ASHRAE Standard 188 is modeled after HACCP — a widely used method to prevent disease from infectious organisms transmitted from food and water. The effectiveness of this approach for assessing the hazards of Legionella in building water systems is yet to be proven, but it nevertheless provides a structured course of action aimed at reducing risk for waterborne pathogens.
Responding to Legionella in your water system will require a team effort. ASHRAE recommends that the first step is to convene a risk management team consisting of a combination of employees, suppliers and consultants. Who is on the team is more important than the number of members. Nevertheless, ASHRAE requires at least one person who is familiar with HACCP principles and one person that understands the building water systems. An optimal team might consist of someone in your organization with knowledge of safety and health issues, a representative from your water treatment company, a Legionella risk management professional and a laboratory with Legionella expertise.
Once the team is established, its task is to conduct a hazard analysis of the building's potable and utility water; creating diagrams of water systems; identifying control points; determining critical control points; establishing monitoring procedures and corrective actions; verifying that Legionella is controlled; and creating documentation concerning all procedures and records appropriate to these principles. ASHRAE specifically requires that for every critical control point (i.e., where the presence of Legionella bacteria is of most concern), the team must address four issues about the hazard control method being applied:
(1) critical control limit of Legionella bacteria,
(2) hazard control monitoring method,
(3) frequency of monitoring hazard control, and
(4) corrective actions to be taken if the critical control limit is exceeded.
ASHRAE 188 requires a written comprehensive prevention plan. The HACCP documentation should include process flow diagrams, hazard analysis summaries, the monitoring schedule, equipment device maintenance schedules, validation summary, verification schedule and planned responses to disruptions in water services.
The written plan should include procedures for maintenance of each potable or utility water device identified in the process flow diagrams; cleaning and disinfection before commissioning any new system; restarting safely after a drained shutdown or any unplanned loss of energy; treatments following water supply interruption or breaks in water supply piping; and the method and frequency of temperature measurements in the water heaters and in the distribution system.
In addition, facility managers must identify conditions that could allow cooling tower exhaust (drift) to infiltrate buildings and develop water treatment procedures to control Legionella in cooling towers and evaporative condensers. Other aerosol-generating equipment (decorative fountains, misters, air coolers, humidifiers, and air washers) that disperse small water droplets into the air also require procedures to guard against the amplification and dissemination of Legionella bacteria.
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