'The air that we breathe' - how to minimise Covid -19 risk at work

Our aim in writing this article was to produce a 'laypersons guide' to workplace air quality, to identify some of the things that affect it and to provide some practical ways to help minimise Covid -19 risk.

Usually there will be a Nominated Person with responsibility for the maintenance and establishment of safe systems of work and safe working procedures with respect to air flows within their building(s).

 Whoever this is should have basic knowledge and understanding of key issues including:

• Factors affecting air quality.
• The need for planned preventive maintenance.
• What to do if problems are identified.
• How temperature, humidity, and air conditioning (including fan coil and condenser units) affect air quality.

COVID -19 basic facts

The main risk for COVID-19 transmission is from a-symptomatic or pre-symptomatic people who are in your building without knowledge that they are shedding viral particles.

The SARS-CoV-2 virus which causes COVID-19 can be spread by very small particles – called aerosols – which are released by an infected person when they cough, sneeze, talk and breathe, alongside the larger droplets that are released.

The larger droplets fall by gravity, hence social distancing measures to reduce their spread. The fine aerosols, however, can remain airborne for several hours.

Evidence gained from airborne aerosol transmission shows high rates of infection in poorly ventilated rooms - a potential transmission route.

These aerosols are at the highest concentration in exhaled puff and the idea behind social distancing was to help reduce exposure.

Aerosols that are small enough to remain airborne become diluted in the indoor air and without suitable ventilation they can build up, increasing the risk of exposure for susceptible individuals. 

Risk is a function of exposure and duration exposed.

The risk of airborne infection to an individual can therefore be reduced by:

• Reducing time spent in a location
• Reducing airborne exposure concentration of infectious material.
• Reducing risk of contact spread through regular handwashing and surface cleaning.

The ventilation rate and how it is delivered influences both airborne exposure and deposition rate (i.e., how much of the virus settles internally within the body). 

Why ventilation is important for air quality

Ventilation is important as it can help to minimise the build-up of aerosols in a space and effective ventilation will reduce exposure risk. To achieve a good ventilation flow, you need to:

• Increase ventilation as much as possible by increasing the flow of outside air and prevent the build-up of any pockets of stagnant air.

• Avoid the recirculation of air within a building to reduce the risk of transmission (unfortunately, this may also lead to an increase in overall energy bills!).

• Calculate the appropriate volume of outside air and reconfigure your existing air handling systems (you may need to call on specialist advice for this).

 There are three basic approaches that you can adopt either individually or in combination to improve overall ventilation.

1. Natural ventilationvia passive air flow through windows, doors and air vents that can be fully or partially opened.

2. Mechanical ventilationusing fans and ducts to bring in fresh air from outside.

3. A combination of both natural and mechanical ventilation, for example where mechanical ventilation relies on natural ventilation to maximise fresh air.

It is important to remember that ventilation needs to be considered alongside other controls to reduce the risk of transmission, such as social distancing, keeping a workplace clean and everyone adopting frequent handwashing.

You will need to make a Risk Assessment of the air quality within your workplace, most notably:

- Assess the risk from aerosol transmission in enclosed areas.

- Identify any poorly ventilated areas.

- Decide the steps you can take to improve overall ventilation.

Your priority should be to identify areas that are usually occupied but are also poorly ventilated. You should prioritise those areas, taking action to reduce the risk from aerosol transmission.

What do 'specialist building engineers' currently say about Covid-19 and air quality?

• Transmission commonly occurs in enclosed indoor
• There is very low risk from infectious aerosols passing through ventilation system air ducts.
• Well-maintained heating, ventilation, and air conditioning (HVAC) systems, including air-conditioning units, will securely filter large droplets containing COVID-19.
• Re-circulated air can assist in the spread of COVID-19 aerosols (small droplets) through HVAC systems within buildings or vehicles, including stand-alone air-conditioning units.
• You can help to decrease indoor transmission through increasing the rate of air change, decreasing the re-circulation of air, and increasing the use of outdoor air.
• Heating, ventilation, and air-conditioning systems should be maintained according to manufacturer's current instructions, particularly when cleaning and changing filters - there is no benefit from, or need for, additional maintenance cycles.
• You should think about extending your HVAC systems current operating times.
• Direct air flow should be diverted away from groups of individuals to avoid possible dispersion and transmission of infectious aerosols.
• Try to avoid using re-circulated air as much as possible.

Next time: COVID – 19, Sick Building Syndrome, the effects of Ozone, VOC’s, Carbon Monoxide, Carbon Dioxide and Radon gas.

In our next article we will consider other air quality related health issues such as COVID – 19, Sick Building Syndrome, the effects of Ozone, VOC’s, Carbon Monoxide, Carbon Dioxide and Radon gas affecting air quality.