Legionnaires' disease: The control of legionella bacteria in water systems

Why was the original document (HS(G)70) revised?

In 1991 HSE introduced The prevention or control of legionellosis (including legionnaires' disease) (HS(G)70). However, this document was not fully clear where responsibilities lay.. The new publication, Legionnaires' disease: The control of legionella bacteria in water systems (L8), consolidates the information from both HS(G)70 and its Approved Code of Practice (ACoP) into a single document. The revised document includes more advice on the competence and training for staff responsible for developing, managing and conducting the risk assessment and implementing the controls. It also stresses the duties on suppliers of products and services to carry out work effectively and safely and to liaise with the client duty holders when deficiencies are identified.

What are the key changes?

The key changes in this document are: The removal of the 300 litre limit in domestic hot water services. This is because it was recognised that systems below 300 litres could present a potential risk. The ACoP now clearly applies to any workplace or undertaking where water is used or stored and there is a reasonably foreseeable risk of legionellosis; Guidance for when hot and cold water systems should be sampled and tested for legionella. The recommendation that cooling water systems are sampled and tested quarterly for legionella, (and particularly during outbreaks), and the actions recommended when legionella is detected.

How can the risk of legionellosis be minimised?

The original guidance concentrated on reducing the risk by avoiding conditions where legionella could proliferate and, where possible, avoiding unnecessary exposure to aerosols. In some cases, this led to replacing wet cooling processes with dry ones. Where this was not an economic or practical option, legionella growth was controlled through chemical dosing of cooling water systems and ensuring water temperatures for domestic services were maintained outside of the optimum legionella growth range, (20 to 45°C with a peak growth rate around 37°C ). However, in non-domestic properties, where the throughput of water relative to the system volume can be low, legionella bacteria can become established and reach high concentrations, even where temperature regimes are followed. Legionella bacteria can survive for hours, even at 50ºC. The new guidance reiterates the concept that it is not the absence (or presence) of legionella in a single sample that is significant. It is the existence of the circumstances that could lead to rapid growth of legionella to potentially hazardous levels. Ideally, these should be minimised by good design and operation but regular flushing may also be required where stagnation cannot be eliminated with certainty. Other issues such as water storage, circulation and system cleanliness are also discussed in detail.

What are your responsibilities under the new guidance?

The ACoP and guidance covers five key areas of equal importance: Identification and assessment of the risk A suitable and sufficient assessment is required to establish what risks of exposure to legionella bacteria exist from both the water systems and work activities. It should identify the necessary measures to prevent, or adequately control, the risk from exposure to legionella bacteria. The ACoP states that a risk assessment should be carried out by a competent person, (i.e. someone who understands water systems and the risk from exposure to legionella bacteria associated with them). As part of the risk assessment, the guidance recommends that an asset register of all associated plant, pumps, strainers and other relevant items be provided along with a schematic diagram showing the layout of the plant or system.

Managing the risk: management responsibilities, training and competence

If the assessment shows that there is a risk from exposure to legionella bacteria, someone should be appointed to take responsibility for and supervise the implementation of the necessary precautions. This person should be a manager, director, or have a similar status and sufficient authority. They should also be competent and have the knowledge of the systems to ensure that all operational procedures are carried out in a timely and effective manner. This person is often appointed from a supplier if there is nobody in the organisation with the expertise. Training should be provided for anyone carrying out the control measures, (such as a maintenance engineer), to ensure the tasks are carried out in a safe and technically competent manner. Training records should be kept, including details of any refresher training. Staff responsibilities and lines of communication, both internally and between your suppliers, should be properly defined and clearly documented.

Preventing or controlling the risk from exposure to legionella bacteria.

Once the risk has been identified and assessed, a written scheme should be prepared for preventing or controlling it. This should include:

  • An up-to-date schematic of the system;
  • A description of the correct and safe operation of the system;
  • The precautions to be taken;
  • Checks to be carried out to ensure the scheme is successful and the frequency of such checks;
Remedial action to be taken in the event that the scheme is shown not to be effective. Conditions which allow legionella bacteria to proliferate should be avoided, (e.g. Water temperatures between 20ºC and 45ºC) as should the creation of aerosols and sprays.

Record keeping

A record of the assessment, precautionary measures and the treatments should be kept. All records should be signed by those people performing the various tasks assigned to them. This should ensure that precautions continue to be carried out and that adequate information is available.

Responsibilities of manufacturers, importers, suppliers and installers

Designers, manufacturers, importers or suppliers of water systems have a legal obligation to ensure their systems can be operated, cleaned and maintained safely. The guidance provides a number of points to consider for the design and construction of water systems. These include fitting effective drift eliminators, (cooling tower systems) and reducing stored cold water to a minimum required to meet peak periods, (hot and cold water systems).

Risk assessment

This involves a thorough analysis of the risks of exposure posed by your water systems. A report is provided with recommendations on how deficient areas can be improved as well as an asset register of plant and detailed schematics. We has been undertaking water water risk assessment audits for 20 years, so our knowledge of the dangers posed by legionella is extensive. This is further supported by our UKAS accreditation for laboratory testing.

Risk assessment review

The guidance recommends that a risk assessment should be reviewed at least every 24 months. With the recent changes to the ACoP and guidance, it is important to ensure that your current risk assessment is meeting the new requirements of L8. This includes having schematic diagrams of your water system. We can review your existing risk assessment and advise you on any further action required.

Water management systems

Record keeping is an important part of any legionella control system. We can provide you with a tailored document to help you monitor the performance of those involved in the control process. It will also provide you with documented evidence to demonstrate to the enforcement agencies that you have satisfactory procedures in place to reduce the risk of Legionnaires' disease. Training It is important that those with the responsibility for implementing the controls to reduce the exposure to legionella are adequately trained. We can provide bespoke training courses for your staff to ensure they understand the controls required to minimise the risk.