NAFI CFEI Exam Evaluation – National Association of
Fire Investigators (NAFI) – 2026/2027
DOMAIN I: FIRE SCIENCE & CHEMISTRY
Questions 1–20
Question 1
Which of the following BEST describes the fire tetrahedron?
A) Fuel, oxygen, heat, and a chemical chain reaction
B) Fuel, oxygen, heat, and an ignition source
C) Fuel, oxygen, ignition temperature, and combustion
D) Fuel, oxygen, heat, and flame
Correct Answer: A
Rationale: The fire tetrahedron expands upon the traditional fire triangle by
adding the chemical chain reaction as the fourth component. NFPA 921 identifies
these four elements—fuel, oxygen, heat, and the uninhibited chemical chain
reaction—as necessary for sustained combustion. Option B incorrectly substitutes
"ignition source" for the chain reaction; option C uses incorrect terminology; and
option D omits the chain reaction component entirely.
Question 2
Pyrolysis is BEST defined as:
A) The spontaneous ignition of materials without an external heat source
B) The chemical decomposition of a material through the action of heat
C) The rapid oxidation of a fuel that produces heat and light
D) The process by which flammable liquids vaporize at room temperature
Correct Answer: B
Rationale: Per NFPA 921, pyrolysis is the chemical decomposition of a
material through the action of heat, producing combustible vapors that can later
,ignite. Option A describes spontaneous ignition; option C describes combustion
generally; option D describes evaporation, not pyrolysis.
Question 3
A fire investigator observes that a room fire has reached a point where all
combustible contents in the room have simultaneously ignited. This phenomenon
is known as:
A) Backdraft
B) Flashover
C) Rollover
D) Flameover
Correct Answer: B
Rationale: Flashover is the transition phase in a compartment fire where all
exposed combustible surfaces reach ignition temperature nearly simultaneously,
resulting in full-room involvement. Backdraft (A) is a smoke explosion caused by
sudden introduction of oxygen; rollover (C) is flame rolling across the ceiling;
flameover (D) is a less common term for a similar phenomenon.
Question 4 (SATA)
Which of the following are modes of heat transfer recognized in fire science?
(Select all that apply.)
A) Conduction
B) Convection
C) Radiation
D) Reflection
E) Advection
Correct Answers: A, B, C
Rationale: NFPA 921 identifies three primary modes of heat
transfer: conduction (through solid materials), convection (through fluids/gases),
and radiation (through electromagnetic waves). Reflection (D) is not a mode of
,heat transfer; advection (E) is sometimes discussed but is not one of the three
primary modes recognized in NFPA 921 for fire investigation purposes.
Question 5
The lower flammable limit (LFL) of a substance refers to:
A) The minimum temperature at which a liquid produces ignitable vapors
B) The minimum concentration of a gas or vapor in air that will support
combustion
C) The maximum concentration of a gas or vapor in air that will support
combustion
D) The temperature at which a material will spontaneously ignite
Correct Answer: B
Rationale: The lower flammable limit (LFL) is the minimum concentration of a
gas or vapor in air below which combustion will not occur (the mixture is too
lean). Option A describes flash point; option C describes the upper flammable
limit (UFL); option D describes autoignition temperature.
Question 6
Which of the following statements about stoichiometry in combustion is MOST
accurate?
A) Stoichiometric mixtures always burn with the highest flame temperature
B) Stoichiometric mixtures contain the exact ratio of fuel to oxygen for complete
combustion
C) Stoichiometric combustion produces carbon monoxide as the primary product
D) Stoichiometry only applies to liquid fuels, not solids or gases
Correct Answer: B
Rationale: Stoichiometry refers to the ideal ratio of fuel to oxidizer (typically
oxygen) that results in complete combustion with no excess of either
reactant. Option A is incorrect because while stoichiometric mixtures are
efficient, highest flame temperature may vary; option C is incorrect because
, complete combustion produces CO₂ and H₂O, not CO; option D is incorrect
because stoichiometry applies to all fuel types.
Question 7
The heat release rate (HRR) of a fire is a critical measurement that:
A) Determines the color of the flames
B) Describes the total amount of heat energy released per unit time
C) Measures the temperature at the ceiling of a compartment
D) Indicates the oxygen concentration in the fire plume
Correct Answer: B
Rationale: Heat Release Rate (HRR) is the rate at which heat energy is
released by a fire, typically measured in kilowatts (kW) or megawatts (MW). It is
one of the most important parameters in fire dynamics. Option A is incorrect
(flame color relates to temperature and fuel); option C describes ceiling
temperature; option D describes oxygen concentration measurement.
Question 8
Which type of ignition occurs when a material reaches its ignition temperature
without an external spark or flame?
A) Piloted ignition
B) Autoignition
C) Forced ignition
D) Propagated ignition
Correct Answer: B
Rationale: Autoignition (also called spontaneous ignition) occurs when a
material reaches its autoignition temperature and ignites without an external
ignition source such as a spark or flame. Piloted ignition (A) requires an external
ignition source; forced ignition (C) and propagated ignition (D) are not standard
terms in NFPA 921.
