The American Legion held a convention where 221 became ill and 34 died. The culprit: bacteria inside the cooling tower that was spread by the air-conditioning system.
As both a HVAC professional and a member of The American Legion, I find Legionnaires’ disease to be one of the most troubling problems facing our industry. For those too young to remember, in July 1976, The American Legion held a convention in Philadelphia, where 221 people became ill and 34 died from a severe form of pneumonia caused by a previously unidentified strain of bacteria, subsequently named Legionella, that had been breeding inside the hotel’s cooling tower and was spread by the building’s air-conditioning system.
Because many of the veterans attending the convention were older adults who smoked, it is not surprising they were affected so significantly, as those with weakened or compromised immune systems are most susceptible to infection. The good news is that antibiotics are relatively effective if treatment is started early and the disease is not spread by direct contact. Most cases occur when water mist contaminated with Legionnaires' disease bacteria (LDB) is inhaled. Hot-water heaters, cooling towers, and other aquatic systems (e.g., hot tubs and whirlpool spas, showers, water features, ice machines, and the water misters used in grocery-store produce sections) account for most of the reported infections. Respiratory-care devices, such as humidifiers and nebulizers, also can pose a threat unless used with sterile water.
As one would expect, our industry—particularly ASHRAE—has taken the initiative (in collaboration with health-care/public-health professionals, of course) in finding solutions. Foremost in that effort has been the development of proposed ANSI/ASHRAE Standard 188P, Prevention of Legionellosis Associated With Building Water Systems. When the standard finally is issued and adopted, the promulgated practices are expected to require buildings to identify the risk of LDB exposure to occupants and visitors and, in some cases, to establish a water-management team to address those risks.
Although Standard 188P probably will not define the specific building water processes to be implemented, it undoubtedly will identify areas of possible contamination and the best practices for addressing them. For example, there has been much discussion about domestic-hot-water (DHW) systems that operate, store, and deliver water at temperatures too low to kill LDB. Most systems, if they’re not already, probably will be adjusted to store and distribute water at 140 F and provide it at the point of use at not less than 122 F. Procedures to eliminate dead legs and for high-temperature flushing also will be recommended. Originally, the proposed “super heat and flush” procedure required a supply temperature of 160 F to 170 F for a minimum of 30 min to effectively kill LDB. However, those temperatures could cause scalding injuries and damage piping components, such as gaskets and valves. Also, there are possible conflicts with other codes and standards. Here in Florida, for instance, hospitals are licensed by the Agency for Health Care Administration, which requires DHW in hospitals to not exceed 120 F.
There are alternatives to high temperature for controlling LDB. One of the more promising appears to be the use of in-situ ozone in place of chemical biocides. Advantages include fewer hazardous byproducts and, because of its short half-life, no residual presence. It has been used successfully in Europe for several years, and the U.S. Food and Drug Administrationrecognizes its antimicrobial properties in food processing. A new terminal at London’s Heathrow Airport will be using this process for its cooling-tower water treatment; it is expected to control Legionella while reducing both water consumption and the risks associated with transporting, storing, and handling oxidizing biocides. The process is commercially available in the United States. Let’s hope it meets our expectations.