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    Control of legionella

    The Control of Legionella Bacteria in Water Systems

    Fri 29/04/2016 - 01:19

    ACoP Legionnaires’ disease: The control of Legionella bacteria in water systems (L8), HSG 274 Parts 1-3, what are the changes?


    The current version of the ACoP L8 was published in 2000 as joint Approved Code of Practice (Part 1) and Technical Guidance (Part 2). It has proven to be one the most popular documents the HSE has produced. It has been reviewed following Lord Young’s report on compensation culture in the UK and Professor Löfstedt’s review of Health & Safety Law in the UK which started in 2011. The review of the ACoP was undertaken through 2013 and the revised version 4 of the ACoP and the Technical Guidance documents were published on the 25th November 2013. The previous version has now been withdrawn. The revision of L8 means that the document is now in two parts and gives a clearer distinction between legal requirements and guidance:

    1. The new ACoP L8

    2. Technical Guidance HSG 274 which is in 3 parts:

    • Part 1 - The Control of Legionella bacteria in evaporative cooling Systems
    • Part 2 - The control of Legionella bacteria in domestic hot and cold water systems (Interim document copied from version 3 of L8. New guidance now out for consultation and due for publication in March 2014
    • Part 3 - The control of Legionella bacteria in other risk systems

    What’s new in version 4 of the ACoP L8?

    Firstly it is important to clarify this is a review and not a re-write and that those already complying with the law do not need to change what they are doing. The fundamentals of Legionella management and control remain the same:

    • Identify and assess sources of risk
    • Prepare a written scheme for preventing or controlling the risk (if appropriate)
    • Implement, manage and monitor precautions
    • Appoint competent person or persons to manage the risk. Otherwise known as the responsible person
    • Keep records

    The ACoP still carries special legal status.

    The changes in the ACoP are (those in bold are sections with new ACoP status):

    1. The document is much clearer and concise. It is easier to read and understand. It is easier for a Duty Holder (DH) and Responsible Person (RP) to understand legal duties.
    2. The scope and application is more detailed and now includes reference to spa pools and describes what a low risk situation is.
    3. There are now summary boxes prior to each ACoP highlighting what is required to comply with the law.
    4. Paragraph (P)29 is new and highlights the need for the duty holder to ensure that the risk assessor and the other providing advice are competent to do so. (Eg Membership of the Legionella Control Association).
    5. P32 states that not only should the risk assessment be reviewed regularly but is should include a review of the management and communication procedures.
    6. Proportional risk management in low risk systems.
    7. ACoP status now given to ‘Carrying out a risk assessment’ (P38). Previously this was guidance.
    8. The guidance on carrying out a risk assessment is more informative and includes the importance of schematics (P40) and three new factors to consider when risk assessment is undertaken, disinfection, a review of current control measures and the local environment.
    9. Greater emphasis on the sharing of information with employees and their representatives (ie Trade Unions) (P35&44 and summary boxes) and consideration of at risk employees (P70).
    10. 1The risk assessment should be considered a ‘living document’ (as stated in BS8580). There is now no guidance to review every two years (as stated in previous ACoP P38). Specific reasons to review are still listed and now include ‘changes to key personnel’. This change puts it in line with other ACoP. A risk based approach is required based on simple or complex systems, types of occupants and types of fittings. Auditing by the DH or RP is required on a regular basis.
    11. There is a greater emphasis for the DH to be more responsible and for key decisions meaning they must have adequate knowledge and understanding of the law and their water systems so key decisions can be made with confidence.
    12. The DH should appoint a competent person or persons. This is a change from version 3 (P44) which states appoint a person for day-to-day control. This acknowledges the Corporate Manslaughter and Corporate Homicide Act 2007 which has removed the notion of the ‘controlling mind’. It indicates that in large and complex systems, such as hospitals responsibility should sit with more than one person.
    13. P48 states a DH ‘may need to appoint people from outside the organisation’ as the competent person. A change for version 3 which stated it may be necessary to enlist help’. A significant change that could mean in-house facilities management (FM) companies could be made RP. The RP must have day-to-day responsibility and sufficient authority, competence and knowledge (a change from director/manager version 3 P44) so must be a direct employee or a contractor on site most days.
    14. ACoP Preventing or controlling the risk from exposure to legionella bacteria is clearer and more detailed, but there are no significant changes. Written scheme should make reference to the risk assessment. Emphasises the importance of a management audit in the risk assessment.
    15. ACoP status now given to ‘Review of control measures: monitoring and routine inspection’. Highlights the importance of undertaking internal and external audits.
    16. More reference to spa pools throughout the document.
    17. Record keeping – P70 states that an employer with less than five employees does not need to keep records, but states it may be useful to keep a written record.
    18. P74 states that results of any biological monitoring should be recorded.
    19. ACoP for responsibilities of manufacturers, importers, suppliers and installers now includes designers. Systems need to be designed to minimise the risk from legionella. BS8580 recommends design risk assessments followed by a risk assessment upon occupation. The AcoP is now much more detailed to emphasise design considerations, these were previously only guidance (version 3 P73-81).

