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