COVID-19 is a disease potentially arising from exposure to a novel coronavirus. From a prevention standpoint, we are still learning about key issues such as infective dose and the most important routes of viral transmission. This presentation looks at the exposure science evidence and uses an occupational hygiene lens to frame COVID-19 risk assessment. Understanding the relative importance of exposure mechanisms, and the likely effectiveness of control options will assist in risk management and communication.

1. Occupational Hygiene and COVID-19
– Litany or Risk Assessment?
School of Public Health, Faculty of Health & Medical Sciences

2. Overview
• 2020 – the year that blurred occupational health and
public health
• Framing the COVID-19 problem
• An occupational hygiene approach to risk assessment
• From litany to risk assessment and prioritised hazard
control
University of Adelaide 2

3. 2020 – Natural disasters
- when public health blurred occupational health
Bushfires
- Smoke exposure
University of Adelaide 3
COVID-19
- Virus exposure

4. And when home became the workplace, because
someone said it was too risky to be at the office
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5. And chief public health officers and fire chiefs
became celebrities
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6. And when we were just told what to do ..
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A litany?

7. But how do we translate
community messages
into workplace
messages, using our
language, our
frameworks and our
logic?
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8. The central role of risk assessment
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Risk assessment
incorporating
hazard
assessment
Hazard
controls
Training
Health
surveillance
Risk
communication

9. What are the differences between public and occupational
health risk assessment and management?
• The hazard control hierarchy (Section 36 of the WHS Model
Regulations)
• Risk assessment is very common in WHS legislation, and implied
with regard to many hazards and controls (e.g. PPE)
• The “work, worker, workplace” risk analysis concept
• Clear definitions of WHS duty holders and responsibilities
• Specific requirements for consultation
• Occupational health: risk assessment guidelines for chemicals 1994
• Environmental health” risk assessment guidelines 2002
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Occupational health risk assessment and management
more mature?

10. This begs the following questions
• Is the guidance on COVID-19 risk assessment well developed, based
on WHS frameworks and systems? Or is it a rough adaptation of
public health and infection control principles, without sufficient
structure? Has something been lost in translation?
• Have we got the right priorities for COVID-19 in the workplace?
• Given that the public and workers have become more aware of viral
diseases (SARS, Ebola, COVID-19 etc), do WHS professionals need
public health training and do public health professionals need
occupational health training?
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11. An occupational hygiene perspective
on COVID-19
• Focus on the virus (the hazard agent) and the hazard
source. As a respiratory virus, the most important source
is the human mouth/nose.
• Understand the virus and how it behaves once it leaves
the mouth/nose (propagation, stability etc.)
• Understand how exposure to the virus occurs (routes,
mechanisms and pathways)
• Undertake a risk assessment (based on exposure and
susceptibility), using the “work”, “worker” and
“workplace” framework.
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12. An occupational hygiene perspective on COVID-19 (cont.)
• Apply the hazard control hierarchy, but making sure that all virus
exposure mechanisms are addressed.
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Inhalation
of aerosols
(< 100um)
Ocular
contact
Ingestion
Inhalation of
droplets
Note that fomite transmission is an indirect pathway.
It is not included in many infection risk models.

13. An occupational hygiene perspective on COVID-19 (cont.)
However, we are dealing with humans as the source, and so
administrative controls take on extra importance
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Engineering
controls
Administrative
controls PPE
Elimination
and Isolation

14. Clinician model?
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15. The problem is exacerbated indoors, with limited air exchange and/or poorly
directed air flow, where there might be assisted delivery, and a buildup of
aerosols. Infective dose is achieved slowly.
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Avoid unprotected face to face conversation, where the source is close
to the receiver. The infective dose is achieved quickly.
Priorities
BetterBad

16. Let’s be clear about the hazard ..
Since the virus is not actually alive, it might be helpful to consider
coronavirus as a biological dust or smoke problem, with the virus being
the dust or smoke and people’s mouths as the main source of dust or
smoke. There is invisible dust on their hands etc., because people
touch their mouths very often.
The individual virus particle is extremely small, and can float in the
air.

17. University of Adelaide 17

18. Can you measure the exposure?
Concentrations of airborne virus
In principle yes, but so far, the levels have been found to be low and
sophisticated techniques are required.
In addition there is no exposure standard for comparison. The infective dose is
poorly understood. In fact, the infective dose is not known for many biological
hazards.
Surface residues
This can be done with analysis of wipes, but is not routine. It is mostly used as a
quality control measure for cleaning.
You would need the services of a professional occupational hygienist for proper
sampling, and an environmental microbiology laboratory with expertise in
viruses. https://www.skcltd.com/knowledge-library/covid-19-facts-and-
sampling.html
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19. Available infection risk estimators
There are many assumptions and they generally only consider one route of exposure.
Jose Jimenez Univ of Colorado 2020 COVID-19 Aerosol Transmission Estimator
https://tinyurl.com/covid-estimator
VA Sciences COVID-19 Infection Risk Manager
https://vue-covid-product.web.app/
Alex Mikszewski AIRC (Airborne Infection Risk Calculator)
https://research.qut.edu.au/ilaqh/wp-content/uploads/sites/174/2020/10/AIRC-v2.1-
Users-Manual.pdf
NIST FaTIMA
Fate and Transport of Indoor Microbiological Aerosols
https://www.nist.gov/services-resources/software/fatima
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20. The “smoker” comparison
You’re in your office and someone comes in for a meeting. They light up
a cigarette and blow the smoke towards your face.
Then some visitors arrive and start smoking as they tour the premises,
speaking with various workers, some of whom are pregnant.
What do you do?
Issue respirators?
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21. Ventilation for COVID-19
(what it does, what it doesn’t do, what it could do)
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There is no way that ordinary office air conditioning (or even in some
industrial ventilation systems) can cope with a sneeze, cough or singing
directed towards someone’s face at close range. You would need a
powerful extraction system near the infected person’s face. Could you
prevent smoke from a smoker reaching your face?
At best, fans can direct air away from their face. In other words,
ventilation is mainly for preventing build up of contaminated air. Some
systems can adequately filter the supplied or recirculated air, but these
require high performance filters for fine particles (often termed HEPA
filters). A personal HEPA-filtered fan could be used, but this is not
practical if staff move around.
Opening windows, reducing the amount of recirculation and increasing
the volume air of air supplied will help to some extent.
Switching off the air conditioning system will not help.

22. Ventilation for COVID-19 (cont.)
(what it does, what it doesn’t do, what it could do)
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So the emphasis needs to be on the control of the infected person.
That means eliminating known infected persons.
Where there is a possible infection, the use of masks is more likely to
be effective than ventilation.
There is some evidence that virus spread can occur via the air
conditioning system. However, that is essentially in healthcare
environments where multiple patients have obvious symptoms and
shed large amounts of virus. So it is very unlikely that normal air
conditioning systems can spread the virus.
That said, some systems can be fitted with UV germicidal lamps in
the ductwork to further reduce the possibility.

23. Take home messages
• We need to filter community messaging about COVID-19
“spread”, and think about COVID-19 in terms of our
normal hazard control approach even if we don’t know
what the infective dose is.
• We have a well established framework for risk
assessment, and WHS systems which are more mature
than public health systems in many respects
• Administrative controls assume greater importance, in
recognition of humans as the source of the hazard
• It’s not just about physical distancing, it’s also about
direction
• Ultimately, we need to convert public litany to workplace
risk assessment
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