Fire Investigators (NAFI) – 2026/2027
DOMAIN I: FIRE SCIENCE & CHEMISTRY
Questions 1–20
Question 1
Which of the following BEST describes the fire tetrahedron?
A) Fuel, oxygen, heat, and a chemical chain reaction
B) Fuel, oxygen, heat, and an ignition source
C) Fuel, oxygen, ignition temperature, and combustion
D) Fuel, oxygen, heat, and flame
Correct Answer: A
Rationale: The fire tetrahedron expands upon the traditional fire triangle by
adding the chemical chain reaction as the fourth component. NFPA 921 identifies
these four elements—fuel, oxygen, heat, and the uninhibited chemical chain
reaction—as necessary for sustained combustion. Option B incorrectly substitutes
"ignition source" for the chain reaction; option C uses incorrect terminology; and
option D omits the chain reaction component entirely.
Question 2
Pyrolysis is BEST defined as:
A) The spontaneous ignition of materials without an external heat source
B) The chemical decomposition of a material through the action of heat
C) The rapid oxidation of a fuel that produces heat and light
D) The process by which flammable liquids vaporize at room temperature
Correct Answer: B
Rationale: Per NFPA 921, pyrolysis is the chemical decomposition of a
material through the action of heat, producing combustible vapors that can later
,ignite. Option A describes spontaneous ignition; option C describes combustion
generally; option D describes evaporation, not pyrolysis.
Question 3
A fire investigator observes that a room fire has reached a point where all
combustible contents in the room have simultaneously ignited. This phenomenon
is known as:
A) Backdraft
B) Flashover
C) Rollover
D) Flameover
Correct Answer: B
Rationale: Flashover is the transition phase in a compartment fire where all
exposed combustible surfaces reach ignition temperature nearly simultaneously,
resulting in full-room involvement. Backdraft (A) is a smoke explosion caused by
sudden introduction of oxygen; rollover (C) is flame rolling across the ceiling;
flameover (D) is a less common term for a similar phenomenon.
Question 4 (SATA)
Which of the following are modes of heat transfer recognized in fire science?
(Select all that apply.)
A) Conduction
B) Convection
C) Radiation
D) Reflection
E) Advection
Correct Answers: A, B, C
Rationale: NFPA 921 identifies three primary modes of heat
transfer: conduction (through solid materials), convection (through fluids/gases),
and radiation (through electromagnetic waves). Reflection (D) is not a mode of
,heat transfer; advection (E) is sometimes discussed but is not one of the three
primary modes recognized in NFPA 921 for fire investigation purposes.
Question 5
The lower flammable limit (LFL) of a substance refers to:
A) The minimum temperature at which a liquid produces ignitable vapors
B) The minimum concentration of a gas or vapor in air that will support
combustion
C) The maximum concentration of a gas or vapor in air that will support
combustion
D) The temperature at which a material will spontaneously ignite
Correct Answer: B
Rationale: The lower flammable limit (LFL) is the minimum concentration of a
gas or vapor in air below which combustion will not occur (the mixture is too
lean). Option A describes flash point; option C describes the upper flammable
limit (UFL); option D describes autoignition temperature.
Question 6
Which of the following statements about stoichiometry in combustion is MOST
accurate?
A) Stoichiometric mixtures always burn with the highest flame temperature
B) Stoichiometric mixtures contain the exact ratio of fuel to oxygen for complete
combustion
C) Stoichiometric combustion produces carbon monoxide as the primary product
D) Stoichiometry only applies to liquid fuels, not solids or gases
Correct Answer: B
Rationale: Stoichiometry refers to the ideal ratio of fuel to oxidizer (typically
oxygen) that results in complete combustion with no excess of either
reactant. Option A is incorrect because while stoichiometric mixtures are
efficient, highest flame temperature may vary; option C is incorrect because
, complete combustion produces CO₂ and H₂O, not CO; option D is incorrect
because stoichiometry applies to all fuel types.
Question 7
The heat release rate (HRR) of a fire is a critical measurement that:
A) Determines the color of the flames
B) Describes the total amount of heat energy released per unit time
C) Measures the temperature at the ceiling of a compartment
D) Indicates the oxygen concentration in the fire plume
Correct Answer: B
Rationale: Heat Release Rate (HRR) is the rate at which heat energy is
released by a fire, typically measured in kilowatts (kW) or megawatts (MW). It is
one of the most important parameters in fire dynamics. Option A is incorrect
(flame color relates to temperature and fuel); option C describes ceiling
temperature; option D describes oxygen concentration measurement.
Question 8
Which type of ignition occurs when a material reaches its ignition temperature
without an external spark or flame?
A) Piloted ignition
B) Autoignition
C) Forced ignition
D) Propagated ignition
Correct Answer: B
Rationale: Autoignition (also called spontaneous ignition) occurs when a
material reaches its autoignition temperature and ignites without an external
ignition source such as a spark or flame. Piloted ignition (A) requires an external
ignition source; forced ignition (C) and propagated ignition (D) are not standard
terms in NFPA 921.
