Air Handling Systems (AHU) MCQs With Answer

Air Handling Systems (AHU) MCQs With Answer — Introduction

Understanding Air Handling Units (AHUs) is essential for M.Pharm students involved in pharmaceutical production, where controlled environments maintain product quality and patient safety. This quiz collection focuses on AHU design, components, operation, validation and regulatory expectations relevant to cleanrooms and controlled areas. Questions address filters (HEPA/MERV), airflow patterns, pressurization strategies, temperature and humidity control, monitoring, maintenance and energy-efficient features. Emphasis is placed on linking engineering principles to Good Manufacturing Practices (GMP) and standards such as ISO 14644 and EU GMP Annex 1. Use these MCQs to test and deepen your comprehension before practical design, operation or validation tasks.

Q1. What is the primary function of an Air Handling Unit (AHU) in pharmaceutical cleanrooms?

• To sterilize all incoming air using chemical agents
• To control and deliver air quality, temperature, humidity and pressure for a controlled environment
• To replace the need for cleanroom garments and personal protective equipment
• To remove final product contaminants from packaging

Correct Answer: To control and deliver air quality, temperature, humidity and pressure for a controlled environment

Q2. Which filter type is most commonly used as the final air filter in critical pharmaceutical areas to achieve ISO Class 5 or EU Grade A/B?

• Carbon filter
• Pre-filter (G4)
• HEPA filter (H13/H14)
• Bag filter (F8)

Correct Answer: HEPA filter (H13/H14)

Q3. In AHU design for cleanrooms, what does “air changes per hour (ACH)” primarily describe?

• The speed at which air passes through a HEPA filter
• The number of times the entire room air volume is replaced in one hour
• The static pressure needed to maintain room differential
• The temperature fluctuation allowed per hour

Correct Answer: The number of times the entire room air volume is replaced in one hour

Q4. Which standard is most commonly referenced for airborne cleanliness classification for cleanrooms?

• ASTM D4169
• ISO 14644-1
• USP General Chapter for excipients
• IEC 60601

Correct Answer: ISO 14644-1

Q5. For maintaining unidirectional (laminar) flow in an aseptic area, which AHU design parameter is most critical?

• Use of carbon dioxide scrubbers
• Low, uniform face velocity through HEPA filters
• High humidity to settle particles
• Intermittent operation cycles

Correct Answer: Low, uniform face velocity through HEPA filters

Q6. Differential pressure between adjacent cleanroom zones is maintained primarily to:

• Minimize heat transfer between rooms
• Prevent particle migration from lower to higher cleanliness areas
• Increase the efficiency of UV lamps
• Reduce noise transmission

Correct Answer: Prevent particle migration from lower to higher cleanliness areas

Q7. Which fan type is typically preferred in AHUs for better control of airflow and static pressure in pharmaceutical HVAC systems?

• Axial fan without variable drive
• Centrifugal backward-curved fan with variable frequency drive (VFD)
• Propeller fan with fixed speed
• Mixed-flow fan with manual damper only

Correct Answer: Centrifugal backward-curved fan with variable frequency drive (VFD)

Q8. What is the main purpose of a pre-filter stage in an AHU before the HEPA filter?

• To sterilize air to sterility assurance level
• To remove large particles and extend HEPA life
• To increase air humidity
• To cool the supply air to desired temperature

Correct Answer: To remove large particles and extend HEPA life

Q9. Which test aerosol is commonly used for HEPA filter integrity testing during qualification?

• Polystyrene latex (PSL)
• Chlorofluorocarbon (CFC)
• Polyalphaolefin (PAO) or DOP surrogate
• Isopropyl alcohol vapor

Correct Answer: Polyalphaolefin (PAO) or DOP surrogate

Q10. In pharmaceutical AHU systems, what does “recirculation” of air typically aim to achieve?

• Supply sterile water to processes
• Reduce heating/cooling load and maintain cleanliness by re-filtering room air
• Increase infiltration from adjacent areas
• Eliminate the need for differential pressure control

Correct Answer: Reduce heating/cooling load and maintain cleanliness by re-filtering room air

Q11. According to GMP and Annex 1 principles, what is the preferred airflow pattern in an aseptic filling area?

• Turbulent mixing flow from walls to center
• Unidirectional (laminar) downward flow over the critical zone
• Reverse flow from floor to ceiling
• Intermittent pulsating flow

Correct Answer: Unidirectional (laminar) downward flow over the critical zone

Q12. Which parameter is most important to monitor continuously in an AHU to ensure maintenance of room cleanliness classification?

• CO2 concentration only
• Differential pressure, temperature and particle counts
• Noise level in dB
• Lighting intensity

Correct Answer: Differential pressure, temperature and particle counts

Q13. What is the effect of leaking joints or bypass around HEPA filters in a pharmaceutical AHU?

• Improved energy efficiency
• Compromised downstream cleanliness due to unfiltered air entry
• Increased humidity control accuracy
• Extended HEPA filter life

Correct Answer: Compromised downstream cleanliness due to unfiltered air entry

Q14. Which heat recovery device in AHUs reduces energy use by transferring energy between exhaust and supply air streams?

• Mixing damper
• Plate heat exchanger or heat wheel (enthalpy wheel)
• Humidifier
• HEPA filter bank

Correct Answer: Plate heat exchanger or heat wheel (enthalpy wheel)

Q15. Ultraviolet germicidal irradiation (UVGI) in AHU systems is primarily used to:

• Inactivate microorganisms on surfaces and in the air stream when used appropriately
• Replace HEPA filtration for particulate removal
• Increase particle size for easier filtration
• Neutralize volatile organic compounds (VOCs)

Correct Answer: Inactivate microorganisms on surfaces and in the air stream when used appropriately

Q16. What is the typical consequence of excessive relative humidity in controlled pharmaceutical areas?

• Improved HEPA filter efficiency
• Increased microbial growth risk and product stability issues
• Reduced condensation on equipment
• Lower energy consumption for cooling

Correct Answer: Increased microbial growth risk and product stability issues

Q17. Which method is used to qualify airflow and velocity uniformity across a HEPA filter face in a cleanroom?

• Temperature mapping only
• Tracer gas decay and anemometer traverses for velocity profile
• Visual inspection under ambient light
• Acoustic measurement

Correct Answer: Tracer gas decay and anemometer traverses for velocity profile

Q18. When commissioning an AHU for a critical area, what should be included in the performance qualification (PQ)?

• Only visual inspection of ductwork
• Verification of temperature, humidity, pressure differentials, airflow patterns and particle counts under operational conditions
• Replacement of all filters without testing
• Turning the unit on and off several times without measurements

Correct Answer: Verification of temperature, humidity, pressure differentials, airflow patterns and particle counts under operational conditions

Q19. What is “makeup air” in the context of AHU systems for pharmaceutical facilities?

• Air intentionally bypassing HEPA filters
• Fresh outdoor air introduced to replace exhaust and maintain pressure balance
• Return air recycled without filtration
• Air used only for equipment cooling

Correct Answer: Fresh outdoor air introduced to replace exhaust and maintain pressure balance

Q20. Which maintenance practice is critical to ensure long-term AHU performance and cleanroom compliance?

• Extending HEPA filter change intervals indefinitely
• Routine scheduled filter replacement, leak testing, calibration of sensors and documentation
• Painting HEPA filter frames to prevent corrosion
• Disabling alarm setpoints to avoid nuisance trips

Correct Answer: Routine scheduled filter replacement, leak testing, calibration of sensors and documentation

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