Technical
ADDRESSING LEGIONELLA
IN MECHANICAL SYSTEMS
By Zalmie Hussein , development administrator at the International Association of Plumbing & Mechanical Officials
Legionnaires ’ disease was first identified in 1976 and is caused by water contaminated with Legionella pneumophilia which , when disseminated in droplets into the atmosphere and inhaled , may infect a person .
Georgia State University
The interest and concern in Legionella management and control within building water and air systems has continued to grow as Legionella outbreaks increase . Although plumbing systems are a common source of such outbreaks , mechanical systems such as cooling towers , air distribution systems , spas , fountains , and hot water tanks can also act as breeding grounds for the bacteria that causes Legionnaires ' disease .
During the 2024 edition of the Uniform Mechanical Code ( UMC ) code cycle , the UMC Technical Committee formed a task group to address Legionella in mechanical systems for the UMC . Prior to the formation of this group , the Uniform Plumbing Code ( UPC ) Technical Committee formed a task group for the 2021 edition of the UPC , which resulted in the creation of a new Appendix N ( Impact of Water Temperature on the Potential for Scalding and Legionella Growth ).
The Uniform Codes published by IAPMO consistently endeavour to integrate major health and safety concerns , earning the reputation of being all-inclusive safety codes in an ever-changing environment . The UMC is developed via an ANSIapproved development process , which ensures consensus and due process in its development .
The structure of Legionella pneumophila .
Legionella outbreaks are more likely to occur in buildings with mismanaged water systems and in stagnant water . Therefore , a water management programme is the preferred approach to controlling Legionella in building water and air systems . Legionella bacteria thrive in cooling towers where standing water is common .
A Legionella management plan should include preventive measures for all systems that present a significant risk of Legionella growth and transmission . Where a management programme is implemented , it is typical for a water management team to be formed to provide a description of the water system , identify potential areas of Legionella growth with temperature ranges , etc . A water management programme may be established when required by the authority having jurisdiction . Cooling towers , evaporative condensers and indirect evaporative air-cooling equipment are standard components used in large building air conditioning systems and have been the source of numerous Legionella outbreaks . These systems use the natural cooling process of evaporation to remove heat from water or to directly cool the air . The warm and wet environment of cooling towers provides an ideal environment for Legionella to grow .
Legionella control in cooling towers should start early , preferably during the design and commissioning phases . Chapter 11 Part II of the UMC addresses the installation and construction of cooling towers . Section 1122.0 ( Chemical Treatment Systems ) has been a useful resource for developing a water treatment plan using chemical disinfectant .
Section 1126.0 ( Drift Eliminators ) requires drift eliminators to be installed in cooling towers to reduce the quantity of mist or water droplets that is carried away from the cooling tower . Drift eliminators can assist with reducing the spread of waterborne pathogens into the airstream . Compliance with these code requirements will ensure a safer and more efficient cooling tower . The Legionella Task Group will look into expanding these safety provisions for cooling towers .
Regular monitoring and testing of the water quality are some of the most common steps used to control Legionella
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RACA Journal I March 2022 www . hvacronline . co . za