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Legionnaires' Disease

Section III:A. Investigation Protocols: Level One

Level One InvestigationConduct a level one investigation when there is a probable basis for suspecting that workplace water sources have been contaminated with Legionnaires' disease bacteria (LDB), or when there is information that no more than one case of Legionnaires' disease has been reported.

OSHA personnel are encouraged to inform local health authorities of the investigation. Local health authorities may be helpful in the collection and analysis of water samples after the resolution of any issues related to sample confidentiality, including medical privilege of information, rights of the employer, and authority of local health departments.

Use the following procedure when Legionnaires' disease may be related to the work environment:
  1. Obtain an overview of all water systems
  2. Conduct a walk-through inspection
  3. Assess the results
  4. Recommend control actions

TopStep 1: Obtain an overview of all water systems
A facilities engineer or experienced member of the building maintenance staff with a working knowledge of the system's design and current operation is needed to assist in the walk through inspection. An overview of the water systems includes plumbing systems, heating-ventilating-air-conditioning (HVAC) systems, and other water reservoirs.

A review of the plumbing system includes:
Fig. 1: Investigate storage tanks as part of the plumbing system review
Fig. 1: Investigate storage tanks as part of the plumbing system review
  • Hot and cold domestic water systems
  • Water heaters
  • Distribution pipes
  • Water coolers
  • Water treatment equipment
  • Connections to process water systems
  • Storage tanks
The HVAC system review includes:
  • Cooling towers
  • Evaporative condensers
  • Fluid coolers
  • Humidifiers
  • Direct and indirect evaporative air-cooling equipment
  • Air washers for filtration
  • Note the location of the fresh-air intakes of the building's air-handling units relative to water sources such as the cooling towers
Investigate other potential sources of employee exposure including:
  • Decorative fountains
  • Whirlpools and spas
  • Plant misters and grocery produce misters
  • Humidifiers
  • Water for cooling industrial processes
  • Tepid-water
  • Eye-washes and safety showers
Review maintenance records on water systems including water heaters and cooling towers.
  • Review records of temperature checks of domestic water supplies, visual and physical inspections of cooling towers, and reports of cooling-tower water-quality assessment and chemical treatment.
Identify the locations where other problems may exist:
  • Inspect locations of the system where water is allowed to stagnate such as storage tanks, unused plumbing pipe sections ("dead legs"), or infrequently used faucets.

  • Check for cross-connections between domestic and process water systems, and note the condition and type of back-flow prevention devices in use.

  • Investigate recent major maintenance or changes in the system's operation.

  • Determine if there were recent or frequent losses of water pressure from the incoming water supply due to line breakage or street repairs. The failure of a back-flow prevention device under loss of pressure can contaminate the system.


TopStep 2: Conduct a walk-through inspection
Fig. 2: Thermometer on a storage tank
Fig. 2: Thermometer on a storage tank
Equipment List for walk-through inspections:
  • Respirator

  • Thermometer for measuring water temperatures

  • Flashlight

  • Film or video camera to record observations
General conditions:
  • If an operating cooling tower is suspected of being contaminated, turn it off before entering and wear appropriate respiratory protection in the form of a half-face respirator equipped with a HEPA or similar type of filter capable of effectively collecting one-micrometer particles during the examination of the system. For more information on outbreak response, see Section IV: Control Actions.

    • Record the general condition of the cooling tower.

    • Determine the presence and condition of drift eliminators, which are designed to limit the vapor release from the units, along with the basin temperature of the water in the cooling tower if it is currently being operated.
  • Record the location of the tower relative to outdoor-air intakes, kitchen exhausts, plant material, or other sources of organic material that might contribute to the growth of LDB.

  • Note the location and evaluate the condition of the sumps for the cooling towers, evaporative condensers, and fluid coolers. These sumps are sometimes located indoors to protect them from freezing.

  • The lack of a regular maintenance schedule or water-treatment program for a cooling tower or evaporative condenser system suggests a potential for LDB contamination.
Water Temperature:
  • Measure and record the temperature of water drawn from each storage-type water heater in the facility. This temperature may be significantly below the water heater's gauge temperature because of heat stratification.

  • Record the maximum temperature of water at faucets connected to each water heater in the system.

    • Record temperatures at locations near, intermediate, and distant from the heaters.

    • It may be necessary to run the water for several minutes before it reaches a maximum temperature.
  • Examine the water temperature and the potential for stagnation of cold-water storage tanks used for reserve capacity or to maintain hydrostatic pressure.

    • Storage tanks should be protected from temperature extremes and covered to prevent contamination.

    • Record the temperature of the domestic cold-water lines at various locations throughout the facility.

    • Note both the initial temperature and the final equilibrium temperature on the cold-water line and record the time required to reach equilibrium; this can be an indicator of the amount of stagnation in the system.
Bio-film and Scale Buildup:
  • Evaluate cooling towers, evaporative condensers, and fluid coolers for bio-film growth, scale buildup, and turbidity.

  • Note the presence of rust and scale in the water, which may indicate infrequent use, corrosion, or bio-film formation.
Cross Contamination:
  • Record the locations of any cross-connections between the cooling tower water system and any domestic water system. These may supply a back-up source of cool water to refrigeration condenser units or serve to supply auxiliary cooling units.


TopStep 3: Assess the results
Fig. 3: Determine a course of action based on investigation findings
Fig. 3: Determine a course of action based on investigation findings
Use the walkthrough inspection to determine a course of action.
  • Recommend corrective actions if the system is poorly maintained and operating temperatures for water heaters are below the recommended minimum or cold-water systems are above the recommended maximums.

  • No further action is necessary if:

    • Operating temperatures measured at water heaters are 140°F (60°C) or above.

    • The delivery temperature at distant faucets is 122°F (50°C) or higher.

    • Cold-water temperature is below 20C (68F).


TopStep 4: Recommend control actions
Water Sampling: For a level one investigation, the absence of proper operating conditions alone is sufficient evidence that LDB may be present in the system, that the water system poses an unnecessary risk to employees, and that corrective measures are needed.
  • The employer may want to obtain samples before beginning these control actions to assess the extent of the problem.

  • The employer should take necessary control actions even if the results of pre-treatment tests are negative.

    • Water sampling can produce false-negative results, a contaminated portion of the system may have been missed, and the absence of LDB organisms at the time of sampling does not ensure that the system will remain negative.
  • If the employer sampled before undertaking corrective measures, water samples also should be collected after the completion of the control actions to determine if the corrective measures were successful.
Control actions may include:
  • Disinfection of the domestic water system via heat treatment.

    • Control actions limited to raising the water heater temperature without evaluating the system for points of stagnation, heat loss and gain, cross-contamination, and other factors that contribute to growth are generally not sufficient. 
  • Biocide treatment such as chlorine.

  • A process for cleaning heat rejection systems that follows sound practices to minimize potential for LDB growth.

  • If, after control actions, the LDB levels in a water source exceed the suggested recommendations in Section II:E. Water Sampling Guidelines, re-examine the water system to determine if potential contamination points within the system were overlooked and reassess control procedures to determine if they were performed properly.

    • Repeat the procedures as needed until contamination levels meet the guidelines.
Additional actions may include:
  • Eliminate dead legs in the plumbing system.

  • Insulate plumbing lines and install heat tracing to maintain proper temperatures in the system.

  • Eliminate rubber gaskets.

  • Remove or frequently clean fixtures such as aerators and shower heads.
Additional information (App II:A-1) on biocides is also available.
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