Room and air disinfection
Fogging is a technique used to disinfect the air and surfaces by applying certain chemicals as fog or vapour. The biocidal active substances most commonly used are hydrogen peroxide or active chlorine released from sodium hypochlorite in diluted aqueous solutions. As disinfectants can be dangerous to humans, animals and the environment, extreme caution is required.
Room and air disinfection by fogging of disinfectants
Not always the method of choice
Depending on the status of the approval of an active substance and the authorisation of a product, precautions and precise instructions for use are prescribed by the authorities. Although products may also be marketed without authorisation under certain circumstances (see chapter “Legal background”), there is insufficient information on their efficacy and safe use.
Fogging is well established, for example for use in hospital operating rooms with non-absorbent surfaces, sparse furniture and defined ventilation conditions; the use of unauthorised products in public or private spaces such as hotels, restaurants, shops, offices, schools or private households is not advisable.
Efficacy
The active substances used are very reactive or can release reactive substances. This makes them suitable for killing bacteria, fungi and viruses.
The concentration of active substances needed to achieve sufficient effectiveness on surfaces in a given contact time is determined by many factors. These factors include the target organism, the ambient temperature, the level of contamination of the surfaces to be treated and the type of application.
Fogging applications in indoor air should take account of the size of the room, the air change rate and the room furniture, in order to achieve sufficient saturation of the air with the active substance. It is also important to ensure that the surfaces to be treated are not touched during the treatment so that a continuous effect can be achieved.
At the moment there are only a few studies available on fogging in normally furnished rooms, which were carried out using a very high concentration of active ingredients (30-40 % v/v). It is therefore not possible at the present stage to draw scientifically sound conclusions about the effect of fogging in such rooms. It would be necessary to carry out respective on-site testing with the products to be used in order to prove that sufficient effectiveness is achieved.
Risks to health and the environment
In contact with organic material, active substances or their reaction products enter into innumerable new compounds whose identity and harmful effects on human health and the environment have not been sufficiently clarified.
Disinfection by fogging is carried out by machine distribution of an aerosol that is spread throughout the whole room. Many active substances used in fogging can cause irritation of the skin and/or respiratory tract. This is also the case with hydrogen peroxide and active chlorine released from sodium hypochlorite.
The health risk depends on the concentration of the active substance in the room air and on compliance with specified limits throughout the treatment. If there are residues on surfaces, possible skin contact with the surface must also be taken into account. Depending on the active ingredient, it may be necessary to neutralise or clean the surfaces after the disinfectant has been applied.
The biocidal substances mentioned above may also have adverse effects on environmental organisms.
The concentration of the active substance in the room air increases during the fogging process. This has to be considered when assessing the potential risk of the treatment; the classification of a product as dangerous alone does not say anything about the real risk associated with its use.
Highly concentrated disinfectants: only for professional users
Therefore, fogging processes that achieve high indoor air concentrations may only be carried out by professional users with additional qualifications who take all measures necessary to ensure the safe use of the disinfectant. This includes complete sealing of the room, evacuation of all persons present and putting up signs to indicate which area is being treated. Re-entering the room is not permitted until an acceptable concentration of the active substance has been reached (checking e.g. by appropriate measurement), an appropriate safety waiting time has been observed and spilled product and empty containers have been cleaned away and disposed of (which must also be done by qualified staff).
Fogging without qualified professionals is only possible if indoor air concentrations can be kept so low (throughout the whole fogging process) that no limit values are exceeded. However, it must be clarified beforehand whether full effectiveness is still guaranteed and whether it can also be guaranteed that the limit value is not exceeded during the entire treatment. If active substances are used that lead to potentially harmful residues on surfaces, the risk to humans after contact with the surfaces has to be assessed as well.
Recommendations
Fogging has been tested in rooms with non-absorbent surfaces, sparse furniture and defined ventilation conditions. For other settings, for example hotels, restaurants, as well as shops, offices, schools or private households, the use of this method is not recommended until sufficient scientifically sound efficacy data on such settings is available. Depending on the nature, size and furnishing of the rooms, and on the way a room is used and for how long, individual solutions would have to be developed beforehand to determine safe and effective conditions of use.
A distinction also has to be made as to whether an appropriate fogging or vapour technology is designed for the disinfection of room surfaces or also for the disinfection of the air itself. If a process is designed for disinfecting the air to reduce the potential risk of infection, it should be considered that the effect is only maintained until the virus particles have decreased, after which surface disinfection (e.g. for objects, tables, door handles) is necessary. Similarly, an adequate effect would have to be achieved very quickly to reduce the risk of catching the virus from people carrying the disease who are entering or staying in the room and regularly release new virus particles into the air. Regular, sufficient air changes, for example by opening the windows wide or by means of a ventilation system, would also reduce the risk of infection.
Recommendations concerning SARS-CoV-2
Coronaviruses are enveloped viruses; the envelope can be destroyed by soap and the virus can thus be inactivated. Surfaces should therefore preferably be cleaned with conventional cleaning products, unless disinfection is necessary or generally prescribed for medical reasons. Similarly, air disinfection is not useful under normal conditions, as the presence of humans is usually not permitted during disinfection and the disinfection effect does not last long afterwards. What is recommended instead is regular cross ventilation.
Legal background
Disinfectants are biocidal products that are subject to the extensive provisions of the Biocidal Products Regulation which is applicable throughout the EU. It lays down the legal requirements which ensure that only effective products are used which do not pose an unacceptable risk to humans, animals or the environment.
In a two-stage process active substances are first approved, after which applications for authorisation can be submitted for biocidal products containing active substances that have already been approved. Both the approval of an active substance and the authorisation of a biocidal product apply only to companies involved in these procedures.
Both hydrogen peroxide and active active chlorine released from sodium hypochlorite are approved active substances. This means that products containing these active substances may only be used if the suppliers’ products have been authorised or are in the process of being authorised. The use of other products for disinfection which contain (exclusively) these active substances is not allowed.
In contrast to the two substances mentioned above, there are some active substances whose evaluation has not yet been finalised. As long as the procedures for evaluating these active substances have not been completed and approval has not been obtained, specific transitional arrangements apply to biocidal products containing these active substances, depending on the respective EU Member State.
Further information
The Austrian Society of Hygiene, Microbiology and preventative Medicine informs about room disinfection and SARS-CoV-2.
ÖGHMP - room disinfection and its effectiveness against SARS-CoV-2 (German only)
The following links give general information on disinfection, the authorisation process and excemptions: