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There are currently minimal provisions in the Uniform Plumbing Code, International Plumbing Code, International Property Maintenance Code or the International Existing Building Code to require scald protection for existing plumbing installations. There are existing installations where scalding is a hazard, but the hazards cannot be addressed because they are existing conditions and building owners claim they are grandfathered inhandle) shower valves are installed. Many of these scald incidents seem to occur shortly after a water heater is replaced or the thermostat or a mixing valve is adjusted causing a change in the hot water distribution system temperature.
The code changes were due for the international codes in mid-January, and I submitted some code changes to address these scalding hazards in existing buildings. I’m sure there will be groups that will fight this changes for purely monetary reasons. I submitted the changes for the hundreds of children, elderly and handicapped that have touched my life seeing their burns, their pain, their disfigurements and associated depression. I submitted the code change on behalf of these people and the thousands more who will join them if the codes are allowed to continue as is.
When we saw older building were unsafe for fires, we made them put in smoke detectors to save lives. These code changes are like the smoke detectors. They will save lives if they are implemented. The building owners will not want to spend some a little money to make repairs to eliminate the scald hazards. These code changes allow several less expensive options for compliance. An existing bathroom should be able to be in compliance using temperature actuated flow reduction valves for about $10.00 or less. That’s less than the cost of a smoke detector.
I am often asked, "What is a safe hot water temperature for domestic hot water systems?"
The model codes, address maximum temperatures at various fixtures in Chapter 4. The International Code lists the maximum allowable hot water temperature for a shower, bathtub, whirlpool bathtub, or public lavatory as 120 ºF.
The warning labels on most water heaters list the maximum hot water temperature as 125 ºF. The 125-degree limit probably allows for some temperature loss before the hot water gets to the plumbing fixtures. Most water heater literature and warning labels mention the availability of thermostatic mixing valves or automatic temperature compensating valves and they recommend use of tempering valves to control hot water delivery temperatures to minimize scalding.
Many of the industry standards for shower mixing valves require the shower control valves to have limit-stops that are adjustable to limit the maximum temperature of the hot water to 120 ºF. The testing in the standards gives test criteria for testing the shower valves to these limits.
I have served on the working groups for several plumbing industry standards committees for temperature actuated mixing valves and shower valves and it is generally agreed that 120 °F is the maximum, safe hot water temperature. I also have served on hot water system design standards committees where the participants had agreed that maximum domestic hot water temperature from plumbing fixtures used for bathing and washing purposes should be 120 °F. There are a few exceptions for bidets, sitz baths, whirlpool bathtubs and emergency eye/face wash fixtures that have temperatures lower than 120 °F for the maximum safe temperatures to prevent scalding or eye damage. It also should be noted that some other equipment like commercial dishwashers and laundries may need temperatures higher than 120 °F. There were two temperatures discussed for each fixture during the design standard meetings. One temperature was the "use temperature" and the other temperature was "the maximum temperature" to prevent scalding.
It's generally agreed that 120 °F is the maximum safe hot water temperature that should be delivered from a fixture. Therefore hot water above 120 °F should be considered hazardous.
The codes generally agree if there is a hazardous condition or a condition that is unsafe or a nuisance to life, health and property it should be corrected but in the existing building code and property maintenance code there is little guidance. It is also generally agreed that water above 120 °F at fixtures for bathing and washing with a few exceptions for lower temperatures mentioned above can be considered dangerous and proper precautions should be taken to prevent the hot water from being a scalding hazard by using the proper safety devices.
When I hear about people adjusting their water heater thermostat to 120 °F to prevent scalding, I understand they have good intentions. But, I realize if they are relying on the thermostat for scald control they just do not understand what the control is for. The thermostat on a water heater will not accurately control hot water temperature leaving a water heater.
Several ASSE working groups that I have served on dealing with hot water temperature controls have all have discussed the reaction time of bathers and they have taken into consideration that children, the elderly and people with disabilities usually take longer to get out of harm's way if the water suddenly gets hot and they agreed 120 °F is the maximum safe hot water temperature that a tub faucet or shower valve should deliver.
At 120 °F it takes about 80 seconds to develop a second degree burn in a child and it takes about 8 minutes to develop a second degree burn in an adult. The 120 °F temperature limit gives bathers or users what the committees considered an adequate amount of time to get out of harm's way before an irreversible scald burn injury can occur. Each of these committees looked back to the data that was the result of burn studies done by Dr. Moritz and Dr. Henrique's at Harvard Medical College in the 1940s.
