Each month, new headlines blare about legionella outbreaks leading to illnesses and, in some cases, deaths.
According to tracking by HC Info, July 2018 legionella incidences in the United States included 27 illnesses and one death following an outbreak in a cooling tower in New York City’s Washington Heights neighborhood; 11 illnesses and one death suspected to be caused by legionella in a church cooling tower in Cleveland; and two confirmed contractions of Legionnaire’s from a pool in Palm Springs, Calif.
Water Quality Products magazine reported in June that six buildings at Wayne State University in Detroit tested positive for legionella in cooling towers after a worker came down with Legionnaire’s Disease.
In fact, Michigan has seen a 30% increase in contraction of legionellosis this year versus last year. “The incidence of Legionnaire’s disease is increasing both nationally and in Michigan in a similar trend line,” Michigan Department of Health and Human Services Spokeswoman Lynn Suftin told Water Quality Products. “However, the incidence of disease in Michigan remains consistently higher than the national average.”
Though not all outbreaks are attributed to pipes and HVAC systems, some pipe materials and projects are particularly vulnerable. Biofilm, a slimy glue-like substance that can harbor bacteria such as Legionella, forms on certain piping materials when biomass adhere to surfaces in wet conditions and provides the bacteria protection from thermal and oxidative disinfection methods including chlorine, monochloramine, chlorine dioxide, and Ultraviolet and copper and/or silver ion treatments.
Legionella is a naturally occurring waterborne bacteria that multiplies in biofilm at various common temperatures of plumbing systems.
Hot tubs, electronic faucets, faucet aerators, faucet flow restrictors, ice machines, showerheads, and water filters are particularly prone to potential issues, as are hot and cold water storage tanks, water heaters, expansion tanks, water-hammer arrestors, eyewash stations and emergency showers and other areas in the plumbing system with infrequent use, stagnant water, and portions with tepid temperatures.
Key factors that help legionella grow are sediment that can protect legionella from chemical disinfectants; water age (low-flow conditions caused by erratic occupancy, dead legs in system design, and low consumption fixture usage); and inadequate disinfectant residual.
Temperature is another key factor. Legionella’s ideal growth range is 68 to 120 degrees F. The disinfection range for legionella starts at approximately 158 degrees F.
Pipe Material Considerations
Another major consideration is the material of the pipes themselves, whose characteristics, such as surface roughness and impact from sanitization, can impact the likelihood of a legionella issue.
Biofilm provides a safe harbor for legionella growth, and some materials create more biofilm-friendly environments than others, due, in part, to surface roughness—pipe materials with a smoother surface have less potential for biofilm growth. CPVC and PEX are two of the smoothest, with consistent surface roughness of 12.1 µm and 13.7 µm, respectively. Copper starts smooth at 7.9 µm but as it ages it becomes rougher, to 2600 µm, dramatically increasing its biofilm growth potential.
Treatments recommended for disinfection also can have an impact on all plumbing system components. Disinfection for legionella requires elevated levels of chlorination and/or temperatures requiring a deeper understanding of piping material limitations and strengths.
CPVC is exceptionally useful for handling corrosive fluids up to 180⁰ F. CPVC is a recommended piping for chlorine dioxide and sodium hypochlorite conveyance in water treatment facilities as well as used by chlor-alkali industry for chlorine production piping, ducting, and vessel lining. However, chloramines indirectly affect corrosion in copper pipes due to changing pH levels. Per, ASTM F2023, the Oxidative Resistance to Hot Chlorinated Water for PEX and Polypropylene is evaluated at 4.0 ppm Chlorine, pH 6.8, 80 psi and temperatures 73.4⁰ F and 140⁰ F. Long term requirements may be reduced due to frequent or continuous exposure to conditions of aggressive water quality, higher pressures or temperatures and may cause premature oxidation and eventual brittleness. Polypropylene manufacturers don’t recommend the use of chlorine dioxide without their prior approval.