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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?
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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 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.
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
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In addition to any citations in the article above, a full list is available on request.
"AS/NZS 3500.2:2003 A4 Plumbing and drainage - Sanitary plumbing and drainage." Website: http://www.dbh.govt.nz
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.
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
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 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.
"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
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
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