In this slide we cover the relationship between Legionella proliferation and temperature.
Proliferation being the posh word for the bacteria multiplying or increasing in numbers.
We can see on the graph that below 20°C the organism is in a dormant phase, little or no multiplication is taking place.
This is the region for operating cold water, not killing the bacteria but preventing it from increasing.
Proliferation then occurs at an increasing rate up to 37°C with cell division possibly up to every few hours at the peak, but more likely days at the lower ends.
The bacteria is also more virulent when grown at 37°C, the RAMBO of bugs if you will.
Cooling towers, spa baths and many other systems including Thermostatic Mixing Valves (TMVs) operate in this range and will therefore need to be controlled by something other than temperature.
Then somewhere between 45 and 47°C proliferation stops and we enter a destructive or Death phase. AT 50 death is likely to take 2 hours at 60 2 mins.
However these are guides not absolutes and depend on things like supporting biofilms.
Calorifiers if operated at 60°C will then fairly quickly destroy Legionella.