Legionnaire's Disease (Legionellosis) and Evaporative Cooling System Maintenance Recommendations

What is Legionnaire's Disease

It is a bacterial infection that is characterized by pneumonia. According to the Center for Disease Control (CDC), legionnaire's disease is caused by bacteria known as Legionella pneumophila. There are at least 43 species of legionella however, it is the Legionella pneumophila strain that causes over 90% of legionnaire disease deaths.

In the United States, it is estimated that as many as 18,000 cases occur each year. Death results in 5 - 15% of the cases.

Legionella are commonly found in low concentrations in both natural and unnatural (man-made) aquatic environments. Within unnatural environments, where water is used in an evaporative heat exchange process, warm temperatures combined with poorly treated cooling water can create an environment ideal for proliferation of this deadly bacteria.

Because cooling towers, evaporative condensers and chillers are highly efficient at drawing large volumes of air to support the evaporative cooling process, airborne organic material such as leaves, insects, pollen, birds, cotton wood and other debris is usually drawn into the water system and if not maintained can accumulate, decompose and contribute to system fouling and microbial growth including legionella pneumophila.

Ideal conditions for legionella proliferation include water temperatures between 77 - 108 degrees Fahrenheit (25 - 42 degrees Centigrade), presence of organic debris, sediment, scale, stagnant conditions and presence of amoebae. Legionella naturally preys on amoebae and incidentally prey on phagocytic cells (part of human immune system) when inhaled thus leading to Legionnaire's Disease. The legionella bacteria is transmitted by aerosol (mist) from devices such as cooling towers showers and faucets and aspiration of contaminated water. Person-to-Person transmission does not occur.

Controlling Legionella in Cooling Towers & Evaporative Cooling Systems.

Based upon a six-year committee effort, ASHRAE board of directors approved guidelines (known as guideline 12) that provides environmental and operational guidelines for maintaining safe evaporative water cooling systems. The guidelines are intended for use by: commercial cooling system designers, maintenance engineers, equipment manufactures, owners, operators and users.

Key Maintenance Recommendations (Guideline 12)

• Keep system clean using a microbial treatment program.
• Use a qualified water treatment consultant to establish and oversee a water treatment program.
• Keep system free of debris that can contribute to the food source for legionella. (Air Intake Filters can help to control debris and organic material build-up).
• Inspect and clean cooling equipment if it is found to have a build-up of dirt, organic matter or other debris.
• Inspect drift eliminators and clean or replace as needed.
• Keep maintenance and operational records that include equipment manufacturers maintenance manuals, description and dates of the water treatment program, inspection dates, MSDS documentation on all treatment chemicals, equipment repair records including dates, system water volume records, and the names and phone numbers of individuals responsible for system start-up, maintenance and shut-down.

Cooling Tower Locations Recommendations (Guideline 12)

• Locate cooling towers far from fresh air intakes and windows that can be opened.
• Consider prevailing wind direction and don't locate upwind or upstream of outdoor public areas.
• Don't locate in areas that can contribute debris and organic material.
• Consider the direction of prevailing winds and don't locate upstreamof any outdoor public areas.
• Consider future construction, including that on nearby sites.