ENVIRONMENT and ENERGY
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Temperature approach for legionella control A risk management approach to control legionella in premise plumbing systems may include thermal control of hot and cold water loops in addition to secondary disinfection or other control measures . Thermal control involves maintaining the temperature in hot and cold water systems outside of the range in which legionella can ideally grow ( between 35 ° C and 46 ° C , or 95 – 115 ° F ). Although cold water systems are usually maintained at a temperature less than 20 ° C ( 68 ° F ), the temperature can increase during periods of low flow or non-usage ( VHA , 2014 ) as well as during seasonal temperature fluctuations .
A number of entities suggest raising the hot water temperature to a certain level for effective control of legionella growth . To inhibit legionella growth in health care facilities , nursing homes , and other high-risk premise plumbing systems , several reports suggest that the hot water temperature be at least greater than 50 ° C ( 122 ° F ) at outlets ( HSE , 2014 ; Hruba , 2009 ; WHO , 2007 ; Blanc et al ., 2005 ; ASHRAE , 2000 ; Ezzeddine et al ., 1989 ). Specific suggestions for hot water temperature control include the following :
• Bédard et al . ( 2016 ) reported that corrective measures were implemented to control L . pneumophila in the hot water system of a hospital . The corrective measures included increasing the hot water temperature from 55 ° C ( 131 ° F ) to 60 ° C ( 140 ° F ).
• Bédard et al . ( 2015 ) found that systems in which water temperature was maintained higher than 60 ° C ( 140 ° F ) coming out of water heaters and greater than 55 ° C ( 131 ° F ) throughout the hot water system were negative for L . pneumophila .
• The United Kingdom ’ s Health and Safety Executive recommends the water heater temperature be maintained at greater than 60 ° C ( 140 ° F ), with the temperatures at the outlets reaching 55 ° C ( 131 ° F ) in health care premises and 50 ° C ( 122 ° F ) in other building types within one minute ( HSE , 2014 ).
• The Veterans Health Administration ( VHA ) requires that all VHA-owned facilities where patients , residents or visitors stay overnight maintain water temperatures at 51.1 ° C ( 124 ° F ) or higher in hot water systems to inhibit legionella growth ( VHA , 2014 ).
• In France , regulations for legionella control were recently extended to all public buildings . Target values for water temperature include greater than 55 ° C ( 131 ° F ) at the water heater outlet and greater than 50 ° C ( 122 ° F ) for any points in the hot water system , including points of use and return loops ( République Française , 2010 ).
• Blanc et al . ( 2005 ) reported that after increasing the water heater temperature from 50 ° C to 65 ° C ( 149 ° F ), a Swiss hospital experienced a significant reduction in the occurrence of legionella . The temperature at most outlets was greater than 50 ° C ( 122 ° F ).
• Darelid et al . ( 2002 ) reported that maintenance of a circulating hot water temperature greater than 55 ° C ( 131 ° F ), together with a 10-year surveillance programme , had successfully controlled legionnaires ’ disease in a Swedish hospital .
Circulation of water throughout the hot water distribution system may be necessary for effective thermal control . Accelerating the flow of water in a system has resulted in a noticeable reduction in the concentration of legionella ( Ezzedine et al ., 1989 ). Positive legionella detections have occurred at outlets where water circulation was known to be poor ( Blanc et al ., 2005 ). Bédard et al . ( 2015 ) suggested that nightly shutdown of water recirculation loops be avoided since temperature losses in dead end loops in the system can result in conditions favourable to legionella growth .
To monitor efficacy of thermal control in a WSP , temperature monitoring at the main components in the system and temperature profiling at outlets can be considered to help identify and correct risks ( Bédard et al ., 2015 ). Temperature profiling at intermediate locations , such as subordinate flow and return loops feeding different floors of a facility , allows discovery of dead legs and flow rate deficiencies ( Bédard et al ., 2016 ). It may be difficult for older buildings to raise their water heater temperature sufficiently to maintain elevated temperatures at outlets ( HSE , 2014 ; WHO , 2007 ). The efficacy of temperature control in distal low flow areas is important to consider , as legionella growth has been shown to be more abundant — with few exceptions — in the hot water system where temperatures are less than 45 ° C ( 113 ° F ) ( Serrano-Suárez et al ., 2013 ).
Heating water to temperatures necessary to control for legionella can result in greater energy use . While increasing temperature is an effective form of controlling legionella growth , increasing energy use can result in other negative environmental impacts . For more information on how to mitigate other environmental impacts , please visit the ENERGY STAR ® website at https :// www . energystar . gov / buildings , and the WaterSense ® website at http :// www3 . epa . gov / watersense / commercial / index . html . PA
Reference Technologies for legionella control in premise plumbing systems : scientific literature review . Republished with permission from the Environmental Protection Agency .
www . plumbingafrica . co . za March 2017 Volume 23 I Number 1