Review of HSG274 Part 1 2024 Update – Legionella in Evaporative Cooling Systems
In 2024 the Health and Safety Executive (HSE) updated their technical guidance HSG274 Part 1, which focuses on how to control Legionella in evaporative cooling systems. This update of the guidance, first published in 2014 is relevant to you if you operate or take responsibility for any type of cooling system, including evaporative condensers and cooling towers.
Our expert team have reviewed the latest publication of HSG274-1 in some detail to identify the main changes between the 2024 version and the previous/first edition published in 2014. To download a copy of our full review please follow the link provided further down this article. You should note the disclaimer at the end of our review before proceeding or taking any action and note that the HSE has provided updates only to Part 1 and not to the remaining two parts of the overall technical guidance.
A version of this article highlighting the changes to the 2024 update of HSG274 Part 1 first appeared in Legionella Control International’s newsletter. To get it in your inbox, sign up for free here.
What is HSG274 Part 1?
HSG274 Part 1 is for duty holders and those with responsibility for evaporative cooling systems to help them comply with their legal duties. It gives practical advice and guidance on how to assess and control the risks due to Legionella bacteria.
Any water system that has the right environmental conditions could potentially be a source for Legionella bacteria growth. There is a reasonably foreseeable Legionella risk in your water system if:
- water is stored or recirculated as part of your system;
- the water temperature in all or some part of the system may be between 20 and 45°C;
- there are deposits that can support bacterial growth, such as rust, sludge, scale and organic matter;
- it is possible for water droplets to be produced and, if so, they can be dispersed;
- it is likely that any of your employees, contractors, visitors etc. could be exposed to contaminated water droplets.
What are the main changes to HSG274 Part 1 – 2024?
Because of the high risk nature of evaporative cooling systems, we have summarised the main changes to HSG274 Part 1 here. Our full review of the guidance can be downloaded below and it will help you quickly understand what has changed and how this may affect you. It also includes pertinent comments for clarity.
The introduction to HSG274-1 now clarifies when written records should be kept
Previously, HSG274-1 referred to written records not being required for ‘fewer than five employees.’ This has been edited to say, ‘if there are five employees or fewer’ to clarify the number of employees without doubt.
Further information for those running a wet/dry hybrid cooling system
Those running such a system are now pointed to the HSE website for information about dry/wet cooling systems. Some may not be sure whether it constitutes a notifiable device, so the guidance now points people in the right direction.
Requirements of a cooling water treatment programme
Paragraph 1.58 refers to measuring residual oxidising biocide in the water, encouraging caution when conducting the tests to ensure accuracy in the results. This is to ensure the test result for free halogen is correct for the measured system pH. The guidance points to Info Box 1.5, where further details have been added to support measuring, ensuring the results reflect system conditions.
Wording has also been added to base the amount and frequency of oxidising biocide based on the size of the water system and how much water is recirculated. This refers to the considerations when shot or manual dosing. Dosing automatically controlled in response to ORP (redox) or amperometric control will automatically take care of the required quantity and frequency.
Examples of non-oxidising biocides and corresponding available field test methods have been added to Info Box 1.5. There is some manufacturer advice to address limitations and a disclaimer as to their efficacy.
The segment on ultrasonics and cavitation provides further consideration
Sonication is mentioned and confirmed to be short lived, while hydrodynamic cavitation is confirmed to have a similar effect when breaking down organic matter. Both are discussed as being dependent on the water chemistry, with details added that suggest further biocides or treatments may be required alongside them.
This section of the guidance may have been added to help manage users’ expectations. The previous technical guidance covered the process but did not consider its efficacy in the same way the edited material does.
Health and safety measures added for cleaning and disinfection procedures
Paragraph 1.78 contains information about wearing appropriate respiratory protective equipment (RPE). This is clearly in consideration of the requirement for health and safety precautionary measures for those inspecting or conducting cleaning and disinfection procedures.
Inspecting a cooling system
HSG274-1 2024 – Table 1.2 has been added to provide more prescriptive recommendations with regard to inspections tasks and their frequency. Further, paragraph 1.86 now has an added sentence regarding photographs taken before and after cleaning. This suggests that photographs should be taken to assist with deciding on frequency for cleaning.
