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Ultra Low Volume (ULV) Fogging

Ultra Low Volume (ULV) Fogging is the use of machines that push out disinfectant in a fine mist to cover all surfaces.

Because the mist is pushed out under pressure the disinfectant spreads across a wide area and can get into hard to reach areas. Fogging takes place after cleaning. It does not preclude the need to clean first. Operators must wear full protective clothing (mask, goggles and gloves) and be well trained on both the equipment and the chemicals they are using. EN 14476 compliant chemicals should be used. EN14476 is the European standard for virucidal efficacy, and it is clearly labelled on any compliant disinfectant product. The disinfectant fluids used in a ULV fogger are no different to the brands that you would buy for use in a pump spray bottle

It is not mandatory to use a fogger. A key advantage to fogging is that the room is safe to be reopened after 15 minutes. 30 minutes to re-open a room to public may be advisable, especially if the room is cold or was fogged with too much density, as evaporation can take a little longer so there could still be wet surfaces (for example, the floor could still be slippery). Ventilation is always a positive method to remove any airborn virus, although evidence suggests that the virus does not remain airborn for long. Ventilation is not required, however, after using a fogger. Bacteria is destroyed within 30 seconds to 1 minute using a fogger.

Fogging with a suitable disinfecting fluid will destroy a virus within 5 minutes. The fine fog lands on all surfaces and condenses. On glass, this may appear to leave a ‘smear’. This can be wiped off with a microfibre cloth after 15 minutes. Curtains and soft furnishings should be fogged from a distance, to avoid over saturating it. When used correctly, material should be dry within 6-7 minutes. It may be advisable to do a spot test on some materials.

I’ve heard that the particles from foggers can suspend in the air inside a room for several hours and that this might be unpleasant or dangerous for people breathing it in. Is this true?

Cold foggers (such as the Sterimax ULV Fogger) produce a mist with micron sizes of at least 20 microns. A 20 micron particle in still air has a “settle velocity” of about 43 metres per hour so from a height of 8 feet the settle time is 3.5 minutes – and is much, much shorter for larger droplets. So, air suspension of disinfectant chemical particles is not an issue or a threat with cold foggers, allowing rooms to be reopened very quickly. It delivers a clear mist with particle sizes that have too much mass to suspend in the air for more than 3 or 4 minutes. This type of machine should more accurately be called a “mister”.

Thermal foggers on the other hand vapourise the liquid into a true fog-like emission and can spray out particles as small as 0.5 microns in size. A 0.5 micron particle has a settle time from 8 feet of 41 hours. Clearly not the type of thing you can use indoors and open up to people quickly. This is a thermal fogger. You’ll have seen them in use recently on Covid related TV news reports from Asia. 

“Having tested the Sterimax machine, I feel confident using it. It comes with very detailed instructions and you can contact the supplier, which is a huge plus. They also have a comprehensive Q&A page and you can watch a demo on the website which is very useful considering it’s not particularly easy to find concise and useful information about foggers. I fear there may be some unscrupulous companies out there, so take care. A fogger should be used in conjunction with the advice given by the cleaning protocols designed by the Association of Scotland’s Self-Caterers and the Professional Association of Self-Caterers. Should you use one? That has to a decision made by each individual business. It is your business and your choice. But if you decide that fogging is for you, I’m comfortable suggesting you get in touch with Sterimax. The guys at Sterimax are really friendly and were extremely patient with answering all my questions!” Fiona Campbell, Chief Executive, Association of Scotland’s Self-Caterers. 

You can find out more about the fogging machine here: Sterimax ULV Fogger – User guide.

Frequently Asked Questions

nb: WHO updated their guidance on 14th May: “In indoor spaces, routine application of disinfectants to environmental surfaces via spraying or fogging (also known as fumigation or misting) is not recommended. Spraying environmental surfaces in both health care and non-healthcare settings (e.g. patient households) with disinfectants will not be effective and may pose harm to individuals.  If disinfectants are to be applied, manual surface cleaning with detergent and water using applied friction (e.g. brushing, scrubbing) must be performed first to ensure physical removal of organic materials, followed by use of a cloth or wipe which is soaked in the disinfectant”. 

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