With reference to the risk of legionella bacteria in air conditioning plants: (a) state FOUR main areas which are considered to be a breeding ground for the bacteria, outlining a reason for EACH;(8) (b) describe how the risks of the existence of the bacteria can be reduced.(2)
(a) Four main areas considered breeding grounds for Legionella bacteria, with reasons (8 marks)
Cooling towers / evaporative condensers
Reason: Warm water (20–45°C) combined with air and nutrients provides an ideal environment for bacterial growth.
Air conditioning condensate drains and trays
Reason: Stagnant water accumulates, often warm and untreated, allowing bacteria to multiply.
Humidifiers and evaporative pads
Reason: Constant presence of warm, moist surfaces with organic material encourages bacterial proliferation.
Pipework and storage tanks with stagnant water
Reason: Dead-legs, low flow, and warm temperatures promote bacterial survival and biofilm formation.
(b) Reducing the risk of Legionella (2 marks)
Maintain cleanliness and water treatment: Regular cleaning, disinfection, and chemical dosing (biocides) of cooling systems, tanks, and trays.
Temperature control and circulation: Keep hot water >60°C, cold water <20°C, and ensure water is not left stagnant.
