Certified Air Filter Specialist (CAFS) Certification
Exam Prep 2026-2027 With 200 Questions and
Correct answers with Rationales Compiled from
Previous Test/ NAFA CAFS Exam Prep 2027
Question 1: 1 millionth of a meter is called a?
A) Nanometer
B) Micrometer or Micron
C) Millimeter
D) Picometer
Correct Answer: B
Rationale: A micrometer, commonly called a micron, is the standard unit of
measurement for particle size in air filtration, equivalent to one-millionth of a
meter .
Question 2: The air we breathe is composed mainly of?
A) Oxygen
B) Carbon Dioxide
C) Nitrogen
D) Argon
Correct Answer: C
Rationale: The air we breathe is approximately 78% nitrogen, making it the
primary component .
Question 3: The size of particles in outdoor air are mainly _____ and smaller.
A) 100 micrometers
B) 50 micrometers
C) 10 micrometers
D) 1 micrometer
1
,Correct Answer: D
Rationale: The majority of particles found in outdoor air are 1 micrometer in
diameter or smaller .
Question 4: Which of the following particles behave like a gas, have negligible
settling rates, and are affected by Brownian Motion?
A) Particles larger than 10 micrometers
B) Particles between 5 and 10 micrometers
C) Particles between 1 and 5 micrometers
D) Particles less than 0.1 micrometers
Correct Answer: D
Rationale: Particles smaller than 0.1 micrometers exhibit gas-like behavior due to
their negligible mass. Their movement is dominated by Brownian Motion
(diffusion) rather than gravity or inertia .
Question 5: The rated flow of air through a filter at a specified pressure drop is
called?
A) Efficiency
B) Dust Holding Capacity
C) Capacity
D) Resistance
Correct Answer: C
Rationale: Capacity is defined as the amount of airflow (e.g., CFM) a filter can
handle at a given rated pressure drop .
Question 6: What are the four principles of air filtration?
A) Straining, Impingement, Interception, Diffusion
B) Adsorption, Absorption, Straining, Diffusion
C) Impingement, Inertial Separation, Electrostatic Attraction, Straining
D) Diffusion, Sieving, Gravity Settling, Adhesion
Correct Answer: A
Rationale: The four fundamental mechanical principles by which air filters
2
,capture particles are Straining, Impingement (Inertial Impaction), Interception, and
Diffusion .
Question 7: If Static Pressure goes up, Velocity Pressure goes?
A) Up
B) Down
C) Stays the same
D) Doubles
Correct Answer: B
Rationale: Total Pressure is the sum of Static Pressure and Velocity Pressure (TP
= SP + VP). In a system with constant total pressure, if SP increases, VP must
decrease .
Question 8: In the filter industry, a manometer is used to measure?
A) Airflow (CFM)
B) Air velocity (FPM)
C) Pressure drop across a filter
D) Relative humidity
Correct Answer: C
Rationale: A manometer is the standard instrument used to measure the pressure
difference (resistance) upstream and downstream of a filter .
Question 9: An Electronic Air Cleaner (EAC) collects particles by?
A) Mechanical straining
B) Adhesive-coated fibers
C) Electrostatically charging them and collecting them on oppositely charged
plates
D) High velocity impaction on oil-wetted media
Correct Answer: C
Rationale: Electronic Air Cleaners (including two-stage electrostatic precipitators)
use an ionizer section to charge particles and a collector section with oppositely
charged plates to attract and hold them .
3
, Question 10: What is the formula for expressing air flow through a duct?
A) Q = P/V
B) Q = AV
C) Q = V/A
D) Q = PA
Correct Answer: B
Rationale: The volumetric flow rate (Q) is calculated by multiplying the cross-
sectional area of the duct (A) by the average air velocity (V) .
Question 11: Which pressure is capable of bursting a duct and may be positive or
negative?
A) Velocity Pressure
B) Total Pressure
C) Atmospheric Pressure
D) Static Pressure
Correct Answer: D
Rationale: Static Pressure exerts force equally in all directions on duct walls. A
high positive static pressure can cause a duct to burst, while a high negative static
pressure can cause it to collapse .
Question 12: Velocity Pressure must always be?
A) Negative
B) Positive
C) Zero
D) Variable
Correct Answer: B
Rationale: Velocity pressure is the pressure associated with the movement of air
and is always a positive value in the direction of flow .
Question 13: The sum of the static pressure and velocity pressure is?
