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Dr John Holah, Principal Corporate Scientist FS&PH, Kersia
Following on from our previous blog, Dr John Holah looks at Chemical fogging controlling airborne coronavirus.
Following the presence of a known COVID-19 incident in an enclosed space such as a food production area or a public transport vehicle, decontamination will be required before the space can be returned to routine operations.
Many studies have been undertaken on the survival of coronaviruses in the air and on surfaces, with estimates of survival ranging from 72 hours-64 days on surfaces and up to 24 hours in the air, dependent on temperature, humidity and ventilation (Duan et. al., 2003, Riddell et.al., 2020, Smither et. al., 2020).
Time is the best control of coronavirus, allowing natural inactivation of the virus wherever it is in the enclosed space, but this is clearly impractical with the need to recommence the routine activities taking place in the enclosed space as quickly as possible.
But what about air? Chemical fogging is an obvious choice as it uses the same disinfectant chemicals as for surfaces, is easy to undertake using readily available application equipment, and is a traditional technique used in the food industry. We must be conscious of terminology, however. Chemical fogging is an automated technique applying large volumes of chemical into the air via compressed air and should not be confused with the use of hand-held surface misters or ‘foggers’ which have become common during the COVID-19 pandemic for applying small quantities of disinfectants to low-level, room surfaces. Chemical fogging is undertaken after personnel have vacated the enclosed space and incorporates a settlement time flowing fogging to allow for the fogged droplets to settle out of the air or be diluted via ventilation. Following the settlement time, personnel can then re-enter the workspace.
The bactericidal efficacy of fogging, and its use as a practical technique in the food industry, was established in 1998 via a Ministry of Agriculture Fisheries and Food funded LINK project undertaken at Campden BRI. A 2-3 log reduction of airborne bacteria following fogging for 30-90 min was established (Burfoot et.al., 1999), but viruses were not tested as they were not perceived of as an issue at this time (within the food industry).
The performance of chemical fogging for the control of viruses in the air was thus unproven. Holchem, and part of Kersia Group, commissioned Campden BRI to look at viral survival in the air following fogging using typical non-oxidative (triamine) and oxidative (peracetic acid or PAA) Kersia disinfectants and using industry fogging equipment. Trials were undertaken in a dedicated aerobiology testing facility using surrogate enveloped and non-enveloped viruses of a similar size and shape to target pathogens (e.g. coronaviruses and norovirus).
The Triamine based product achieved a >4 log reduction of enveloped viruses following 30 min fogging and 1 hour settlement. The PAA based product achieved a >4 log reduction of enveloped and non-enveloped viruses following 30 min fogging and 1 hour settlement (Anon 2021). Chemical fogging within these parameters thus achieved a similar level of virus inactivation in the air (>4 log orders) as would be required to ‘pass’ a European standard disinfection test (EN14476) for surface adhered viruses.
Chemical fogging, using an appropriate disinfectant and disinfectant concentration, volume and contact time, can be used to decontaminate the air in an enclosed space in approximately 90 min. The speed of this technique thus allows its consideration for both post-incident decontamination or routine decontamination of enclosed spaces more likely to have a COVID-19 incident because of high human use.
Further information is available on Fogging best practice for viruses.