Every year, in the United States, thousands of people suffer serious scald injuries in showers or tub-showers after the hot water system temperature has been adjusted. These injuries can be prevented with the proper controls and adjustments of the maximum temperature limit-stop on each shower valve.  

Compensating type shower valves with maximum temperature limit-stops have been around for many years before they were required in the model codes. In 1976, ASSE published the first edition of the shower valve standard (ASSE 1016) which covered performance and safety requirements for shower valves. The Standard was controversial because it required shower valves to have a maximum temperature limit-stop adjustment that could be adjusted to limit the maximum temperature of hot water flowing from a shower or tub-shower valve in order to minimize the risk of scalding.  

The advent of this shower valve standard meant the old two-handle shower valves that did not compensate for pressure or temperature changes in the plumbing system would soon be phased out and bathers would no longer be exposed to thermal shock and scalding when someone flushed a toilet or used another fixture in the building while they were in the shower.  

History of Compensating Shower Valves with Limit-Stops code

Soon after the publication of the ASSE 1016 standard, in the late 1970s and early 1980s code change proposals were submitted to add the ASSE 1016 shower valve standard to the codes. Originally, the standard was titled: ASSE 1016 standard for individual shower valves. The Standard went through a couple of revision cycles and title changes and in recent years, the shower valve standard has been harmonized with the American Society of Mechanical Engineers Standards (ASME) and the Canadian Standards Association (CSA) standard CSA B125. The standard is now called: ASSE 1016/ASME A112.1016/CSA B125.16 - 2017 Performance Requirements for Automatic Compensating Valves for Individual Showers.  

The original code change proposals were not without resistance, because there were manufacturers that did not want to redesign their valves and builders and developers and building owners that did not want to spend money on renovations and new construction to purchase the slightly more expensive pressure or temperature compensating shower valves.  A code change was proposed to require all shower valves to comply with the new ASSE standard and there was a lot of debate back and forth between cost and safety.  At one of the code hearings, the late, John E. Matthews, PE, from Michigan and Eastern Michigan Chapter ASPE member and Michigan chapter ASSE member was attending the code hearings where the code change to require shower valves to comply with the ASSE industry standard was discussed. 

About 10 years later, John and I were at the code hearings with John Nussbaum, who was the executive director of the PHCC of SE Michigan at the time and he told John Nussbaum and I the story about the code hearings where he testified for the ASSE shower valve standard. He had a big smile and with an index finger pointing upward as if to make a emphasize his point, he said the code change was not doing too well as a bunch of lobbyists lined up to speak against the code change. He said he had talked to Julius Ballanco, who I believe was the staff engineer for the Building Officials and Code Administrators (BOCA) at the time. Julius was known by all and John knew this code change was important, but there was considerable opposition to adding the code language requiring all shower valves to meet the new ASSE 1016 shower valve standard. John told me that he knew Julius and had become friends with him. After considerable debate and a lot of people speaking in opposition to the code change for mostly monetary reasons, John Matthews got up to the microphone and reminded everyone that this was a safety issue and then he made a personal plea. He said something to the effect of “I’m not asking you to accept this code change for me, I’m asking you to do this to protect Julius’ children”.  

That personalized the issue to the code committee members that were considering the vote and it seemed to be a watershed moment. The code change passed and soon after, every model code has now required pressure or temperature compensating shower valves conforming to the harmonized shower valve standard. Every new shower valve is now required have an adjustable maximum temperature limit-stop as a safety feature to limit the rotation of the shower valve toward the hot setting or in some form, it must limit the maximum temperature flowing from the shower to 120F or less to prevent scald injuries. Unfortunately for the residents of North Carolina, their State plumbing code is influenced heavily by the home builders’ associations and they have a lot of influence in the code process. 

