The Centers for Disease Control and Prevention (CDC) has guidance for businesses and employers to plan for and respond to COVID-19. This guidance includes simple strategies that many employers already have in place, such as actively encouraging sick employees to stay home, providing information on whom to contact if employees become sick, and providing employees with access to soap, water, hand hygiene, and cleaning supplies.

Current evidence suggests that SARS-CoV-2 may remain viable for hours to days on surfaces made from a variety of materials. For construction workers specifically, potential exposures might occur by touching their nose, mouth, or eyes after touching surfaces contaminated with COVID-19 or handling items that others with COVID-19 have touched or handled. CDC suggests all construction workers take steps to prevent exposures and the spread of COVID-19:

• Workers should put a distance of 6 feet between themselves and others, including other workers, to the extent possible.
• Workers should limit their numbers to maintain a distance of at least 6 feet between each other in small areas, such as jobsite elevators, trailers, and vehicles.
• Workers should wear cloth face coverings in settings where other social distancing measures are difficult to maintain. Cloth face coverings may slow the spread of the virus and keep people who may have the virus and do not know it from transmitting it to others. Cloth face coverings are NOT surgical masks or respirators and are not appropriate substitutes for them in workplaces where masks or respirators are recommended or required.
• Workers should routinely clean and disinfect frequently touched surfaces such as shared tools, machines, vehicles, and other equipment, handrails, doorknobs, and portable toilets.
• Workers should wash their hands often:
• Wash hands with soap and water for at least 20 seconds, especially after a potential exposure, or after blowing their nose, coughing, or sneezing.
• If soap and water are not readily available, use a hand sanitizer that contains at least 60 percent alcohol.
• Avoid touching eyes, nose, or mouth with unwashed hands.

Employers of construction workers should take steps to protect their employees, including:

• Institute measures to physically separate or increase distance between employees, other coworkers, and customers, such as modifying work schedules and restricting access to reduce the number of workers in enclosed areas.
• Explore alternative ways to promote hand hygiene, if there is difficulty sourcing hand sanitizer or providing running water on site, such as installing temporary hand washing stations.
• Clean and disinfect frequently touched surfaces, and provide disposable disinfectant wipes, cleaner, or spray so employees can wipe down frequently touched surfaces such as those in workspaces and breakrooms.

COVID-19 & HVAC Systems

CDC has not posted guidance on the decontamination of building HVAC systems potentially exposed to SARS-CoV-2. To date, we have not identified confirmatory evidence to demonstrate that viable virus is contaminating these systems. Should such systems actually become contaminated with viable virus, the most likely scenario is believed to be that the deposited virus would lose its viability naturally within hours-to-days, and thus, there is no guidance advocating proactive system shutdown for decontamination and/or filter exchange.  

The 3 hour reference that is sometimes reported, is a misunderstanding of data resulting from a recent NIH-led experiment where intentionally aerosolized SARS-CoV-2 virus remained viable in aerosols throughout the duration of the experiment. There was still viable virus in the air at the conclusion of the 3-hour experiment. The same researchers determined that the half-life for the intentionally aerosolized virus was 2.7 hours. It is important to note that it is not yet known if naturally-aerosolized SARS-CoV-2 virus would behave similarly. It is also important to note that to date, infectious SARS-CoV-2 virus has not been isolated from aerosol samples collected in the treatment rooms of patients with COVID-19. 

So how does this information affect HVAC technicians? There should probably be screening questions asked of the residence occupants prior to arrival, similar to those asked of international travelers arriving at U.S. airports. If there is no reason to suspect that the occupant may be infected with COVID-19, then the HVAC technician may reasonably conduct the repair/maintenance activities using the same social distancing rules they would use in the general community.

If there was reason to suspect the residence may have recently been occupied by a known/suspected COVID-19 positive person, then it is reasonable to suggest some period of time for the residence to remain vacant prior to entry by the HVAC technician. The exact amount of time would vary considerably, based upon a multitude of factors related to the infected person(s) and the residence design/operation.

One approach might be to use the guidance for re-entry that is posted by CDC for Cleaning and Disinfection for Community Facilities. This guidance suggests opening outside windows and doors to ventilate the area and waiting 24 hours or as long as practical before re-entering the area to begin cleaning and disinfection.

Using similar logic, an HVAC technician entering a residence previously occupied by a person with known/suspect COVID-19 disease might use a similar waiting period, then utilize appropriate gloves, shoe covers, eye protection and a face covering prior to entering the residence for HVAC repair.

It’s important to note that in this circumstance, the face covering is not intended for respiratory protection, but is intended to assist the technician from inadvertent touching of their face. If available, an N95 or greater respirator, used in conjunction with an OSHA-compliant respiratory protection program, could be used instead of the face mask. 

COVID-19 Cluster At Restaurant in Guangzhou, China

It is important to note that in the report of a COVID-19 cluster associated with a restaurant in Guangzhou, China, airborne transmission was not thought to have occurred over long distances and the HVAC system itself was not suspected to have been recirculating viable virus aerosols. Rather, the authors theorized that the presence of strong air currents generated by the air conditioner may have assisted the dissemination of aerosolized droplets moderately beyond the range usually associated with droplet transmission.

This scenario is insufficient to warrant abandoning air-conditioning altogether but it does encourage reasonable consideration as to how it is utilized. Perhaps the biggest takeaway from the engineering evaluation from the same COVID-19 cluster was the lack of outdoor air that was supplied into the occupied restaurant environment. As opposed to the described restaurant scenario where the same indoor air was persistently recirculated, an HVAC system that appropriately introduces outdoor air combined with air filtration should help to dilute any indoor aerosol concentrations.

Other indoor interventions such as upper-room UVGI can also contribute to a more protected indoor environment. However, when outdoor conditions allow, a highly ventilated space with lots of natural ventilation is also a practical approach to preventing indoor aerosol accumulation.

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