Mitigation of Disease Spread in Hospitals: How to convert a positive pressure room to negative pressure

Here at JM Engineering PLLC we are committed to providing informative material to our clients. Over the next few weeks, we will be publishing a series of articles that highlight ways to remain healthy and reduce the spread of COVID-19 and how our engineering solutions in Heating, Ventilation & Air Conditioning (HVAC) can help. Our first suggested system modification is the temporary conversion of potential COVID-19 patient rooms from positive to negative pressure environments.    

The difference between positive and negative pressure spaces are as follows:   

Positive pressure rooms maintain a higher pressure inside the treated area than that of the surrounding environment. This means air can leave the room without circulating back in. In this way, any airborne particle that originates in the room will be filtered out. Germs, particles, and other potential contaminants in the surrounding environment will not enter the room. In medical settings, a positive pressure room allows staff to keep vulnerable patients safe from infections and disease.   

In contrast, a negative pressure room maintains lower air pressure to allow outside air into the segregated environment. This scenario traps potentially harmful particles within the negative pressure room by preventing internal air from leaving the space. Negative pressure rooms in medical facilities isolate patients with infectious conditions and protect everyone else from exposure.  

 “We want every Medical Facility to have the knowledge on how they can create short-term negative pressure areas for the treatment of COVID-19 patients” says John Melvin, PE, Principal of JM Engineering PLLC (Missoula, MT).   This is accomplished by looking for existing patient areas of a hospital where access to the COVID-19 patient treatment areas can be controlled, such that interaction via systematic air between the COVID-19 patients and the remaining areas and patient/staff populations is minimized.   Spaces within the controlled patient area can then be fully converted to outside air supply/exhaust, with supply and exhaust airflows set so rooms are in a slightly negative pressure condition relative to the adjacent corridor. “The goal of negative pressure rooms is to ensure that air from rooms with potential COVID-19 patients is not recirculated into other areas of the hospital, keeping healthcare workers and other patients safe in Medical Facilities,” Melvin explains.   

Physically converting systems to negative pressure can be done in several ways, one of which includes adding valves to the air system that can redirect airflow to temporarily stop the recirculation of air in patient treatment areas. If you are considering the option of converting your system, please reach out to a certified professional for help to ensure you can maintain a healthy hospital environment.   

Lastly, it’s important that facilities and design teams understand that the modifications discussed here can result in airflows to the modified patient rooms that are not code compliant as traditional isolation rooms. The solutions discussed in this article are proposed as temporary solutions to mitigate the spread of disease in emergency situations, not permanent system modifications.   

For more information on positive and negative pressure rooms, visit:     

For more information on “Negative Pressure Patient Room Options” visit the ASHE website.   

Unit Conversion Example Airside Economizer *** Provided by ASHEwebsite***

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