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

• 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.