    In conclusion the new ACoP is more detailed and but also more concise and easier to read and understand. There is a greater emphasis on the role of the Duty Holder and the importance of training, review of control measures, communication, auditing and design. The Duty Holder must lead legionella control with their premises and ensure they are complying with the law they cannot be absolved of duty.

    What are the changes to HSG 274 Part 1: The control of Legionella bacteria in evaporative cooling systems?

    The Technical Guidance for evaporative cooling systems is now a separate document. There are not many changes in what is required to manage and control the risk from Legionella in these systems but what is different is the clarity and how much easier it is to understand for the Duty Holder.

    The main changes are:

    1. No set time intervals required for cleaning and disinfection (P1.11 & P1.79-81 &1.84) but should be based on an assessment fouling potential, history of control of the system and other factors such as the environment. A regular inspection of the system is required to include all components, tanks, heat exchangers etc.
    2. Guidance on cleaning frequencies is given in paragraph 1.84 and on page 39 and now includes quarterly inspections in dirty environments, possibly leading to quarterly cleaning.
    3. The guidance now contains information through tables and photos making it much clearer on what is a ‘clean system’ and how to interpret chemical and microbiological results and what to look for in an inspection; helping the DH understand what is being and what needs to be done to control the risk.
    4. There is more information on corrosion control (page17/18) and scale control (p18/19). Recommend monitoring of corrosion rates in an evaporative cooling system.
    5. More information on the use of alternative treatments (p1.67-1.72).
    6. Monthly legionella analysis should be carried out on towers that cannot be shut down.
    7. P1.22 on page 13 gives information on drift eliminators being easy to handle, readily removable and discusses how they can become brittle.
    8. Typical on-site monitoring requirements have changed (table1.8, page 41). Magnesium hardness, sulphate, suspended solids, temperature and soluble iron tests removed. These are consolidated in the other tests listed.
    9. Table 1 page 44 new; advice on legionella sampling results. Not detected does not mean not present or there is no risk.
    10. Figure 1.8 page 46 shows a typical cooling tower water service report.
    11. Appendices 1 and 2 give guidance on legionella risk assessment and written scheme.

    What are the changes to HSG 274 Part 2: Domestic hot and cold water systems?

    Currently the published document is the same as the guidance in version 3 ACoP and guidance L8. Until the new version is published no changes are required.

    The revised edition is currently out for consultation and is due to be published by the end of March 2014. The guidance is very different in its look to the old guidance.  Like the other guidance documents the information is clearer more concise and is easier to read.

    The draft provides updated and, in some cases, new guidance on:

    1. Technological advancements
    2. Types and application of hot and cold water systems
    3. Design and commissioning
    4. Solar heated hot water
    5. Large and complex systems
    6. Water treatment and control programmes
    7. Shared premises
    8. Shared premises and landlords residential accommodation
    9. Special considerations for healthcare and care homes – including water safety groups and water safety plans
    10. Schematic diagrams
    11. Expansion vessels
    12. The use of point of use filters
    13. Commissioning small and large developments
    14. Definition of low risk systems
    15. 1Additional guidance on a monitoring programme on pages 31-33

    A full review will be undertaken by ESG once it is published by the HSE in Spring 2014.

    What are the changes to HSG 274 Part 3: Other risk systems?

    Now a full guidance which is a significant increase from the few paragraphs in the version 3 L8. The guidance now includes the following improvements/changes:

    1. The list of other risk systems greatly increased, page 2.
    2. Reference to WMSOC guidance on other risk systems, page 4.
    3. Spray humidifiers have been separated from air washer and wet scrubbers on the monitoring table. Air washers and wet scrubber monitoring now as indicated by the risk assessment.
    4. Emergency shower and eye wash tanks to be inspected monthly. Shower head, nozzles, tanks and associated fitting to be cleaned and disinfected quarterly.
    5. Spa pool identified as the most significant other risk system (P3.4). Spa pool guidance references detailed HSE/PSE guidance: Management of Spa Pools controlling the risk of infection.
    6. Whirlpool baths are now included.
    7. Horticultural misting systems now require a quarterly clean and disinfection to include spray head, tanks, pipework and all wetted surface. An increase from annually.
    8. More detailed information on dental chairs and reference to HTM01-05.
    9. Vehicle wash systems now need to be sampled quarterly.
    10. Lathes and machine tool coolant systems have been removed – now covered by industrial process water systems.

