Chapter 2: Legionella risk and hazard assessment

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2.1 General

2.2 System risk assessment

Table 2.1: System risk and hazard assessment guidelines
System type Hazard characteristics Risk level
Cooling tower No evaporative condenser Low
Located more than 10 m from air intake Low
Located less than 10 m from air intake High
Excessive drift from tower exhaust High
Water temperature always below 20 °C at any point in the system Low
Water temperature in 20-35 °C range at any point in the system Medium
Water temperature exceeds 35 °C at any point in the system High
Located within 10 m of kitchen exhausts, vegetation etc. High
Recent history of elevated bacterial levels High
Open water systems Water temperature always below 20 °C at any point in the system Low
Water temperature in 20-35 °C range at any point in the system Medium
Water temperature exceeds 35 °C at any point in the system High
Aerosolization of water occurs High
Located within 10 m of kitchen exhausts, vegetation etc. High
Located close to public areas Medium
Recent history of elevated bacteria levels High
Humidifiers Direct steam, infrared or gas humidifier Low
Any other type of humidifier High
Water stagnation exists Medium
Drain pans Water stagnation exists Medium
No water stagnation Low
Domestic cold water systems Piping subjected to periods of prolonged water stagnation Low to Medium
Water temperature always below 20 °C Low
Water temperature in 20-35 °C range Medium
Potential for cross-contamination with process water High
Piping is not insulated to Code Medium
Shower facilities connected Medium
Domestic hot water system Water storage temperature exceeds 60 °C Low
Water storage temperature in 50-60 °C range Medium
Water storage temperatures below 50 °C High
Water distribution temperature below 50 °C High
Piping subjected to periods of prolonged water stagnation High
No re-circulation pump High
Shower facilities connected High

2.3 Facility risk assessment

Table 2.2: Facility risk assessment
System risk level (based on Table 2.1) Facility risk level
Contains any high risk system, High
Contains only medium & low risk systems Medium
Contains only low risk systems Low

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