Workers Health & Safety Centre

Aerosol spread of COVID-19 virus, evidence and experts support urgent action

Despite much debate, the evidence is clear —without preventive measures, small aerosol particles in indoor settings can be a primary source of transmission of the COVID-19 virus.
 
Since the outset of the COVID-19 pandemic, efforts to prevent transmission have focused on person-to-person close contact. In short, addressing situations where an infected person emits large respiratory droplets that quickly settle in the mouth, nose or eyes or inhaled directly into the lungs of anyone in the immediate vicinity. This route of transmission remains a common source of potential exposure and as such, at the heart of measures to prevent the spread of COVID-19.

The evidence

However, understandings have changed when it comes to small respiratory aerosols emitted by infected persons. According to scientists a significant lesson driven home through the experience of the pandemic is “the distinction between [large] ‘droplet’ and [small] ‘aerosol’ spread is a false dichotomy that is inconsistent with contemporary knowledge about respiratory aerosols.” Persons infected with the virus — even with no symptoms — can emit both large droplets and smaller aerosols, even when they talk or breathe and not just when they cough or sneeze. Smaller infectious viral particles can remain suspended and accumulate in the air, especially in poorly ventilated indoor spaces, for hours. They can also travel distances greater than six feet depending on the surrounding air flow.
 
So, while current public health directives (including physical distancing, wearing masks and respirators, proper sneeze/cough etiquette, hand hygiene and enhanced cleaning and disinfecting protocols) are critical, many are proposing further reasonable precautions in the form of enhanced ventilation and even better masking to help prevent or reduce exposure and transmission.

The experts

To this end, hundreds of Canadian and international experts and advocates sent an open letter in January to Canadian federal, provincial and territorial governments and Medical Officers of Health calling for urgent updates to COVID-19 guidance that fully account for aerosol transmission of the virus in workplaces, public spaces and private homes. "Investing in ventilation, indoor air quality and appropriate personal protective equipment now will save lives and prevent economic hardship in the future," the letter read.
 
Recently, the same group of experts sent a similar follow up letter, citing the emergence of virus variants and as slower than anticipated supply of vaccines as reasons behind their renewed appeal for action, which must include clear public messaging and education about the risk of aerosol transmission and what to do about it.
 
The Public Health Agency of Canada (PHAC) updated their guidance document suggesting, “Outbreaks have been linked to poor ventilation where the virus appears to have been transmitted through aerosol production from infected individuals that became concentrated in the air over time.” PHAC adds, “In addition to other public health measures, ventilation has an important role in reducing the transmission of COVID-19 indoors.” 
 
Most provincial and territorial government agencies, on the other hand, including Public Health Ontario, have yet to recognize aerosol transmission as a key public and workplace source of COVID-spread.

Enhanced ventilation

Calls to address aerosol transmission of the virus through enhanced ventilation are not new. Globally-recognized standard setting organization, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), published a position document in April, 2020, stating “Transmission of SARS-CoV-2 [the virus that causes COVID-19 disease] through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures.”
 
In July, a group of international experts published an open letter stating their belief the evidence is sufficient to warrant enhanced ventilation measures among the many ways to reduce transmission of the COVID-19 virus indoors and in confined spaces.
 
In September, a report by Canada’s Chief Science Advisor Expert Panel on COVID-19 offered specific strategies for improving ventilation and filtration to reduce transmission and improve indoor air quality, including mandatory ventilation management in public and crowded spaces.
 
On January, 12, 2021, the Ontario Society of Professional Engineers weighed in on the need for enhanced ventilation as well.
 
More recently, a group of American experts forwarded similar concerns and recommendations to the U.S. government calling for updated guidelines including enhanced ventilation. They also called for better respiratory protection—particularly for health care and other frontline workers.

Enhanced respiratory protection

Concerns with the virus variants are also driving calls to revisit masking requirements. For health care workers and some essential workers, signatories to the above-mentioned Canadian letters urge access to fit-tested respirators (N95, elastomeric or equivalent).
 
Here in Ontario, wearing a non-medical mask, such as a cloth mask, that covers the nose, mouth and chin is mandatory in almost all public indoor situations and settings across Ontario, including workplaces and businesses outside of health care settings. In these non-health care instances, the Public Health Agency of Canada recommends the use of three-layer non-medical masks. This guidance, however, was advanced before the virus variants first appeared in Canada.   
 
Since then, some European countries have mandated better protections by imposing new masking requirements to enhance public and worker safety. Germany, for instance, is moving away from cloth masks, now requiring medical-grade masks in shops and on public transit. Austria implemented similar requirements for those over 14 years of age on public transit, businesses open to the public, indoor and outdoor markets, even carpooling. The French government announced similar masking recommendations, also citing the need to assure better protection than can be afforded by cloth masks. 
 
Most recently the CDC published research and guidance on the effectiveness of double masking, where a cloth mask is worn over a medical mask. They also looked at the effectiveness of using a medical mask whose ear loops are knotted and extra material is tucked and flattened close to the face. The findings suggest benefits with either of these enhancements derived from a combination of reducing exposure to potentially infectious aerosols from the wearer (source control) and reduced exposure of the uninfected wearer (personal protection). Exposure decreased by upwards of 95 per cent when both infectious wearer and uninfected wearer adopted either of these measures. The CDC concluded, “Innovative efforts to improve the fit of cloth and medical procedure masks to enhance their performance merit attention.”

WHSC can help

To assist workers, joint health and safety committees (JHSCs), worker health and safety reps, supervisors, employers and others during the pandemic, the Workers Health & Safety Centre (WHSC) has kept pace with evidence and expert advice by updating and expanding a series of comprehensive fact sheets detailing effective COVID-19 control measures and procedures. These include recently updated sheets on enhanced ventilation plus respiratory and eye protection
 
While information is important, training, real training, not just the sharing of information, is a key way employers meet their significant information and instruction obligations outlined in Ontario’s Occupational Health and Safety ActWHSC COVID-19 training, delivered in our virtual classroom to ensure the safety of participants and the instructor, will help employers meet this significant obligation. This training also prepares workplace parties for their critical roles in pursuit of safer, healthier work. To register for this course, and equally important training like Certification training for JHSCs, be sure to visit our website’s training registration page.
 
Need more information still?
Call a WHSC training services representative in your area.
Email: contactus@whsc.on.ca
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Additional related resources:
Enhanced Ventilation: prudent actions to help control airborne virus transmission
Respiratory and eye protection: safeguarding workers confronting COVID-19
ASHRAE technical resources relating to airborne transmission
OHCOW COVID-19 resources