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  • Feature Story

Cooling Towers: Preventing Legionnaires Disease and Mitigating Risk in Buildings

July 16, 2018

By: Gregory J. Smith ULLC Program Manager / UL Field Engineering

When was the last time you walked through a manufacturing location, hotel, by a public fountain, or visited a health care facility? Have you ever considered what helps to assure you, and others, are safe from water or airborne diseases that can cause serious illness or even death?

Since 2000, the number of cases of Legionnaires’ disease has increased 400 %![i]  More troubling is the fact that 10 % of those contracting Legionnaires’ will die from it. That number elevates to more than 25 % with individuals in health care facilities.[ii]

Many examples exist to illustrate the impact that a Legionnaires’ outbreak can have on a company. Consider that in the Summer of 2015, a Legionnaires’ disease outbreak in South Bronx was attributed to Legionella-contaminated cooling towers. One hundred and thirty-eight cases were confirmed, resulting in 16 deaths.[iii] Additionally, fifteen cases of Legionnaires’ disease were identified in Flushing, NY (New York City area) in October of that year. NYC Health investigators tested several cooling towers and ordered disinfection of the ones in which Legionella was found.[iv]

One of the unfortunate situations with these outbreaks is that many individuals may not be reporting occurrences, or they are not being correctly diagnosed. Thus, the actual number is more than likely higher. As a result of the Legionella outbreak of 2015 in New York, both New York City and the State issued Rules and Regulations requiring owners of buildings with cooling towers to manage the risk of Legionella outbreaks.

In June 2015, the American Society of Heating, Refrigeration and Air Conditioning Engineers  (ASHRAE) published ANSI/ASHRAE 188-2015, Legionellosis Risk Management for Building Water Systems. ASHRAE- 188 established a new Standard-of-Care as the first industry-consensus standard for managing building water systems to prevent Legionnaires’ disease.

Both NYC and NYS have also created requirements for the maintenance of cooling towers. All of these require that a Maintenance Program and Plan (MPP) is developed, implemented, and documented. As a result of these new reqiurements, UL recently developed a comprehensive, practical, and efficient way to assure cooling towers are safe.

The unfortunate truth is that the laws regulating cooling towers overlap and can be confusing, time consuming, and complicated. Not meeting these requirements can also result in heavy fines. It is estimated that over $ 20 million dollars in fines were levied against building owners from 2016 to 2017. UL’s new program eliminates the need for building owners or property managers to navigate through these requirements.

So how does Legionnaires’ disease actually manifest itself?

Legionella & Legionnaires’ disease:

  • Legionella is the bacterium that causes Legionnaires' disease. Under certain circumstances, it can flourish in the water within cooling tower systems that are used for building air conditioning and other systems.
  • This disease results from inhaling bacteria in microscopic water droplets released from cooling towers.
  • Smokers, the geriatric population and cancer patients are at especially high risk. Legionella infection can lead to respiratory failure and death.

Cooling Towers & Legionnaires’ disease:

  • Under certain cooling tower operating conditions, small numbers of Legionella from the environment can grow to very large numbers.
  • Legionnaires' disease results from inhaling Legionella-contaminated water mist (drift) released from cooling towers.

What are the benefits of UL’s Cooling Tower Program?

  • Reduces the likelihood of a Legionnaires outbreak
  • Protects the customer’s brand
  • Prevents fines (public)
  • Minimizes litigation
  • Reduces costly business interruptions

Why should building owners have a third-party audit of cooling towers?

 An effective MPP can significantly reduce the likelihood of a Legionnaires outbreak. UL’s auditing process provides a practical and efficient way of minimizing risk of liability by helping to ensure the MPP is implemented and continuously followed.

For more information, please contact: [email protected] or call 920-387-9738 and [email protected] 617-293-7510.


[1] Christian Nordquist, 17 July 2017, “Legionnaires disease: What you need to know”, Medical News Today

[1] CDC “Legionnaires Disease: A problem for Health Care Facilities” taken from

[1] CDC “Legionnaires’ Disease Outbreak Caused by Endemic Strain of Legionella pneumophila, New York, New York” taken from

[1] Recent Legionnaires Disease Outbreaks taken from