Prevention of Legionellosis Associated with Building Water Systems

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has developed a draft standard addressing the issue of Legionellosis, a disease caused by infection with the bacterium Legionella pneumophila. The bacterium received this name from the infamous incident that occurred at the 1976 American Legion conference in Philadelphia, where many attendees suffered from an outbreak of a type of pneumonia – resulting in 34 deaths. Legionella pneumophila is spread by the release of small droplets of contaminated water into the air from equipment such as air conditioning cooling towers, showers, misters, and humidifiers. In the Philadelphia Legionnaires’ disease outbreak, the hotel’s cooling tower was identified as the likely source of the disease, although domestic water sources were not evaluated.

Legionnaire’s disease is considered to be fairly common and serious in the United States. It is frequently characterized as an “opportunistic” disease that most frequently attacks individuals with an underlying illness or weakened immune system. The most susceptible include persons who are elderly, smokers, or immuno-suppressed.  Although approximately 1,000 cases are reported annually to the Center for Disease Control, it is estimated that over 25,000 cases occur each year and cause more than 4,000 deaths.

ASHRAE’s Proposed New Standard 188

The goal of ASHRAE’s proposed standard – applicable to human-occupied  buildings, excluding single-family residences – is to assist those in building design and facility management in preventing the occurrence of Legionellosis associated with building water systems. The standard addresses the risk of Legionellosis through the identification/characterization of hazards, design of the potable water system, maintenance of the water system, and operational controls to be instituted to reduce this risk.

Identification/Characterization of Hazards – Determining the risk hazards at a facility is the first step to  reducing potential exposure to Legionella pneumophila. The risk identification/characterization typically includes evaluating:

  • Type of facility (healthcare facility, multiple housing units, etc.)
  • Facility occupants (immuno-compromised, etc.)
  • Aerosol-generating features (ornamental fountains, misters, evaporative coolers, etc.)
  • Existing potable water treatment systems
  •  Cooling towers and evaporative condensers

Based on the results of the initial survey, Hazard Analysis and Critical Control Point (HACCP) risk management can be used to reduce the potential of Legionellosis.

Design and Operation of the Potable Water System – The design and operation of the potable water system should be evaluated and designed to reduce the potential of Legionellosis. Areas that are critical to this design include hot water heater and storage vessel components. Potable water systems with deficiencies in these areas may require secondary disinfection systems. Operation parameters include the storage and distribution temperatures of designated cold and hot water systems.

Maintenance of the Potable Water System – The maintenance of the potable water system includes  scheduled inspections of thermostats, draining of hot water tanks, and inspection and cleaning of raised water storage systems.

OSHA’s Stand

Although this standard is not an OSHA regulation, when it is finalized it will be looked upon as a national  standard on Legionellosis exposure control methods for facility owners and operators. Chapter 7 of the OSHA Technical Manual specifically addresses controlling Legionellosis by identifying the source of potential contamination, implementing controls, and employee training. It is also important to note that the General Duty Clause of the Occupational Safety and Health Act requires that employees protect their employees and visitors from known hazards. With the introduction of a national standard addressing the source and prevention of Legionellosis, employers and facility owners are responsible to protect employees/occupants from this hazard.

Preventing Exposure…HETI Can Help

By establishing adequate barriers to transmission of Legionella bacteria, implementing sound maintenance procedures, and utilizing persistent and effective control mechanisms, users of the proposed ASHRAE standard can reduce the possibility of exposure of at-risk individuals.

Hydro-Environmental Technologies, Inc. (HETI) can assist you in assessing a facility for the risk of Legionella pneumophila exposure. Whether conducting a risk characterization survey, developing controls/measures to reduce the risk of Legionellosis, or assessing implemented controls and programs, HETI has the experience and technical expertise to assist you in reducing the risk of Legionellosis at a facility.