Legionnaires Disease Expert Article

In this article, mechanical engineer Rene Basulto discusses the 2015 outbreak of Legionnaires' Disease in New York City, the suspected role that mechanical building systems play in the outbreak of the disease, and the changing standards that are designed to control the growth of the Legionella bacteria.

Legionnaires’ Outbreak - Death Count Increases to 12

August 18, 2015 Death count increases to 12, with 124 confirmed cases of Legionellosis in New York City’s South Bronx. The situation has local and state officials investigating alongside the CDC, and they have narrowed down the source to the usual suspect, cooling towers. Testing of cooling towers in the area revealed 20 contaminated with the Legionella bacteria, with 14 inside the “affected area”. Evaporative heat rejection equipment, such as cooling towers, have been implicated in numerous outbreaks of Legionnaires’ disease, and studies have shown that detectable levels of Legionella are present in many, if not most, such devices. Therefore, it is not surprising that so many cooling towers in the area have tested positive. The number of cooling towers found with the bacteria prompted the New York City Health Commissioner late last week to issue an order that requires cooling tower registration as well as adherence to ASHRAE’s newly published Legionella standard 188 and Cooling Technology Institute Guidelines WTB-148. For many years, the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) has provided guidance on preventing legionellosis associated with building water systems. ASHRAE is an industry organization that develops and publishes handbooks, guidelines, and standards for heating, ventilating, and air conditioning system design. Members, who are practicing engineers, in a consensus-based process, develop handbooks, guidelines and standards. In addition to ASHRAE, The World Health Organization (WHO), and Cooling Technology Institute (CTI), among others have also provided guidelines and best practices for control of Legionella throughout the years.

Ashrae Standard 188

The standard, ASHRAE Standard 188 - Legionellosis: Risk Management for Building Water Systems, provides minimum Legionellosis risk managements for the design, construction, commissioning, operation, maintenance, repair, replacement and expansion of new and existing buildings and their associated water systems and components. ASHRAE published it in June of 2015. It is fortunate that the city council has incorporated the new standard, perhaps recognizing that just inspections of cooling towers, which can harbor the Legionella bacteria, will not do much to prevent outbreaks unless proper maintenance and treatment programs are set in place by building owners as outlined in the newly released standard. The ASHRAE 188 establishes the standard of care for building owners for minimum Legionellosis risk management requirements for building water systems. The guidelines and best practices available from ASHRAE, WHO, CTI and others are a value resource for designers, owners and building managers to assist in implementing a water management program. The new standard actually references ASHRAE Guideline 12 - Minimizing the Risk of Legionellosis Associated with Building Water Systems, in essence making it part of the standard. Testing alone is not a substitute for sound maintenance practices and water treatment. Presence of the organism cannot be directly equated to the risk of infection. The bacterium is frequently present in water systems without being associated with known cases of disease. Design, location and maintenance of equipment are crucial components of a proper and effective water management program. The standard requires the establishment by building owners of a program team and water management program in order to comply with the standard.

What Is the Exact Source?

The question still remains as to where the exact source is, and why are we experiencing such an increase in Legionnaires’. Legionella bacteria are commonly present in natural and man-made aquatic environments. The organism is occasionally found in other sources, such as mud from streams and potting soils; however, the overall importance of non-aquatic environmental sources in human disease is not yet known. In natural water sources and municipal water systems, Legionella are generally present in very low or undetectable concentrations. However, under certain circumstances within man-made water systems, the concentration of organisms may increase markedly, a process termed “amplification.” According to ASHRAE, conditions that are favorable for the amplification of Legionella growth include water temperatures of 25-42°C (77-108°F), stagnation, scale and sediment, biofilms, and the presence of amoebae. A cooling tower is an evaporative heat transfer device in which atmospheric air cools warm water, with direct contact between the water and the air, by evaporating part of the water. The typical temperature of the water in cooling towers ranges from 29°C (85°F) to 35°C (95°F) although temperatures can be above 49°C (120°F) depending on system heat load, ambient temperature, and system operating strategy. During summer months it is very common to have ambient conditions that will result in higher cooling tower temperatures. When analyzing the cooling tower temperatures, one easily notices that conditions are ideal for the amplification of Legionella growth. Perhaps this is the reason why we have seen such a pronounced increase this summer. More importantly this should highlight the importance of having a water management program as required by the new standard. A properly executed program will ensure that the tower is properly maintained and treated with biocides to prevent the growth of the bacteria.

Requirements in the Standard

The standard requires facilities to implement a water management program that includes a written document with certain components and Legionella control measures. More specifically, a water management program will be required if a building or site has any cooling towers, evaporative condensers, hot tubs, ornamental fountains, misters, atomizers, air washers, humidifiers, or any devices that release water droplets into the air. It is important to note that ASHRAE 188 is a national standard, and is THE standard of care to be followed by building owners. Local legislation is not required for it to be used as the standard of care to measure owner’s responsibility. The standard establishes a base line for the minimum requirements for building owners, changing the landscape for litigation of Legionnaires’ disease cases. However, it is also equally important to note that even if a building management/owner is lacking the written plan in strict accordance with the standard, it may very well be in compliance with the intent of the standard if the equipment has been properly designed, located and maintained, with an effective water treatment regimen.

Investigating Legionnaires’ Outbreaks

An expert with thorough knowledge of the standards, who is experienced with facility design and management will be crucial to fully understanding causation as it relates to incidents of Legionnaires’ disease. Robson Forensic offers highly qualified mechanical engineers, specializing in building systems, who can assist in this capacity. Please contact the author of this article or your local Robson Forensic office to discuss your case and which of our experts is best qualified to assist.

Featured Expert

Rene Basulto, Mechanical Engineer & Building Systems Expert

Rene Basulto, P.E., MSEM, CGC, C.F.E.I.

Mechanical Engineer & Building Systems Expert
Rene is a mechanical engineer with 40 years of experience in the design, construction and maintenance of building systems, including HVAC, plumbing, industrial systems, and fire protection systems. He… read more.


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