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Legionnaires disease is caused by bacteria which flourishes in stagnant water or sludge . It can also be found in wet matrix filters, which may be found in the ships filtration system for the air conditioning plant. Affected areas 1) Air inlet arrangements-This may be direct or indirect from the air conditioning room via jalousies, which, when incorrectly designed may lead rain water onto the filters. It may also be allowed to accumulate in the space where drainage is not efficient. 2) Filters-These filters made of a 25mm thick synthetic material can trap water as well as insects and soot and provide a rapid growth area for the bacteria. Regular washing is essential. 3) Cooler unit (dehumidifier)-Ineffective drainage can allow water to stagnate in the catchment sumps. Also, where air velocities are high over the block, air can become entrained and carry moisture into the air stream. An efficient moisture eliminator is required. 4) Humidifier-Steam humidifiers, where fitted, do not appear to be a problem. However, adiabatic humidifiers of which the water spray type appears to offer a special hazard. The enclosed tank and matrix elements provide an ideal breeding ground for the bacteria which may then be carried into the air stream when sprayed. 5) Plenum Insualtion-Where the PVC GRP facing of the rock wool insulation and sound deadening breaks down the considerable levels of water may be present. Countermeasures: 1) Filters-Should be washed in 50ppm solution on a regular basis. 2) Coolers-Special attention to drainage arrangements as well as superchlorinating the condensate sump every 3months. 3) Plenum insulation-Insulation to be examined at refit and damaged areas resealed.

Related Terms


In an air conditioning system, the final step in treatment, in the event the temperature is too low.


Heating, Ventilating, and Air Conditioning.


A room unit which performs part or all of the air conditioning functions. It may or may not be used with a central fan system.


The simultaneous control of the physical and the chemical conditions of the atmosphere within a structure. This is achieved by affecting some or all of the following air conditions: temperature, humidity, motion, distribution, pressure, dust, bacteria, odours, toxic gases, and ionization.


A heating or air conditioning system in which air is forced through a plenum chamber for distribution to ducts.
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