Engineered Systems - February 2008 - (Page 50) Eight Ways To Keep Legionella Out significantly rusted. • Keep all coils leak-free. The chilled and heating water systems are theoretically closed loops, but if coil leaks occur, contaminated water will spray directly into the ducts and could enter rooms via the airstream. • Ensure that air filters are dry. Wet filters provide a habitat for bacteria. In addition, airborne water droplets can be distributed to occupied spaces. Air filters should be cleaned and replaced as recommended by the manufacturer. • Locate cooling towers far from outdoor air intakes. A minimum of 33 ft (10 meters) has been suggested, but at least 100 ft (33 meters) is much safer. Cooling towers should also be located as far as reasonably possible from operable windows, parking lots, roads If Legionella bacteria counts are above the target level, consider using side-stream filtration to reduce suspended solids and the demand on the biocide. In most i t cases, filtering 3% to 5% of the %f circulated water to 10 to 15 microns is sufficient. and driveways, sidewalks, and outdoor areas frequented by people. Also, make cooling towers inaccessible to visitors and passersby (e.g., with a fence or wall). In hospitals, patient windows should be kept closed. Scientific literature includes several reports of Legionnaires’ outbreak investigations indicating that Legionella bacteria can travel several hundred feet from a cooling tower, even more than a kilometer, and still cause infection, so maintaining cooling towers for Legionella control is a must regardless of the location. • Control Legionella in cooling towers. Covering all the recommended Legionella control measures for cooling towers would take another article, at least. Let’s proceed with a brief synopsis. COOLING TOWERS = POTENTIAL HOTSPOTS Treat cooling towers for control of scale, corrosion, and microbes including protozoa and Legionella. Be sure that the water treatment service agrees with these objectives. The water treatment company should not be expected to guarantee zero Legionella bacteria, but should agree that control of Legionella and other microbes is an objective of the treatment program. Each situation is different, so the water treatment company or other water treatment expert who is familiar with the cooling tower should determine the details of the treatment program. However, be sure to consider the guidelines issued by the Cooling Technology Institute (Legionellosis Guideline: Best Practices for Control of Legionella, www. FREE INFO: 89 50 En gi neer ed S y stem s February 2008 1/18/08 1:31:55 PM ESM02084Messe.indd 1 http://www.light-building.messefrankfurt.com http://www.light-building.messefrankfurt.com http://www.cti.org
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