Preventing Legionnaires’ disease from cooling towers and evaporative condensers

Legionella bacteria can infect humans and cause legionellosis and Legionnaires’ disease. The bacteria can grow on the wet surfaces of cooling towers, evaporative condensers (cooling plant) and scrubbers. Poorly positioned air intakes for air conditioning units can also capture the bacterial plume and draw it into buildings.

We have produced guidance for PCBUs that have cooling towers or evaporative condensers (cooling plant) on how to minimise or eliminate the risk of Legionella bacteria growing in their workplace.

Preventing Legionnaires’ disease from cooling towers and evaporative condensers provides advice on the roles, duties and extent of influence/control held by different PCBUs and guidance for installing a new cooling plant or maintaining an existing plant.

This fact sheet provides advice to persons conducting a business or undertaking (PCBUs) who have cooling towers or evaporative condensers (cooling plant). This includes (but is not limited to) cooling plant that is part of: any building air conditioning system, commercial premises with refrigeration plant (eg bulk storage of chilled or frozen food), or industrial process.

Legionella bacteria grow on the wet surfaces of cooling towers, evaporative condensers (cooling plant) and scrubbers, and can cause a pneumonia called Legionnaires’ disease. Legionnaires’ disease is often severe and can be fatal. Those at higher risk of becoming infected are adults over 50, males, smokers, people with lung disease or low immunity.

Legionella become airborne when fine water droplets (aerosols) carrying the Legionella bacteria are expelled from the exhaust fans of this equipment and may be inhaled by those nearby. Poorly positioned air intakes for air conditioning units can also capture the bacterial plume and draw it into buildings.

PCBUs whose work involves buildings, industrial or commercial premises that operate one or more cooling towers or evaporative condensers (cooling plant) must eliminate the risks from Legionella colonisation and dissemination so far as is reasonably practicable. If a risk can’t be eliminated, it must be minimised, so far as is reasonably practicable.

In relation to cooling plant, there will be different PCBUs with overlapping health and safety duties. When this happens, PCBUs must, so far as is reasonably practicable, consult, co-operate and co-ordinate activities.

The extent of the duty to manage risks depends on the ability of each PCBU to influence and control the matter. Table 1 describes the different types of PCBUs that may be involved, their duties and likely extent of their influence or control.

Role	Duty	Extent of influence/control
PCBUs who are designers, manufacturers, importers and suppliers of the plant and structures	ensure plant, substances, or structures are without health and safety risks so far as is reasonably practicable test to make sure the plant designed/ manufactured/supplied is without health and safety risks so far as is reasonably practicable (or arrange the carrying out of such tests) give adequate information to people who are given the design/plant, substance or structure.	Upstream PCBUs can influence and often eliminate health and safety risks through designing, manufacturing or installing plant that is safe for the operator. Designers of cooling plant are in a unique position in that they have the opportunity to eliminate or minimise risks by adopting the principles of health and safety in design. The elimination or minimisation of risks after installation of plant is usually less effective, and more costly.
PCBUs who are installers, constructors and commissioners of plant and structures	ensure the way plant or structures are installed, constructed or commissioned are without health and safety risks so far as is reasonably practicable.
PCBUs who manage or control the workplace	ensure that, so far as is reasonably practicable, the workplace and anything else arising from the workplace are without health and safety risks to any person ensure, so far as is reasonably practicable, the provision and maintenance of safe plant and structures.	This PCBU has influence and control over who manages, maintains or services the cooling plant. This PCBU could carry out these actions themselves or contract someone else to do it. For new buildings or renovations, this PCBU will have significant influence or control over the type of cooling plant installed.
PCBUs who manage or control the workplace	ensure, so far as is reasonably practicable, the health and safety of workers, and that others (eg visitors to the workplace or members of the public not associated with the premises) are not put at risk by its work (the managing, maintaining or servicing the cooling plant) ensure, so far as is reasonably practicable, that any fixtures, fittings or plant they manage or control are without risks to the health and safety of any person.	This PCBU has influence and control over who manages, maintains or services the cooling plant. This PCBU could carry out these actions themselves or contract someone else to do it. For new buildings or renovations, this PCBU will have significant influence or control over the type of cooling plant installed.
PCBUs [DLM1] who manage, maintain or service the cooling plant	ensure, so far as is reasonably practicable, the health and safety of workers, and that others (eg visitors to the workplace or members of the public not associated with the premises) are not put at risk by its work (the managing, maintaining or servicing the cooling plant) ensure, so far as is reasonably practicable, that any fixtures, fittings or plant they manage or control are without risks to the health and safety of any person.	This PCBU has influence and control over eliminating or minimising the day-to-day health and safety risks from Legionella in cooling plant. They should have effective systems in place to maintain, monitor, treat and report on their sampling/testing/ reporting procedures.
PCBUs who are solely tenants in buildings with cooling plant as part of air conditioning system	ensure, so far as is reasonably practicable, the health and safety of workers, and that others (eg visitors to the workplace or members of the public not associated with the premises) are not put at risk by its work.	This PCBU is likely to have a a limited extent to influence or control the health and safety risks. The extent of this duty will likely involve: confirming that the PCBU who manages or controls the workplace has a maintenance schedule and monthly water quality testing programme in place either receiving these reports or being notified if Legionella is detected and what actions are being taken to address this keeping workers informed when Legionella is detected.
Table 1: Different PCBUs with overlapping duties

Recommended actions

Tables 2 and 3 describe recommended actions when intending to install new cooling plant, and when dealing with cooling plant on an ongoing basis.
Seek the views of your workers about the ways to eliminate or minimise the risks from Legionella in cooling plant.

