Commercial Water: Minimizing Risk

Oct. 29, 2015
New ASHRAE standard addresses legionellosis risk management for building water systems

About the author: Paul Lindahl is director – market development for SPX Thermal Equipment & Services, and vice chair for ASHRAE SSPC188. Lindahl can be reached at [email protected]. W.E. (Bill) Pearson II, CWT, is vice president, consulting and technical services for Southeastern Laboratories Inc. and member of ASHRAE SSPC188. Pearson can be reached at [email protected].


ASHRAE published the new ANSI/ASHRAE Standard 188-2015, Legionellosis Risk Management for Building Water Systems in June 2015. This long-awaited document establishes minimum legionellosis risk management requirements for building water systems.

The term “legionellosis” refers to any illness contracted from exposure to Legionella bacteria. There are two predominant legionellosis illnesses. The more severe form, called Legionnaires’ disease, results in pneumonia. The Centers for Disease Control and Prevention estimate that 8,000 to 18,000 cases of Legionnaires’ disease occur per year in the U.S., with more than 10% of those cases becoming fatal. A less severe form of legionellosis illness, known as Pontiac Fever, results in flu-like symptoms. It is important that requirements are put in place to manage the risk of exposure to these bacteria from building water systems, from which a significant percentage of reported exposures occur. 

The risk of disease or illness from exposure to Legionella bacteria is not as simple as the microbe just being present in a building water system. Other factors that contribute to the risk are environmental conditions that promote the growth and amplification of the bacteria, a means of transmitting the bacteria to people in the building (particularly by aerosolizing water containing the bacteria), and exposure of susceptible people to colonized water that is inhaled or aspirated into the lungs. The bacteria are not transmitted person to person, or through normal ingestion of water. People at high risk for legionellosis include, among others, the elderly, dialysis patients, smokers and those with compromised immune systems.  

A New Standard

Standard 188 is intended for use by owners and managers of human-occupied buildings and those involved in the design, construction, installation, commissioning, operation, maintenance and service of centralized building water systems and components.

The standard specifies minimum legionellosis risk management requirements for human-occupied buildings excluding residential buildings, and their associated potable and non-potable water systems. Specific compliance pathways are defined in the standard for building designers, building owners and healthcare facilities.

The compliance pathways direct each user group to a building survey (and recommend frequency of repeated surveys with a minimum annual survey), and to appropriate general and building water system-specific requirements. The building survey evaluates the presence of certain potential aerosol generators in a water system, and certain risk factors that relate to legionellosis. The results of the survey determine the compliance pathway that must be followed for that group, for that particular building and for each particular building water system.

Water Management Programs

The standard includes requirements for building owners to establish a program team of one or more individuals and, in turn, the development of a water management program for which it is responsible. This program must meet specific, detailed requirements for what legionellosis control strategies must accomplish and how they must be documented, but not which specific strategies must be used or applied.  

Reference should be made to the standard for specifics, but note that buildings meeting certain risk criteria or characteristics related to legionellosis are required to develop a plan that includes potable water systems in addition to any of the listed potential aerosol-generating water systems present. If none of the building risk factors are present, then the plan must include only the potential aerosol generators found to be present.

In addition to the general requirements for development of the water management program, specific preventive measure requirements for the following building water systems are required as indicated above for:
• Potable water systems (when risk factors are found in the survey). Requirements include system startup and shutdown, system maintenance, water treatment and contingency response plans.
• Open- and closed-circuit cooling towers and evaporative condensers. Requirements include equipment siting, new system startup, system maintenance, water treatment, shutdown and startup, disinfection, location of makeup valves, and contingency response plans.
• Whirlpool spas. Requirements include bather-related requirements, filter operation and maintenance, water quality, disinfection, monitoring, microbiology, microbiological testing when contamination is discovered, contingency response plan, and operating manuals.
• Ornamental fountains and other water features. Requirements include equipment siting, operation, maintenance, water treatment and contingency response plans.
• Aerosol-generating misters, atomizers, air washers and humidifiers. Requirements include equipment siting, new system startup, system maintenance, water treatment, system shutdown and startup, disinfection and contingency response plans.

Requirements are included for designing building water systems for new construction, renovations, refurbishment, replacement or repurposing of a facility. These requirements include details on general requirements, final installation documents, balancing and commissioning.

Healthcare Facilities & More

A normative annex with requirements for healthcare facilities is a part of the standard. This includes requirements for healthcare facilities that meet certain criteria as to facility accreditation and staff who are certified as infection preventionists or with a minimum graduate degree in epidemiology. The annex is written using terminology consistent with that used in the healthcare industry for risk management programs. The intent of the annex is to be minimally equal to the requirements in the base (standard) document. Healthcare facilities that do not meet the criteria to use the annex must follow the base document. 

Standard 188 consists of normative sections followed by normative and informative annexes. The normative sections and normative annex specify the requirements for compliance to the standard. Building water systems can vary significantly in design, and in the potential for the risk and associated transmission of Legionella, as well as the presence of susceptible individuals. 

Scientific evidence is not available or is inconclusive regarding some aspects of Legionella control. The informative annexes and informative references provide suggestions, recommendations and references for guidance to develop water management plans for specific buildings. Of particular note is the existing ASHRAE Legionellosis Guideline 12-2000, which is currently being updated.

Standard 188 is published and has been placed in continuous maintenance status by ASHRAE.

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