NAFA CERTIFIED AIR FILTER SPECIALIST (CAFS) EXAM PRACTICE TEST |
COMPLETE QUESTIONS AND DETAILED ANSWERS WITH RATIONALES
|CAFS EXAM PREP LATEST 2026/2027 UPDATE
SECTION 1: AIR FILTRATION FUNDAMENTALS
Questions 1-35
Q1. Which statement best explains why airborne particulate filtration is
considered essential for maintaining acceptable indoor environmental quality
in commercial buildings?
A) Filters increase indoor humidity levels automatically
B) Filters remove contaminants that can affect occupants, equipment, and
processes
C) Filters eliminate all airborne gases and odors completely
D) Filters replace the need for outdoor air ventilation
✅ Answer: B
Rationale: Air filters primarily remove airborne particulates that may impact
health, productivity, equipment performance, and sensitive manufacturing
processes. Filters do not control humidity, eliminate all gases, or replace
ventilation.
Q2. Which particle size range is generally considered the most difficult for
many mechanical air filters to capture efficiently?
A) Larger than 50 microns
B) Between 0.3 and 1.0 microns
C) Larger than 100 microns
D) Between 20 and 50 microns
✅ Answer: B
Rationale: The 0.3-1.0 micron size range represents the Most Penetrating
Particle Size (MPPS) for many mechanical filters. Particles in this range
are difficult to capture because they are too small for inertial impaction
and too large for diffusion.
1
,Q3. What is the primary mechanism by which a mechanical air filter captures
larger particles (typically above 1 micron)?
A) Diffusion
B) Electrostatic attraction
C) Inertial impaction
D) Interception
✅ Answer: C
Rationale: Inertial impaction is the primary mechanism for capturing larger
particles. As air changes direction around fibers, larger particles have
enough momentum to continue in their original path and collide with fibers.
Q4. Which filtration mechanism is most effective at capturing submicron
particles (below 0.1 micron)?
A) Inertial impaction
B) Interception
C) Diffusion
D) Sieving/Straining
✅ Answer: C
Rationale: Diffusion is most effective for submicron particles. These small
particles are subject to Brownian motion, causing them to diffuse and
collide with filter fibers.
Q5. What is the "Most Penetrating Particle Size" (MPPS)?
A) The smallest particle that can be captured
B) The largest particle that can pass through
C) The particle size that has the lowest filtration efficiency
D) The particle size that has the highest filtration efficiency
✅ Answer: C
Rationale: The MPPS is the particle size at which the filter exhibits its
lowest efficiency. For mechanical filters, this is typically between 0.1
and 0.5 microns.
2
,Q6. Which of the following is NOT a primary filtration mechanism?
A) Inertial impaction
B) Interception
C) Diffusion
D) Absorption
✅ Answer: D
Rationale: Absorption is not a filtration mechanism. The four primary
mechanical filtration mechanisms are inertial impaction, interception,
diffusion, and electrostatic attraction (for electret media).
Q7. What is "interception" as a filtration mechanism?
A) Particles collide with fibers due to their inertia
B) Particles are captured by diffusing to fibers
C) Particles follow airflow and are captured when they contact fibers
D) Particles are captured by electrostatic forces
✅ Answer: C
Rationale: Interception occurs when particles follow the airstream and are
captured when they physically contact a fiber as the air flows around it.
Q8. Which type of filter relies primarily on electrostatic attraction for
particle capture?
A) Mechanical pleated filter
B) Electret filter (charged media)
C) HEPA filter
D) Carbon filter
✅ Answer: B
Rationale: Electret filters use charged media to attract and capture
particles electrostatically. Mechanical filters rely on physical mechanisms;
HEPA filters use mechanical mechanisms; carbon filters adsorb gases.
Q9. What happens to the efficiency of an electret filter over time?
A) Efficiency increases indefinitely
3
, B) Efficiency remains constant
C) Efficiency may decrease due to loss of charge
D) Efficiency is not affected by time
✅ Answer: C
Rationale: Electret filters can lose their electrostatic charge over time,
especially when exposed to certain contaminants (oils, smoke). This can
decrease efficiency.
Q10. What is "sieving" or "straining" as a filtration mechanism?
A) Capturing particles smaller than the pore size
B) Capturing particles larger than the pore size
C) Capturing particles by diffusion
D) Capturing particles by electrostatic attraction
✅ Answer: B
Rationale: Sieving or straining captures particles that are larger than the
pores or gaps between filter fibers. This is the simplest filtration
mechanism.
Q11. Which particle size range is of greatest concern for respiratory health?
A) Greater than 50 microns
B) 10-50 microns
C) 2.5-10 microns (PM10)
D) Less than 2.5 microns (PM2.5) and ultrafine particles
✅ Answer: D
Rationale: PM2.5 and ultrafine particles are of greatest concern because
they can penetrate deep into the respiratory system, reaching the alveoli
and entering the bloodstream.
Q12. What is the primary purpose of a pre-filter in a multi-stage filtration
system?
