Legionella bacteria are naturally present at very low levels in most surface waters, including streams, rivers, ponds, and lakes. Warm, stagnant water provides ideal conditions for growth. The organisms can multiply at temperatures between 20°C and 50°C (68–122°F); they thrive at temperatures of 32–40°C (90–105°F). Rust, scale, contaminants that serve as nutrients, and the presence of other microorganisms can also promote the growth of the bacteria. So it is not surprising that many cases of Legionnaire’s disease can be traced to cooling towers.
Three conditions must exist for a Legionnaire’s disease infection, or legionellosis, to occur: the presence of Legionella bacteria, the creation of contaminated aerosols, and the presence of people vulnerable to infection in the airspace that contains these contaminated aerosols.
In June 2015, after nearly a decade of effort, ASHRAE released “ANSI/ASHRAE Standard 188-2015, Legionellosis: Risk Management for Building Water Systems” (1) to provide guidance to owners and managers of human-occupied buildings and professionals involved in the design, construction, installation, commissioning, operation, maintenance, and service of centralized building water systems and components. The standard’s risk-management approach is a sound methodology, similar to the process safety management (PSM) framework.
Compliance with this standard is voluntary unless local or state authorities incorporate the standard into building codes or other legislation, such as the state legislation enacted following the outbreak of Legionnaire’s disease in the Bronx, NY, in the summer of 2015.
ASHRAE’s press release (2) explicitly defines the scope of the standard as water systems and cooling towers associated with buildings. However, the standard does not specifically exclude cooling towers used in industrial processes. (The New York legislation requires owners of all cooling towers to register and comply with the standard’s requirements, because both industrial and comfort cooling towers have been implicated in past outbreaks.)
The Cooling Technology Institute (CTI) has published a guideline (3) that defines best practices for operating and monitoring cooling towers to minimize the risk of Legionella. However, CTI has terminated its efforts to create a standard to control the risk of Legionella specifically for owners of industrial cooling...
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