As the mercury hovers above 30 Deg C buzzing air conditioning units working overtime are commonplace in street and offices across the city. And if you’re a facility operator or business owner you also need to ensure that the air conditioning system is properly maintained, not only to maintain energy efficiency but also to prevent spreading disease. If we had a Legionella threat level it would now be ORANGE!
Air conditioning systems are a documented source of Legionella , the system has all the necessary elements, the capacity to harbour, breed, and distribute Legionella into the air we breathe. Microscopic water droplets contaminated with Legionella can be easily inhaled, risking the potentially fatal Legionnaires disease infection.
Legionella comes from nature, its found at low concentrations in lakes, streams, and groundwater. Also one type thrives in compost and soil. Legionella escapes conventional water treatment and low concentrations are piped into our buildings, given the right conditions Legionella can proliferate and then your problems begin.
Since the infection dose is small, and the incubation period is 7-10 days, you can see that just one contaminated cooling tower is a risk, and might expose thousands of people, before the first infected person seeks medical attention, that is how an outbreak occurs.
The EMSD Code of Practice for the control of Legionella [link] places the emphasis firmly on the business and owner to identify and assess any risk, and then act to minimise that risk, however many firms lack the expertise and need to contract this work to specialist consultant like Kelcroft [link]
Regular auditing of air conditioning systems lowers the risk of spreading disease than those left unattended. Thankfully, we now have simple tests that can detect the presence of bacteria, and they should be performed in addition to regular maintenance.
Buildings using WCAS (water cooled air conditioning systems) have devices called cooling towers used to reject the waste heat heat to atmosphere, using water, and these type of systems have been identified by government as a specific threat, and mandates that the owner must conduct an independent third party annual audit report and submit to EMSD every year.
Understand Legionella is important, I visited a industrial facility last year and found a heat recovery system with all the elements. The system pre-heated fresh water, stored the warm water at the prefect temperature for Legionella breeding and growth then pumped the warm water across the factory to distant spray-heads – a preventable outbreak waiting to happen!
— John A Herbert, Consultant, Kelcroft E&M Limited
 Note also other misting devices have been documented to harbour and spread Legionella, including but not limited to, decorative fountains, machinery coolant, hot water systems, heat recovery systems, showers, misting cabinets, spa baths, and humidifiers.