Paragraph 1.9 also provides further details about the pre-cleaning inspection, including inspecting fouling, once again mentioning photographs of previous inspections and cleaning. This again emphasises the importance of photographs and inspections to schedule appropriate frequencies more accurately for cleaning and disinfection.
Finally, paragraph 1.114 also has a new sentence on post-cleaning disinfection, again relating to the importance of photographic records to evidence efficacy of the clean.
Changes made to the section on monitoring water quality and understanding water treatment analytical reports
There are five new paragraphs here as follows:
- Paragraph 1.118 – recommendation that susceptible persons should not be involved in sampling or investigations
- Paragraph 1.119 – recommendation for dynamic risk assessment for sampling or monitoring activity; minimisation of risks via precautionary measures, procedural and engineering controls, and provision of RPE
- Paragraph 1.120 – staff training detailed for monitoring, sampling, and relevant operating procedures and control measures
- Paragraph 1.121 – examples of where RPE should be worn for sampling and monitoring procedures
- paragraph 1.122 – points to sources of further information about task risk assessment and selection of RPE (for example, BS7592 and HSG53 appendix 6)
All the above have been added to this version and emphasise the need for recognising and assessing the risk to those involved in sampling, monitoring, and inspections. It also covers the instigation of suitable measures to reduce risk.
Monitoring and analysis section covers use of accredited laboratories
The HSG274 guidance highlights the use of UKAS-accredited laboratories. It does state this is not a legal requirement, mentioning that there are other ways for laboratories to demonstrate competence.
Paragraph 1.137 also goes into more detail concerning lab techniques for detecting levels below 100 cfu/l and reducing the limit of detection (LOD). Our experts believe this is too much information for the average Responsible Person; however, it does provide further insight into the concept of LOD. It may also be useful for high-risk environments and scenarios where investigations are attempting to eliminate Legionella.
This is further supported by a footer added to table 1.11, noting that different laboratory methods may result in LODs above 100 cfu/litre. It notes that the RP should focus on controls and keep general aerobic counts low. This suggests the RP should understand the implication of LOD and work with laboratories to ensure the limits of detection are as low as possible.
New section added for rapid sampling for Legionella
This covers quantitative polymerase chain reaction or qPCR. It effectively legitimises using qPCR in certain situations, suggesting three main uses:
- Rapid detection for screening (for example, if there has been an outbreak of Legionnaires’ disease)
- Indicating effectiveness of cleaning and disinfection (for example, following on from remediation)
- Complementary tool for monitoring the effectiveness of Legionella control measures
It does not reference whether qPCR would be acceptable if applied to the same scenarios in a hot or cold water or other system.
There is a further new paragraph urging consideration of how results are interpreted. For example:
- The assay detects Legionella DNA from both live and dead cells
- The units of measurement are not directly comparable with the action and alert levels for the bacterial culture (cfu/l)
There is no suggestion of control limits provided in the guidance.
There follows a new paragraph, 1.141, stating the methodology for qPCR sampling and testing. This is in accordance with PD ISO/TS 12869:2019.
Finally, Info Box 1.6 under Calcium Balance has been more clearly presented than previously.
Appendix changes
Several public agencies are noted in Appendix 3, Action in the event of an outbreak of legionellosis, given changes in names. Further, there are updated references to published guidance for the investigation and management of incidents, outbreaks, and clusters of Legionnaires’ disease for England, Scotland, and Wales.
There are two new additions to Part 1 as well – an appendix offering examples of sentinel points in a simple hot water system, and another with examples in a complex hot water system. These would seem to be better suited to Part 2 – Hot and cold water systems, but they have been included in this new version. The same applies to a checklist included as Appendix 6, which covers the recommended frequency of inspection for other risk systems.
Disclaimer notice;
The material and information contained in this review of the 2024 update to the Health and Safety Executive HSG274 Part 1 is provided for general information purposes only and while we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about the content, completeness, accuracy, reliability, legality, suitability, or availability. Any reliance you place on such information is therefore strictly at your own risk.
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The water safety specialists at Legionella Control International help business owners and those responsible for the control of Legionella and other waterborne pathogens manage their workplace risks to maintain regulatory compliance and keep people safe.
We are experienced water safety specialists and deliver full range of services including cooling tower risk assessments for Legionella. We also offer Authorising Engineer support, compliance auditing, water quality testing, City & Guilds training and other health and safety risk management services that help keep businesses compliant with the law and workers and others safe.
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