Legionella Risk Assessment At Large Retailer

The following observations relate to a legionella risk assessment carried out  by Ames some time ago in the UK, at a large retail store. Upon first inspection it appeared that it would contain a compliant water system with a Water Regulations compliant system. I talked with the building services manager over the phone, who informed me that as a company there was already a comprehensive monitoring system in place and that there should be no problems…

Soon after the beginning of the inspection it appeared that there were serious problems with some parts of the plumbing system which would seriously increase the risk of Legionella. After tracing the pipework from the main restaurant, I found a large cold water storage tank positioned above the kitchen, which fed a single spray head pot washer and a wash hand basin. The tank was heavily contaminated with sediment and, due to the heat from the kitchen and a lack of adequate insulation, stored water measured 30°C – the perfect environment for Legionella proliferation. I took detailed notes and photographs on this part of the system and a Legionella and TVC sample, and continued with the survey.

Later in the day, I came across a hot water cylinder which was fully compliant with the Water Regulations and which looked in good working order. When this was checked, the operating temperature of on the cylinder was 43°C, however, and I realised that it was installed to feed a set of showers in the staff area. It became clear there was a serious problem. I took samples from the base of the cylinder and from one of the showers.

The risk associated with both of the above problems relates to the temperature at which water was being stored, the sediment, and the fact that they fed a spray head, which creates an aerosol. Water stored between 20°C-45°C is the ideal temperature for the legionella bacteria to proliferate. Due to the design of showers, they are classed as a potentially ‘high risk’, area as aerosols are formed and Legionellosis occurs by the inhalation of water aerosols containing the Legionella bacteria.

There is also a legal requirement that all shower heads and hoses are cleaned, descaled and disinfected on a quarterly basis, in order to eliminate the risk of the Legionella bacteria proliferating beneath any scale which has developed in or on the shower head or hose.

Our contact at the store was not aware that there was even a tank above the kitchen area, and as a consequence, the tank had not been cleaned or chlorinated at all in the previous 5 years. Furthermore, due to a mis-understanding of a previous risk assessment carried out in the past by another company, our contact did not know that shower heads were supposed to be cleaned, descaled and disinfected quarterly, and thought that because the hot water cylinder was fed by the cold water mains, it was not a risk and did not want it to produce water any hotter to prevent shower users from scalding themselves.

It was exceptionally fortunate that there had been no reported cases of legionellosis by any building users – particularly as when the laboratory analysed the water samples taken, the Legionella samples taken were critically high. An emergency clean and chlorination of the tanks was booked in for the following day, and all showers were placed ‘out of use’ until they were cleaned, descaled and disinfected. The set temperature of the water cylinder simply required increasing to 60°C and a Thermostatic Miving Valve, which limits the temperature of hot water at the outlet, needed to be fitted to each shower, to prevent scalding.

Notwithstanding how awful an outbreak of Legionellosis can be to the sufferers and their families, an outbreak in a store such as this would have been catastrophic to the company owners and, as well as producing international bad publicity, the owners could have also faced prosecution. They had not nominated a responsible person in writing and did not provide relevant training to their maintenance staff.

All in all, a crisis really was averted that day – and similar problems can arise in much smaller buildings and businesses. It just shows how important a legionella risk assessment is, and how important it is for the relevant person to be able to discuss the assessment’s findings with the surveyor – something AMES uniquely offers as a free post-assessment survey.

If you haven’t got an up-to-date legionella risk assessment, and you do not have a regular monitoring regime which was generated from the assessment, then public health, and in severe cases, lives could be risked and your business’s reputation could be compromised.





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