Can HVAC Cleaning Stop Virus Spread?
This article explores the ways in which a virus can spread within a commercial building.
In particular, it outlines the ways in which a company like Clean Air Filtration Services can minimise the chance of virus spread through its HVAC cleaning and Compliance programs.
How Does A Virus Spread Within A Building?
A virus can be spread in a number of ways. Typically, the spread starts with an infected person coughing or sneezing droplets onto a surface, into the air, or onto a person nearby.
Other people can be infected if:
- The droplets land directly in their eyes, nose or mouth.
- The person touches a surface on which the droplets have landed and then they transmit the droplets to their mouth.
- Very small droplet particles stay airborne long enough to travel & infect areas & people outside the original sneeze zone. This is called airborne transmission.
Can An Air Conditioner Spread An Airborne Virus?
The short answer is that it is possible for an air conditioner to spread an airborne virus and contaminate adjacent areas.
The likelihood of this happening is dependent upon:
- The potency of the droplet particles.
- The length of time the virus stays infectious within the droplet particles.
- The length of time the droplet particles stay airborne.
In a recent NETFLIX documentary outlining the spread of SARS they state:
“…a fan blew the virus back up into the building’s ventilation, and into the apartments above. Then the wind was likely blowing the virus to nearby buildings making it much more difficult to contain… In total 329 people were infected in this apartment complex…”
(Netflix, ‘EXPLAINED, The Next Pandemic’, 13.3 minutes in)
Note that the World Health Organisation has stated in March 2020 that they are not seeing airborne transmission of Coronavirus. This is despite some studies reporting that Coronavirus stays airborne for up to 3 hours.
Can An Air Filter Trap An Airborne Virus?
Most viruses vary in diameter from around 20 nanometers to 400 nanometers.
A HEPA filter is able to filter particles down to 300 nanometers.
In addition, a smaller virus particle will generally not move in a straight line and is therefore likely to make contact with the filter fibres. Once trapped, the virus particle would stay safely on the filter until it becomes inactive. Therefore, although a typical Coronavirus particle is about 100 nanometers it is still likely to be trapped by a HEPA filter.
Other filters that can kill a virus include:
- Ultraviolet (UV) Based Filter – Several minutes of UV light exposure can break down the virus molecule and render it inactive.
- Photocatalytic Based Filter – Virus can be broken down by electrostatic and oxidation processes.
- Catechin Based Filter – Can have antiviral properties.
What Substances Can Be Used To Deactivate The Coronavirus?
The virus molecule has a lipid or fat-like covering. Therefore many cleaning agents are effective because they destroy the virus by attacking this fat layer. Once the lipid layer is destroyed the fragile virus molecule is exposed and quickly becomes inactive.
Some substances used to successfully deactivate the virus molecule include:
- Soap – Can break down the lipid layer.
- Bleach – Can break down the lipid layer and the enclosed virus molecule.
- Peroxide – Can break down the lipid layer and the enclosed virus molecule.
- Alcohol – Can break down the lipid layer.
- Heat – Can melt the lipid layer.
Why Is It So Important To Kill HVAC Bacteria & Bio-contaminants During A Pandemic?
Australian Standards AS 3666 Part 2 states that HVAC:
- Coils – should be inspected monthly and cleaned when necessary
- Ductwork – should be inspected annually and cleaned when necessary
- Fans – should be inspected at three monthly intervals and cleaned or repaired as necessary
This is the minimum period between inspections and cleaning.
However, there are two very good reasons why you may need to clean your HVAC system more regularly than this during a pandemic:
1) Secondary Infections Become Deadly
Death rates due to coronavirus are significantly higher in people with a pre-existing condition. Therefore, if a resident of your building were to be infected with legionella due to poor HVAC cleaning practises, they would be open to an even more serious problem if they were to then catch Coronavirus.
2) The Virus Will Be Infectious For Longer
Viruses need a host cell, which can be bacteria, fungi, or an animal, including a human. With help from the host, viruses are then able to multiply.
If a virus finds a host in the HVAC system it could remain dangerous for a long period of time. It is therefore important to clean your HVAC system more regularly to ensure that it is clear of bacteria, fungi and bio-contaminants.
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4 年Awesome write up you've got there Darren. Thanks for sharing
Director at IAQ Projects Pty Ltd.
4 年I’d also be asking- if the virus is 100 nanometers as you state, are you then installing HEPA filtration to restrict its movement? As most filtration is ineffective in restricting the movement of the virus due to the particle size. Given the range of airborne transfer of the virus and where it settles on surfaces, how do you feel that any filter other than a HEPA has any chance of limiting transfer down the supply side of a system? Writing about legionella as a co-morbidity danger is reckless as well. The research is currently backing surface transfer as the primary community transmission. AC airborne transfer given the distance in most cases between return air-AC system- supply air would be limited or very minor risk as an airborne risk as this would primarily be contacted by droplets in environments where near face to face contact would occur - ie someone coughs and the next person walks through the droplets.
Helping Scientific, Healthcare, Pharma and Food Industries with Hygiene Consulting, Contamination and Decontamination
4 年Excellent article. COVID-19 has been shown to last for up to 3 hours in air and therefore can be re-entrained back into return air
Managing Director of UV Solutionz Ltd
4 年Good advice Darren. I do however question the requirement...Coils – should be inspected monthly and cleaned when necessary. How do you visually inspect for something that is microscopic? Cooling coils are a great big incubator and ideally are continuously disinfected by a retrofit UVC system