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Reversing a COVID-19 Negative Pressure Unit Back to Normal Operations

As the coronavirus pandemic continues to evolve, there will come a point when the temporary spaces made for patient treatment will need to be returned to their original configuration. While it may be tempting just to undo the changes made, it is beneficial to comprehensively review the original condition and have a detailed plan to revert back.

What goes into creating a temporary Negative Pressure Suite

It is important to understand what actions were taken when originally converting the space into an isolation or negative pressure suite. Typically, this may have involved converting the serving air handler to once through operation by closing the return air damper and treating the return fan as an exhaust system. In addition, the spaces would have been rebalanced to provide negative pressure in the isolation suite. Finally, the controls often needed to be reworked to support the temporary configuration.

In some instances, ductwork may have also been reconfigured or added to support the temporary negative pressure scenario. A great example of this would be the addition of ductwork to a plenum return system in order to create a fully ducted path for the contaminated air being exhausted from the negative pressure suite.

Due to the temporary nature of these types of projects it is vitally important that records of both the initial conditions as well as the modifications be kept. When it comes time to revert the system, knowing exactly what changed, and by how much, can be a vital starting point when putting together a plan of action, and make the whole process relatively quick and painless.

What to Plan for

When it comes time to revert the system, it may be tempting just to reverse the previous changes made. However, there are several items to consider, and a plan should be put together for a safe and most advantageous “conversion” back. In some instances, the original airflow testing numbers (prior to negative pressure work) may not be a good base to return to. In one recent project, during initial balancing, faulty fire dampers were found closed in the system, limiting exhaust air flow; this system’s original performance out of compliance with the original design intent. Any plan should address the following:

First, what is the intended use of the space in the future? If the space is going back to its previous occupancy, then this may be a simple question to answer. Even in that case, it is a good idea to review the latest FGI guidelines when putting together your plan to revert the space. Where possible, spaces should meet the most recent version of applicable codes and guidelines. This is especially relevant if the space converted was an older space. Updates to the code and guidelines may have changed the original minimum room requirements.

Second, the system should be reviewed from an infectious control standpoint. As the ductwork and air handlers were set to temporarily handle potentially contaminated exhaust, the system should be thoroughly cleaned and disinfected following CDC guidance prior to a return to service.

In some cases, physical modifications may have also been required to create the initial negative pressure space (i.e. additional doors, above ceiling wall extensions, etc.). When recommissioning the system, it is important to consider the impact these changes will have on the system as a whole. If ductwork was added to a plenum return system for example, the impact on system’s return fan performance should be evaluated.

Plan Execution

Once the plan has been developed, it is time to execute. Like the initial reconfiguration, changing the space back should be a collaborative effort between the owner, engineer, and contractor. Having representatives from each on site during the process can provide flexibility to handle any unforeseen issues that crop up.

Through having a detailed plan and the proper team members on site, it is possible for a successful reconfiguration and ultimately restore a space’s operating performance to better than original condition and in line with current codes and guidelines.

Written by:

Aaron Valentine, EIT

Mechanical Project Engineer


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