    HSG274 Part 2 - A summary and interpretation of the new guidance for legionella control in domestic hot and cold water systems


    The HSE published their review of the 3rd edition ACoP Legionnaires’ disease: The control of legionella bacteria in water systems in November 2013 along with technical guidance documents HSG274 Parts 1-3. Part 2: The control of legionella bacteria in hot and cold water systems at the time was published as an interim document; the new document was published April 2014. 

    A long overdue review of legionella control procedures, HSG274 Part 2 aims to provide clearer and more detailed practical advice on the management and control of legionella in domestic hot and cold water systems.

    Firstly it is important to note that the principals of legionella management and control remain the same: identify and assess sources of risk; prepare a written scheme for preventing or controlling the risk (if appropriate); implement, manage and monitor precautions; appoint a competent person or persons to manage the risk and keep records.

    The risk assessment remains the starting point for legionella control; it should be considered a living document and should be reviewed on a regular basis. The risk assessment should lead the duty holder and responsible person on how best to manage and control the risk from legionella.

    The new document is 4 times larger than the previous guidance for hot and cold water systems, but does bigger mean better? We believe it does; many cases of legionnaires’ disease are attributed to domestic hot and cold water systems so it is important that everything is covered clearly and in detail. All buildings will have domestic hot and cold water systems so this document is applicable to owners, operators, contractors, designers, installers, manufacturers and anyone with or working on domestic water systems. Over the next few paragraphs each section in HSG274 Part 2 will be summarised with changes from the previous guidance highlighted.

    Types and application of hot and cold water systems

    HSG274 Part 2 provides significantly more information on types and application of hot and cold water systems. Specific reference is made to smaller low risk water systems which are typically mains fed and supplied by instant or point of use (POU) water heaters or combination boilers with a capacity of no more than15 litres, low risk users and no showers. These types of systems are becoming increasingly common as duty holders and responsible persons look to reduce the legionella risk and maintenance overheads in their properties. Paragraph 25 in L8 4th edition states that elaborate control measures may not be required in low risk systems. A risk based approach can be taken on these types of systems as to the frequency and type of control measures and monitoring. Combination water heaters (with an integral cold water tank) are also common on these types of systems, but will require more different and more frequent monitoring as discussed later.

    More complex water systems with cold water tanks, calorifiers, showers and a large number of outlets are also clearly explained. Different types of calorifiers, their potential faults and benefits, such are direct gas fired units which have a lower incidence of legionella colonisation, are clearly explained. A new section refers directly to solar heated calorifiers and how they should be installed. Complex systems will require current control measures to continue but may require an increase in the tasks and frequencies required which is covered later on.

    Water system design and commissioning

    A section that has expanded considerably from the previous guidance and as always, the key is to design and commission a system that will not increase the potential for bacterial growth.  Low risk systems should always be considered as the ideal option and consideration should be given to self flushing systems, such as automated sensor outlets. Installing measures to reduce water usage and improve energy efficiency need to be carefully considered to ensure legionella control is maintained. Consideration needs to be given to design guidelines for healthcare buildings and HTM04-01 should be followed. Flexible pipework with EPDM lining should not be used in healthcare domestic water systems. All components of a domestic hot and cold water system must be easily accessible.

    Hot and cold water systems should always be designed to avoid encouraging legionella growth, good movement/turnover and good temperature control. Cold water temperatures still need to be below 20°C with heat gain kept to a minimum (the 2°C maximum recommended heat gain in the 3rd edition of L8 has been removed). Hot water system information has not changed significantly but more information is provided on circulating pump design and balancing the hot water system to ensure good water movement and temperature control. Storage temperatures in calorifiers still need to be at least 60°C with a minimum 50°C at outlets and on hot water returns (increased to 55°C in healthcare premises). 

    A significant amount of new information is provided on expansion vessel design and installation as recent research has suggested, they can become accumulated with biofilm and have been considered dead legs for some time now in risk assessments. Ideally flow through designs should be used, if not, then isolation valves and drains need to be fitted.

