CORONAVIRUS - CLEANING - 02.07.2020

Should you get “fogging”?

You’ll have seen the images of staff and contractors walking around spraying disinfectant from a “fogging” machine. Is this an effective method of controlling the spread of coronavirus?

What is it?

Fogging has historically been used for the application of a range of substances to large areas, including disinfectants, biocides, fungicides and pesticides, whether in farming, pest control or elsewhere. In the pandemic it’s being used in public spaces, transport networks and large workplaces to destroy coronavirus. The equipment generates a fog or mist formed of fine droplets of disinfectant of between 5 and 50 microns in diameter.

Claims

Since the outbreak cleaning companies have jumped on the fogging bandwagon and most now offer it to disinfect large areas. When using fogging against coronavirus, the operators tend to use chemicals such as chlorine, sodium hypochlorite and hypochlorous acid solution. Many companies claim that when used alongside manual cleaning methods fogging can enable areas to be used again quickly by reducing the number of pathogens in the air and on surfaces.

Is this the best option?

The World Health Organization recently published guidance which states that spraying surfaces may not be effective in removing organic material and may miss surfaces shielded by objects, folded fabrics or surfaces with intricate designs. It says that if disinfectants are to be applied, this should be done with a soaked cloth or wipe.

Spraying disinfectants can also result in risks to the eyes, respiratory system and skin irritation. There’s also a risk of degradation of the materials on which the mist settles.

Tip. Fogging should never replace conventional cleaning methods as the primary method of disinfection.

Pros and cons

Extensive research has been carried out by the Society of Food Hygiene and Technology (SFHT) on the benefits and downsides of this method of disinfection. It found that fogging is effective on the upper side of horizontal surfaces, but works less effectively on vertical surfaces and the undersides of furniture etc. It is also effective in reducing airborne microbiological contamination.

Tip. There are some benefits, provided it is done correctly. For example the SFHT has published guidance on technicalities such as droplet size and velocity which should be followed (see The next step ). These guidelines recommend that it takes a minimum of 15 to 30 minutes to have the anticipated effect and that an additional period of 45 to 60 minutes is needed for the droplets to settle.

Tip. Portable electric fogging machines do not operate at sufficient volume flow rates for most applications and are therefore not recommended. Instead, if you go down this route, use a compressed-air-driven fogging nozzle.

Warning. The sight of a fogger at work gives reassurance to the public and this in itself might make it worthwhile to you. But don’t lose sight of the science or ignore the fact that it introduces a chemical hazard to the individuals operating the equipment - a hazard which also needs to be managed.

Although fogging as a primary control measure is not recommended, it can be useful alongside surface cleaning. To have a real benefit it needs to be carried out with compressed-air-driven equipment rather than electric. You must also manage the chemical risk during its application.

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