HSE's Approved Code of Practice L8 - Part 7

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

Preventing or controlling the risk from exposure to legionella bacteria

Approved Code of Practice and guidance

Guidance

55 - Once the risk has been identified and assessed, a written scheme should be prepared for preventing or controlling it. In particular, it should contain such information about the system as is necessary to control the risk from exposure.

56 - The primary objective should be to avoid conditions which permit legionella bacteria to proliferate and to avoid creating a spray or aerosol. It may be possible to prevent the risk of exposure by, for example, using dry cooling plant, adiabatic cooling systems or point-of-use heaters (with minimal or no storage). Where this is impractical, the risk may be controlled by minimising the release of droplets and by ensuring water conditions which prevent the proliferation of legionella bacteria. This might include engineering controls, cleaning protocols and other control strategies. Decisions should be made about the maintenance procedures and intervals, where relevant, on equipment used for carrying out the control measures. Legionella bacteria may be present in very low numbers in many water systems but careful control will prevent them from multiplying.

57 - In general, proliferation of legionella bacteria may be prevented by:

(a) avoiding water temperatures between 20°C and 45°C – water temperature is a particularly important factor in controlling the risks;

(b) avoiding water stagnation, which may encourage the growth of biofilm;

(c) avoiding the use of materials in the system that can harbour or provide nutrients for bacteria and other organisms;

(d) keeping the system clean to avoid the build-up of sediments which may harbour bacteria (and also provide a nutrient source for them);

(e) the use of a suitable water treatment programme where it is appropriate and safe to do so; and

(f) ensuring that the system operates safely and correctly and is well maintained.

58 - The scheme should give details on how to use and carry out the various control measures and water treatment regimes including:

(a) the physical treatment programme – for example, the use of temperature control for hot and cold water systems;

(b) the chemical treatment programme, including a description of the manufacturer’s data on effectiveness, the concentrations and contact time required;

(c) health and safety information for storage, handling, use and disposal of chemicals;

(d) system control parameters (together with allowable tolerances); physical, chemical and biological parameters, together with measurement methods and sampling locations, test frequencies and procedures for maintaining consistency;

(e) remedial measures to be taken in case the control limits are exceeded, including lines of communication; and

(f) cleaning and disinfection procedures.

59 - The scheme should also describe the correct operation of the water system plant including:

(a) commissioning and recommissioning procedures;

(b) shutdown procedures;

(c) checks of warning systems and diagnostic systems in case of the system malfunctions;

(d) maintenance requirements and frequencies; and

(e) operating cycles – including when the system plant is in use or idle.

60 - Detailed guidance on how to effectively prevent or control exposure can be found in Part 2.

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Extracted with permission from "Approved Code of Practice (ACoP) and Guidance "Legionnaires' disease: The control of Legionella bacteria in water systems" (L8)" © Crown copyright

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