The PIEV theory for reaction time
There is a PIEV theory relates to reaction time.The PIEV theory is most commonly used to address braking distance in automobile accidents. It addresses the amount of time it takes a driver to sense a problem and decide to react, then the reaction time is added to the braking time for the total distance that a car travels before stopping.
This is expressed in a formula as: Reaction Distance (RD) + Braking Distance (BD) = Stopping Distance (SD).
The PIEV theory can also apply to reaction times for a bather with respect to hot water scalds in a very similar way.
PIEV relates to the amount of time it takes a person to react to a hazard. PIEV stands for - Perception, Intellection, Emotion and Volition. Before we recognize and react to a hazard, four specific areas of activity need to be processed by the brain for the muscles to react. Those processes are:
1. Perception - We need to perceive or gain a Perception of a hazard. There can be delays in the perception with limitation in sight, sound, feeling, or any other of our senses.
2. Intellection - We go through a period called, Intellection or the act or process of using the intellect by thinking or reasoning. The bather must determine if the hazard is legitimate and deciding either move out of the way of the hazard or eliminate the hazard by adjusting the controls or in some cases where the bather may be sitting out of the reach of the controls the bather may choose to pull the shower curtain in front of them. If the adjustment of the shower controls is the choice one must decide which control to turn and try to remember which way to turn each control to adjust the temperature or turn the water off in order to eliminate the hazard. If a wrong choice is made during this process it could compound the situation by making the water even hotter. I travel a lot and I often find that shower controls can be very confusing with respect to how to adjust the controls. I still find two handle shower controls that do not meet code requirements.
This is critically important when there is no temperature limit on the shower controls.
For example if the shower has a two-handle shower valve and 160-degree hot water is supplied to the system, then turning of the cold water first could lead to instant scalding injuries. Turning down the hot water to 120 °F or below creates a system where it could incubate Legionella Bacteria to very high levels.
3. Emotion - There is an Emotion or evaluation factor which is defined as a conscious mental reaction (as anger or fear) subjectively experienced as strong feeling usually directed toward a specific object and typically accompanied by physiological and behavioral changes in the body with respect to deciding or assessing how we want to react. A person with reduced mental capacity or someone that is just very old will take longer to process this information and ultimately decide to react.
4. Volition - There is the physical Volition or deciding/choosing to act and acting. In the case of braking distance it is when the choice is made to move the foot from the gas pedal to the brake pedal and pressing on the brake pedal. This can be related to the time the bather chooses to adjust the control, and they move their hand to the shower control valve, plus the time to rotate or re-adjust the shower valve plus the time from the adjustment until the water temperature changes coming out of the shower head. Often it can take as much as 3-5 seconds to re-adjust the shower head and several seconds more until the water temperature changes coming out of the shower head. For ultra-low-flow (ULF) showers the delay from the time of the adjustment of the shower valve is made until the water temperature changes coming out of the shower head can be even longer. Many people may not be aware that burns can become more severe with ULF shower heads used on non-code compliant shower valves. This is one more area where water conservations measures can unintentionally make plumbing systems less safe.
As the hot water temperature increases in the hot water distribution system, the PIEV reaction time becomes more significant with respect to the potential severity of a burn. It is like increasing the speed of a car increases the risk of an accident.
Using a code compliant bathtub/shower controller with a single handle with a rotational limit-stop adjustment to allow for adjustment to a safe temperature would reduce the risk of scalding.
If the water is at 140 °F it will take about 0.8 seconds for a child to receive a second degree irreversible burn injuries and it will take about 5.6 seconds for an adult male to receive an irreversible burn injury. Everyone else will fall somewhere in between. An adult will often find it very difficult to react to a sudden change in temperature within five seconds. If the shower head is an Ultra-Low-Flow (ULF) shower head the delay in reducing the temperature can be several seconds longer before the water temperature is reduced because the mixed water temperature must evacuate or flush out the existing hot water that is already flowing in the riser pipe between the shower valve and the shower head.
There is simply not enough time to react at higher temperatures. For a typical adult that is alert and aware, the PIEV theory shows it can take well over five seconds to recognize the hazard, decide how to react and then react and then wait for the water temperature to change when there is a sudden burst of hot water in a shower. For an elderly person or a small child that is confused unaware of how to adjust the controls, they often move to a corner and cry or shout and it could take a significant time before they are able to react or get out of harm’s way.
There has been a lot of information that suggests reducing the domestic hot water temperature to 120 °F or less as it flows from the fixtures will minimize scalding and allow most people to react or get out of harm's way before a serious scald injury can occur.
