Back to Basics, Injuries and Illness, Personnel Safety

Back to Basics: Control and Prevention of Legionella in Water Systems

Back to Basics is a weekly feature that highlights important but possibly overlooked information that any EHS professional should know. This week, we examine how to control and prevent the growth of Legionella bacteria in your water systems.

Legionellosis, which can lead to Legionnaires’ disease and Pontiac Fever, is spread primarily through inhaling Legionella-contaminated, aerosolized water. In other rare cases, exposure is also possible from breathing in Legionella-contaminated soil or while drinking water. It’s important to have a water management program in place to prevent Legionella growth in your water systems.

To prevent exposure to Legionella in the workplace, the Occupational Safety and Health Administration (OSHA) recommends having awareness about water systems where the bacteria could grow, performing water system maintenance to prevent growth, and checking for unexpected growth should preventive measures fail.

Maintenance and disinfection

Conducting effective maintenance and visual inspections should prevent scale buildup, sediment, and gradual water organism accumulation on structural surfaces–all of which can support Legionella growth. Keep records of the following:

  • Operating system descriptions for all components in the system and the make-up water supply to the system
  • Written procedures for the system’s proper operation and maintenance covering scale and corrosion inhibitor use, antifoaming agent use, and biocide or chlorine use
  • Inspection, cleaning, disinfection dates
  • Test results of any sampling performed
  • System maintenance/monitoring dates and work description/results

Treating water systems periodically with biocide can prevent or reduce Legionella growth. Current evidence suggests that halogen oxidizers (including certain chlorine and bromine compounds), ozone, peroxides, and non-oxidizing biocides can help control Legionella when used properly.

Clean water is critical to the effectiveness of water treatment because water with organic matter and dissolved solids in high concentrations will reduce biocide effectiveness, according to OSHA. In addition, recent data about quaternary ammonium compounds, which are used to control biofouling in cooling towers, suggest that they may not be fully effective in controlling the growth of Legionella. Non-chemical water treatment techniques such as ultraviolet light or ultrasonic waves have been shown to kill Legionella bacteria under certain conditions.


In cases where Legionella hazards can’t be controlled with engineering and administrative controls, personal protective equipment (PPE) may be needed to prevent worker exposures and infections. There are no specific OSHA standards regarding Legionella or other non-bloodborne, biological hazards, but there are several existing requirements that may apply to occupational exposure to the bacteria. These include OSHA standards for PPE (29 CFR 1910.132), eye and face protection (29 CFR 1910.133), respiratory protection (29 CFR 1910.134), hand protection (29 CFR 1910.138), and foot protection (29 CFR 1910.136), and the General Duty Clause.

Employers should provide appropriate PPE and encourage its use when workers perform any routine maintenance, cleaning, or disinfection activities on water systems that may be contaminated with Legionella. This includes work on hot and cold domestic water systems; cooling towers; and heating, ventilation, and air conditioning (HVAC) equipment. If Legionella contamination is possible, but a Legionellosis outbreak is not necessarily known or suspected, consider encouraging voluntary use of respirators in according with the following criteria:

  • Use a NIOSH-approved respirator at least as protective as an N95 respirator.
  • Workers using biocides to clean and disinfect systems should be equipped with eye protection (chemical goggles or face shield with safety glasses), protective gloves, and suitable protective clothing as recommended by the chemical manufacturer.
  • Workers doing tower cleaning must wear, at a minimum, the PPE required for any chemicals being used, and a half-face air-purifying respirator (APR) equipped with an N-100 cartrdige.
  • When selecting respiratory protection, consider the agents used for decontamination and provide combination cartridge respirators where both particulate and chemical hazards may be present. If organic vapor cartridges are used, implement a cartridge change schedule.
  • Tasks that involve an increase in moisture and spray, including cleaning and decontamination activities, may adversely affect disposable N95 respirators and certain other respirators. In these cases, consider providing a Supplied-Air Respirator (SAR) to improve worker protection.
  • Just like worksites with mandatory use of respirators, employers who permit voluntary use of respirators must implement a respiratory protection program that complies with the applicable provisions of OSHA’s Respiratory Protection standard (29 CFR 1910.134). This includes compliance with the standard’s requirements for obtaining medical clearance for wearing the respirator and for conducting fit testing prior to actual use of respirators. It also must comply with the provisions set forth in the standard’s Appendix D (Mandatory) – Information for Employees Using Respirators When Not Required Under the Standard.
  • To achieve proper fit, workers with facial hair that interferes with the respirator seal (beards and/or large moustaches) may require the use of alternative respirators, such as full facepiece negative-pressure respirators, PAPRs, or SARs.

In the event of a known or suspected Legionellosis outbreak, workers who may be exposed to aerosolized Legionella must wear respirators. For most exposures, respirators should be equipped with N100 filters or a similar type of filter media capable of effectively collecting particles in the one-micron size range. Workers with potential exposure include those examining the affected water system, conducting disinfection activities on the system, or performing other essential tasks in areas near contaminated cooling towers or serviced by contaminated HVAC units. The employer should conduct a hazard analysis to identify which workers are at risk of exposure, any additional hazards that may present, and the appropriate measures to control worker exposures.

Visit OSHA for more information on water system-specific design, operation, maintenance, and disinfection guidelines.

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