Legionella sp. bacteria hazards in water heaters & hot water plumbing systems:

This article explains why there is a risk of harmful or even dangerous Legionella sp. bacteria formation in hot water heating systems and describes the minimum temperature required in these systems to avoid the Legionella hazard.

What hot water temperatures protect against Legionella & related Anti-Scald Regulations?

Legionella Bacteria & Legionnaires' disease hazards in water heaters, hot water tanks & hot water cylinders or geyers

Here we discuss steps to prevent dangerous Legionella bacteria growth in water heaters. Krause (2019), in developing a tool for improved assessment of the probable Legionellosis risk based on objective data from building investigation, cites these key factors in the probability of growth of Legionella bacteria in a building water system:

• Water temperature
  
  Legionella survives but typically does not amplify at temperatures below 70F (21C). Above 130F (54C) Legionella begins to die and its amplification is severly inhibited. The ideal temperature range for Legionella amplification [that's what you do NOT want] has been reported to be 90-108F (32-42C) with a mean of 99 F (37C). : - Krause (2019)
  
  Safer at higher temperatures: Water temperatures exceeding 124 degrees Fahrenheit (°F) (51 degrees Celsius (°C)) are necessary to prevent the rapid growth of Legionella, the causative agent of Legionella pneumonia (traditionally known as Legionnaires’ disease) in hot water systems. Cold water systems (below approximately 68°F (20°C)) tend to be too cold to foster rapid growth of the organism.
• Oxidant concentrations - where oxidants, by oxidizing bacteria, are in effect a disinfectant.
  
  Adequate disinfection: Maintaining free chlorine concentrations above 2.0 mg/L (ppm), at a pH of 7.2 to 7.8 has been reported to ... control Legionella growth or prevent its amplification. (Op. Cit).
• Water age
  
  Remove stagnant water & disinfect containers: Infrequently-used or stagnat water has been associated with increased risk of biofilm development and Legionella amplification. Frequent use, maintenance of inhibitory temperature and oxidant levels at distal fixtures and short branch runs between circulating water and points of use are factors that help reduce water age. (Op. Cit).
  
  Watch out: this is probably an argument in favor of frequent cleaning and disinfection of any household system that may otherwise accumulate stagnant water, such as humidifiers, dehumidifiers, and air conditioner or heat pump condensate handling systems, particularly when there is an extra risk of injecting bacteria attached to water droplets, mist, or dust into the building air such as through an HVAC duct system.

Aside from or perhaps even independent from testing potable water for legionella bacteria, most experts focus on setting a sufficiently-high water heater temperature to kill bacteria and to prevent its growth in water heater tanks or hot water cylinders, calorifiers, or geysers.

Separately at Legionella BACTERIA & HVAC EQUIPMENT we discuss Legionella hazards and Legionellosis or Pontiac Fever traced to building air conditioning systems and cooling towers.

Watch out: attempts to avoid scalding burn hazards by lowering the maintenance temperature of the water heater itself convey a new hazard: at lower temperatures in water heaters there is a risk of formation of Legionella sp. bacteria. Regarding prevention of Legionella, cf Veterans Administration source in citations at the end of this article. Quoting:

Water temperatures exceeding 124 degrees Fahrenheit (°F) (51 degrees Celsius (°C)) are necessary to prevent the rapid growth of Legionella, the causative agent of Legionella pneumonia (traditionally known as Legionnaires’ disease) in hot water systems. Cold water systems (below approximately 68°F (20°C)) tend to be too cold to foster rapid growth of the organism.

For normal or otherwise healthy individuals, 120°F at the sink tap is adequate to minimize the risk of scalding. Some patients, due to illness, disabilities, advanced age or side effects of medication, may be less sensitive to temperature and thus be at increased risk for tissue damage caused by extended exposure to hot water.

