NFPA 921 EXAM 2025/2026 QUESTIONS WITH ANSWERS
GRADED A+
✔✔Kelvin - ✔✔Begins at absolute zero and water freezes at 273.15 Kelvin. Uses
Celsius increments
✔✔Rankine - ✔✔Freezing point: 491.67
Uses Fahrenheit increments
✔✔Heats of Combustion Typically Range From - ✔✔10 to 45 MJ/kg.
✔✔Fuel Load Density - ✔✔The potential combustion energy output per unit floor area
[MJ/m2 (Btu/ft2)] or the mass of fuel per unit floor area [kg/m2 (lb/ft2)].
✔✔The HHR job a liquid fuel fire is dependent on two primary factors? - ✔✔The
physical characteristics of the release (i.e., surface area and depth), and the
combustion properties of the fuel.
✔✔Continuous Flame Height - ✔✔The height over which flames are visible at all
instances.
✔✔Average Flame Height - ✔✔The height over which flames are visible 50 percent of
the time.
✔✔Flame Tip Height - ✔✔The greatest height over which flames are visible at any time.
✔✔Continuous Flaming Region - ✔✔Lower portion of visible flame.
✔✔Intermittently Flaming Region - ✔✔Upper portion of the visible flame.
✔✔Plume Region - ✔✔Above the visible flame.
✔✔Heskestad Correlation - ✔✔Used to calculate flame heights
✔✔Continuous Flame Region Centerline Temperatures are approximately constant
around? - ✔✔1000C (1832F)
✔✔Intermittent Flame Region temperatures? - ✔✔about 500C (932F)
✔✔Plume Region Temperatures? - ✔✔about 300C (572F)
✔✔AIT - ✔✔Auto Ignition Temperature. The lowest temperature at which a flammable
gas-air mixture can be ignited without a pilot.
, ✔✔Flash Point - ✔✔The liquid temperature above which an ignitable concentration of
flammable vapors is generated.
✔✔Fire Point - ✔✔Burning of the vaporizing liquid fuel can be sustained as a pool fire.
✔✔CAT - ✔✔Critical Ambient Temperature
✔✔Unsaturated molecules contain? - ✔✔Carbon-to-carbon double bonds, which are
reactive.
✔✔Saturated hydrocarbons contain? - ✔✔carbon-to-carbon single bonds, which are far
less reactive than unsaturated oils.
✔✔Polyunsaturated fatty acids - ✔✔Animal and vegetable fats and oils.
✔✔Saturated hydrocarbons - ✔✔Motor oil or lubricating oil
✔✔Thermal Runaway - ✔✔Condition in which the heat generated exceeds the heat
losses to the environment.
✔✔Self-heating to ignition requires? - ✔✔Porous, permeable, and oxidizable material.
✔✔The most common self-heating substrates? - ✔✔Organic solids derived from plant
materials, such as cotton fabrics, wood and wood products, agricultural products, and
coal.
✔✔Pyrophoric - ✔✔Descriptive of any substance that ignites spontaneously when
exposed to air.
✔✔Transitions to flaming in upholstered furniture have been observed in time ranging
from? - ✔✔20 minutes to many hours.
✔✔Range off ignition temperatures for solids? - ✔✔270c to 450c (518F to 842F)
✔✔Ignition temperatures for non-fire retardant plastics range from? - ✔✔270C to 360C
(518F to 680F)
✔✔Ignition temperatures of wood based products range from? - ✔✔330C to 375C
(626F to 707F)
✔✔Ignition temperature of fire retardant material? - ✔✔Above 400C (752F)
✔✔For most materials, the critical radiant heat flux is in the range of? - ✔✔10 to 15
kW/m2
GRADED A+
✔✔Kelvin - ✔✔Begins at absolute zero and water freezes at 273.15 Kelvin. Uses
Celsius increments
✔✔Rankine - ✔✔Freezing point: 491.67
Uses Fahrenheit increments
✔✔Heats of Combustion Typically Range From - ✔✔10 to 45 MJ/kg.
✔✔Fuel Load Density - ✔✔The potential combustion energy output per unit floor area
[MJ/m2 (Btu/ft2)] or the mass of fuel per unit floor area [kg/m2 (lb/ft2)].
✔✔The HHR job a liquid fuel fire is dependent on two primary factors? - ✔✔The
physical characteristics of the release (i.e., surface area and depth), and the
combustion properties of the fuel.
✔✔Continuous Flame Height - ✔✔The height over which flames are visible at all
instances.
✔✔Average Flame Height - ✔✔The height over which flames are visible 50 percent of
the time.
✔✔Flame Tip Height - ✔✔The greatest height over which flames are visible at any time.
✔✔Continuous Flaming Region - ✔✔Lower portion of visible flame.
✔✔Intermittently Flaming Region - ✔✔Upper portion of the visible flame.
✔✔Plume Region - ✔✔Above the visible flame.
✔✔Heskestad Correlation - ✔✔Used to calculate flame heights
✔✔Continuous Flame Region Centerline Temperatures are approximately constant
around? - ✔✔1000C (1832F)
✔✔Intermittent Flame Region temperatures? - ✔✔about 500C (932F)
✔✔Plume Region Temperatures? - ✔✔about 300C (572F)
✔✔AIT - ✔✔Auto Ignition Temperature. The lowest temperature at which a flammable
gas-air mixture can be ignited without a pilot.
, ✔✔Flash Point - ✔✔The liquid temperature above which an ignitable concentration of
flammable vapors is generated.
✔✔Fire Point - ✔✔Burning of the vaporizing liquid fuel can be sustained as a pool fire.
✔✔CAT - ✔✔Critical Ambient Temperature
✔✔Unsaturated molecules contain? - ✔✔Carbon-to-carbon double bonds, which are
reactive.
✔✔Saturated hydrocarbons contain? - ✔✔carbon-to-carbon single bonds, which are far
less reactive than unsaturated oils.
✔✔Polyunsaturated fatty acids - ✔✔Animal and vegetable fats and oils.
✔✔Saturated hydrocarbons - ✔✔Motor oil or lubricating oil
✔✔Thermal Runaway - ✔✔Condition in which the heat generated exceeds the heat
losses to the environment.
✔✔Self-heating to ignition requires? - ✔✔Porous, permeable, and oxidizable material.
✔✔The most common self-heating substrates? - ✔✔Organic solids derived from plant
materials, such as cotton fabrics, wood and wood products, agricultural products, and
coal.
✔✔Pyrophoric - ✔✔Descriptive of any substance that ignites spontaneously when
exposed to air.
✔✔Transitions to flaming in upholstered furniture have been observed in time ranging
from? - ✔✔20 minutes to many hours.
✔✔Range off ignition temperatures for solids? - ✔✔270c to 450c (518F to 842F)
✔✔Ignition temperatures for non-fire retardant plastics range from? - ✔✔270C to 360C
(518F to 680F)
✔✔Ignition temperatures of wood based products range from? - ✔✔330C to 375C
(626F to 707F)
✔✔Ignition temperature of fire retardant material? - ✔✔Above 400C (752F)
✔✔For most materials, the critical radiant heat flux is in the range of? - ✔✔10 to 15
kW/m2