A) Total Pressure
4
Exam Prep 2026-2027 With 200 Questions and
Correct answers with Rationales Compiled from
Previous Test/ NAFA CAFS Exam Prep 2027
Question 1: 1 millionth of a meter is called a?
A) Nanometer
B) Micrometer or Micron
C) Millimeter
D) Picometer
Correct Answer: B
Rationale: A micrometer, commonly called a micron, is the standard unit of
measurement for particle size in air filtration, equivalent to one-millionth of a
meter .
Question 2: The air we breathe is composed mainly of?
A) Oxygen
B) Carbon Dioxide
C) Nitrogen
D) Argon
Correct Answer: C
Rationale: The air we breathe is approximately 78% nitrogen, making it the
primary component .
Question 3: The size of particles in outdoor air are mainly _____ and smaller.
A) 100 micrometers
B) 50 micrometers
C) 10 micrometers
D) 1 micrometer
1
,Correct Answer: D
Rationale: The majority of particles found in outdoor air are 1 micrometer in
diameter or smaller .
Question 4: Which of the following particles behave like a gas, have negligible
settling rates, and are affected by Brownian Motion?
A) Particles larger than 10 micrometers
B) Particles between 5 and 10 micrometers
C) Particles between 1 and 5 micrometers
D) Particles less than 0.1 micrometers
Correct Answer: D
Rationale: Particles smaller than 0.1 micrometers exhibit gas-like behavior due to
their negligible mass. Their movement is dominated by Brownian Motion
(diffusion) rather than gravity or inertia .
Question 5: The rated flow of air through a filter at a specified pressure drop is
called?
A) Efficiency
B) Dust Holding Capacity
C) Capacity
D) Resistance
Correct Answer: C
Rationale: Capacity is defined as the amount of airflow (e.g., CFM) a filter can
handle at a given rated pressure drop .
Question 6: What are the four principles of air filtration?
A) Straining, Impingement, Interception, Diffusion
B) Adsorption, Absorption, Straining, Diffusion
C) Impingement, Inertial Separation, Electrostatic Attraction, Straining
D) Diffusion, Sieving, Gravity Settling, Adhesion
Correct Answer: A
Rationale: The four fundamental mechanical principles by which air filters
2
,capture particles are Straining, Impingement (Inertial Impaction), Interception, and
Diffusion .
Question 7: If Static Pressure goes up, Velocity Pressure goes?
A) Up
B) Down
C) Stays the same
D) Doubles
Correct Answer: B
Rationale: Total Pressure is the sum of Static Pressure and Velocity Pressure (TP
= SP + VP). In a system with constant total pressure, if SP increases, VP must
decrease .
Question 8: In the filter industry, a manometer is used to measure?
A) Airflow (CFM)
B) Air velocity (FPM)
C) Pressure drop across a filter
D) Relative humidity
Correct Answer: C
Rationale: A manometer is the standard instrument used to measure the pressure
difference (resistance) upstream and downstream of a filter .
Question 9: An Electronic Air Cleaner (EAC) collects particles by?
A) Mechanical straining
B) Adhesive-coated fibers
C) Electrostatically charging them and collecting them on oppositely charged
plates
D) High velocity impaction on oil-wetted media
Correct Answer: C
Rationale: Electronic Air Cleaners (including two-stage electrostatic precipitators)
use an ionizer section to charge particles and a collector section with oppositely
charged plates to attract and hold them .
3
, Question 10: What is the formula for expressing air flow through a duct?
A) Q = P/V
B) Q = AV
C) Q = V/A
D) Q = PA
Correct Answer: B
Rationale: The volumetric flow rate (Q) is calculated by multiplying the cross-
sectional area of the duct (A) by the average air velocity (V) .
Question 11: Which pressure is capable of bursting a duct and may be positive or
negative?
A) Velocity Pressure
B) Total Pressure
C) Atmospheric Pressure
D) Static Pressure
Correct Answer: D
Rationale: Static Pressure exerts force equally in all directions on duct walls. A
high positive static pressure can cause a duct to burst, while a high negative static
pressure can cause it to collapse .
Question 12: Velocity Pressure must always be?
A) Negative
B) Positive
C) Zero
D) Variable
Correct Answer: B
Rationale: Velocity pressure is the pressure associated with the movement of air
and is always a positive value in the direction of flow .
Question 13: The sum of the static pressure and velocity pressure is?
A) Total Pressure
4
