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Legionnaire’s Disease and Cooling Towers: Risk Management

Aug 19, 2015 6:00:00 AM

On August 6th, the Commissioner of the New York City department of health issued an order[1] to all commercial building owners/operators in the City requiring the adoption of a new standard, issued in June 2015 by ASHRAE[2], titled Standard 188 - Legionellosis: Risk Management for Building Water Systems. The order to adopt this standard was in response to the recent Legionellosis outbreak (also known as Legionnaire’s Disease), which has resulted in 12 deaths, sickened more than 100 people, and is believed to have originated from a rooftop cooling tower above a deli in the South Bronx[3].

Legionella pneumophila bacterium. Legionella pneumophila bacterium. Image courtesy Centers for Disease Control

Legionellosis (and its milder relative Pontiac Fever, which has influenza-like symptoms) is caused by the Legionella bacterium, which can grow in warm water found in cooling towers, hot tubs, domestic hot and cold water systems, and public fountains. When larger concentrations of these bacteria are able to grow, become aerosolized, and are inhaled by humans, a potentially life-threatening respiratory infection can result. Individuals who are either immunocompromised or have chronic lung conditions are especially vulnerable. Preventing significant microbial growth in these building systems/environments through various mitigation strategies can substantially mitigate this risk to public health.

So what is ASHRAE Standard 188?

The newly issued ASHRAE Standard 188 provides minimum requirements for Legionellosis risk management in building water systems in all phases of a building lifecycle—from design, construction, and commissioning phases through day-to-day maintenance, operation, and repair. Another publication, ASHRAE Guideline 12 - Minimizing the Risk of Legionellosis Associated with Building Water Systems has been in publication for many years, but this original guideline provides no set minimum requirements for preventing Legionellosis and is not written in a form readily adoptable by city/state/federal authorities. ASHRAE Standard 188 now provides these minimum requirements for facilities operations and is ready for adoption by authorities having jurisdiction (AHJs) around the country.

Cooling tower. Cooling tower.

How is this useful for my building?

Standard 188 has actionable guidance on minimum requirements for establishing a risk mitigation program for Legionellosis at a facility. This guidance includes a framework for reviewing existing facility risk, establishing a treatment and monitoring program to prevent/detect increased levels of contamination, creating an action plan for treatment of contaminant levels above the allowable limits, and establishes hazard communication protocols. The new Standard also provides a system for verifying program operation and documenting performance, which in the case of an outbreak will allow for clearer determination of whether best practices were being followed, or if negligence has led to an outbreak. The standard may help to protect operators from potential liability by first preventing an outbreak but also by establishing best practices by which to measure facility performance—though if an owner is not meeting the minimum standards this improvement in assessment metrics may also allow for a clearer finding of negligence in the event of litigation.


We now have a great resource for managing the risk of Legionellosis in facilities and protecting public health. Regardless of whether your facility is in NYC and is now required by law to adopt the new ASHRAE Standard 188, or if your state will adopt it in a few years, consider adopting it now to verify your facility’s compliance and reduce your risk of hosting an outbreak.


[1] NYC Health Order

[2] ASHRAE refers to the American Society for Heating, Refrigeration, and Air-conditioning Engineers.

[3] New York Times Article covering 2015 outbreak:

Written by Ben Fowler