A guide to major Legionella risk sources and what measures to take to assess and minimise Legionella growth is provided by Noel Arnold and Associates.
To help control Legionella risk, the systems in a facility that present a risk need to be identified. Systems where Legionella bacteria can potentially multiply and become a concern to health include cooling towers, hot and cold water systems, spa pools, humidifiers, air washers, air-handling units, emergency showers, fire sprinklers, eye wash sprays, decorative fountains, water softeners and rainwater harvesting systems.
There is a reasonably foreseeable Legionella risk if the water system has any of these factors:
- has a water temperature between 20 and 45 degrees Celsius (as in cooling towers and many hot water systems with temperature mixing valves)
- creates and/or spreads breathable droplets; for example, aerosol, showers and fountains
- stores or recirculates water, and/or
- is likely to contain a source of food for the organism; for example, presence of sludge, scale or fouling.
As we live in a country with extremes of temperature, care must be taken and monitoring and maintenance must be carried out throughout the year. The Victorian Government has legislative guidelines to help control Legionella risk in many building systems including cooling towers and hot/warm water systems. Many institutions in Queensland follow these guidelines as best practice; however, they are not mandatory in Queensland. This may change following the recent incidents in Queensland hospitals.
Many facilities in Queensland that use cooling towers as part of their air-handling systems and heat exchangers for plant are conducting annual risk assessments of the system in line with the Victorian guidelines and Australian Standards. Cooling tower management also requires regular chemical dosing, chemical and bacterial testing and cleaning. Other building systems where Legionella can proliferate, however, are often overlooked. A risk management plan should be developed to:
- identify Legionella risk
- assess Legionella risk
- implement treatment/method of control, which must comply with any relevant standards, and
- establish the need for monitoring, testing, reporting, communication, response strategies and review
See Table 1 for a guide to major Legionella risk sources (other than cooling towers) and what measures need to be taken to assess and minimise Legionella growth.
Table 1: Checklist for hot and cold water services
|Hot water services||Arrange for samples to be taken from hot water calorifiers/boilers/heaters in order to note condition of drain water |
|As identified through risk assessment|
|Check flow and return temperatures at calorifiers/boilers/heaters are at least 60 degrees Celsius (outflow) and 50 degrees Celsius (return) |
|Check the water has reached 50 degrees Celsius after running the water for up to one minute at the sentinel outlets (nearest and furthest outlet on a network distribution loop) |
|Visually check on internal surfaces of calorifiers/boilers/heaters for scale and sludge, and check representative taps for temperature as above on a rotational basis |
|Cold water services||Check tank water temperatures remote from ball valve and mains temperature at ball valve, and note maximum temperatures recorded by fixed max/min thermometer |
|Check the water is below 20 degrees Celsius after running the water for up to two minutes in the sentinel outlets |
|Visually inspect cold water storage tanks and carry out remedial work where necessary, and check representative taps for temperature as above on a rotational basis |
|Showerheads||Dismantle, clean and descale showerheads and hoses (especially if plastic) |
|Quarterly or as necessary|
|Little-used outlets||Flush through and purge to drain, or purge to drain immediately before use, without release of aerosols |
|Bacterial analysis||Samples should be taken from appropriate outlets and storage tanks/cylinders, and these should be analysed by a NATA-accredited lab |
|Periodically (as identified through risk assessment)|
Source: Noel Arnold and Associates
For more on avoiding Legionnaires’ disease outbreaks read Stuart Adcock, Legionella team leader for the Department of Health, Victoria’s article on why outbreaks of Legionnaires’ disease are still occurring and how they can be proactively avoided.