They have allowed an exception to using the shower valves that meet the industry standard, if the water heater thermostat is set to 120F. I believe that code language has led to thermal shock and scald injuries for many and it allows a condition where water heater first draw capacity is diminished because of lower storage temperatures and Legionella bacteria can thrive in the temperatures that they allow for the hot water in the tank and distribution piping system. 

The 120F Maximum Temperature debate

The model codes have settled on 120F as the maximum allowable temperature flowing from the shower head or tub spout to minimize the chance of scalding. The hot water temperature in the storage tank and distribution piping is not covered in the plumbing codes and many people mistakenly think the maximum shower temperature is the maximum storage temperature. The maximum allowable temperature flowing from various fixtures has been debated over the years in AdHoc code committees dealing with hot water temperatures in the codes, standards and industry scald awareness, technical publication, and scald awareness white paper committees with various organizations including ICC, IAPMO, ASSE, ASME, ASHRAE, and ASPE.  

I have participated in just about all of them and they have all concluded 120F is the maximum safe temperature for showers or tub-showers with the exception of a few jurisdictions where they a slightly lower maximum hot water temperature flowing from the shower valve.  These discussions were centered on evaluating the burn studies by Doctors Moritz and Henriques at Harvard Medical College from the 1930s and 1940s. Most systems are stored at 140F - 150F and distributed at temperatures well above the legionella growth temperature of 122F.   

Moritz and Henriques studies

The burn studies by Doctors Moritz and Henriques showed that at 110F if was nearly impossible for an adult male to receive a burn injury. At 111F, an adult male could have blistering second degree burns in 3.6 hours of exposure, which gives a very large safety factor. As the hot water temperature goes up, the exposure time before a blistering burn injury occurs goes down. At 115F, the data from the Moritz and Henrique data indicates it would take about 28 minutes to 30 minutes for an adult male to receive a second degree burn injury. Women, children and the elderly have thinner skin and they can receive burn injuries in less time at the same water temperatures. At 120F, the data shows it should take about 4.1 to 4.8 minutes to receive a second degree burn injury. All of the committees agree that about four minutes was sufficient time for the bather to cry out for help, or react to the hot water or get out of harms way. However, if there is a facility with elderly people, children or handicapped persons, it is a good idea to adjust the maximum temperature limit-stop down to about 110F or slightly lower to eliminate any possibility of scalding.  

The Moritz and Henriques burn studies were originally done on adult male soldiers for first degree burn injuries. For second degree injuries, they had trouble getting volunteers, so they decided to use baby pigs because at a young age, the baby pigs had approximately the same skin thickness as an adult male. They continued with their burn studies by cutting a hole in a sponge about the size of a half dollar and using a plate with rubber tubing to flow a controlled temperature of hot water to a spot on the pig skin. They would circle the spot with a permanent marker, not the temperature and duration of exposure and they would repeat.  By the time they were done the pig had a lot of red spots on its skin. The pig was euthanized and then an autopsy and cross-sections of tissue samples were taken in order to determine the depth of the burn injuries at each location. This data was the basis for establishing the time versus temperature charts for burn injuries.

Dr. Kenneth Diller, a professor at the University of Texas, published a report evaluating the Moritz & Henriques Data and he has developed a mathematical model for predicting burn injury as a function of applied surface temperature and time is used to identify these equivalent conditions. Data from the literature of ultrasound sonographic measurements indicate a representative ratio of child to adult skin thickness of 0.72 for a child as compared to 1.0 for an adult. The mathematical model shows that the equivalent surface temperature for a threshold scald injury in children is dependent on the depth into the skin at which the injury is identified. For example, the injury produced by a 120F with a ten-second exposure at a depth of 600 micrometers in an adult is matched in a child at 72 percent of the depth or 432 micrometers by an exposure of 115.9F for the same duration. The recommendation is that existing hot water standards be reduced by 3 to 4 degrees Fahrenheit to provide an equivalent level of scald protection to children. The elderly and disabled would also benefit from reduced burn injury severity with a maximum temperature limit reduction to 115F.

