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Cashins & Associates Blog

Return To Work - Localized General Exhaust Ventilation and COVID-19

Posted by Robert Cashins on Tue, Jun, 09, 2020 @ 13:06 PM

COVID-19 VentilationPeople are concerned about returning to work in an environment that may expose them to the Coronavirus. To minimize their concern, companies are considering a variety of changes that will potentially reduce the spread of the virus. Inhalation of droplets from coughing or sneezing is thought to be the major route of exposure. Social distancing can alleviate the exposure to large droplets (>5 microns) and the inhalation of those large droplets. Cloth masks and surgical masks provide limited if any protection.

Droplet nuclei (very small particles, mostly <2 microns) may be more difficult to control due to their small size and ability to follow room air currents and to remain suspended in air for long periods of time. Aside from properly fitted respirators and NIOSH Certified N95 filtering facepiece respirators there appears to be very little benefit from the use of cloth or surgical masks.

In an office or any interior environment, it is important to look beyond masks to minimize the spread of the Coronavirus. A basic principle of industrial hygiene is to use ventilation to control the release of a contaminant.

Local exhaust is placed as close to the source of release as possible to remove the contaminant at its source. A less effective control is to use general ventilation to dilute the contaminant. With the Coronavirus, the source is an infected individual. It is not feasible to control the release at the source (exhaled breath). It is also less than ideal to use general office ventilation that requires the airborne droplet nuclei to travel across the room before being captured by an HVAC return air opening in a wall.

A third alternative, localized general exhaust ventilation, may be a viable option. The sketch shows one possible option. By placing an exhaust duct close to where a group of workers generally spend most of their time, the droplet nuclei can be captured by the HVAC system very soon after being released by an infected worker. The concept is not 100% effective but may be a step up from a traditional HVAC return air setup.

The sketch shows one possible arrangement. Creative people can conceive of many other arrangements.

The same concept would work at a restaurant if the exhaust inlet were placed above the center of a table.

The exhaust air could be provided by the facility HVAC system with a MERV 14 filter or better or by a recirculating HEPA filter unit.

We can assist with ventilation design concepts that are specific to your needs. Contact us and see how we can help you return to work safely!COVID-19 Getting Back to Work Safely - We can Help!

Topics: exhaust ventilation, Coronavirus

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