When installing new cooling plant

Role	Recommended action
PCBUs who are designers, manufacturers, importers and suppliers of the plant	Design, manufacture, import and supply cooling plant: that use processes that restrict bacterial growth (for example: a hot water unit with mixing valves instead of a warm water storage system) have parts that avoid sludge build-up. Legionella grow better in sludge avoid dead legs in pipe work so bacteria cannot grow in them use well designed drift eliminators for effective capture of aerosols have easy access for maintenance and cleaning use a continuously-operating disinfection process to kill bacteria use a closed-circuit system instead of an open circuit – this removes bacteria growth surfaces.
PCBUs who are installers, constructors and commissioners of plant and structures	Install and construct cooling plant following relevant specifications. Install cooling plant so that potentially-contaminated aerosols from other discharges are not drawn into the building air intakes. Do not start up cooling plant until all water treatment systems are operational.
PCBUs who manage or control the workplace	Use a plant design based on air-cooling rather than water cooling. This eliminates the risk of Legionella growth. If the above is not reasonably practicable, use water cooling plant that is designed to minimise the risk of Legionella growth. Such plant should be easy to access and keep clean.
Table 2: Recommended actions when intending to install new cooling plan

Note - Buildings (including their air-conditioning systems) must comply with the requirements under the Building Act(external link)

For existing cooling plant

Role	Recommended action
PCBUs who manage or control the workplace	Ensure the water cooling plant is kept clean and well maintained. Make enquires to ensure the PCBU used to manage, maintain or service the cooling plant is competent and qualified to complete the task. Insist on timely receipt of water quality reports with clear explanations of findings. The PCBU should keep written records to demonstrate ongoing compliance to relevant authorities. The records should also show actions taken when results indicate an increased microbial growth in the water. After consulting with the PCBU who manages, maintains or services the cooling plant, decide the actions to be taken to protect workers and others when microbial growth is found. Provide copies of all water quality reports to building tenants or provide reports to tenants/visitors when levels of Legionella requiring action are found.
PCBUs who manage, maintain or service the cooling plant	Keep the water cooling plant clean and well maintained. Consider steam cleaning as part of maintenance schedule of wetted surfaces. Treat the water with chemicals – if needed, use specialist advice for help with: selecting and running the chemical dosing equipment the design of bleed-off techniques to avoid chemical residue build-up choosing biocides – effectiveness versus ecotoxicity regular water sampling, testing, and reporting of findings (in accordance with AS/NZS3666.3 Air handling and water systems of buildings – Microbial control – Part 3: Performance based maintenance of cooling water systems). Ensure the person who monitors, tests or treats water or records microbial growth is competent and qualified to complete the task. If the cooling plant is in a start-up phase after being shut down, more frequent sampling may be initially needed. If earth works are occurring in the vicinity to the cooling plant, more frequent sampling may be needed. Provide the PCBU who manages or controls the workplace with water quality reports as soon as possible. the reports should contain clear explanations of the findings (see aS/NZS3666.3 and the New Zealand Building Code). Alert the PCBU who manages or controls the workplace immediately if results indicate an increased microbial growth in the water and inform them what actions should be taken to address this.
Table 3: Recommended actions for day-to-day operations

Note - The Institute of Environmental Science and Research’s guidelines Environmental Sampling for Legionella Bacteria provide procedures for collecting samples from cooling plant for testing. These guidelines are available from: www.esr.cri.nz(external link)

Further information

Download Preventing Legionnaires’ disease from cooling towers and evaporative condensers [PDF 64KB] [PDF, 64 KB]

Environmental Sampling for Legionella Bacteria - available from the Institute of Environmental Science and Research(external link).

The Prevention of Legionellosis in New Zealand: Guidelines for the Control of Legionella Bacteria(external link) available from the Ministry of Health.

NSW Code of Practice for the Control of Legionnaires’ disease available from the New South Wales Department of Health(external link) or download the PDF here [PDF, 1.7 MB].

The following standards are available from Standards New Zealand(external link)

AS/NZS3666.3 Air handling and water systems of buildings – Microbial control – Part 3: Performance-based maintenance of cooling water systems
NZS4302 Code of practice for the control of hygiene in air and water systems in buildings
AS/NZS4020 Testing of products for use in contact with drinking water.