NASCLA Accredited Commercial General ContractorSpecialties and EquipmentHard
A general contractor is installing a new cleanroom facility for a pharmaceutical manufacturing plant. The client specifies ISO Class 7 requirements. Which of the following is the most critical design parameter for the HVAC system to achieve and maintain this classification?
- AAchieving a minimum of 60 air changes per hour (ACH) with HEPA filtration.
- BUtilizing only stainless steel ductwork throughout the entire system.
- CMaintaining a constant room temperature of 72°F (22°C).
- DEnsuring a positive pressure differential relative to adjacent less-clean areas.
Show answer & explanationAnswer & explanation
Correct answer: A. Achieving a minimum of 60 air changes per hour (ACH) with HEPA filtration.
ISO Class 7 cleanrooms require a high number of air changes per hour (typically 60-90 ACH) combined with HEPA filtration to continuously remove airborne particulates, which is the primary mechanism for maintaining the specified particle count limits.
Why the other options are wrong
- B. While beneficial for cleanliness and corrosion resistance, stainless steel ductwork is not the primary factor for achieving particle count classification; proper filtration and airflow are.
- C. Temperature control is important for process and comfort, but not the primary driver for particle count classification.
- D. Positive pressure is crucial to prevent ingress of contaminants, but it's a secondary control that supports the primary function of high ACH and HEPA filtration in achieving the particle count.
ISO Cleanroom Classification
A standard (ISO 14644-1) that classifies cleanrooms based on the concentration of airborne particles per cubic meter at specified particle sizes. Lower ISO classes indicate fewer particles and higher cleanliness.
- ISO Class 7 allows up to 352,000 particles/m³ at 0.5 µm.
- Achieved primarily through high air changes per hour and HEPA/ULPA filtration.
- Positive pressure prevents unfiltered air ingress.
Memory trick: Cleanrooms need 'High Air' and 'HEPA' filters to 'Class' up.