Something's in the air
For more than a year, scientists have been sounding the alarm that Covid-19 can be transmitted through the air by small aerosols. Across the globe, experts have submitted studies and reviews for publication in peer reviewed literature and have explained the importance of ‘airborne transmission’ through social and popular media.
Open letters from experts calling for action on airborne transmission have been widely published, including in Canada, Australia, and the USA. Despite this, national guidance outlining practical measures to minimise the risk of airborne transmission of Covid-19 remains sparse, even in the face of such strong evidence.
Hand hygiene, thorough cleaning and physical distancing have been promoted as the ways to prevent transmission, the missing piece is understanding and controlling airborne risk. This is important, because respiratory aerosols are generated when we breathe, speak, cough, or sing. They are produced in a range of sizes, yet those which are smaller than 100 microns remain airborne and are able to be breathed in.
So, what practical measures can be implemented to mitigate this risk of airborne infection?
Health and safety professionals select control measures starting with those that provide the highest level of protection and reliability to those that provide the lowest – known as the ‘hierarchy of control’. When applied to airborne transmission of Covid-19, the areas that typically need specific additional attention are engineering controls and personal protective equipment (PPE).
The smaller the aerosols, the longer they will stay airborne and move around in air currents. Ventilation therefore plays a crucial role in reducing airborne transmission. Practical measures include moving work activities to areas with good ventilation (eg outside), and where not practicable, working to improve ventilation.
Assessing and modifying ventilation in buildings is a complex task best left for professionals such as HVAC engineers and occupational hygienists. Engaging these professionals is important to enable an assessment of the building or enclosed space to help identify areas of improvement and areas of potential high risk. Some control measures include:
- Maximising airflow supply to occupied spaces (ie: can demand-controlled ventilation controls that reduce air supply based on occupancy or temperature be disabled?)
- Maximising the amount of outdoor air provided into enclosed spaces and reducing the recirculation of air.
- Maximising the time period that the ventilation system is running (ideally a few hours before a building is occupied).
- Ensuring that the system is maintained and serviced appropriately.
- Considering the use of portable air cleaning devices to supplement the existing system (eg appropriately sized HEPA units) where ventilation cannot be improved.
- Providing advice on the maximum number of people within the same indoor environment based on the ventilation assessment.
An assessment of ventilation is critical and is performed using sophisticated tools by professionals. However, the lay person can also use real-time monitoring as a preliminary indicator to see if basic improvements can be made in the interim.
Measuring concentrations of carbon dioxide in enclosed spaces can be a useful surrogate measure of indoor air quality and airborne infection risk of Covid-19. We all breathe out carbon dioxide, and high concentrations in enclosed spaces generally means that there is a higher risk of transmission if an infected person is or has been in that space.
If people are in poorly ventilated spaces for a long time then they can be at a higher risk, even if they are physically distancing, because air moves around. Carbon dioxide measured above 600-700ppm indoors is a good trigger to take action to work improve indoor air flow.
Getting PPE right
The use of fit-tested respiratory protection such as P2/N95 respirators is important, because unlike surgical masks, only respirators are designed and manufactured to provide respiratory protection to the wearer.
Surgical masks do not provide any rated level of wearer respiratory protection, and as they do not provide a seal around the wearers face, they enable aerosols to be breathed in around the gaps in the mask.
Therefore, P2/N95 respirators are recognised as the minimum level of PPE to provide protection to workers from airborne contaminants, including Covid-19.
Controlling the risk of airborne transmission has not been given the necessary attention needed to prevent workplace-acquired infection, as guidance has traditionally focused on transmission from surfaces or from ‘droplets’ in close range to other people.
Acknowledging the importance of airborne transmission and putting practical control measures in place is critical to effectively manage workplace health and safety in a pandemic.
Kate Cole is a Certified Occupational Hygienist and Churchill Fellow with degrees in science, engineering and occupational hygiene. Named as one of the Top 100 Women of Influence by the Australian Financial Review, she is a passionate advocate for protecting the health of workers and has supported the Covid-19 pandemic with her specialist expertise on respiratory protection and health and safety more broadly.
She is speaking at the 2021 Safeguard conference on 1-2 June.