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Preventing Legionnaires’ disease from cooling towers and evaporative condensers
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Preventing Legionnaires’ disease from cooling towers and evaporative condensers

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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.

PCBU who manages, maintains or services 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 plant

Note: Buildings (including their air-conditioning systems) must comply with the requirements under the Building act

 

 

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.

PCBU who manages, maintains or services 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.

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

Table 3: Recommended actions for day-to-day operations

 

Further information

Environmental Sampling for Legionella Bacteria. available from the Institute of Environmental Science and Research

The Prevention of Legionellosis in New Zealand: Guidelines for the Control of Legionella Bacteria. 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

The following standards are available from Standards New Zealand

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

 


Published: January 2017. Current until review in 2019.

Last updated 15 February 2017

PLEASE NOTE

On Monday 4 April 2016, the New Health and Safety at Work Act 2015 (HSWA) came into effect.

HSWA repeals the Health and Safety in Employment Act 1992, with immediate effect.

All references to the 1992 Act on this website and within our guidance will be progressively removed.