Legionella pneumophila is not so much a clear – in fact, often far from it – as it is a present danger, and is prone to be found lurking in the darker recesses of cooling systems, and as typically located in a number of establishments. While legionella bacterium is primarily a threat in respirable form – and only then when exposed to susceptible individuals via inhalation in aerosols and/or water droplets – that’s not to say it doesn’t, potentially pose a risk to a significant volume of people when and where it’s discovered. What’s more, said bacteria can take root in just 5mm of water droplets and can, if the health conditions of the person/general circumstances of those who come into direct contact with it lend itself/contribute, ultimately prove fatal. Which is why it’s imperative that measures are taken to combat the threat before it comes to bear.

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One of the predominant culprits – and unseen breeding grounds – for the spread of legionella bacterium is the type of widespread cooling systems adopted by a multitude of buildings commonly utilised by scores of individuals for various reasons. If these examples of essential water temperature-governing infrastructures fail to be managed correctly, then the dormant risk posed to public health is brought into sharp focus. Although legionella control guidance is enveloped by the existing legislation documented in detail within the pages of HSG274 Part 1 (and in the Approved Code of Practice L8 2013 – The Control of Legionella Bacteria in Water Systems (ACoP L8), people’s health is continued to be put at risk should negligence on the part of the individuals responsible for the curation of cooling systems come into play.

One of the primary reasons these systems (and towers, specifically) fall victim to instances of legionella bacterium manifesting is because of their open-circuit system design and layout. But that’s not to say such everyday installations are pre-destined to become conducive to attracting the bacterial growth, as a fastidious approach and application of control and management of systems in place can effectively eliminate such underlying issues and ensure safe operational practice and protocol from those whose remit it belongs to. The key to legionella risk management is both the safeguarding of the entire set-up and assemblage to counter the threat and the prevention of the amplification of an episode in the event of legionella being confirmed in situ. Among the critical proactive and reactive responses to legionella infiltrating a cooling system, the following procedures are strenuously suggested by leading authorities. Notably such measures include focus on system cleanliness from the outset (eradicating any microbial deposits and biofilms which can lead to the formation of slime on surfaces in water-based equipment), while it’s now acknowledged that cooling towers which pump water to distribution trays – and cause water to cascade over plastic fill rather than spray pressurised water, thus creating mists and aerosols – are far less likely to proliferate the disease-causing bacterium, courtesy of significantly reduced whole water dissemination equalling less exposure. Meanwhile ambient temperature water (heating it, using it for cooling water) certainly encourages the ecology of legionella, as amoebas essentially graze on the resultant biofilm produced when conditions are rife to foster the emergence of the bacteria in the first instance. Remove the biofilm population and with it diminish the food source for amoeba, according to a number of think tanks on the subject.

Back to successfully managing the risk in cooling systems though, and the first port of call is of course, carrying out a full and pretty much exhaustive risk assessment. Beneath we’ve bullet-pointed a couple of core factors which comprise a HSE-spec dossier on this very topic.

• Duty Holders should arrange to review the assessment regularly and specifically when there may be a reason to suspect that the assessment is no longer valid.
• Elsewhere reviews should also take place when there are changes to the water system or its use, revisions to the use of the building in which the water system is installed; additional or new information about risks (or control measures) becomes available, results of checks indicating that control measures are no longer effective and/or a case of Legionnaires’ Disease/Legionellosis being associated with the system
• RE: new buildings; whoever designs, manufactures, imports or supplies water systems that may create a risk of exposure to Legionella bacteria should (so far as reasonably practicable); ensure that the water system is designed/constructed to be safe and without risks to health when used at work, provide adequate information for the user about the risk and measures necessary to ensure that the water systems will be safe (and without risks to health when used at work)

What are the Practical Applications of Performing Risk Management?

Although not a definitive description of what lengths may need to be gone to in a bid to keep abreast of any potential legionella issues, the following affords you a general idea of what’s accepted practice from the get-go. Understandably water treatments vary depending on water quality and individual system requirements, yet the elements cited below will nearly always need to be considered.

• Pre-treatment - Clarification (via settlement or filtration, softening, reverse osmosis or de-mineralisation methods)
• Corrosion control - Where wetted components are deemed susceptible to corrosion. Usually this requires measured automatic dosing of a proprietary corrosion inhibitor
• Scale control - Where  the  water  is  hard,  scale  control  can  sometimes  be  achieved  by measured automatic dosing of a proprietary scale inhibitor
• Fouling - Wetted surfaces  in  the  air  stream  frequently  collect  contaminants,  whilst  hard  water can form scale deposits; so a regime of inspection and cleaning may be required
• Bleed – Re-circulating systems accumulate impurities, so a means of controlling the level is more often than not necessary. This often  takes  the  form  of  an  automatic  bleed  of  part  of  all  of  the water
• Microbiological control - Biocidal control of the make-up water is likely to be necessary where operation in wet mode is infrequent (less than weekly); where make-up water  is stored, where cooling water re-circulates and where the water is discharged in a spray rather than trickle-fed onto a medium without splashing
• Disinfection - Disinfection of part (or all) of the water system may be required; for example prior to start-up after a period of operation in dry mode, or if indicated by risk assessment, monitoring or inspection

Acknowledged Due Diligence

Any risk assessment which tackles the subject of managing the legionella risk in these systems should always take in to account the comprehensiveness of an agreed maintenance schedule, the frequency of cleaning and disinfection, the ease of access to those components that necessitate routine cleaning and the dangers to the operatives who are carrying out the maintenance and cleaning; along with others in the vicinity during the work. A method statement for the cleaning and disinfection process should be available. Legionella risk assessments need to be regularly reviewed so as to ensure that existing facts and figures remain relevant and the assessed risk, effectively controlled. With regards to record keeping, all records of work carried out - i.e., control measure checks, maintenance, updating of the risk assessment, safe systems, system diagrams, management structure and training - should be kept for a minimum of 5 years.

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