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Legionnaires’ disease from water systems left idle

What is the potential risk?

Stagnant water in idle water systems and piping can provide an opportunity for harmful bacteria such as Legionella to survive and grow. In unused cold-water and hot-water systems, the water temperature can shift into the Legionella bacteria growth range. These bacteria multiply in warm water and can potentially be found in water sources — such as swimming pools, hot tubs, water tanks, and cooling towers used in residential or commercial buildings. In addition, during a prolonged shutdown, disinfectants or biocides in the water  such as chlorine (which would normally prevent Legionella growth) — can break down, reducing the concentration and their effectiveness.

If water containing Legionella bacteria becomes aerosolized — such as via mist or vapour from water jets, showers, faucets, or air conditioning and ventilation systems — it may be inhaled by workers or members of the public. Those exposed to the bacteria may be at risk of developing Legionnaires’ disease, which produces symptoms similar to severe pneumonia. People with decreased immune function or chronic lung problems are at an increased risk of developing the disease if they are exposed. Legionnaires’ disease cannot be transmitted from human to human and can be effectively treated with antibiotics.

Which workplaces may be at risk?

All workplaces that have a running water supply are at risk, especially those that have hot tubs, spas, showers, evaporative cooling systems (e.g., cooling towers), pressure washers, swimming pools, or decorative water features (e.g., fountains and waterfalls). If your building or water system has been shut down, it’s important to consider this risk as you develop your startup procedures.

How can I reduce the risk in my workplace?

As an employer, you need to know if there is the potential for Legionella to be present in your workplace. It’s your responsibility to regularly inspect your workplace, and to ensure that your safety procedures and practices control the risk.

Here are ways you can reduce Legionella bacteria that may have grown in idle water systems:

  • Flush both your hot and cold water systems, including all piping, faucets, shower heads, and ice machines.
  • Clean and disinfect outlets such as faucets and shower heads.
  • Clean all decorative water features, such as ponds and fountains, to make sure they are free of slime or biofilm.
  • Ensure all swimming pools, hot tubs, and spas are cleaned and free of slime or biofilm.
  • Ensure cooling towers are clean, have been properly maintained, and that the tower and basin are free of slime and biofilm.
  • Flush safety equipment, including fire sprinkler systems, eye wash stations, and safety showers.
  • In health care and dental facilities, make sure that medical and dental irrigation systems for patients are flushed and maintained in accordance with manufacturers’ instructions before use.
  • If your systems require a disinfectant or biocide, make sure that the concentration of the chemical meets manufacturer or industry specifications.

The following sections of the Occupational Health and Safety Regulation are most relevant to this risk.

Section 4.78 requires you to have an effective preventive maintenance program for your ventilation system. This includes inspecting for conditions that would promote the growth of micro-organisms, such as water leaks or stagnant water pools. This also includes ensuring there is adequate treatment of open-water systems associated with ventilation equipment, such as cooling towers and humidifiers, to control biological growth.

Section 5.2 requires that if a worker is, or may be, exposed to a biological agent that could cause adverse health effects, you must prepare and implement written procedures to eliminate or minimize the risk of exposure to the biological agent.

Where can I find resources?

Learn more about managing risk.

Publication Date: Jul 2021 Asset type: Risk Advisory Reference: RA 2020-02