What are the challenges in decontaminating air? Michael Rollins, Consultant Healthcare Environment Infection Prevention talks about the equipment, chemicals and procedures required to maintain air hygiene in healthcare settings.
How Coronavirus can spread through the air
COVID-19 transmits as an aerosol. This is probably the most challenging aspect of the transmission of the virus. Obviously, it’s invisible - particularly in this situation where we are uncertain about the characterization of the virus, which is causing this problem. Because of lack of investigation, all we can rely on is prior investigation of MERS-COV and SARS over the years. The trouble is that it is very difficult to identify and isolate. There are certain techniques that we can adopt to achieve this within a controlled environment, but as soon as we move to domestic environments, they present a completely different challenge. This is primarily the reason governments across the world are locking down and encouraging people to stay home and stopping transmission at point of source. That is in principle the first step for prevention and protection of yourself. Therefore, social distancing becomes quite important.
When it comes to COVID-19, there is a concept called viral droplet nuclei - a very fine aerosol that is completely invisible. If somebody sneezes or coughs or even laughs and talks, these aerosols may contain droplet nuclei, which may stay in the air for a certain period of time and spread at a considerable distance. This really is the main challenge in terms of contact with other people, and my advice is that while we are working as key workers, we have to maintain a distance with people and must consider that everybody may be potentially infected because a characteristic of this virus is the asymptomatic cases. People might not be expressing any symptoms of illness and yet they might be carriers. The incubation period is somewhere between 7 and 14 days. These two factors are the primary reasons the rate of transmission has been so horrendous in the early stages of fighting the Coronavirus.
Methods by which air can be decontaminated effectively
The only solution is to shut down an area and completely fog it or vaporise it with a disinfectant, and a typical methodology would be to use hydrogen peroxide vapour. It should be noted that hydrogen peroxide is a toxic substance and unless you are wearing a respirator, you can’t be in that space during the process. Even after the process, a considerable amount of time must be devoted to aerate it to remove the hydrogen peroxide from that space.
Other than that, there are various forms of hydrogen peroxide formulations like ionized hydrogen peroxide in which you take the H2O2 molecule and split it into free radicals, which are very aggressive in oxidizing. They will scavenge out any viruses in the air. But, this, too, is a highly toxic process and not practical anywhere except a controlled healthcare setting or a shutdown facility. This method also requires you to shut down all ventilation systems of a facility to have still air.
In some circumstances, you may also have to isolate a particular area by mechanical means (e.g. use of polythene) to make a large area smaller. This makes it easier to calculate the correct dosing of chemicals for that space.
Appropriate equipment to disinfect air
There are air scrubbers, negative air machines and positive air machines where we can move air into or through filtration. The viral particle we are talking about is particularly small, approximately 0.2 microns and would require an ultra high HEPA filter that would be efficient to 99.99% which is very high level pharmacy grade air movement in air filtration.
The majority of the air machines used normally work at an efficiency of 99.95% at 0.3 micron. But there are reports that the coronavirus may be smaller than this in size. The most effective method is to complete the air changes, decontaminate a defined area and replace it with fresh air. It may take somewhere around 30 minutes to reduce the viral load of a patient room to safe levels.
The challenges in decontaminating air
Decontaminating air is a well documented process in a healthcare setting. We have the ability to isolate and also to have filtration - that’s not always possible outside so putting it in the context of an outsidehealthcare environment, it’s an extremely challenging issue. The issue is actually how you can effectively move air from one place to another. So, we are exchanging and diluting what may be floating in the air or alternatively processing the air flow HEPA filtration. This is virtually impossible in a dynamic environment such as a supermarket where you have a very large environment to deal with. This is the main challenge outside of a healthcare setting. Having said that, with the increasing demand on healthcare, it’s not always possible to have those isolation facilities, which are called airborne infection isolation rooms, where negative pressure is put on the room and allows us to accelerate air changes.
This helps to create a safe environment for the healthcare workers in the sense that the air is constantly being changed and any particles are extracted and filtered and fresh air brought into that space. Outside of that, it’s a whole different ball game. In any setting, apart from healthcare, it is very difficult to decontaminate air. In practical terms, it’s more about ventilation, and the key strategy, as mentioned before, is to keep diluting the air.