Patient exposure to heated water occurs via a number of mechanisms (e.g., bathing, hydrotherapy, showering). For immersion bath wa ter, scalding is possible at temperatures exceeding normal body temperature; however, the risk is small below 105°F. At 117°F, scalding risk increases significantly. At 140°F, second degree burns may occur after only 3 seconds of exposure. Some patients are extremely sensitive to scalding.

It is not possible to maintain water temperatures at the outlet that prevent the growth of Legionella and simultaneously eliminate the possibility of scald injury in persons partially or fully insensitive to hot water temperature.

The requirement to keep water quite hot in the water heater or piping systems of buildings in turn leads to the need for ANTI SCALD VALVES & TEMPERATURE CONTROL / MIXING VALVES to provide scald protection for building occupants.

Reference Citations for Anti-Scald Temperature Limits, information & regulations

• "AS/NZS 3500.2:2003 A4 Plumbing and drainage - Sanitary plumbing and drainage." Website: http://www.dbh.govt.nz
• Cerovac S, and Roberts AHN. Burns Sustained by Hot Bath and Shower Water. Burns 26:251-259; 2000.
• Henriques, FC. Studies of Thermal Injury; Predictability and Significance of Thermally Induced Rate Processes Leading to Irreversible Epidermal Injury. Archives of Pathology 43:489-502, 1947. NOTE: Although published several decades ago, this reference is a landmark study on thermal injury.
• Moritz AR and Henriques FC. Studies of Thermal Injury; the Relative Importance of Time and Surface Temperature in the Causation of Cutaneous Burns. American Journal of Pathology 23:695-720, 1947. NOTE [from the US VA]: Although published several decades ago, this reference is a landmark study on thermal injury.
• Stephen FR, and Murray JP. Prevention of Hot Tap Water Burns – a Comparative Study of Three Types of Automatic Mixing Valves. Burns 19(1):56-62, 1993.
• Standards for temperature controls for hot water systems
  • ASSE 1016 - Automatic Compensating Valves for Individual Showers and Tub/Shower Combinations
  • ASSE 1017 - Temperature Actuated Mixing Valves for Hot Water Distribution Systems.
  • ASSE 1062 - Temperature Actuated Flow Reduction Devices
  • ASSE 1066 - Individual Pressure Balancing Valves for Individual Fixture Fittings
  • ASSE 1069 - Automatic Temperature Control Mixing Valves
  • ASSE 1070 - Water Temperature Limiting Devices
• "Domestic Hot Water Temperature Limits for Legionella Prevention an Scald Control", VHA Directive 2009-009, (Feb 2009) [USA] Department of Veterans Affairs, Veterans Health Administration, Washington D.C. retrieved 3/21/2014, original source: http://www.va.gov/vhapublications/ViewPublication.asp?pub_ID=1853
• Domestic Hot Water Scald Burn Lawsuits... D. Bynum et als., "Legislation to Prevent Scalding from Hot Water, A quick guide to English, Welsh and Scottish Regulations", retrieved 3/20/14, original source: www.showerright.co.uk
• "Hot Water System Information", Ron George Design & Consulting Services, retrieve 3/21/2014, original source: http://www.rongeorgedesign.com/Hot_Water_System_Info/Hot_Water_System_Info.htm
• "How the dual issues of scalding an Legionnaire's Disease are being handled around the world", AntiScald, Inc., 70-40 137th St., Flushing NY 11367, USA, Tel: 718-268-7126, email: information@antiscald.com retrieved 3/20/14, original source: http://www.antiscald.com/prevention/legionnaires/dual_issues.php This company is a distributor of anti-scalding products.
• Safe Water Ltd., Safe Water Ltd · PO Box 100 · Picton · New Zealand
  Mobile 021 800 825 · Email safewater@xtra.co.nz Website: http://www.safewater.co.nz/ distributes anti-scald safety products in New Zealand
• "Recommended Code of Practice for Safe Water Temperatures", Thermostatic Mixing Valve Manufacturers Association (TMVA), TMVA, Westminster Tower, 3 Albert Embankment, London SE1 7SL Tel: 020 7793 3008 Fax: 020 7793 9730 e-mail: tmva@beama.org.uk www.tmva.org.uk, retrieved 3/21/2014, original source: www.beama.org.uk
• "Guidelines for Safe Recreational Water Environments, Vol. 2, Swimming Pools & Similar Environments", World Health Organization, WHO, retrieved 3/21/2014. Original source: http://www.who.int/water_sanitation_health/bathing/srwe2full.pdf

