Disinfectant Fogging

Jul 3, 2020

Last decade, when the world was normal, we didn’t go in for large scale disinfection. Humans can live in harmony with microbes, and it’s normally sufficient to simply remove most of the dirt. The Covid-19 pandemic has changed everything. Now many people feel safer if surfaces that strangers have touched are disinfected.

It has become common practice for “touch points”, such as light switches, door handles, arm rests and supermarket trolley handles to be wiped down with disinfectant. But what if you want to disinfect more than touch points? What if the item you want to disinfect is fabric and can’t easily be wiped? What if you want to disinfect a whole room or a whole holiday cottage? The easiest way to do this is to use a fogger.

Unfortunately fogging cannot replace cleaning. It’s always recommended to remove dirt before disinfecting, whether with fogging or wiping down, otherwise you’re just disinfecting the top layer of dirt. Yet imagine trying to wipe every surface in a school hall or a gym. Obviously, you can’t do that, so you just clean away any visible dirt before the fogging takes place.

You’ve probably seen fogging on the news recently. You might have seen people in hazmat suits carrying out what looks like crop spraying, only they’re spraying inside buildings or spraying outdoor public facilities. The process is similar to spraying pesticides on crops, though with disinfectant fogging, the machines are filled with an antimicrobial and antiviral agent and the droplet size is so tiny that the surfaces don’t actually become wet.

ULV disinfectant fogging has been used in hospital wards, operating theatres and other medical settings for some time. Increasingly, though, it’s being carried out in schools, airports, offices, factories, hotels and cruise ships. Before spraying most chemical disinfectants, the area must be cleared of people and animals. The fogging machine operators wear full PPE, including respirator masks.

Here are some examples of disinfectants used for fogging:

In all of these the active ingredients are quaternary ammonium compounds (quats). Some of them are safe for food contact surfaces and some aren’t. When spraying a kitchen, nursery, school or holiday cottage, a food-safe product should be chosen. The codes on the product indicate what it is effective against. The codes EN14675 and EN14476 mean the product has antiviral activity. The code EN14476:2013+A3*:2019 means the product has been tested and proven to kill the SARS-Cov2 virus.

Before people are allowed back into an area following fogging, test strips are used to check that the disinfectant no longer remains in the air. A dried residue of disinfectant remains on surfaces and will kill microbes and viruses landing on it for at least the next 24 hours. Some companies claim the residual effect lasts weeks, but 24 hours is probably more realistic. The residual effect of the disinfectant lasts longer on surfaces not touched frequently.


There is another type of fogging disinfectant that’s much more user-friendly than the quat type. It’s called hypochlorous acid and is sometimes referred to as electrolysed water. Hypochlorous acid has some great advantages:

  • It’s so non-toxic to humans you can put it on your skin (and in fact it has been used as a wound disinfectant)
  • There is no need for operators to wear PPE and no need to seal off the area
  • It has broad spectrum activity against bacteria, fungi, protozoa and viruses
  • It’s cost-effective
  • It’s fast-acting
  • It’s safe for food surfaces (even crockery and cutlery)
  • It’s pH-neutral
  • It doesn’t harm most surfaces
  • You don’t have to remove bedding before fogging with hypochlorous
  • People can re-enter an area directly after fogging
  • There is little or no residual left on surfaces

The fact that hypochlorous doesn’t have a residual effect is advantageous or disadvantageous depending on the circumstances. If you’re planning regular weekly or fortnightly fogging in premises where a lot of people come and go, a disinfectant with residual activity would be of benefit. However, if you need to quickly disinfect properties or areas between guests, and intend to do this as soon as each group departs, you don’t especially need or want residual activity. In this case it would be more important to use a really safe product with little wait-time.

Hypochlorous disinfection is used in some dental surgeries – they fog between patients. It’s quicker to fog the treatment room than it is to wipe everything down with disinfectant. And if there happened to be viruses or other pathogens in the air, they would likely be killed by the hypochlorous fog, whereas they wouldn’t be with disinfectant wiping. Norwegian cruise ships use hypochlorous fogging to disinfect cabins between guests. They have the equipment to make hypochlorous acid on board the ship, so there is no need for them to carry stores of it.

Which type of fogging would I choose for my holiday let? Hypochlorous, hands down. It’s true that hypochlorous acid probably does not have the same power to kill bacteria and viruses as many of the quat-containing disinfectants. Most of the specialist antiviral quat disinfectants are log kill 6, which means they kill 99.9999% of microbes or viruses when used as instructed. Hypochlorous acid probably kills 99.99-99.999% of microbes and viruses (log kill 4-5), depending on the concentration. However, it is a safer product for use in an area where people will be living for a week or more. Hypochlorous acid fogging is also a cheaper option (partly because PPE isn’t needed), therefore using this for fogging would not result in huge price increases for the guests.

So long as the coronavirus pandemic continues, social distancing, hand sanitising and mask-wearing will be part of life. Fogging machines won’t change that. Nevertheless, ULV (ultra-low volume) disinfectant fogging may be a tool that allows leisure activities, such as going on holiday, to go ahead with less risk to the public. It may also give peace of mind to the clients and employees of your business.