How Are Hospital Airborne Infection Isolation Rooms Built?

The pressure cascade runs corridor to anteroom to patient room, each step slightly more negative than the last. The anteroom is the airlock: staff don protective equipment there, and the two doors are interlocked or procedurally managed so both are never open together. Without the anteroom, every entry and exit is a pressure event that pushes room air into the corridor. Envelope tightness makes or breaks the design. Partitions extend to the structure above, every pipe and duct penetration is sealed, doors are gasketed with minimal undercuts, and even electrical boxes get sealed. The test-and-balance contractor must be able to achieve and hold the design pressure differential with the HVAC system at normal operation, and the design should include enough exhaust margin that the relationship survives filter loading and normal door traffic.

Twelve air changes per hour is the common design target for new airborne infection isolation rooms, with exhaust exceeding supply to maintain the negative relationship. Exhaust ductwork runs directly to the outdoors, discharged well away from outdoor air intakes, operable windows, and property lines; where that routing is impossible, HEPA filtration on the exhaust is the accepted alternative. Exhaust fans should be on the hospital's essential power so containment survives a utility outage. Continuous monitoring is what turns a design into a reliable room. A wall-mounted pressure monitor with a clear in-range indicator sits outside the room where staff check it before entering, and it alarms locally on pressure loss. The building automation system should trend the readings so facilities can spot a degrading envelope or a failing damper before it becomes a containment failure.

Use this checklist during design and plan check: • Patient room negative to anteroom, anteroom negative to corridor, per design differentials • Anteroom with interlocked or procedurally managed doors for donning and doffing • High air change rates per ASHRAE 170 with exhaust exceeding supply by design margin • Sealed envelope: partitions to structure, sealed penetrations, gasketed doors • Exhaust routed directly outdoors away from intakes, or HEPA-filtered • Continuous pressure monitor with local display and alarm at the room entry • Exhaust fans on essential power so containment survives utility outages • Self-contained patient toilet and hands-free handwash to keep the door closed