ANSI/ASHRAE 188-2018: Minimizing the Risk Associated with Legionella

In June of 2015 the ASHRAE Standards Committee developed Standard 188-2015, Legionellosis: Risk Management for Building Water Systems. The most recent updated document (188-2018) outlines the minimum requirements for the development, implementation and ongoing maintenance of a Legionella risk management program in new and existing buildings. The Standard is a culmination of several years of work by experts in the fields of engineering, biology and environmental health. The current version of Standard 188-2018 can be obtained from the ASHRAE website.

Scope of Standard
The standard applies to human occupied buildings excluding single family residential buildings. This standard is also intended for those involved in design, construction, installation, commissioning, operation, maintenance and service of centralized building water systems and components.

Water systems included:

  • Cooling towers or evaporative condensers
  • Ornamental fountains
  • Whirlpool spas
  • Misters, air washer, humidifiers
  • Devices that release water droplets

Buildings included:

  • Buildings that have more than 10 stories
  • Multiple housing units with a centralized hot water system
  • Housing for occupants over the age of 65
  • Patients staying over 24 hours
  • Patients that have a compromised immune system

General Requirements

The requirements of the standard involve both building designers and building owners.

  1. Development of a risk mitigation program: Program Team – identify responsible individual(s) involved in development and execution of the Legionella risk mitigation program.
  2. Flow Diagrams: Building designers and owners must develop simplified water system schematics that identify potable and non-potable water systems for the building(s) involved in the program.
  3. Building Survey: Identify potential hazardous conditions involving aerosolized water contact with building occupants.
  4. Control Measures: Identify locations that require control measures and control limits.
  5. Monitoring and/or Corrective actions: Establish control procedures for established limits. For any out of control limit – establish corrective actions.
  6. Confirmation: Procedures must be in place for – Verification – is the program being applied as designed? Validation – the program effectively controls building hazards as identified in the building survey.
  7. Documentation: Document and communicate procedures for all Program activities.

It is important to note that this standard provides a framework and guidance only; the specifics of the program are unique to each building and the different types of exposure hazards that exist. The standard does however call out specifics for documentation, responsible persons and the different types of water systems that should be included in the program.

Complying with the Standard

Building Owners

  • Develop a team of responsible individuals with knowledge of the building water use and design. Healthcare facilities would also want to involve the infection control department. Water treatment professionals may also be included along with equipment manufacturers. The ownership of the program however belongs to the building owner.
  • Draw out and detail a water system flow schematic. This schematic does not need to be blueprint quality but should identify stagnation points (deadlegs), aerosolizing areas, water treatment equipment, etc. There should be two separate schematics – potable and non-potable.
  • Develop operating procedures. This will include hazard control limits and control measures. This is one of the most important aspects of this standard and should be detailed carefully. These control measures and the response to out of control limits will define the success or failure of the program.
    • Examples of control limits: monitoring free chlorine in hot and cold water, logging hot water temperatures or establishing biocide use in a cooling tower.
    • Examples of control measures: using supplemental chlorine feed, flushing hot water tanks to prevent temperature stratification or increasing biocide use for cooling towers in the summer months.
  • Monitor and document all the critical points of the risk minimization plan. This should include corrective actions taken when measured values are outside of the control limits.
  • Verify and validate the program is working as designed. The program effectiveness must be validated, testing for Legionella is the most direct method for validation; Standard 188-2018 discusses this as an option but it is not required. Many building owners/managers conduct Legionella sampling as part of their program.
  • The building owner must conduct and document compliance determination at least once per year and any time renovations, additions or modifications are made to the building.

Building Designers

  • When new construction or renovation is being considered, design engineers and contractors have a responsibility to the building owner. They must provide documentation, schematics and instructions on monitoring and control systems, calibration procedures and startup commissioning. Instruction on water system filling, disinfection, draining, design flow rates, volume capacities, design temperatures and balancing.
  • Contractors involved in disinfection of water systems must do so within three weeks of building occupancy.
Healthcare facilities
Healthcare facilities may have additional requirements which can be found in the Normative Annex A of the standard. The Annex requires that a senior member of the management with authority to make decisions regarding water restrictions be on the designated team. Additionally, a member of the facilities management staff along with a Board Certified infection preventionist must be on the team.

Healthcare facilities have a higher level of risk to Legionella infections due to patients that may have compromised immunity.

Legionella bacteria are ubiquitous; it is estimated that close to 70% of plumbing systems harbor some level of the bacteria. Each year over 8,000 cases of legionellosis are diagnosed in the United States; it is estimated that 10 percent of those cases are fatal. The standard represents best available technology for keeping building occupants safe from Legionella exposure and if 188-2018 is widely applied, the number of illnesses will be dramatically reduced.

With publication of the standard, all building owners that meet the requirements will have a guidance document that will help reduce the risk and potential liability involved with Legionella . Health departments will also have a resource for Legionella risk management and this could be an aid when involved in an outbreak condition.

The standard has also been proposed for code adoption with the International Plumbing Code and the International Mechanical Code. If this acceptance by these agencies occurs, the standard could become law, which will have far reaching implications.

Legionella control strategies and risk minimization may seem to be an overwhelming task, particularly for large buildings and centralized complex water systems. ASHRAE 188-2018 is designed to make this program manageable and there are many competent professionals that can assist with working through the details of a program.

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