Foodlink News Item

Hygienic fogs

Report by Steve Parkin

Almost all food processed in the UK comes into contact with surfaces that are treated with chemical disinfectants. During breaks in production, processing areas and equipment are cleaned and then treated with disinfection to reduce microbial infection. Although fogging is an effective method of applying disinfectants to upward-facing surfaces it is ineffective for vertical surfaces and the undersides of equipment. A recently completed project has shown that vertical and underside surfaces can be successfully disinfected using electrostatically charged fogs. The parameters that effect deposition have been investigated and improved microbiological control demonstrated.

Improving deposition

An electrostatic fogging nozzle was found to meet the specifications for disinfectant fogging. The deposition performance of the nozzle was established from measurements in a fogging chamber at the Silsoe Research Institute (SRI), in a larger chamber at Campden and Chorleywood Food Research Association (CCFRA), and in a food factory. In all cases, deposition onto walls, ceilings and underside surfaces was improved. For example, in the SRI fogging chamber, deposition onto walls and ceilings was improved 2- to 4-fold. Deposition onto objects such as tray stacks, pipes and heat exchangers was improved but the degree of underside deposition depended on the airborne concentration of fog.

Measurements showed that there was an airborne concentration effect with charged fogs. Calculations identified that this was due to the influence of space charge forces. Space charge forces result when unipolar charged particles are in close proximity. To provide design guidelines, a calculation scheme was developed that allows the number of nozzles required to adequately fog a given sized room to be calculated. The scheme was based on scaling laws, mathematical models and deposition data from experiments in the different sized chambers.

Improving hygiene

Microbiological studies with Pseudomonas aeruginosa and a range of commercial disinfectants indicated that charged fogs gave increased levels of control. In paired charge-on/charge-off tests, P.aeruginosa counts on inoculated coupons placed on difficult-to-cover surfaces were lower when electrostatic charging was applied. The increased reduction in counts due to electrostatic charging varied with surface, but was typically 1 log. Tests on food-processing equipment showed similar reductions.

Improving efficiency

During pilot- and full-scale tests, it was observed that charged fogs deposited more rapidly onto surfaces than uncharged fogs, and also cleared more quickly when fogging stopped. In areas where fogging is carried out frequently, this feature could produce significant savings in downtime and possible improvements in safety.

Project Consortium

The project consortium included the following:

Research partners - Silsoe Research Institute, Campden & Chorleywood Food Research Association, and Brunel University.

Equipment manufacturers - H & M Disinfection and Micron Sprayers.

Disinfectant suppliers - Certis Europe, Holchem Laboratories, Solvay Interox, and Ozone Systems.

Food producers - Uniq Prepared Foods and Northern Foods.

Further Information - AFM 121

Anyone interested in more information on this project should contact:

Dr Steve Parkin

Silsoe Research Institute

Wrest Park

Bedford

MK45 4HS

Tel: 01525 864030

Email :

Measuring charged fogging deposition in a test chamber

Results from charged fogging deposition tests

Steve Parkin