Health and Safety
Executive / Commission
Surface engineering
The Health and Safety Executive (HSE) held a Legionella Awareness Seminar in Birmingham on 27th March, 2009 following two cases of Legionnaires’ disease contracted from a large, conveyorised, aqueous tunnel washer.
Over 120 attendees (inluding equipment suppliers, user companies and water treatment specialists) received details about this newly identified problem and received practical advice on minimising risk from this type of wash process, typically found in the finishing of automotive components, motors, panels and white goods.
HSE’s action followed a recent investigation carried out after two workers at a large engineering company became seriously ill. It was discovered that they had contracted Legionnaires’ disease from a previously unidentified source: contaminated water in a tunnel washer.
Such equipment typically consists of a number of wash, rinse and surface treatment stations containing aqueous solutions sprayed through banks of nozzles. Metal components travel through the washer, suspended from an overhead monorail, before being dried and painted.
In the installation where the problem was identified, rinse water was stored in tanks at the side of the tunnel, notionally at ambient temperature. However, carry-over of heated wash solution from the cleaning process caused the rinse water temperature to rise to between 25 and 45°C. This water temperature range, together with rust and scale build up in the tanks, provided conditions under which the legionella bacteria could proliferate. As the contaminated wash solution was sprayed onto the components, some of the contaminated spray mist leaked out of the tunnel where it could be inhaled by nearby workers. For plant fitted with extraction an additional risk exists, as the same vapour discharged outside could potentially expose the public to airborne bacteria.
HSE Principal Inspector Peter Woolgar advised: "A legionella risk assessment needs to cover all water systems on sites where water is sprayed or water mists generated, particularly for companies with this sort of plant. Unless there is someone with appropriate expertise on site, specialist advice should be sought.
"Where a legionella risk is identified, microbiological sampling will usually be necessary to find out the level of contamination. Then a regime for draining-down, cleaning, disinfecting and monitoring the system should be put in place.
"Manufacturers and suppliers, as well as users and water treatment specialists, should not underestimate the risk of this type of equipment giving rise to this life-threatening disease and should ensure all the usual precautions against legionella are in place."
Further information on Legionnaires’ disease is available on the HSE legionnaires website and the Health Protection Agency’s website.