aerial disinfection

Aerial disinfection - fogging

There may be a need to fog in certain food processes to effect a reduction in airborne microorganisms.

Fogging is primarily carried out in high hygiene processing environments particularly cheese manufacture, salad, sandwich, ready meals, cooked meats and dairies.  It is estimated that more than 50% of chilled food manufacturers conduct this method of disinfection in conjunction with the normal cleaning and disinfection routines.  However, where there is a problem with moulds and spores in environments, regardless if they are low or high risk, fogging of airspace with a peracetic disinfectant can be carried out.

There may be a need to fog in certain food processes to ensure a reduction in airborne microorganisms that may have come from low risk areas, people and fabric of the building or as aerosols from the cleaning process.  Microbiological sampling as part of the factory hygiene procedure should identify where there is a need for fogging.  Unacceptably high airborne or surface counts may warrant corrective action.

Fogging should only be conducted after all cleaning and disinfection of food contact surfaces has taken place.  It should never be used as an alternative to surface disinfection.

Fogging Equipment

It can be carried out with a 1-3% disinfectant solution via a compressed air fogging unit.  The liquid foggers work by supersaturating the atmosphere with a disinfectant fog.  The area they can cover will vary dependent on the fogger. The disinfectant fog in the atmosphere helps to bring down any airborne microorganisms onto the disinfected surfaces.

Several types of mobile fogging units are used throughout the food industry, the following tending to be the most common:

Satellite Drum Top Fogjet - Powered by a compressed air supply, the simple lance fits into a standard 25litre keg and is the most economically priced unit employed for fogging.  Output is a constant 0.15 l/min. Particle size is dependent on air pressure and is variable from sub-micron to 100 micron, typically utilised for fogging rooms of volume up to 100-200m³.

Satellite Fogjet Trolley - As with the Drum Top Fogjet, it too is powered by a compressed air supply but has three fogging nozzles. The trolley is completely portable and holds 25 litres of diluted disinfectant solution.  Output is a constant 0.50 l/min per nozzle. Particle size is dependent on air pressure and is variable from sub-micron to 100 micron and appropriate for fogging rooms of a volume up to 600m³.

Electric Fog Units - Holchem strongly recommend against using these mains powered units unless a full risk assessment has been carried out.

A Built-in-System will typically be used for production areas larger than e.g. 1800m³, where more than three portable fogging units would be required.  The disinfectant fog is generated through the system into the local atmosphere by charging the unit with compressed air and forcing the disinfectant solution through the dedicated nozzles at a 1-3% solution.

Fogging procedure

The fogging unit should be left to run its course which takes approx. 30-45 minutes to complete.  No personnel should be in the area that is being fogged as the fog will cause breathing difficulties.  It may take up to 1 hour after the fogger has emptied before access to the area is possible.  For fogging to be effective a settling period of 45-60 minutes is recommended.

When fogging, it is always recommended that sensitive equipment such as checkweighers, metal detectors, printers etc. should be covered with clean polythene (or removed from the area to be fogged if possible) to prevent liquid ingress.  Polythene should then be removed after the process and the equipment wiped over.

Dependent on the nature of the process and from results of micro sampling and air plate testing, fogging will typically take place on a weekly basis in a high hygiene food processing area.  Items such as Blast Chills and Blast Freezers may need to be fogged daily, dependent on the nature of the product being chilled or frozen, although in some cases where production is required to be running 20 hours per day 6/7 days a week, fogging is not always possible.


Usually a formulated and independently tested QAC or Triamine based disinfectant, such as Holquat or Tribac, will be used for fogging at a 3% solution.  However, if the site has a problem with spores, a QAC disinfectant will not be as effective.  An option would be to use a peracetic based disinfectant, such as Perbac, at a 1-2% solution.

To ensure that fogging has been successful and reached the hardest to reach air spaces, it is good practice to locate Quat test paper (for Quat disinfectants) or PAA test strips (for peracetic acid based disinfectants) in these areas to ensure that the fog has reached these areas.  Ideally, the colour change on these test strips should be reflecting at least 1000ppm on a Quat test paper and 200 ppm on a PAA test strip.

Aerial disinfection - research

Extensive research has been conducted into the pros and cons of fogging, the following being some of the main points identified:

  1. Fogging was found to have a good disinfecting effect on upwardly facing horizontal surfaces (up to 6 log reductions after 60 minutes).
  2. Fogging is not an effective method for disinfection of vertical surfaces, the undersides of equipment or dismantled components because of the lack of chemical coverage on such surfaces.
  3. Airborne microbiological contamination can be reduced by fogging (2 log reductions after 30 minutes; 3 log reductions after 60 minutes).
  4. Fogging is most effective with particle sizes in the range 10-20 micron with an air velocity at the nozzle of 100m/s.  Larger particle sizes can be used if the air velocity is increased or fans are used to assist the distribution of the droplets.
  5. Under typical factory conditions, fogging needs to be carried out for a minimum 15-30 minutes to enable the fog to disperse, the air to become saturate and the chemical / microorganism contact time to occur.  After fogging an additional period of 45-60 minutes is required to allow the droplets to settle and reduce the risk of operators inhaling the chemical droplets.
  6. Compressed air driven fogging nozzles are recommended, either plumbed in systems or mobile units.
  7. Portable electric fogging machines do not operate at sufficient volume flow rate for most applications and are therefore not recommended.
  8. Where possible, nozzles should not be placed near the floor or be pointed at surfaces within the range of the plume generated by the nozzle.