< Browse more articles


hrai5apr302020It is true that some “ultraviolet C” (UVC) light can and does help break down viruses, and will probably in time be shown to mitigate the threat of COVID-19 (though conclusively proven yet). It can also, however, make humans very sick if exposed to it directly.  It will burn the skin and eyes very seriously in a matter of seconds and could cause skin cancer and cataracts. “It’s like an arc weld flash. Very unsafe,” says Tom Wilson, air purification manager for CGF Products in Toronto. Wilson helps write HRAI Indoor Air Quality training materials.

UVC light is used by HVAC professionals to help achieve the aforementioned disruption of viruses, as it did with the SARS and MERS viruses. It is expected to do the same with COVID-19. Ultraviolet Germicidal Irradiation (UVGI) has been used for many years to disinfect the air, water, surgical instruments and other objects in hospitals, objects at airports, food production plants, and elsewhere.

Technologies include airstream UVC disinfection, upper-air UVC fixtures, surface ultraviolet disinfection, and others. Short-wavelength UV light (200-280 nm) inactivates microorganisms by destroying nucleic acids and disrupting their DNA.


HVAC professionals can provide this equipment as part of enhancements that reduce risk but would be very unwise to suggest that it is in any way ‘guaranteed’ to purify air 100% or prevent any disease. There are many ways to contract a communicable disease and it is often difficult to say categorically which were at play in a given situation.

It is reported that there are three ways that COVID-19 can be transmitted. It can move directly from person to person through vapour droplets. It can be transmitted via surfaces when one infected person contaminates a surface and the virus remains alive for a period of time, then another person touches the same surface, and perhaps unconsciously touches their own face, allowing the virus to enter the body through the nose, eyes or mouth.

The third possibility, airborne transmission, might be described as the least likely but is possible nonetheless. And with this disease, it is imperative that we leave nothing to chance.


Preventing airborne transmission is the business of HVAC professionals. HRAI offers indoor air quality training with a virtual training session coming up on May 12-13. Learn more here.[i]


ASHRAE presidential member William Bahnfleth was interviewed about COVID-19 and HVAC systems in early March 2020 by the ACHR News.[ii] He cautioned HVAC professionals to avoid making inaccurate promises about prevention measures.  He noted that the virus that causes COVID-19 moves mostly via droplet transfer, but “it's not impossible that infectious particles in the air could stay aloft long enough to be collected, say at the return grille of an HVAC system, go through a duct, and infect someone in a different space,” He suggested that ventilation, filters, and UV disinfection could all have some mitigation impact. “Using a dedicated outdoor air system also cuts down on contaminated air.”

ASHRAE has created a special COVID-19 task force to provide industry guidance during the pandemic. The group has issued a statement to counter another myth that has surfaced about the “dangers” of air conditioning use.  ASHRAE states that it is not a good idea to turn your HVAC system off -- quite the opposite:

Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 (the virus that causes COVID-19) and thus the risk of transmission through the air…In general, disabling of heating, ventilating, and air-conditioning systems is NOT a recommended measure to reduce the transmission of the virus.

The HRAI and the Air-Conditioning, Heating & Refrigeration Institute (AHRI) in Arlington, Virginia have relayed the same message in similar statements. The AHRI statement quotes Dr. Joseph Allen, Director of the Healthy Buildings program at Harvard University’s T.H. Chan School of Public Health, saying “…bringing in more outdoor air in buildings with heating and ventilation systems (or opening windows in buildings that don’t) helps dilute airborne contaminants, making infection less likely.”

Bahnfleth also noted that proper ventilation reduces the potential impact of the virus, especially if relative humidity is kept between 40% and 60%. Although filters are useful for many airborne problems, in the ACHR article Aaron Engel from Fresh-Aire UV put this in perspective. He said that currently popular and effective HEPA filters have been shown to be effective at trapping particles down to 0.3 microns in size. But the COVID-19 virus is very small, measuring between 0.06 and 0.14 microns.

According to Bahnfleth, “contractors are now learning that…surface ultraviolet disinfection and airstream UV disinfection are effective at inactivating pathogens. UV germicidal systems have also been shown to reduce microbial load and pathogens …within the HVAC system and drain pan.”

“Airborne droplets containing infectious agents can remain in room air for six minutes and longer,” said Daniel Jones, from UV Resources. “Scientists have found that COVID-19 can remain infectious on surfaces at room temperature for up to nine days.”

“The effectiveness of disinfection using UVC light is a function of three variables,” says Wilson. “The nature of the contaminant, the intensity of the UV light, and the time of exposure.” His company’s products use UVC lamps that emit, for example, 135 microwatts per centimetre2 at a distance of one metre. In a study at the University of Waterloo in 2013, these specifications were effective at breaking down the coronavirus (MERS) by 53% in one pass. Wilson cautions users that UVC light products require adherence to manufacturers’ lamp replacement schedules (example: replaced every two years). “Sometimes even when the blue light is still visibly shining, it has lost its effectiveness.”

Good indoor air quality is implied in most building codes. Codes in Canada and the United States often refer to ASHRAE Standard 62.1-2010 - Ventilation for Acceptable Indoor Air Quality. The specifications in this standard are based on comfort, so in extraordinary situations such as the current pandemic, they should be seen as minimum operating guidelines.

According to Standard 62.1-2010, “The value of 615 ppm above the outdoor concentration indicates approximately 15 cubic feet per minute of outdoor air per adult occupant doing sedentary office work where outdoor air contains 385 ppm, the current global average atmospheric CO2 concentration. In classrooms, the requirements in the ASHRAE standard 62.1, Ventilation for Acceptable Indoor Air Quality, would typically result in about 3 air changes per hour, depending on the occupant density.”

Net-zero, passive house, and other tighter and/or smaller homes employ energy recovery ventilators or heat recovery ventilators. A dedicated outdoor air system often brings in 100% fresh air at significantly reduced flow (and less total air by volume), however, with a UVC device, 100% of the building’s air would pass through it within a matter of hours.

Along with ASHRAE guidelines, The International Building Code and International Mechanical Code have specific criteria on ventilation rates for building or use type, which dictates the position of HVAC louvers, the sizing, and the positioning of ventilation fans, and provide suggestions for optimizing indoor ventilation using CO2 detectors.

Collected data can be used to adjust outside air-flow in real-time for a more efficient (and less expensive) operation. General advice to improve indoor air also includes regular duct cleanings, inspections, air filter replacement, opening, and unblocking of air vents.

For Canadians, the outbreak has meant being indoors more, primarily at home or in some other single building for long periods. People may start thinking about indoor air quality in a more generalized sense, beyond the mitigation of the virus, and this will create opportunities. Paying more attention to ventilation and filtration can decrease hazardous volatile organic compounds and substances such as methane, propane, butane, acetone, formaldehyde, allergens, and of course, viruses.

According to the Canadian Centre for Occupational Health and Safety,[iii] indoor air contaminants can also include dust, dust mites, fibreglass, asbestos, gases from building materials, vapours from cleansers, solvents, pesticides, disinfectants, glues, off-gas emissions from furniture, carpets, and paints, microbial contaminants, fungi, moulds, bacteria, ozone from electric motors, electrostatic air cleaners and photocopiers, carbon dioxide, perfume, body odours, and tobacco smoke.


Some of the recent mainstream media confusion about UVC light may have been caused by reports that prototypes of “Far-UVC light,” lamps have been developed, based on research published by Columbia University in 2018. These lamps are said to be effective for killing most viruses and are not harmful to humans but they have not yet been fully tested, approved, and commercialized.

These Far-UVC lamps, in production by Ushio America Inc. and Eden Park Illumination, are said to be about nine months from approval and manufacturing. There is a chance the FDA will accelerate their approval, if it’s possible to complete proper testing and if it thinks they will be a useful tool in the battle against COVID-19. It should be remembered that proper safety testing could become a matter of life and death, despite what careless people who are in a hurry might say or do. 

Let’s not be hurrying and careless. Let’s keep the HVAC system running. Let’s not expose UVC light to human bodies. Stay safe out there; and indoors.