A) To remove gases and odors
B) To capture larger particles and extend the life of the final filter
4
COMPLETE QUESTIONS AND DETAILED ANSWERS WITH RATIONALES
|CAFS EXAM PREP LATEST 2026/2027 UPDATE
SECTION 1: AIR FILTRATION FUNDAMENTALS
Questions 1-35
Q1. Which statement best explains why airborne particulate filtration is
considered essential for maintaining acceptable indoor environmental quality
in commercial buildings?
A) Filters increase indoor humidity levels automatically
B) Filters remove contaminants that can affect occupants, equipment, and
processes
C) Filters eliminate all airborne gases and odors completely
D) Filters replace the need for outdoor air ventilation
✅ Answer: B
Rationale: Air filters primarily remove airborne particulates that may impact
health, productivity, equipment performance, and sensitive manufacturing
processes. Filters do not control humidity, eliminate all gases, or replace
ventilation.
Q2. Which particle size range is generally considered the most difficult for
many mechanical air filters to capture efficiently?
A) Larger than 50 microns
B) Between 0.3 and 1.0 microns
C) Larger than 100 microns
D) Between 20 and 50 microns
✅ Answer: B
Rationale: The 0.3-1.0 micron size range represents the Most Penetrating
Particle Size (MPPS) for many mechanical filters. Particles in this range
are difficult to capture because they are too small for inertial impaction
and too large for diffusion.
1
,Q3. What is the primary mechanism by which a mechanical air filter captures
larger particles (typically above 1 micron)?
A) Diffusion
B) Electrostatic attraction
C) Inertial impaction
D) Interception
✅ Answer: C
Rationale: Inertial impaction is the primary mechanism for capturing larger
particles. As air changes direction around fibers, larger particles have
enough momentum to continue in their original path and collide with fibers.
Q4. Which filtration mechanism is most effective at capturing submicron
particles (below 0.1 micron)?
A) Inertial impaction
B) Interception
C) Diffusion
D) Sieving/Straining
✅ Answer: C
Rationale: Diffusion is most effective for submicron particles. These small
particles are subject to Brownian motion, causing them to diffuse and
collide with filter fibers.
Q5. What is the "Most Penetrating Particle Size" (MPPS)?
A) The smallest particle that can be captured
B) The largest particle that can pass through
C) The particle size that has the lowest filtration efficiency
D) The particle size that has the highest filtration efficiency
✅ Answer: C
Rationale: The MPPS is the particle size at which the filter exhibits its
lowest efficiency. For mechanical filters, this is typically between 0.1
and 0.5 microns.
2
,Q6. Which of the following is NOT a primary filtration mechanism?
A) Inertial impaction
B) Interception
C) Diffusion
D) Absorption
✅ Answer: D
Rationale: Absorption is not a filtration mechanism. The four primary
mechanical filtration mechanisms are inertial impaction, interception,
diffusion, and electrostatic attraction (for electret media).
Q7. What is "interception" as a filtration mechanism?
A) Particles collide with fibers due to their inertia
B) Particles are captured by diffusing to fibers
C) Particles follow airflow and are captured when they contact fibers
D) Particles are captured by electrostatic forces
✅ Answer: C
Rationale: Interception occurs when particles follow the airstream and are
captured when they physically contact a fiber as the air flows around it.
Q8. Which type of filter relies primarily on electrostatic attraction for
particle capture?
A) Mechanical pleated filter
B) Electret filter (charged media)
C) HEPA filter
D) Carbon filter
✅ Answer: B
Rationale: Electret filters use charged media to attract and capture
particles electrostatically. Mechanical filters rely on physical mechanisms;
HEPA filters use mechanical mechanisms; carbon filters adsorb gases.
Q9. What happens to the efficiency of an electret filter over time?
A) Efficiency increases indefinitely
3
, B) Efficiency remains constant
C) Efficiency may decrease due to loss of charge
D) Efficiency is not affected by time
✅ Answer: C
Rationale: Electret filters can lose their electrostatic charge over time,
especially when exposed to certain contaminants (oils, smoke). This can
decrease efficiency.
Q10. What is "sieving" or "straining" as a filtration mechanism?
A) Capturing particles smaller than the pore size
B) Capturing particles larger than the pore size
C) Capturing particles by diffusion
D) Capturing particles by electrostatic attraction
✅ Answer: B
Rationale: Sieving or straining captures particles that are larger than the
pores or gaps between filter fibers. This is the simplest filtration
mechanism.
Q11. Which particle size range is of greatest concern for respiratory health?
A) Greater than 50 microns
B) 10-50 microns
C) 2.5-10 microns (PM10)
D) Less than 2.5 microns (PM2.5) and ultrafine particles
✅ Answer: D
Rationale: PM2.5 and ultrafine particles are of greatest concern because
they can penetrate deep into the respiratory system, reaching the alveoli
and entering the bloodstream.
Q12. What is the primary purpose of a pre-filter in a multi-stage filtration
system?
A) To remove gases and odors
B) To capture larger particles and extend the life of the final filter
4