Manufacturers with good intentions

Soon after the shower valve standard was originally published in 1976 many shower valve manufacturers jumped on the shower safety band wagon started shipping their shower valves with the limit-stops pre-adjusted to the lowest setting and with instructions on how to adjust the limit-stop when the shower valve is installed. The problem was there was no education campaign to go along with the decision to change so, soon after the change was made to ship the valves at the lowest setting, the manufacturer’s technical support phones were flooded with phone calls complaining about the new shower valve not getting any hot water. Many shower valves were removed and shipped back to the manufacturer’s demanding a refund and to add insult to injury, the valves were replaced with a competitor’s brand of shower valve. The shower valve manufacturers got a black eye over that issue, so the easy solution for them was to ship the shower valves with the limit-stop in the wide-open position where someone can get scalded with the shower valve right out of the box and they included instructions for how to set the maximum temperature limit stop.  

Checking Maximum Temperature Limit-Stops 

I gave a presentation at the ASSE Conference on scalding that inspired the ASSE Scald awareness committee. Since then, the ASSE scald awareness committee has been working hard to educate the plumbing industry about many issues that contribute to scald injuries.  The Scald awareness committee has published several white papers dealing with eliminating scald hazards. (White papers can be found on ASSE website.

In my travels and at speaking events at various association meetings and seminars, I have asked plumbers, inspectors and building owners if they know what a maximum temperature limit stop is. Many of them know what the maximum temperature limit-stop is and there are many that have never heard of limit-stops. What is often alarming, is when I ask how many of people set the limit-stops on their projects or check to see if the limit-stops are set to a safe temperature. This is when it gets quiet for a few seconds and you hear crickets or the hum of the Air conditioner. People start looking left and right to see who might checks for shower valve temperatures. Occasionally, someone will speak up and say “setting the limit-stops are not in their bid,” or “it takes too long to set the limit-stops” or one inspector said “his jurisdiction does not pay for temperature measuring equipment.” The code requires the limit-stops on shower valves to be adjusted to a maximum of 120F or lower, so setting the temperature is required to be done by the contractor and checking the limit-stops should be checked by the inspector who should have a temperature gauge. Temperature gauges are available from most grocery stores for less than ten dollars. Not checking the maximum hot water temperatures in showers and bathtubs is risking lives.     

I have investigated many scald incidents that have occurred in non-code compliant installations and many that have occurred in installations with compensating type shower valves that did not have the limit-stops set. The story is usually the same, someone was scalded in a bathtub or shower and is seriously injured or killed. The child and protective services typically go after and prosecute the parents or caretakers of the burned children and a building owner who creates dangerous, hazard with hot water in excess of 150F or 160F and has violated the code is not cited or prosecuted for the injuries or death they caused by not providing a safe premises for the tenants in their shower or tub-shower with hot water at or below 120F.  The bottom line is there are still many preventable scald incidents occurring daily and education is needed.  

Updating older shower valves for health and safety

Many of these injuries occur in homes or buildings with older style two-handle shower valves that do not compensate or automatically adjust for changes in the incoming pressure or temperatures in the shower. Many of these commercial building owners, apartments owners, or hotel building owners that resist installing a code compliant shower valve rely on a code section that is commonly referred to as the “grandfather clause.”  The model code section is worded as follows: “Plumbing systems lawfully in existence at the time of the adoption of this code shall be permitted to have their use and maintenance continued if the use, maintenance or repair is in accordance with the original design and no hazard to life, health or property is created by such plumbing system.”

The key words are “no hazard to life, health … is created.” The problem is a two-handled or non-compensating type shower valve is not defined in the codes as a hazard, yet they can be deadly.  Hot water temperatures above 120F are not defined as a hazard, yet excessive hot water temperatures can be deadly. If hot water in excess of 120F or non-compensating shower valves are defined as being a hazard to life and health, then it would allow plumbing inspectors to require older style two handle shower valves to be replaced with compensating type shower valves with maximum temperature limit-stops. The codes need to add language to address this issue in the plumbing codes and in property maintenance codes. Insurance companies should require this as part of the sale of a home. Home inspectors should check for this.  

