OCCUPATIONAL AND ENVIRONMENTAL MEDICINE

Dr. Wayne Evans has provided consultation and ongoing health and safety management for a variety of corporations in Ontario. He has done so for over 3 decades managing a range of concerns including hearing conservation, air quality, chemical exposure, and repetitive strain injury. He enjoys the role of facilitator in collaborations to optimize human factors integration in ergonomic workstation design and workflow.

He is a member of the OEMAC and the Section on Occupational & Environmental Medicine of the Ontario Medical Association.

The following comments stem from the above industrial workplace analysis experience as well as the perspective of Dr. Evans [as a care provider/clinical director].

Some Updates and Thoughts on the COVID-19 Pandemic

Achievements to Date:
The COVID-19 Pandemic has been an amazing instructor. It has informed humanity on the many variables which may be perceived and variably interpreted which result to modify human behaviour.

It has also informed us of system failures and lessons learned along the way.

I look around the urban community and I see that most people have adjusted to a new normal:

They cross the street (instead of passing you on the sidewalk)
They wear masks if entering a building crammed together in other settings [eg waiting in hallways etc and public transport].
They avoid close proximity to others if possible and will "take the next elevator" in the majority of cases.

So, we should be proud of our public health service in its success in persistent and consistent communications.

New discoveries...more complex problem
We now know more about Covid than we did in March, one small problem is slowly becoming apparent in how Covid-19 may be spread:

We initially learned:

The initial message was to avoid potentially infective droplets as spread from among individuals when cough or even speak or sing.
Thus use of masks and their effectiveness when carefully used has pleasantly allowed more freedoms as our community adjusts to using such tools.
We have come to understand that droplets are small collections of liquid which can fall to the ground and land on surfaces.
We have developed extensive measures to ensure that we can clean surfaces on a regular basis to remove virus containing droplets.
This is now well known behavior in 2020 which we accept and embrace

More recently our understanding has become a bit more refined extending the concept of additional ways which the Covid-19 virus can be spread. The words aerosol transmission is starting to appear in the conversations about virus spread, in addition to droplets.

Aerosol Transmission

What is aerosol transmission anyway?

If water droplets are very small , the droplet may not fall to a surface quickly, and very tiny, may linger, invisibly floating in the air. Covid-19 virus particles are small enough to potentially be clinging to such mini droplets or aerosols.

How does an aerosol cloud move and dissipate?

It may perhaps be more useful to think of the air around any individual very much like we would the cloud of smoke around a smoker outside. As it lingers it is denser near the person emitting it. If you are several feet away from that individual you probably cannot smell or see the cloud of smoke. But it is certainly spread throughout an enclosed room.

Unlike the familiar odor and blueish tinge visible from a aerosol cloud emitted from a person who is smoking a cigarette with cigarette smoke, one challenge with aerosol clouds breathed out by Covid-19 infected individuals is that we can not see or smell that cloud.

So we might not have any notion of this aerosol cloud if we enter a room which has such an invisible cloud of floating particles which can linger for hours.

Inside vs Outside - What's the difference?

What is so special about outside air? Let's consider some familiar settings:

1) A cloud of cigarette smoke inside

When the covid containing cloud of air goes out the window it becomes so diluted that there is no longer enough concentration of covid virus particle to cause an infection.

We are quite familiar with this in avoiding smoke from those smoking in a room. Open the window and the smoke goes out the window and diluted to the comfort of the people in the room.

The airflow through the room and out the window certainly has something to do with diluting and thus dispersing the cloud of smoke to the outside . Keep the window closed and this does not happen.

2) A cloud of cigarette smoke outside

Observing our local environment can provide us a number of clues as to how airflow outside disperses a cloud of smoke. We would also, I believe, generally agree that the disbursement would be much faster on a windy mountain top compared to a calm and narrow pathway in the forest valley.

Outside is the new Buzz Word

The now familiar comments by Dr. Fauci And other public health officials about social distancing and using a mask to avoid virus transmission has started to evolve. Since mid July "Open the window to get some fresh air" has become a common message from public health and others.

So we are now hearing how opening the window is helpful to improve safety against Covid transmission. It seems like a simple message and quite a logical one

Hmmm ... let’s dive a little deeper into what is actually being discussed in that simple comment.

-that short phrase “open the window to air out the place” is actually describing the value of ventilation (ie air movement) through the building .

This ventilation moves clean air in while moving air out of the building which may contain floating virus particles .

