The widespread transmission of COVID-19 across the world has rapidly increased the demand for and importance of specialized ventilation in hospital rooms. Thankfully, there have been modernizations that make patient isolation and maintaining safe distancing standards possible for hospitals. Engineers have designed negative pressure rooms to contain airborne viruses and other aerosol matter.

In general, air will always move from areas of high pressure to areas of low pressure. Negative pressure is just a term used to describe air pressure that is below the normal atmospheric pressure. Negative pressure rooms keep the room air pressure level slightly below the normal air pressure that exists outside of the room, generally in the hallways or prep room/waiting room. This is done by exhausting more air than is supplied to the room. The exhaust air normally passes through a filtration system and is exhausted to the exterior of the building so the contaminated air does not get recirculated back through the system.

Since the air will flow from high to low pressure, air will always enter the room, but not escape out anywhere besides where it is appropriately being exhausted. Precise control is needed to achieve the pressure differentials between the room and surrounding areas. With today’s technology, this is achieved by specialized air valves, pressure sensors, and monitoring devices outside of the rooms. All of the above items are controlled and monitored by the Building Management System (BMS). The BMS can show current conditions and alarm users if a problem exists.

Engineers have to make sure they design their airflow values and control system set points properly in order to maintain the negative pressure. Anterooms, which are waiting and prep rooms between the hallway and isolation room, are sometimes utilized for wash-up and changing into gowns before entering the room. The air pressure within this anteroom will also need to be carefully considered so that the air does not flow from the isolation room into the prep room. Ideally, air would flow from the hallway, into the anteroom, and then from the anteroom into the isolation room. If it was the other way around, the air would be flowing backwards from the room into the hallway, which would potentially endanger anyone outside of the room.

If you have any questions about the design of negative pressure rooms or require mechanical engineering services, contact Director of Engineering Design Tom Gilmartin, PE, PMP, LEED AP, at (716) 592-3980 ext. 124 or [email protected].