient products of incomplete combustion.
3.3.19 Blast Pressure Front - ANSWER✔✔-The expanding leading edge of an explosion reaction
that separates a major difference in pressure between normal ambient pressure ahead of the front
and potentially damaging high pressure at and behind the front.
FOR STUDY PURPOSES ONLY COPYRIGHT © 2025 ALL RIGHTS RESERVED 1
, 3.3.22 British Thermal Unit (Btu) - ANSWER✔✔-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.
3.3.25 Calorie - ANSWER✔✔-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).
3.3.26 Cause. - ANSWER✔✔-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.
3.3.27 Ceiling Jet - ANSWER✔✔-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.
3.3.30 Char Blisters. - ANSWER✔✔-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 - ANSWER✔✔-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.
3.3.35 Combustion - ANSWER✔✔-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.
FOR STUDY PURPOSES ONLY COPYRIGHT © 2025 ALL RIGHTS RESERVED 2