Once outside, the virus particle concentration becomes so dilute so as to be negligible and therefore no longer a concern for the virus transmission to other humans breathing the air .

Lets consider a window that is, say 2.5 feet tall, and you open it 1 foot wide

Well I guess it depends if it’s a windy day or not. Maybe we just say it’s a very gentle breeze of 2 ft./second.

So that air flow is 2.5ft x 1 ft = surface area of 2.5sq ft If is flowing at 2 ft / second Thus the air flow is 2ft / sec x 2.5 sq ft = 5 cu ft / sec or 300cu ft / min

If you open the window widely :2.5 x 2.5 = 6.25 sq ft x 2 ft / sec = 12.5 cu ft / sec or 750 cfm

Can we now calculate how that open window compares with the ventilation system of the building we are in?
600sq ft room x 8 ft celiing = 4800 cu ft to change that every 15 min [ ie 2 changes / hr] need 9600/15 = 640cu ft / min

HVI recommends 1cfm/ sq ft so for 600sq ft = 600cfm

Thus it seems that a single widow can provide as much or more than the mechanical ventilation normally supplied using normal modern buiilding method.

Perhaps this more detailed "open the window" message is really saying:

- covid can be in an invisible cloud not just droplets

- the cloud may linger for hrs

- encouraging the cloud to move outside is a simple way to make a covid cloud harmless [outside = infinitely diluted]

But....we spend a lot of time inside buildings

Besides dilution [ie ventilation],how else can we reduce the number of virus particle which may be present?

Did someone say filter?...Great idea! There are classifications to rate the degree of filtration achieved known as MERV rating* [ie - MERV 13 is nice] . HEPA is a well understood technology which does a splendid job of removing reliably very small particles ... much better than the routinely used paper filters in most homes and small buildings

[*An air filter's minimum efficiency reporting value (MERV) rating measures how effectively the filter stops dust and other contaminants from passing through the filter and into the air stream. Filters with higher MERV ratings trap small particles more effectively than filters with lower MERV ratings.]

What else can we do to make our breathing air cleaner? There is a long list - but if you can dilute and filter as above - you have done well!

Additional Considerations

Let's look at another engineering approach which has been utilized in recent years to improve the outcome of some very delicate surgical procedures which are performed. The concept which is used to avoid contamination is called "laminar flow". Using such principles we are able to have air flow moving in such a way makes it less likely that all the air mixes.

Think of it more like a nozzle of air. Somewhat like how water flows out of a water fountain nozzle

In the operating room special ventilation piping creates laminar flow so the air uniformly moves where the surgeons wish it to. The air falls down on the center of the operating table and then flows off the operating table rolling down the floor where it is captured and flushed out of the room. This prevents any airborne particles which might be in the air from getting near the surgical site which must remain absolutely clean.

Many years ago we discovered how to manage contaminated air to reduce the concentration of chemicals and infective agents and render it harmless. This was determined in detail by mechanical engineers to create containment laboratories so that scientists could examine and learn about very ineffective and dangerous bacteria and viruses.

Containment laboratories and laminar flow operating rooms however cost millions and are gross overkill for general use. It could however be possible to look at these engineering marvels and learn how we may be able to improve the health of our population.

Air Cleaning

Activated Charcoal - fabulous - however it must be changed as it becomes saturated.

Germicidal Ultraviolet Light - probably the most promising among various new offerings being promoted.

Industrial safety generally depends upon good engineering and design so that hazards are managed and humans are not exposed to the hazards.

After all engineering options have been exhausted - PPE is the option to ensure safety.

CONCLUSION Hopefully this explanation helps you understand: Covid has caught us unprepared to manage and thus we have all adjusted to using PPE. PPE is not the solution! It is the last resort! We can do better!Supporting changes to make buildings safer is an urgent need. Why are we not seeing government sponsored programs to support retrofitting to achieve better ventilation and air filtration!

Call your MPP / MP and ask why they are not on this bandwagon to make schools safer!

The above notes are intended to generate innovative thought and support practical solutions to a dreadful situation in which we currently find ourselves; the need to avoid covid clouds as winter comes and we head indoors.

We need to think carefully how the hard work and knowledge of mechanical engineering which has been amassed over the past 50 years can be brought to bear in a cost-effective manner to help us find our way to reduce covid virus transmission.

A.Wayne Evans, MD

Occupational & Environmental Medicine Consultant

4617 Burgoyne St. Mississauga Ont.