NFPA 623 Combustible Wood Dust & Chips
Practice Exam Questions And Correct Answers
(Verified Answers) Plus Rationales 2026 Q&A |
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1. What is the primary hazard associated with wood dust in
industrial facilities?
A. Corrosion of machinery
B. Explosion and fire
C. Water contamination
D. Noise pollution
Rationale: Wood dust is highly combustible and can form explosive dust
clouds when suspended in air. This makes fire and explosion the primary
hazard rather than corrosion, water contamination, or noise.
2. Which particle size of wood dust is considered most dangerous for
dust explosions?
A. >1000 microns
B. 500–1000 microns
C. <500 microns
D. Size does not matter
,Rationale: Finer dust particles (<500 microns) have a higher surface
area-to-volume ratio, allowing rapid combustion and increasing the risk
of explosions.
3. According to NFPA 623, what is the recommended minimum
clearance between wood dust collection ducts and ignition
sources?
A. 6 inches
B. 12 inches
C. 18 inches
D. 24 inches
Rationale: NFPA 623 specifies a minimum clearance of 18 inches to
reduce the risk of ignition from nearby heat sources.
4. Which of the following is an effective method for preventing wood
dust explosions?
A. Increasing ambient humidity
B. Proper dust collection and housekeeping
C. Storing dust in open containers
D. Ignoring static electricity
Rationale: Proper dust collection systems and routine cleaning reduce
accumulation of combustible dust, directly mitigating explosion hazards.
, 5. What type of ventilation is preferred for controlling airborne wood
dust in woodworking facilities?
A. General room ventilation
B. Local exhaust ventilation
C. Natural ventilation only
D. No ventilation
Rationale: Local exhaust ventilation captures dust at the source,
preventing dispersion into the work environment and lowering explosion
risks.
6. Which of the following is considered a secondary explosion hazard
in wood processing facilities?
A. Initial spark from a grinder
B. Combustible chips on the floor
C. Accumulated dust in ductwork
D. Open flames outside the building
Rationale: Secondary explosions occur when dust previously dispersed
or accumulated ignites due to an initial event. Accumulated dust in
ducts is a classic secondary explosion source.
7. NFPA 623 requires that dust collectors be designed to prevent
which of the following?
A. Water accumulation
, B. Internal explosions from ignited dust
C. Noise generation
D. Low airflow
Rationale: Dust collectors must have explosion relief or suppression
systems to prevent internal dust explosions, which are a common hazard
in combustible dust handling.
8. What is the recommended maximum dust layer thickness on
horizontal surfaces to prevent fire hazards?
A. 1 inch
B. 0.5 inch
C. 1/8 inch (≈3 mm)
D. 1/4 inch (≈6 mm)
Rationale: NFPA 623 specifies 1/8 inch as the maximum safe
accumulation; thicker layers can ignite and contribute to explosions.
9. Which of the following ignition sources is most commonly
associated with wood dust fires?
A. Water leaks
B. Mechanical sparks
C. Humidity
D. Plastic wrapping
Practice Exam Questions And Correct Answers
(Verified Answers) Plus Rationales 2026 Q&A |
Instant Download Pdf
1. What is the primary hazard associated with wood dust in
industrial facilities?
A. Corrosion of machinery
B. Explosion and fire
C. Water contamination
D. Noise pollution
Rationale: Wood dust is highly combustible and can form explosive dust
clouds when suspended in air. This makes fire and explosion the primary
hazard rather than corrosion, water contamination, or noise.
2. Which particle size of wood dust is considered most dangerous for
dust explosions?
A. >1000 microns
B. 500–1000 microns
C. <500 microns
D. Size does not matter
,Rationale: Finer dust particles (<500 microns) have a higher surface
area-to-volume ratio, allowing rapid combustion and increasing the risk
of explosions.
3. According to NFPA 623, what is the recommended minimum
clearance between wood dust collection ducts and ignition
sources?
A. 6 inches
B. 12 inches
C. 18 inches
D. 24 inches
Rationale: NFPA 623 specifies a minimum clearance of 18 inches to
reduce the risk of ignition from nearby heat sources.
4. Which of the following is an effective method for preventing wood
dust explosions?
A. Increasing ambient humidity
B. Proper dust collection and housekeeping
C. Storing dust in open containers
D. Ignoring static electricity
Rationale: Proper dust collection systems and routine cleaning reduce
accumulation of combustible dust, directly mitigating explosion hazards.
, 5. What type of ventilation is preferred for controlling airborne wood
dust in woodworking facilities?
A. General room ventilation
B. Local exhaust ventilation
C. Natural ventilation only
D. No ventilation
Rationale: Local exhaust ventilation captures dust at the source,
preventing dispersion into the work environment and lowering explosion
risks.
6. Which of the following is considered a secondary explosion hazard
in wood processing facilities?
A. Initial spark from a grinder
B. Combustible chips on the floor
C. Accumulated dust in ductwork
D. Open flames outside the building
Rationale: Secondary explosions occur when dust previously dispersed
or accumulated ignites due to an initial event. Accumulated dust in
ducts is a classic secondary explosion source.
7. NFPA 623 requires that dust collectors be designed to prevent
which of the following?
A. Water accumulation
, B. Internal explosions from ignited dust
C. Noise generation
D. Low airflow
Rationale: Dust collectors must have explosion relief or suppression
systems to prevent internal dust explosions, which are a common hazard
in combustible dust handling.
8. What is the recommended maximum dust layer thickness on
horizontal surfaces to prevent fire hazards?
A. 1 inch
B. 0.5 inch
C. 1/8 inch (≈3 mm)
D. 1/4 inch (≈6 mm)
Rationale: NFPA 623 specifies 1/8 inch as the maximum safe
accumulation; thicker layers can ignite and contribute to explosions.
9. Which of the following ignition sources is most commonly
associated with wood dust fires?
A. Water leaks
B. Mechanical sparks
C. Humidity
D. Plastic wrapping