Reducing the water temperature flowing from a fixture can be done in several ways by:
1. Using a code compliant shower or tub/shower valve to reducing the hot water temperature at the fixture by adjusting the maximum temperature limit-stop on the shower valve to limit the maximum water temperature that can flow from the shower valve to a safe temperature between 110°F and 120°F. (The best way)
2. Using local mixing valves conforming to ASSE 1070 to reduce the hot water temperature flowing from a faucet to a safe temperature between 110°F and 120°F. (With non-code shower valves, this will not address thermal shock associated with pressure imbalances due to water usage elsewhere within the building)
3. Reducing the temperature at the source (Water Heater) with the use of a master mixing valve or temperature actuated mixing valve conforming to ASSE 1017.(With non-code shower valves, this will not address thermal shock associated with pressure imbalances due to water usage elsewhere within the building)
4. For existing non code compliant shower or tub/shower installations that have two handle non-temperature or non-pressure compensating type tub/shower valves that do not have a maximum temperature limit adjustment, A temperature actuated flow reduction valve could be used in the tub filler spout and between the shower head and the shower arm.
An ASSE 1062 valve is a Temperature Actuated Flow Reduction (TAFR) valve.
If the water flowing from fixture exceeds about 120 °F the TAFR valve will shut the flow of water down to just a trickle so that scalding hot water does not spray onto the bather. It can be reset by adjusting the fixture control valve to a cold water setting and when the cold water reaches the thermostatic element in the valve it will open up again and begin flowing water. This can be a bit of a nuisance in buildings where the hot water temperature is erratic, but it is an inexpensive way to provide scald protection in older buildings that may not have code compliant shower valves with maximum temperature limit-stop adjustments.
Water Heater Thermostats Do Not Control the Water Heater Outlet Temperatures.
If you rely on adjusting the water heater thermostat for the burner or heating element on a water heater down to 120 °F, it will not prevent scalding. Water heater thermostats cannot be relied upon to control the hot water temperature leaving a water heater. Water heater manufacturers recommend that installers set thermostats at 120°F - 125°F, and most of them ship the water heaters at an even lower temperature setting. It is not possible to set a water heater thermostat at a given temperature and get a relatively constant temperature of hot water from a water heater.
Water heater thermostats cannot accurately control the outlet temperature of a water heater.
The water heater thermostat is inserted into the lower portion of a water heater tank and turns the fuel supply to the heater on and off. Most new water heater thermostat dials have no way to know what the temperature in top of the tank is. There is rarely a fixed temperature indicated on the dial, however some manufacturers publish temperatures associated with various marks on the thermostat dial or in their literature even though the dial cannot not control the outlet temperature of the water heater, it only controls when the energy to the heater is turned "on" and "off" by sensing the cold water coming into the bottom of the heater.
Generally, if the water heater thermostat dial is set at 120 °F, the burner would come on when the temperature at the thermostat reaches about 105 °F. The burner would stay on until the water around the thermostat which is near the bottom of the heater reaches about 135 °F. (The "burner off" temperature is about 30 degrees higher than the temperature when the burner came "on" and generally about 15 degrees above the theoretical set point of the thermostat).
There is a phenomenon known as "stacking" or "thermal layering." The hot water is less dense and rises to the top of the hot water tank. Just like hot air rises and lifts a hot air balloon, hot water rises to the top of the tank and the cooler water drops to the bottom of the tank. Stacking or thermal layering occurs when the hot water rises to the top of the heater due to recurring short duration heating cycles caused by a frequent number of small quantity hot water uses. Frequent short draws of hot water cause cold water to enter the bottom of the water heater where the thermostatic element senses the cold water from the bottom of the heater. The cold water causes the water heater to cycle on even when the hot water at the top of the tank is dangerously hot and well above a safe temperature. This phenomenon can occur in any type of storage water heater and generally is more significant in vertical heaters.
I have recorded temperatures as high as 150°F to 166 °F at the top of water heaters that had the thermostats set between 120°F to 125 °F. Temperatures over 151 °F are extremely high temperatures and can cause serious scald burns for adult males in only two seconds of contact with the skin.
The time temperature relationships for estimating burn injuries are based upon the thickness of the skin for adult males. Children and the elderly typically have a thinner layer of the skin or epidermis and the exposure times can be shorter or the same degree of burns can occur in a given amount of time at lower temperatures.
Save water safely and check the water temperatures and the water temperature control devices at your house. I hope all of you can stay out of hot water. n
Ron George, CPD, is president of Plumb-Tech Design & Consulting Services LLC. Visit www.Plumb-TechLLC.com.