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Airconditioning and legionella

Possible contamination of air treatment systems with legionella bacteria

Air treatment systems in buildings, also known as airco or air-conditioning systems (these systems don't just cool but also treat, filter and humidify), are related to the risks of a legionnaires disease outbreak (remember the recent outbreak in a Spanish shopping centre).

What is the origin of the legionella bacteria and what are the risks.

The legionella pneumophila bacteria is naturally occurring in surface water (even in drinking water). However to grow and multiply it needs nutrients, a place to grow, like present in biofilm, and a water temperature between 20 and 55 degrees.

If a group of legionella bacteria is released from the biofilm and the water in which it houses is sprayed and inhaled by people with impaired immune defence it can cause the much feared legionnaires disease.

In Dutch air treatment systems, temperatures above 25 degrees are rare. Also normally there would be no "wet spots" with biofilm in which the legionella bacteria can grow.

What are the possible dangers?

  1. Airco systems suck in fresh air (from outside). This air can contain small drops or aerosols from cooling towers, fountains or other aerosol sources.
  2. Air treatment systems often recirculate air in offices and other buildings, to save reheating energy. If somewhere in the building there is a source of legionella bacteria like in showers, fountains or even plant spraying water, contaminated air is circulated through the entire building.
  3. In winter cold and dry air is humidified because by heating the air, the relative humidity drops. For this, special humidify sections are used. These sections should contain disinfection systems like UV disinfection or ozone treatment that regularly need cleaning from biofilm.

Lenntech is manufacturer and supplier of solutions to the problems above. For information, advice or a quotation you can call, fax or e-mail us.

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