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Engineering ToolBox > Legionella

Legionella pneumophila - bacterium that thrives in water supply and air conditioning systems - causing Legionnairs disease

Legionnaires' disease is an acute respiratory infection caused by the bacterium Legionella pneumophila bacteria. The bacteria can cause a broad spectrum of disease from mild cough and fever to serious pneumonia.

The bacteria thrives at temperatures between 69^oF (20.5^oC) and 122^oF (50^oC) and may be traced in water supply, central heating and air conditioning systems.

Note! Any water system with operating temperatures between 69^oF (20.5^oC) and 122^oF (50^oC) is a potential legionella source. Special attention should be taken for

• cooling towers and evaporative condensers
• scrubber systems with low temperatures
• low temperature hot water supply systems

Regularly cleaning, heat and chemical treatment are often necessary to avoid potential development of the bacteria.

• keep basins and sumps free of mud and organic debris
• use chemical and organic inhibitors where recommended
• avoid water stagnation - circulate the water through the system
• avoid leaks from processes to the cooling water - process water may contain nutrients that may feed the bacteria

The Legionella bacteria cannot survive water temperatures above 131^oF (55^oC) for more than five or six hours. Instantaneous destruction of the bacteria occurs at temperatures above 158^oF (70^oC). General protection against the bacteria can be achieved by designing an operating water temperature of at least 140^oF (60^oC).

For water temperatures below 140^oF (60^oC) special initiatives are necessary regarding cleaning and chemical treatment procedures.