Legionella Risks Explained

The HSE provides advice and guidance to control the risks from exposure to Legionella in man made water systems. The sections below provides a breakdown of the essential requirements you need to be aware of.

This information is designed to help employers and those with responsibility for the control of premises, including landlords, understand what their duties are and how to comply with health and safety law. It applies to premises controlled in connection with a trade, business or other undertaking where water is stored or used, and where there is a means of creating and transmitting breathable water droplets (aerosols), causing a reasonably foreseeable risk of exposure to legionella bacteria.

 Control and Management

  • According to The Health & Safety at Work Act of 1974's Approved Code of Practice L8 (HSG 274), "The Duty Holder should arrange to evaluate the assessment regularly and explicitly where there is reason to fear it is no longer valid." It is important to note when to review the assessment and what factors to take into account.

    -> A change to the water system;

    -> A change to the use of the building where the system is installed;

    -> New information available about risks or control measures;

    -> The results of checks indicating that control measures are no longer effective;

    -> Changes to key personnel;

    -> A case of legionnaires disease.

    At C&M Water, we advise yearly reviews to guarantee that the proper implementation is being carried out. Legionella bacteria have a 15-minute half-life, therefore it's critical to routinely examine your risk assessment and monitoring data.

  • If the risk assessment deems it required, samples from regions where the target control parameters are not fulfilled, areas with low consumption, stagnation, excess storage capacity, dead legs, excessive heat loss, cross flow from water systems, or other anomaly should be taken from hot and cold water systems. HSG 274 part 2, page 212.2 Examine HSG 274 Part 2 to determine when to sample.

  • Records kept for monitoring and inspection should be kept for at least five years. – HSG 274 part 2 p.25

  • All records kept for monitoring and inspection, should be kept for at least five years.” – HSG 274 part 2 p.25

  • Inadequate management, a lack of training, and poor communication can all play a role in legionnaires' disease epidemics. HSG 274 part 2, page 16

  • For management and maintenance purposes, it is crucial that all system components, equipment, and parts are easily accessible. Examples include the tank, calorifiers, thermostatic mixing valves (TMVs), blending valves, circulation pumps, etc. - P2.34 of HSG 274 Part 2

Cold Water Storage Tanks

  • The cold water storage tank should be cleaned, disinfect and any faults rectified”. – HSG 274 part 2 p.2.57

  • Due to insufficient turnover, remove the tank(s) as soon as you can and switch to the mains water supply. Alternatively, remove the tank(s) you already have and install a new one (with correct fittings)

  • The tank is sitting on a secure base which should be suitable for the tank to rest on.

  • Inlet and outlet on opposite sides of the cold water tank to encourage water flow across the tank and avoid low flow areas within the tank” – HSG 274 part 2 figure 2.4

  • “The lid should be closely fitted and in good conditions”. – HSG 274 part 2 p.2.57

  • “The thermal insulation should be in good condition so that it protects from extremes of temperature.” – HSG 274 part 2 p.2.57

  • “Thermal gain should be kept to a minimum by adequate lagging and separation of cold water services pipework and components from hot water services and heating systems” – HSG 274 part 2 p.2.36 point 5

  • Overflow size is not twice the size of the inlet. May not remove water quick enough should the ball valve fail should the inlet be of an equivalent size or smaller.

  • “The insect and vermin screen on the overflow and warning pipes and any vents should be intact and in good condition” – HSG 274 part 2 p.2.57

  • “The insect and vermin screen on the overflow and warning pipes and any vents should be intact and in good condition”

    – HSG 274 part 2 p.2.57

  • “The open vent pipe from the calorifier should be sufficiently raised above the water level” – HSG 274 part 2 p.2.37

  • “The open vent pipe from the calorifier should be sufficiently raised above the water level” – HSG 274 part 2 p.2.37

  • Hollow struts (roof supports) may provide legionella proliferation conditions and should be replaced with solid struts

  • The hot water source is not a suitable capacity for use. Temperatures appear to fluctuate in and out of compliant ranges due to low storage volume.

Expansion Vessels

  • “To minimise the risk of microbial growth, expansion vessels should be installed: in cool areas on cold flowing pipes” – HSG 274 part 2 p2.39

  • “To minimise the risk of microbial growth, expansion vessels should be installed: mounted as close to the incoming water supply as possible” – HSG 274 part 2 p2.39

  • “To minimise the risk of microbial growth, expansion vessels should be installed: mounted vertically on pipework to minimise any trapping of debris” – HSG 274 part 2 p2.39

  • “To minimise the risk of microbial growth, expansion vessels should be installed: with an isolation and drain valve to aid flushing and sampling” – HSG 274 part 2 p2.39

Pipework

  • Cut back redundant pipe work to avoid stagnation.

    According to the Water Regulations Advisory Scheme, "full removal of unnecessary pipe work can reduce this danger." In cases where this is impractical, the pipe should be ended so that any resulting "dead leg" is no longer than twice the pipe's diameter. For instance:

    -> 15mm to be no longer than 30mm (just over 1”)

    -> 22mm to be no longer than 44mm (just under 2”)

    -> 28mm to be no longer than 56mm (just over 2”)

  • You should ensure all flexible hoses comply with the WRAS approval scheme and be tested and comply with BS 6920. “In buildings where there are those with an increased susceptibility to infection or with processes requiring specific water characteristics, materials of an enhanced quality may be required. Healthcare buildings and care homes should specifically take note of alerts and advice from the Department of Health and Health Facilities Scotland. For example, healthcare premises are advised against the use of ethylene propylene diene monomer (EPDM) lined flexible hoses (tails) as these have been shown to be a risk of microbial colonisation. Such flexible connections should therefore only be used in healthcare premises where an installation has to move during operation or is subject to vibration.” –

