Legionnaires’ disease is caused by an infection of the bacterium Legionella, those who are frequently exposed to unclean water sources where legionella breeds are at risk. Infections have been known to occur in people who work with large cooling towers or air conditioning systems.

The people most at risk for contracting Legionnaires’ disease are those with weakened immune systems, as they have little defence against the onset of infection. People with diseases such as HIV/AIDS, cancer, or diabetes; those who are over the age of 65; and those who have recently undergone an organ transplant have a greater risk of infection. Also, those whose lungs are weakened due to smoking or chronic emphysema are more susceptible to the risk of infection after exposure to the bacterium Legionella.

First, consider whether the risk of Legionella can be prevented by considering the type of water or cooling systems needed. For example, identify whether it is possible to replace a wet cooling tower with a dry system. Where this is not reasonably practicable and a wet cooling system is the only realistic option available, a course of action must be devised to manage the risk by implementing effective control measures. The written scheme should be specific and tailored to the systems covered by the risk assessment. 

Temperature control is the traditional strategy for reducing the risk of Legionella in water systems. Cold water systems should be maintained, where possible, at a temperature below 20 °C. Hot water should be stored at least at 60 °C and distributed so that it reaches a temperature of 50 °C (55 °C in healthcare premises) within one minute at the outlets. For most people, the risk of scalding at this temperature is low. However, the risk assessment should take account of susceptible ‘at risk’ people including young children, people who are disabled or elderly and to those with sensory loss for whom the risk is greater. 

In addition to temperature control, e.g., in more complex systems such as large healthcare facilities, additional measures that encourage the regular movement of water are often used to manage the risk from Legionella in water systems. The exact techniques may vary significantly in different water systems and operating conditions. See “HSG 274 Part 1: The control of Legionella bacteria in evaporative cooling systems” paragraphs 2.80–2.118 for further guidance on the use of water treatment techniques and control programmes. 

The cleanliness of the system must be maintained, as Legionella bacteria are more likely to grow in a system fouled with deposits. In hard water areas, softening of the cold-water supply to the hot water distribution system should be considered to reduce the risk of scale being deposited at the base of the calorifier and heating coils, and to reduce the potential for scale build-up within the system pipework and components. See “HSG 274 Part 1: The control of Legionella bacteria in evaporative cooling systems “paragraphs 2.72–2.73. There is further guidance on cleaning and disinfection techniques and requirements for hot and cold-water systems in paragraphs 2.126–2.137. 

Other measures include:

• Ensuring the release of water spray is properly controlled.
• Avoiding conditions that support growth of microorganisms, including Legionella. 
• Ensuring water cannot stagnate anywhere in the system by regular movement of water in all sections of the systems and by keeping pipe lengths as short as possible, and/or removing redundant pipework and deadlegs. 
• Avoiding using materials that harbour bacteria and other microorganisms or provide nutrients for microbial growth (the Water Fittings and Materials Directory lists fittings, materials, and appliances approved for use on the UK Water Supply System by the Water Regulations Advisory Scheme. Those approved are tested against BS 6920).
• Keeping the system and the water in it clean.
• Treating water to either control the growth of microorganisms, including Legionella, or limit their ability to grow. 
• Monitoring any control measures applied.
• Keeping records of these and other actions taken, such as maintenance and repair work.

The ACOP L8 “The Control of Legionella Bacteria in Water Systems”, The Health and Safety at Work Act 1974 and The Control of Substances Hazardous to Health Regulation (1994), place strict obligations on ALL employers, building owners and landlords to undertake a Legionella and Water Hygiene Risk Assessment on all workplace buildings, where there is a foreseeable risk of exposure to Legionella bacteria.

The HSE Approved Code of Practice for The Control of Legionella Bacteria in Water Systems (L8) applies to any business where water is used or stored (for example sinks, taps, showers, water tanks, toilets, hot and cold water supply) and where there is a means of creating and transmitting water droplets which may be inhaled, thereby causing a reasonably foreseeable risk of exposure to Legionella bacteria. If you have water on site that people can be exposed to, you need to undertake a Legionella Risk Assessment and manage the potential risk of Legionella bacteria.

Business these standards are applicable to include care homes, hotels, guest houses, gyms and leisure centres, dental and GP surgeries, health care premises, retail premises, offices, the NHS, schools, universities, colleges and all commercial, manufacturing and distribution sites. This also applies to those who provide residential accommodation or who are responsible for the water system(s) in their premises.

The compliance of legal duties surrounding Legionella placed upon duty holders, including employers, those in control of premises and those with health and safety responsibilities for others, include:

• Identifying and assessing sources of risk.
• Preparing a scheme to prevent or control risk.
• Implementing, managing and monitoring precautions.
• Keeping records of precautions.
• Appointing a manager to be responsible for others.

The legionella risk assessment will find the site to be either low or negligible risk, in which case a simple review of the assessment should be made every two years, according to HSE ACOP L8 The Control of Legionella Bacteria in Water Systems. It is also stated by ACOP L8 the risk assessment should be reviewed if there a reason to suspect the risk assessment is no longer valid, for example:

• Where there have been changes to plant, the water system or its use.
• Where there have been changes to the use of the building.
• Where new information about risk or control measures has become available.
• Where monitoring indicates that control measures are no longer effective.

There may arise an instance where a reasonably foreseeable risk is identified. In such as case, remedial work may be recommended together with a programme for continual monitoring and control. We at Green Hive Management can advise you of any actions and help you implement them as part of our service.