    Commissioning of smaller installations will now only require flushing before occupation but it is important to ensure systems are wet for as shorter amount of time possible before occupation. Larger systems will require, as previously, flushing and disinfection. A flushing regime must be in place once the system is wet. All disinfection must be done as directed by BS8558:2011. Pressure testing systems should ideally be done using air if water is to be used then the system must be flushed weekly or chlorine dioxide added to the system until occupation.

    There is now a section on buildings temporarily out of use. The written scheme should set out how an out of use system is to be left to minimise legionella growth. A flushing regime should be instigated and once recommissioned disinfection should be carried out.

    Operation and inspection of hot and cold systems

    The principles of legionella control and monitoring remain very much the same but there a number of key changes in this section which are bullet pointed below:

    Key change

    What does it mean?

    Pictorial guide to cold water tank internal inspection.

    Useful for risk assessors and those doing monitoring as a guide to when tanks need a clean.

    Annual cold water storage tank temperature check in the summer

    Previously 6 monthly and freeing up resource for other new tasks.

    All spray outlets require quarterly or dependant on rate of fouling, cleaning and disinfecting.

    Extra work as outlets such as spray taps and spray rinses now need to be done. It may be easier to remove the spray inserts.

    Large and complex hot and cold water systems will require more than a nearest and furthest sentinel point temperature check. Circulating return legs and long runs will also require monthly testing from pipework or sample points. If hot water return legs are to be used then the water should reach 50 °C within 30 seconds. 

    Additional monthly monitoring tasks for large complex systems, as they are higher risk. These tasks could be counteracted by less frequent monitoring of low risk systems.

    The risk of scalding needs to be considered in the risk assessment and monitoring.

    Not a major change but extra information provided on use and application of TMVs

    Where a hot tap is blended the cold tap (if separate) should be considered infrequently used and potential dead leg.

    Is the cold tap needed? Is it used? Review and remove if not required. Flush weekly if it is required and not used.

    Point of use and instant water heaters (those with ≤15L capacity including combination boilers) should be supplying hot water at 50-60°C. The temperature can be lower if frequently used by low risk users. All other hot water heaters need to be at 60C.

    50°C has always been the control temperature at hot outlets. Monitoring frequencies can be reduced to as little as 6 monthly. A risk based approach is required for low risk systems and should be reviewed regularly.

    Combination water heaters (with integral tank) should be set at 60°C with flow of 55-60°C at nearest outlet. The tank needs inspecting annually.

    Additional monitoring of the tank section required. Monthly flow temperatures required.

    Expansion vessel should be flushed monthly-6 monthly.

    Isolation points and drain valves are required to allow for flushing.

    All cold water systems require sentinel point temperature check monthly

    A change from 6 monthly incoming cold water checks

    Cold water insulation should be checked for integrity annually.

    An additional annual task

    Hot water temperatures at outlets and calorifier returns need to be at 55°C in healthcare premises.

    Many systems will achieve this but modification may be required on some systems to achieve 55°C

    Hollow support tubes on cold water tanks should be replaced.

    Must be identified in risk assessments and annual inspections and removed.

    Guidance is now given for the use and monitoring of point of use filters, water softeners, multiple use filters and TMVs.

    New guidance on frequency of monitoring if installed. TMVs should be temperature checked and inspected at least annually.

    There is now more detailed guidance on flushing or removal of infrequently used outlets and equipment.

    Confirming what is already done by most people.

    Low risk systems are defined as mains fed, POU water heaters (≤15L), no showers, good usage and low risk occupants.

    Allows for risk based legionella control and monitoring to be put in place.

    Electric showers are to be considered as POU water heaters.

    Temperature checks required at least 6 monthly

    Detailed guidance now present on the installation and use of TMVs.

    Additional advice to prevent scalding

    The risk assessment should always define the control measures that are required and a risk based approach must always be used. Smaller low risk systems with low risk occupants may require a different control regime from larger complex systems. Legionella control and monitoring regimes must continue to be reviewed on a regular basis by the responsible person.

    Water Treatment and control programmes for hot and cold water systems

    The guidance on the use of biocide treatments as a control measure has been expanded, paying particular attention to healthcare premises where temperature control has to be used alongside biocide control measures. Chlorine has made reappearance alongside chlorine dioxide, and copper and silver ionisation; all are widely accepted as excellent biocide control measures and the guidance provides very useful detailed information on their use and the monitoring programmes required when in use. There is new additional guidance on the use of point of use filters on systems where control measures are failing. Often used in healthcare buildings they should be considered a last resort and also a temporary measure until a permanent solution is found.

