NFPA 660 – Combustible Dust Consolidated
Standards Practice Questions And Correct
Answers (Verified Answers) Plus Rationales
2026 Q&A | Instant Download Pdf
1. Which NFPA standard does NFPA 660 consolidate for combustible
dust?
a) NFPA 61 and NFPA 654
b) NFPA 61, NFPA 654, NFPA 484, NFPA 655
c) NFPA 68 and NFPA 69
d) NFPA 10 and NFPA 25
Rationale: NFPA 660 consolidates several combustible dust-related
standards including NFPA 61, 654, 484, and 655 to provide a
comprehensive approach.
2. The primary goal of NFPA 660 is to:
a) Provide fire department response protocols
b) Prevent and mitigate combustible dust fires and explosions
, c) Regulate industrial equipment design
d) Provide electrical safety guidance
Rationale: NFPA 660 focuses on hazard identification, prevention,
and mitigation related to combustible dust in facilities.
3. What is the minimum spacing requirement for combustible dust
accumulation in a general industrial area?
a) 0.25 inch
b) 0.5 inch
c) 1/32 inch (approximately 0.8 mm)
d) 1 inch
Rationale: NFPA 660 references NFPA 654, which specifies that
accumulations exceeding 1/32 inch can present an explosion hazard.
4. Which of the following is considered a combustible dust?
a) Flour
b) Granite
c) Water
d) Concrete
Rationale: Combustible dusts include fine powders of materials that
can ignite and explode; flour is a classic example.
5. What does the term “deflagration” refer to in NFPA 660?
a) Slow chemical reaction
b) Rapid combustion with subsonic flame propagation
c) Electrical short-circuit
, d) Explosive detonation
Rationale: Deflagration is a rapid combustion process where the
flame front moves at subsonic speed, common in dust explosions.
6. NFPA 660 requires hazard analysis for which dust layer thickness?
a) 1 mm
b) 0.25 mm
c) 1/32 inch (0.8 mm)
d) 1/16 inch
Rationale: Layers exceeding 1/32 inch are considered significant
enough to require hazard assessment.
7. Which of the following is a recommended housekeeping method for
combustible dust?
a) Sweeping with a dry broom
b) Vacuuming with an approved industrial vacuum
c) Compressed air blowing
d) Igniting small dust piles
Rationale: Approved industrial vacuums prevent dust clouds that can
ignite; sweeping or compressed air may increase explosion risk.
8. NFPA 660 defines “dust deflagration hazard” primarily based on:
a) Color of the dust
b) Particle size, concentration, and ignition source
c) Dust odor
d) Chemical purity
, Rationale: The deflagration hazard depends on physical properties of
the dust and presence of ignition sources.
9. What is the recommended maximum dust layer thickness on
horizontal surfaces?
a) 1 inch
b) 0.5 inch
c) 1/32 inch
d) 1/16 inch
Rationale: Maintaining dust layers below 1/32 inch reduces
explosion risks.
10. Which type of venting does NFPA 660 suggest for dust
collectors?
a) Explosion venting to a safe location
b) No venting required
c) Roof venting without calculations
d) Manual opening hatches
Rationale: Explosion venting helps relieve pressure from dust
collector explosions and directs it safely away from personnel.
11. Ignition sources for combustible dust can include:
a) Hot surfaces
b) Friction sparks
c) Electrical sparks
d) All of the above
Standards Practice Questions And Correct
Answers (Verified Answers) Plus Rationales
2026 Q&A | Instant Download Pdf
1. Which NFPA standard does NFPA 660 consolidate for combustible
dust?
a) NFPA 61 and NFPA 654
b) NFPA 61, NFPA 654, NFPA 484, NFPA 655
c) NFPA 68 and NFPA 69
d) NFPA 10 and NFPA 25
Rationale: NFPA 660 consolidates several combustible dust-related
standards including NFPA 61, 654, 484, and 655 to provide a
comprehensive approach.
2. The primary goal of NFPA 660 is to:
a) Provide fire department response protocols
b) Prevent and mitigate combustible dust fires and explosions
, c) Regulate industrial equipment design
d) Provide electrical safety guidance
Rationale: NFPA 660 focuses on hazard identification, prevention,
and mitigation related to combustible dust in facilities.
3. What is the minimum spacing requirement for combustible dust
accumulation in a general industrial area?
a) 0.25 inch
b) 0.5 inch
c) 1/32 inch (approximately 0.8 mm)
d) 1 inch
Rationale: NFPA 660 references NFPA 654, which specifies that
accumulations exceeding 1/32 inch can present an explosion hazard.
4. Which of the following is considered a combustible dust?
a) Flour
b) Granite
c) Water
d) Concrete
Rationale: Combustible dusts include fine powders of materials that
can ignite and explode; flour is a classic example.
5. What does the term “deflagration” refer to in NFPA 660?
a) Slow chemical reaction
b) Rapid combustion with subsonic flame propagation
c) Electrical short-circuit
, d) Explosive detonation
Rationale: Deflagration is a rapid combustion process where the
flame front moves at subsonic speed, common in dust explosions.
6. NFPA 660 requires hazard analysis for which dust layer thickness?
a) 1 mm
b) 0.25 mm
c) 1/32 inch (0.8 mm)
d) 1/16 inch
Rationale: Layers exceeding 1/32 inch are considered significant
enough to require hazard assessment.
7. Which of the following is a recommended housekeeping method for
combustible dust?
a) Sweeping with a dry broom
b) Vacuuming with an approved industrial vacuum
c) Compressed air blowing
d) Igniting small dust piles
Rationale: Approved industrial vacuums prevent dust clouds that can
ignite; sweeping or compressed air may increase explosion risk.
8. NFPA 660 defines “dust deflagration hazard” primarily based on:
a) Color of the dust
b) Particle size, concentration, and ignition source
c) Dust odor
d) Chemical purity
, Rationale: The deflagration hazard depends on physical properties of
the dust and presence of ignition sources.
9. What is the recommended maximum dust layer thickness on
horizontal surfaces?
a) 1 inch
b) 0.5 inch
c) 1/32 inch
d) 1/16 inch
Rationale: Maintaining dust layers below 1/32 inch reduces
explosion risks.
10. Which type of venting does NFPA 660 suggest for dust
collectors?
a) Explosion venting to a safe location
b) No venting required
c) Roof venting without calculations
d) Manual opening hatches
Rationale: Explosion venting helps relieve pressure from dust
collector explosions and directs it safely away from personnel.
11. Ignition sources for combustible dust can include:
a) Hot surfaces
b) Friction sparks
c) Electrical sparks
d) All of the above
