Legionella is a family of bacteria, several of which can cause Legionnaires’ disease, which is a potentially fatal form of pneumonia. Whilst it can affect anybody, it principally affects those who are susceptible because of age, illness, immunosuppression, smoking, etc..
Water systems can, under certain circumstances, generate the conditions for the potential spread of Legionnaires’ disease. For this to occur, the water needs to have become contaminated with the bacteria and been dispersed into the atmosphere as a fine spray, mist or fog. Legionnaires' disease is normally contracted by inhaling this spray/mist/fog and not generally by drinking contaminated water.
Improperly managed cooling towers are one of the main sources of Legionella and have been responsible for a number of deaths of members of the public in recent years. Other water systems can also generate the Legionella hazard.
The first step is to complete a risk assessment on all parts of your water systems, including:
- all open circuit cooling towers and their associated pipework;
- all closed circuit cooling systems and their associated pipework;
- all water storage tanks except toilet cisterns;
- all ‘domestic’ water systems, e.g. for kitchens, vending machines, washing facilities and particularly showers used by employees; and
- all ‘wet’ sprinkler systems and fire hoses.
Risk assessment of water systems requires special knowledge. Once again, it is important that people involved in assessing risk and applying precautions are competent, trained and aware of their responsibilities.
Legionella is widespread in the environment and cannot be prevented from entering water systems entirely. However, taking the following precautions in hot and cold water services can reduce the risk of an outbreak developing:
- storage tanks and pipe work should be designed so that water is not allowed to stand undisturbed for long periods;
- storage tanks should be well covered to prevent the entry of dirt, debris and vermin, and should be periodically inspected, cleaned and disinfected;
- water temperatures between 20°C and 45°C should be avoided by insulating cold water tanks and pipes in warm spaces, and by storing hot water at 60°C and circulating at no less than 50°C. Where there is a risk of scalding for the very old and for young children, thermostatically controlled taps may be needed; and
- only water system fittings and materials which comply with water authority requirements should be used: certain materials (e.g. leather, some rubbers and plastics) support the growth of bacteria and should not be used.
Some of these aspects may be covered by local ‘by-laws’ or similar requirements, covering cold water tanks and precautions against back-flow of contaminated water into the mains.
Control measures
Where the risk assessment identifies Legionella as a potential risk, control measures need to be put in place in line with the HSE's The control of legionella bacteria in water systems Approved Code of Practice (ACoP) and guidance (ref L8). The important aspects when managing this risk are:
- The risk assessment needs to be completed in association with a competent person and should clearly specify full details of the control measures that will be put in place in association with a competent contractor.
- The overall control of the water system should be written down in a ‘safe system of work’ to prevent any misunderstandings of ‘who does what’.
- The written procedure should include the regular actions to be taken by both you (the employer) and the competent contractor. In summary, this will provide for you to arrange for :
- regular cleaning and disinfection of the domestic water system, as appropriate;
- regular testing of the water temperatures at hot and cold taps to ensure the water is always above 50°C and below 20°C and, if this is not the case, to take appropriate remedial action. Precautions should be taken to minimise the scalding risks of water from hot taps by using thermostatic valves or, as a minimum, placing appropriate warnings by the taps; and
- regular (usually weekly) dip-slide testing of all open water within the water system. This will include testing the cooling tower reservoir and any open tanks or baths for process water and recording the bacteria level results – with detailed instructions of actions to be taken if defined maximum levels are exceeded.
- Water in cooling towers should be checked, generally at least monthly, by a competent contractor for a variety of parameters. These results should be fully reported to you together with clear advice on any remedial action recommended by the contractor, detailing who will take the action and any follow-up tests needed.
You should satisfy yourself that you fully understand any reports from any competent contractor and that you are convinced that the controls are providing safe operating conditions within the limits prescribed in the HSE's L8.