Legionella Contamination in Drinking Water Research

• Also see citations atReferences or Citations
• American Society for Heating, Refriger ating and Air-conditioning Engineers (ASHRAE). Guideline 12-2000. Minimizing the Risk of Legionellosis Associated with Building Water Systems, 2000.
• ANSI/ASHRAE Standard 188-2018, Legionellosis: Risk Management for Building Water Systems [August 2018]
• "How the dual issues of scalding an Legionnaire's Disease are being handled around the world", AntiScald, Inc., 70-40 137th St., Flushing NY 11367, USA, Tel: 718-268-7126, email: information@antiscald.com retrieved 3/20/14, original source: http://www.antiscald.com/prevention/legionnaires/dual_issues.php This company is a distributor of anti-scalding products.
• ASHRAE: Standard Guideline 12-2000, Minimizing the Risk of Legionellosis Associated with Building Water Systems [February 2000]
• ASTM International: D5952-08, Standard Guide for the Inspection of Water Systems for Legionella and the Investigation of Possible Outbreaks of Legionellosis (Legionnaires' Disease or Pontiac Fever) [July 2008]
• Centers for Disease Control and Prevention (CDC). Guidelines for Environmental Infection Control in Health-care Facilities. Recommendations of CDC and the Healthcare Infection Control Practices Advisory Committ ee (HICPAC). Morbidity and Mortality Weekly Reports (MMWR) 52 (RR10):1-42; 2003. www.cdc.gov/mmwr/preview/mmwrhtml/rr5210a1.htm
• Kim, B. R., J. E. Anderson, S. A. Mueller, W. A. Gaines, and A. M. Kendall. "Literature review—efficacy of various disinfectants agains Legionella in water systems." Water Research 36, no. 18 (2002): 4433-4444
• Krause, J. David, "Performing Legionella Source Risk Assessments, A Hazard Analysis Tool for Data Interpretation", AIHA, American Industrial Hygiene Association, The Synergist, April 2019, pp. 24-28.
• U.S. CDC, "Toolkit for Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings: A practical Guide to Implementing Industry Standards", [PDF] retrieved 2019/06/21, original source: https://www.cdc.gov/legionella/downloads/toolkit.pdf
• VHA, "Domestic Hot Water Temperature Limits for Legionella Prevention an Scald Control", VHA Directive 2009-009, (Feb 2009) [USA] Department of Veterans Affairs, Veterans Health Administration, Washington D.C. retrieved 3/21/2014, original source: http://www.va.gov/vhapublications/ViewPublication.asp?pub_ID=1853
• WHO, "Legionella and the prevention of legionellosis", World Health Organization WHO, retrieved 3/21/2014, original source: http://www.who.int/water_sanitation_health/emerging/legionella.pdf

...

Continue reading at LEGIONNAIRES' DISEASE INFO from CDC or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Legionella Hazard Reduction Articles

• ANTI SCALD VALVES & TEMPERATURE CONTROL / MIXING VALVES
• CONDENSATE HANDLING - home
• DUCTWORK CONTAMINATION
• HOT WATER ANTI-SCALD REGULATIONS preventing Legionella formation in water heating equipment.
• Legionella BACTERIA & HVAC EQUIPMENT
• Legionella BACTERIA in WATER HEATERS
• LEGIONNAIRES' DISEASE INFO from CDC health hazards associated with Legionella and other biological contaminants in HVAC systems
• SWAMP COOLERS
• WISCONSIN PROTOCOL for Cleaning A/C

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