Legionnaires' disease is an illness characterised principally by pneumonia, caused by the bacterium Legionella pneumophila.
According to the National Surveillance Scheme for legionnaires' disease, there were 226 reported cases in England and Wales in 1998, of which 25 proved fatal.
Infection is acquired by the inhalation of airborne water droplets containing Legionella.
The name legionnaires' disease originated in July 1976, when an outbreak occurred at an American Legion Convention in Philadelphia. Since then a number of legislative and guidance documents have been published detailing the required procedures to eliminate or minimise the risk of further outbreaks.
Water temperatures in the range of 2045degreesC favour the growth of Legionella.
They do not survive at temperatures above about 60degreesC. Sediment, sludge, scale and organic matter act as a source of nutrition, as can other organisms in water such as other bacteria and algae. The slime, or biofilm - which often forms on the surface of water - provides favourable conditions for growth.
Plant, storage units, distribution systems and other systems containing water likely to be in the 20-45degreesC temperature range and which may release an aerosol spray (that is, a cloud of droplets and/or droplet nuclei) during operation or maintenance, may present a risk. The following present a particular risk:
water systems incorporating cooling towers and condensers;
hot and cold water services;
spray humidifiers which create a spray of water droplets and in which the water temperature is likely to exceed 20degreesC. Spray systems, which eject water as an aerosol or as droplets, pose the biggest risk, as they can be more easily inhaled and ingested; and spa baths and pools in which warm water is deliberately agitated and recirculated.
Section 8 of the HSE's document 'The prevention or control of legionellosis - (including legionnaires' disease)', requires that 'a suitable and sufficient assessment should be carried out to identify and assess the risk of legionellosis from work activities and water sources on the premises and any precautionary measures'. In existing premises, it is recommended that architects advise facilities managers to undertake a risk assessment which should include a review of:
the systems in place;
whether there are items which could be improved to reduce risk; and the maintenance procedures in place - are they appropriate?
Facilities managers should also produce systems for operations and maintenance. They should:
identify and record a clear structure of responsibility for reviewing and implementing procedures to manage the risk associated with Legionella within building systems;
produce and complete a site log book to aid risk management and record procedures in place;
ensure all staff responsible for maintenance of relevant systems are suitably trained or instructed on how to minimise the risks of Legionella growth;
set in place a structured programme of maintenance, testing, inspection and disinfecting;
ensure all appropriate operating and maintenance documentation is easily available and that any necessary information is reproduced for the Legionella site logbook; and consider installation improvements.
For example, de-stratification pumps on hot water generators.
Operational issues are often the easiest, least expensive and most effective to implement. Once the operational side has been addressed, full consideration can be given to the installation. It is not expected that an older system should be replaced if the risk is small. Capital outlay needs to be rationally compared to the likelihood of hazard occurring.
In an era of health panics, a rational approach is vital.
David Cowles of Buro Happold Facility Management can be contacted on 01225 320600
LEGISLATION AND GUIDANCE The Health and Safety at Work etc Act 1974 (as amended).
The Control of Substances Hazardous to Health Regulations 1999.
Health & Safety Executive (HSE) Approved Code of Practice (L8). [Note: this code does not address the technical aspects of controlling the risk, which can be found in various information published by government departments, trade associations and by the Chartered Institute of Building Services Engineers (CIBSE). ] CIBSE Technical Memoranda 13 (TM13).
HSE Approved Code of Practice L8 (rev) - the prevention or control of legionellosis (including legionnaires'disease). [Note: the ACOP (L8) is due to be revised (August2000) and to incorporate the guidance previously available in HSE guidance note HS (G) 70. ]