How to Test for Legionella in Cooling Towers
If you’ve read reports of Legionnaires’ disease outbreaks over the years, you’ve likely read about cooling towers as well. They’re among the most common culprits for outbreaks of the disease. Proper testing, cleaning and maintenance of these towers is therefore crucial in making sure outbreaks are prevented.
In this article, we’ll look at why cooling towers pose such a big risk, and how to test for legionella in cooling towers, to be sure the risk is as small as possible.
A version of this article about how to test for legionella in cooling towers appeared in Legionella Control International’s newsletter. To get it in your inbox, sign up for free here.
How do cooling towers cause legionella?
To discover the answer, we must first look at what cooling towers do. A cooling tower works to remove heat from a location, acting as a heat exchanger. Its sole job is to lower temperatures that might otherwise be unbearable. Heat is sent into the cooling tower and is cooled by cold water. Sometimes, hot water is sent into the tower and is cooled by colder water.
However, in all cases, water is involved. Moreover, the temperature of that water can be within the 20 – 45-degree Celsius range that encourages the growth and spread of legionella bacteria. That is where the problem lies, and it shows how cooling towers can, if not properly monitored, cleaned and maintained, lead to an outbreak of Legionnaires’ disease.
The design of cooling towers also means they’re exposed to the elements – putting them at far greater risk of being affected by environmental dirt and debris entering the towers from outside. Legionella bacteria thrive on such things as they derive nutrients from them to help them grow and spread.
A cooling tower is almost a perfect storm as a conduit for an outbreak of Legionnaires’ disease, and therefore must be properly maintained and tested to be sure it poses no risk to those in the area.
Can you get Legionnaires’ disease from cooling towers?
Absolutely – the way they work means that the water temperatures inside them can fall into that danger zone legionella bacteria love. While outbreaks are uncommon, thanks to proper maintenance by the businesses that own them, they’re not unheard of.
The bigger risk comes from how cooling towers work. If you’ve seen the giant cooling towers dotted around the UK landscape, you’ll know they often have large plumes of white steam coming from them. But that’s not true – it’s not steam, it is water vapour, and it is the part left over from the process the cooling towers go through. It’s only a tiny part of that process, but if the cooling tower hasn’t been adequately maintained, that water vapour could contain legionella bacteria.
Hence why Legionnaires’ disease outbreaks involving cooling towers sometimes see people affected who have walked past a building rather than being inside it or using the water system. Legionella is carried in water vapour and can be inhaled by anyone in the vicinity.
How to test for legionella in cooling towers
Many water systems do not require sampling for legionella unless there is a clear reason to do so. However, regular sampling is imperative in cooling towers to make sure the water inside the tower is safe. Testing should cover other bacterial species alongside legionella.
Quarterly sampling is the best approach, unless raised bacteria levels are noted that would point to the need for more frequent sampling. Another example whereby more regular legionella sampling would be ideal is when a cooling tower is first installed or commissioned. This is done to confirm that the tower is being properly maintained and treated and has an acceptable level of bacteria that does not go too high. As the cooling tower comes into use, more regular testing will make sure everything is running smoothly and safely. A legionella risk assessment is essential, along with a suitable water treatment programme for the cooling tower which should be established to be sure of continuing safe operation.
Ideally, you should test water from the tower at the same point on each occasion. It is also preferred to follow the same procedure each time to allow for consistency. Water should be taken from the basin of the cooling tower away from the source of make-up water.
The water samples should be tested in a UKAS accredited laboratory, a process which can take several days. If the samples are within safe limits, regular three-monthly testing can continue. If samples indicate there are raised levels of legionella, measures should be taken from there to reduce those levels.
Ample guidance is offered by the Health and Safety Executive in their guidance, HSG274 Part 1 Legionnaires’ disease: The control of Legionella bacteria in evaporative cooling systems. This provides detailed guidance on managing such a system, along with creating a water treatment programme and covering inspection, disinfection, and cleaning topics. Monitoring the water quality inside the cooling tower is also covered.
Who should test cooling towers for legionella and other waterborne bacteria?
The individual responsible for conducting the water testing of cooling towers should be properly trained and have the required experience to do so … they must be competent to do their job. While some business owners can conduct a simple legionella risk assessment themselves if the water system is simple to use and understand, this becomes less likely the more complex it becomes. Given the risks and complexity of the water systems associated with cooling towers, it is highly recommended that an independent and qualified individual takes on this task.
It is the responsibility of the person in charge, the statutory duty holder or responsible person to hire a qualified individual to handle all legionella testing and risk assessments that are required on the site. A legionella expert such as those from Legionella Control International will know how and where to test for legionella in a cooling tower. They will send the samples to a recognised laboratory to receive the results and can also advise on future testing frequency and other elements of the process.
Cooling towers pose one of the biggest Legionnaires’ risks to people in the immediate area if they are not properly maintained. The emission of water vapour from the towers can spread over a wide area if the wind carries it, putting all those in that area at risk of inhaling legionella bacteria.
While towers do pose a significant risk, it is a risk that can be mitigated when the correct steps are taken. By sourcing expert, outside help, you can make sure any cooling towers your business uses are always safe to run so you remain the right side of the law and keep your employees and others safe from harm.
World leading legionella risk management specialists
The water safety specialists at Legionella Control International help employers and those responsible for the control of legionella and other waterborne pathogens in the workplace manage their water risks to ensure regulatory compliance is achieved and then maintained to keep people safe from harm.
We are experienced water safety specialists and deliver full range of services including risk assessments for legionella, and other waterborne pathogens. We also offer Authorising Engineer support, compliance auditing, accredited water quality testing, City & Guilds training and other health and safety risk management services that help keep staff and others safe.
If you would like to speak with one of our legionella specialists about improving your risk management processes call us today on 0330 223 36 86 or contact us here …
