Cooling Towers, Legionella, and Legionnaires Disease
OSHA notes that water sources that frequently provide optimal conditions for growth of the organisms such as Legionella include cooling towers, evaporative condensers, and fluid coolers that use evaporation to reject heat. These include many industrial processes that use water to remove excess heat.
A cooling tower is designed to remove heat from a building or facility by spraying water down through the tower to exchange heat into the inside of the building. Air comes in from the sides of the tower and passes through the falling water. As the air passes through the water, heat is exchanged and some of the water evaporates. This heat and evaporated water flow out the top of the tower in the form of a fine cloud-like mist. The cooled water is collected at the bottom of the tower and pumped back into the plant or building for reuse. Cooling towers provide large scale air-conditioning where land and (or) water are expensive, or regulations prohibit the return of once-through cooling waters
As useful as they are, cooling towers can cause outbreaks of Legionnaires’ Disease when they are not adequately maintained to prevent or control Legionella.
In a Legionella or Legionnaires’ Disease outbreak scenario, identifying cooling towers quickly and accurately is essential to limiting the number of people exposed, according to the CDC.
However, searching for cooling towers during an outbreak can be difficult due to
- Building density
- Poor visibility
- Issues with accessibility
That is one more reason reason that it is important to have a Legionella control water management plan in place, as can include the identification of cooling towers.
Once identified, the NY Department of Health recommends the following:
(1) A schedule for routine bacteriological culture sampling and analysis to assess microbiological activity at intervals should not exceed 30 days while the cooling tower is in use, and that requires additional bacteriological culture sampling and analysis, as needed, to validate process adjustments;
(2) a schedule for routine Legionella culture sampling and analysis within 14 days of seasonal start-up and, thereafter, at intervals not to exceed 90 days while the cooling tower is in use. Cooling towers in use year-round must sample at intervals not to exceed 90 days, and within two weeks after start-up following maintenance;
(3) in addition to the routine Legionella culture sampling and analysis required by paragraph (2) of this subdivision, conditions that require immediate Legionella culture sampling and analysis, which shall include, but are not limited to:
(i) power failure of sufficient duration to allow for the growth of bacteria;
(ii) loss of biocide treatment of sufficient duration to allow for the growth of bacteria;
(iii) failure of conductivity control, or any other control methods, to maintain proper cycles of concentration;
(iv) a determination by the department or local health department that one or more cases of legionellosis is or may be associated with the cooling tower, based upon epidemiologic data or laboratory testing; and
(v) any other conditions specified by the department or local health department.
If you do not have a Legionella control water management plan or program – or have not updated yours recently to include recent construction or all of your cooling towers – it is important that you contact Legionella Control Systems right away. A non-existent or outdated water management plan puts your facility at risk for both health issues and legal liability.
