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Pipes, valves & fittings


Germ warfare


Legionella can turn a water system into a lethal weapon, but there are ways to mitigate the bacteria’s effects, says John Grenville, managing director of ECEX


T


he death of a US Air Force veteran at a hospital in Sayre, Pennsylvania on Tuesday, July 27, 1976 marked the moment that everything changed for the building services industry because it confirmed that air conditioning systems had (and still have) the capacity to kill. Four days previously, the casualty had attended an American Legion convention at the Bellevue- Stratford Hotel on Broad Street in Philadelphia. In the days that followed his tragic death, a mysterious disease causing flu-like symptoms killed another 33 people and made 221 sick. All had attended the same convention. The bacterium that causes what became known as Legionnaires’ disease was finally isolated on January 18, 1977, and further analysis revealed that it thrived in the Bellevue-Stratford Hotel’s cooling tower. Much research followed and the HVAC industry eventually came up with strategies to minimise the risks associated with this opportunistic, but potentially fatal infection. Legionella can grow in any workplace if the


conditions are right. The way to prevent it is, of course, to ensure that the conditions are not right. And that means keeping HVAC systems clean and in good order. But the preventive measures don’t stop there. Legionella is a naturally occurring group of


www.heatingandventilating.net LEGIONNAIRES’ DISEASE: THE FACTS


• To date, over 50 species of legionella have been identified. Of these, 20 are known to cause disease in humans, but the one that we are most concerned about is Legionella Pneumophila (Latin for ‘love of the lung’). This gives rises to Legionnaires’ disease. • On average, there are around 300 reported cases of Legionnaires’ disease each year in the UK. However, some believe that the total number of cases may be an underestimate. • Legionnaires’ disease is an opportunistic disease that tends to attack individuals who have an underlying illness or weakened immune system. It is reckoned to be fatal in around 5 to 15% of cases. • People can get Legionnaires’ disease as they breathe in tiny droplets of water in the air that has been contaminated with legionella bacteria or in droplet nuclei (particles left after infected water has evaporated). • Treatment involves the use of antibiotics; early treatment reduces the severity of symptoms and improves chances of recovery.


• Applying increased control measures if a susceptible population could be exposed to aerosols. This relies on designing, installing, risk assessing and managing water systems effectively. Legionella can lurk in a range of building services equipment including air conditioning cooling towers. The bacteria tend to thrive in lukewarm water where there is stagnation, accumulated rubbish, organic matter, scale and corrosion. Indeed, Legionella requires a very particular set of


Legionella can grow anywhere if conditions are right


bacteria present in natural water systems and can be present in mains (drinking water supply) in low numbers. It is next to impossible to stop and that makes preventing its entry into other types of engineered water systems impractical. However, Legionnaires’ disease can be prevented by: • Controlling the amplification/multiplication of number of bacteria present. • Minimising aerosol production/dissemination. • Curtailing contaminated aerosol inhalation.


HOW TO PROTECT COOLING TOWERS


There are around 30,000 cooling towers in the UK, which makes their protection from an outbreak of Legionnaires’ disease a serious priority. ECEX Air Intake Screens – simple, retro-fitted mesh pre-filters that prevent airborne debris from entering an air intake system without negatively impacting airflow – also help prevent bacterial proliferation by reducing bio loads that provide bacterial growth, which increases water treatment chemical effectiveness. Other measures to protect cooling towers include: • Minimising water spray discharges. • Avoiding dead ends and stagnant corners in pipework where water can accumulate. • Minimising number and length of spurs.


• If the system is new, selecting materials for pipework, joints, valves, and so on that do not support the growth of the legionella bacterium. • Ensuring that all parts of the system requiring maintenance and cleaning are easy to access and that water holding tanks are easy to drain. • Regularly cleaning and draining water holding tanks to avoid contamination and periodically inspecting and cleaning air ducts. • Where possible, installing filters to remove particulate matter to minimise the sludge build-up. • Applying chemicals to fresh water cooling tower systems.


• Maintaining comprehensive records of testing, maintenance and precautionary measures taken.


conditions in order to survive. For example, it needs to live in a temperature range of between 20 and 50˚C. Its optimum temperature for growth is 37˚C, the body core temperature of people, making it efficient at attacking the human body once it gets into the system. Legionella requires nutrition and can survive off other bacteria, algae, scale wood, rust or other organic nutrients present in a water system. There are accepted practices for mitigating the effects of the bacteria and these include removing storage where the mains supply can match demand, decommissioning and removing redundant tanks and pipework, lining tanks with hand-laid GRP for a smooth surface to prevent dirt adhesion and bacterial growth, and general maintenance, repair and refurbishment of tanks. My own company’s skilled engineers can offer all


these, plus other mechanical services that help save water, including: • Downsizing tanks to reduce the amount of water stored.


• Installation of delayed action float valves to reduce volumes in existing tanks. • Alteration of distribution pipework to create a balanced cross flow. • Isolation of twin tank systems to reduce overall storage.


Downsizing water tanks can help to reduce the amount of stored water


 August 2018


www.heatingandventilating.net


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