What is Legionellosis?
Legionellosis refers to two distinct clinical illnesses. There are over 50 species of Legionella, a common aquatic bacterium. When the bacterium Legionella causes pneumonia, the disease is referred to as “Legionnaires” disease (LD). The Centers for Disease Control and Prevention (CDC) estimates that each year there are between 8,000 and 18,000 cases of LD in the United States and more than 10% of these cases are fatal. The Legionella bacterium can be found in natural or man-made water systems, including hot tubs, cooling towers, hot water tanks, and plumbing systems. Legionella prevention is a hot topic right now and will be on the radar of HVAC and plumbing professionals.
Some Measures to Avoid Legionella:
Two main environmental factors will favorably impact the growth of Legionella in a domestic hot water system; Low water temperature and Water stagnation. Measure to avoid:
- Maintain water temperature at 140°F (the bacterium can survive in a temperature range from 68-122°F and grow in range of 77-108°F)
- Avoid “Dead Legs” in pipe design (to avoid any areas of stagnation in piping)
- Use Re-circulation Pumps continuously (to minimize scale and stagnation)
- Make sure backflow preventers are functioning properly
- Perform routine maintenance measures
The most obvious way to avoid this situation is to maintain the system at a higher temperature and recirculate the water continuously. A high/low flow mixing valve should be used in storage systems so the tank can be kept at 140°F to prohibit Legionella growth while providing 110°F water to the fixtures. ASHRAE Standard 188 discusses the risk management requirements. Presumably, system designers will be able to refer to this standard of practice to determine if their building water system design and engineering practices should be reviewed or revised.
The purpose of standard 188 is to establish minimum Legionellosis risk management requirements for the design, construction, commissioning, operation, maintenance, repair, replacement, and expansion of new and existing buildings. Standard 188 aims to reduce the risk of Legionellosis through specific measures that identify and subsequently address the risk of Legionella. It specifies certain practices that are responsibility of the owner to initiate and follow through with in order to reduce their own risks. Requirements that are provided to the building owner or designee are included in Section 8 of the standard:
- Drawing and documents of the actual installation
- Schematic diagrams of water systems
- Monitoring and control diagrams of water systems
- Local, regional, and national code compliance
- Operating instructions and procedures
- No-flow and low-flow portions of the piping and building water systems
- Impact of heat loss from hot water or heat gain by cold water in piping and water system components
- All water systems shall be balanced, and a balance report for all water systems
- Detailed instructions for commissioning of all building water systems
- Procedures for flushing and disinfecting
- Confirmation that building water system performance meets design performance parameters
This is indeed an extraordinary new requirements for building owners/facility managers – one that will no doubt involve a challenging learning curve. Nevertheless, it gives engineers the opportunity to decide on their own baseline preventive measures for Legionella (i.e. re-circulation, temperature, maintenance, etc.), while leaving it up to building owners to identify and address any further action that should be taken.
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