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Chapter 123 : Temperature Regimens versus Ionization and TMVs
Thermal eradication of Legionella bacteria (superheat and flush) is only a temporary palliative when Legionella levels pose an immediate problem. Legionella bacteria are inhibited at 60°C (140°F), but it may be very difficult to maintain this water temperature throughout the system due to heat loss from the pipes, as water frequently takes a long and tortuous path from leaving the heating system to its return via the hot water circulation loop. It has been shown that prior to fitting thermostatic mixing valves (TMVs) devices Legionella bacteria had been absent or in very low numbers, but following the installation of these devices, high levels of Legionella were detected at outlets. Treatment of the hot water may consist of raising the water temperature and/or injecting a chemical such as chlorine, chlorine dioxide, or nonchemical ionization. Micro-pore filters fitted to outlets and showers are very effective at preventing the dissemination of bacteria when present at outlets, particularly in sensitive areas such as intensive care units, operating theaters, and areas where patients have reduced immunity. TMVs were introduced to prevent the scalding of the aged and those unable to react quickly when presented with very hot water. If water temperatures can be reduced and protected by an effective biocidal regimen then the problems and cost associated with TMVs are avoided.