Last edited 11 Nov 2020

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BSRIA Institute / association Website

HSG 274 Legionnaires' disease, Technical guidance

This article originally appeared as a BSRIA article, ‘Legionnaires' disease - have you reacted to changes in L8?’ published in April 2015. It was written by Reginald Brown, Head of Energy & Environment, BSRIA Sustainable Construction Group.

A longer version of this article is available at Comparison of HSE ACOP L8 and HSG 274 guidance with previous versions of the ACOP.


[edit] The Approved Code of Practice

The original Approved Code of Practice (ACOP) for Legionnaires’ disease dates back to 1991 but the document with which people are most familiar is the “Approved code of practice and guidance” published as “L8” in 2000 (Legionnaires' disease. The control of legionella bacteria in water systems).

As a result of public consultations, the HSE decided to separate the ACOP from the guidance, with the latter being developed by industry groups as Health and Safety Guidance (HSG) 274 (Legionnaires' disease, Technical guidance) Parts 1, 2 and 3. These documents were published in 2013/14:

All of the documents may be downloaded from the HSE website:

The original L8 ACOP and guidance contained 61 pages whereas the new set of publications that replace it amount to 158 pages. Most of the increase in bulk has been due to lengthy descriptions of the design and operation of cooling and domestic water systems in HSG 274 Parts 1 & 2. The ACOP itself is little changed (apart from the introduction), with most of wording identical to the original.

The introduction to the ACOP describes the new structure of the documents and emphasises that certain issues now have “ACOP status” including:

  1. Risk assessment.
  2. The specific role of the appointed competent person, known as the ‘responsible person’.
  3. The control scheme and what it should include.
  4. Review of control measures.
  5. Duties and responsibilities of those involved in the supply of water systems including suppliers of services, designers, manufacturers, importers, suppliers and installers of water systems.

However, if you were complying with the intent of the ACOP before 2013, you will almost certainly be compliant now.

New features of the ACOP include the identification of examples of low risk situations that “do not require elaborate control measures” such as buildings without water storage. There is also a desire to simplify the bureaucracy for very small businesses i.e. those with 5 or less employees (para 70). On the other hand employers must now provide information and training to all staff that might influence the risk exposure, not just those those appointed to carry out control measures.

[edit] Guidance on evaporative cooling systems

The previous guidance contained a basic description of the different types of cooling towers followed by a brief section on management, treatment and monitoring. This is replaced by HSG 274 Part 1, which contains an extensive chapter of “Requirements of a cooling water treatment programme”. This has received some criticism for being a general guide to operating cooling towers rather than focussing specifically on the prevention of Legionnaires’ disease. The authors would no doubt argue that maintaining a clean and efficient cooling system is a prerequisite to the successful control of legionella bacteria. However, much of the new text is background information rather than specific guidance.

The new text mentions evaporative air cooling (using evaporation directly or indirectly to cool ventilation air) but then clouds the issue by suggesting that these systems may or may not require notification under the Notification of Cooling Towers and Evaporative Condensers Regulation. The missed point is that these systems should be designed and installed with features that minimise the risk of Legionnaires’ disease and should be included in the risk assessment and written scheme with appropriate monitoring and maintenance procedures. However, as they have little in common with cooling towers it would have made more sense to include them in Part 3.

The chapter on requirements of a cooling water treatment programme actually contain very few requirements or usable guidance other than Table 1.1 ‘Typical cooling water desired outcomes’ which is overridden by ‘The particular desired outcomes and the metrics to be used should be agreed between the system owner/operator and their specialist water treatment service provider’. This is followed by Table 1-2 ‘Example of how to use water analysis results to predict the risk of fouling’, which is not particularly focussed on legionellae.

Overall, the new elements of information and guidance relate to the general operation of cooling towers to reduce fouling and corrosion. The evaluation of microbiological test results in relation to the acute risk of Legionnaires disease has not changed. Maintenance activity may have to be adjusted to meet the new guidance on fouling though it is likely that contractors following good practice would already comply. Plant operators only need to ensure that their operating and maintenance regime for cooling towers is sufficiently well documented to meet the requirements of the ACOP, both in terms of written procedures and the recording of tests and inspections.

[edit] Guidance on domestic water systems

HSG 274 Part 2 section 2 provides a more extensive description of domestic hot water systems than the previous guidance. As in the case of cooling systems, guidance now includes the general design and operation of the system as well as the aspects that are specifically related to the risk of Legionnaires’ disease.

There are several new guidelines that could increase maintenance and monitoring. Of particular note are the requirements for increased monitoring of non-sentinel outlets on a rotational basis and monitoring of sub-loop return temperatures in the domestic hot water circulation. Some of the others are rather obvious maintenance activities that are not specific to Legionnaires’ disease such as checking the condition of external insulation and salt levels at the water softener. There are also a couple of issues that have apparently been deleted, such as cleaning water softeners and measuring the inlet temperature to TMV’s (thermostatic mixer valves). It is not clear whether these were intentionally deleted or lost in the editorial process so it would seem sensible to follow the original guidance.

[edit] Guidance on other risk systems

HSG 274 Part 3 is little more than a list of systems that may be encountered and draws from checklist 3 in the original guidance. There are some additional tasks associated with dental equipment but otherwise the scope and frequency of monitoring and maintenance is the same as previously.

[edit] Conclusions

Overall, there are a few areas where the substantive guidance on minimising the risk of Legionnaires’ disease has significantly changed (the temperature monitoring of hot water loops is one). This does not mean that a risk assessment compiled according to the old guidance is invalid but it is important to regularly review any risk assessment, and consequent operating and maintenance procedures on a regular basis and particularly when circumstances change or new guidance comes along. Apart from exposing your employees to unnecessary risk, failure to keep risk assessments up to date will potentially leave you open to prosecution.


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