This is a serious issue that keeps getting swept under the rug. We need to address the existing, old two-handled or non-pressure or temperature compensating shower and tub-shower valves that are a life and health hazard. I have submitted code changes addressing this issue, and there is always a contingent of lobbyists for property management organizations, building owner and management organizations and other home builder interest groups that don’t want to spend what would be less than one month’s rent to correct this serious safety issue. Many opponents of code change proposals requiring these valves with limit-stops on older installations testify they are opposed to the code change “because of the added cost.”

On one of the model code organization’s code change form, there is a question that asks, “Will this code change increase the cost of construction?” followed by a box to check “yes” or “no” and a reason for your cost estimate/justification. I find it interesting that “construction cost” is a question, that must be answered in order for the code change submittal to be complete. But, there is no question asking if the code change eliminates a hazard to life, health, safety, insurance, legal expenses and medical costs. If the code change proponent does not answer the question about the code change being an increase in construction cost and then providing a justification for the cost, the code change will not be accepted. I would like them to add a question asking, “Will this code change provide life safety or protect the health of the building occupants?”  

With the current code change system, when the box is checked that indicates a code change will increase construction costs, it triggers many groups to oppose the code change proposal simply because it increases construction costs. Their lobbyist groups come with confusing off the wall arguments designed to create doubt and confusion. Historically, when a code committee gets confused, it seems it is easier for them to deny a code change rather than take the time to investigate and research the issue.  

With the scald incidents I investigate, it is common to find that it occurred shortly after someone replaces an existing water heater or adjusts the water heater thermostat temperature or if there is a master temperature actuated mixing valve, and someone significantly increases the outlet temperature that supplies the hot water distribution system.  This change or increase in hot water distribution system temperature requires the checking of and re-adjustment to the maximum temperature limit-stop on each shower or tub-shower valve in the hot water distribution system.  This should be included in water heater installation and maintenance manuals, it should be mentioned in the temperature actuated mixing valve use and care manuals and in the plumbing code under water heater replacements. 

I have found that after discussions with many people in the plumbing industry that many were aware of the need to adjust the limit-stop and just did not want to the spend time waiting for the water heater to heat up and then flowing water from each shower valve to adjust them to a safe temperature. Many other people I have talked to were not aware of what a maximum temperature limit-stop is, where it is located or what it does.  

The model plumbing codes have language similar to this for Individual shower valves and tub-shower valves. See 2018 International Plumbing Code 412.3 Individual shower valves. 

In the prior editions of the International Plumbing Code, there was code language that said something like: The water heater thermostat shall not be considered a suitable control for meeting this provision. When looking back at the code change proposal books for the last few International Plumbing Code change cycles, I could not find where this code language was proposed to be removed or stricken from the plumbing Code. I called the ICC staff and they said they could not find where it was proposed to be removed. Apparently this language may have been inadvertently removed and may have slipped through the cracks in prior code printing process. It seems to have just went away without a code change proposal or code change hearing for removing it. So that begs the question if it should be replaced by issuing an erratum to the code. 

For years, model codes have prohibited the water heater thermostat from being used as the final temperature control for purposes of scald prevention because the tank type water heater thermostats are not accurate enough to serve as a temperature control for purposes of scald prevention. It is possible for an uncirculated storage type water heater to have a thermostat set to 120F and have outlet temperatures in excess of 150F leaving the top of the water heater because of thermal layering and stacking in a hot water tank.  Temperatures in excess of 150F are deadly and can cause scald injuries on an adult male in less than one second.  See the 2018 Uniform Plumbing Code UPC 2018 408.3 - Shower and Tub-Shower Combination Control Valves.