    HSE 274 part 2 p.2.35

    “Flexible hoses should be used only for the following applications: to allow for vibration of equipment; to accommodate vertical displacement of high and low baths and sinks; to facilitate essential maintenance and access of bespoke equipment when no alternative is available. Note – Where fitted, flexible hoses should be kept as short as possible and be kink-free as to no affect flow”. – The Health Technical Memorandum 04-01: Safe water in healthcare premises. Part A: Design, installation, and commissioning states in p.3.41

  • “Isolation valves should be included in all locations to facilitate maintenance and the implementation of control measures” – HSG 274 part 2 p2.34

  • Galvanised/lead pipe work is recommended to be removed as it may lead to legionella proliferation. “Avoid using materials that harbour bacteria and other microorganisms or provide nutrients for microbial growth”. – HSG 274 part 2 p.23

  • “Single check valves are commonly used to prevent backflow” – HSG 274 part 2 p.2.32

Signs

  • “It is important that there should be ease of access to all parts of the system, components and associated equipment for management and maintenance purposes, e.g. tank, calorifiers, thermostatic mixing valves (TMVs), blending valves, circulation pumps etc.” – HSG 274 part 2 p2.34

  • “The Regulations require employers to use a safety sign where there is a significant risk to health and safety” – The Health & Safety (Safety Signs and Signals) Regulations 1996 p.4

    Caution signs are recommended at any location where there is the potential for scalding hot water. This includes where TMVs are located as they may fail.

  • “It is important that there should be ease of access to all parts of the system, components and associated equipment for management and maintenance purposes, e.g. tank, calorifiers, thermostatic mixing valves (TMVs), blending valves, circulation pumps etc.” – HSG 274 part 2 p2.34

Heat Sources

  • Repair broken water heaters that are intended to be brought back into use.

  • “During periods of low usage such as overnight or at weekends, fitting a timer which switches off the immersion heater may prove effective. The timer should be set to switch the immersion heater on again in time to ensure the water is heated sufficiently to achieve microbial control before use” – HSG 274 part 2 p.2.13

  • Fit a hot water cylinder gauge to the flow/ return of the hot water cylinder.

  • “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” – HSG 274 part 2 p.2.6

  • Repair broken water heaters that are intended to be brought back into use.

  • “Consideration should be given to removing infrequently used showers, taps and any associated equipment that users water” – HSG 274 part 2 table 2.1

  • Pump required on the hot water cylinder to aid circulation and improve hot water outlet temperatures.

  • “Stratification, which may occur in large calorifiers, should be avoided and fitting a timer-controlled shunt pump to circulate the water from the top of the calorifier to the base during the period of least demand should be considered” – HSG 274 part 2 p.2.25

  • “Single check valves are commonly used to prevent back flow of hot water to the cold feed” – HSG 274 part 2 p.2.32

Thermostatic Mixing Valves (TMVs)

  • “To maintain protection again scald risk, TMVs require regular routine maintenance carried out by competent persons in accordance with manufacturer’s instructions”. – HSG 274 part 2 table 2.1

  • “Where a scalding risk is assessed as low (e.g. where health users immerse their whole body), type 2 TMVs that can be overridden by the users are required by building regulations. Where a scalding risk is considered significant (e.g. where users are very young, very elderly, infirm or significantly mentally or physically disabled or those with sensory loss) then type 3 TMVs that are pre-set and fail-safe should be provided (but are required at healthcare premises) and should be checked regularly to ensure they are fail-safe if the cold water supply pressure is interrupted”. – HSG 274 part 2 box 2.3

  • “Where a single TMV serves multiple tap outlets, the risk can be increased”. – HSG 274 part 2 p.2.76 This also applied to TMV’s positioning from the outlet.

  • “Where a risk assessment identifies a significant scalding risk is present, e.g., where there are very young, very elderly, infirm or significantly mentally or physically disabled people or those with sensory loss, fitting TMVs at appropriate outlets, such as hand washbasins and sinks is required.” – HSG 274 part 2 p.2.75

    HTM 04-01: Supplement – Performance specification D 08: thermostatic mixing valves (healthcare premises) See HTM 04-41 extract.

    Page 6 – “it is recognised that users of domestic hot water for ablutionary purposes in health and social care establishments, particularly vulnerable people (see Note below), can be at risk of injury by scalding”. “’Vulnerable people’ are defined in Health and Safety Executive’s Health Services Information Sheet 6 as:

    -> children

    -> older people

    -> people with reduced mental capacity, mobility, or temperature sensitivity

    -> people who cannot react appropriately, or quickly enough, to prevent injury”

  • “Where a risk assessment identifies the risk of scalding is insignificant, TMVs are not required” – HSG 274 part 2 p.2.75

Other Areas

  • “Where necessary, hot and cold water services should be cleaned, flushed and disinfected in the following situations, as specified in the NS 8558: on completion of a new water installation or refurbishment of a hot and cold water system. On installation of new components, especially those which have been pressured tested”. – HSG 274 part 2 p.2127. More examples as to when a disinfection is required.

  • “Flush the outlets until the temperature at the outlet stabilises and is comparable to supply water and purge to drain”. – HSG 274 part 2 table 2.1

  • “Dismantle, clean and disinfect removable parts, heads, inserts and hoses where fitted”. – HSG 274 part 2 table 2.1

Download the HSE’s HSG 274 Part 2 Legionella Guidelines for FREE