    Microbiological monitoring

    There remains no requirement for regular biological monitoring of domestic hot and cold water systems that are primarily fed by mains cold water. There needs to be a risk based approach to determine whether biological monitoring is required and where on the system sampling should be carried out. The guidance references BS7592:2008 Sampling for legionella organisms in water systems to provide guidance on how, where and when legionella sampling should be undertaken. Guidance is given for interpreting sample results in healthcare and non-healthcare premises in table 2.2 and 2.3; the difference is that results up to 100cfu/l or negative results should not be ignored due to the susceptibility of the patients.

    Cleaning and disinfection

    Reasons for cleaning and disinfecting hot and cold water systems are detailed making reference to specifications in BS8558:2011. The number of reasons has significantly increased from the old ACoP and includes: after positive legionella sample results, following new installations or components, after prolonged shut down of areas or buildings and significant contamination or biofouling. Methods are provided for thermal and chemical (chlorine based) disinfections.

    Residential Accommodation: Landlords and shared premises

    A new section for HSG274 having not been part of the old ACoP but there was a separate publication from the HSE for residential accommodation. It is always a discussion point as to where responsibilities lie in shared premises. To summarise. the responsibility lies with who has control of the premises and they have a duty of care to all the occupants and users. Single occupant leaseholders may have full repairing lease on the building, therefore responsibility will often lie with them. It all very much depends on how the contract is arranged, if there is no contract then duty is on whoever has control of the premises.

    In residential accommodation, landlords will have responsibility for legionella control; if properties are managed by an agent the contract needs to state who has responsibility. Further advice is provided on risk assessing, monitoring unoccupied premises. The basics of legionella control, temperature control and flushing apply in all instances. Risk assessments can be undertaken on a proportion of properties if they are all the same, but all properties must be risk assessed in a rolling programme.

    Special considerations for healthcare and care homes

    Another new section for the HSG274; patients or residents in healthcare and care homes are more susceptible to contracting legionnaires’ disease and therefore control measures may need to be different to non-healthcare buildings. Differences include hot outlet and return temperatures being no less than 55°C, the consideration of scalding, flushing outlets at least twice weekly, regular legionella sampling in augmented care units and the formation of Water Safety Groups (WSG) and Water Safety Plans (WSP) as legionella is not the waterborne pathogen that be a risk to patients or residents in these types of premises. More detailed advice for healthcare premises is provided in Water systems: Health Technical Memorandum 04-01.

    At the rear of the document are 5 useful appendices, on the content of a risk assessment, written scheme and action to take in the event of an outbreak of Legionellosis. There are also 2 schematics identifying sentinel point location for hot water systems.


    HSG274 is very well written, comprehensive and detailed document covering all aspects of legionella control in domestic hot and cold water systems. Is it an improvement? Most certainly but there are areas missing that are often found in new buildings, such as rainwater harvesting systems and grey water systems, but overall what is required for legionella management and control in domestic water systems is now much clearer to understand. HSG274 Part 2 along with Parts 1 and 3 and the revised ACOP should help make legionella management and control for the duty holder, responsible person and everyone else involved much easier.

    I am a duty holder/responsible person what does the new document mean for me?

    Do you have to do anymore than keep domestic water systems clean, moving, and at the right temperature? The short answer to that is no, but HSG274 Part 2 provides more information on how to go about it. If you already have good control measures in place then it is very much business as usual. However there a number of changes, as described above, that may affect how the risk from legionella in your domestic water systems is managed and controlled. The key message from the HSE is proportional control based on propionate guidance along with regular reviews of the legionella risk assessment and the control measures currently in place to see if any changes or improvements are required.

    How can SOCOTEC help you?

    SOCOTEC will be happy to meet with you and discuss the changes in the ACoP and HSG274 Parts 1-3 and how they affect your management and control of legionella.

    We have a many years of experience in the industry and can offer a comprehensive range of services to help you manage the risk from legionella including:                  

    • Risk assessments for all types of water systems
    • Legionella training
    • Auditing of management and control procedures
    • Writing policy and procedural documents
    • Monitoring and reporting programmes
    • Microbiological analysis at our UKAS accredited laboratories
    • Outbreak and system contamination investigations
    • Water treatment and analysis including chlorine dioxide, ozone, side stream separation and water softeners

    If you need to discuss the contents of revised ACoP L8 4th edition or HSG274 Parts 1-3 or this report please contact us Contact us

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