I previously wrote about the Consumer Product Safety Commission (CPSC) petition, colloquially known as the Seattle Power & Light Petition, in the August 2021 issue. In this petition, the CPSC considered (among other things) whether it should “require that water heaters be fabricated with a maximum thermostat setting of 130 F.”

This column continues the story and explores the response by the CPSC upon receipt of the petition. Ultimately, the CPSC issued a formal response, denying the request, which was published in the Federal Register.  

I have seen manufacturers of water heaters rely upon the published denial of this request as a basis to contend that their water heaters are safe. The CPSC did not say this; rather, it denied a badly-formed request in the petition. There is no design of a residential gas-fired storage type water heater, using only its combination gas control thermostat, that is able to sense, limit or control the outlet temperature from a water heater to within a few degrees of the thermostat set-point.

Before discussing the CPSC proceedings, I will tell you that water heaters are designed and intended to produce hot water in a temperature range that can cause a scald burn in less than one second.  

Water heater standards

Residential, storage-type, gas-fired water heaters are the hot water source in many scald cases that I have investigated around the country. The standards that govern the design and operation of a gas-fired water heater and its combination gas control (thermostat) do not require that either the water heater or its thermostat maintain an outlet water temperature with any accuracy to control against temperature rises that can lead to scald burn injuries.

Even when scalding hot water is produced, water heaters and their integral thermostats are usually functioning as intended and as they are allowed to by the standards to which they are certified. The standards that these water heaters are certified to are not scald prevention standards.

A water heater’s thermostat does not accurately control the temperature of the water leaving the water heater. The combination gas control valve standard, ANSI Z21.78/CSA 6.20, Combination Gas Controls for Gas Appliances, allows a +/- 10-degree tolerance for accuracy of the thermostat.  

The gas water heater standard ANSI Z21.10.1/CSA 4.1, Gas Water Heaters, Storage Water Heaters with Input Ratings of 75,000 BTU/hour or Less, allows an additional 20-degree variation for stacking, for an allowable temperature rise of more than 30 degrees from the thermostat set-point to the outlet temperature of the hot water. The test on gas water heaters is performed on new equipment; the testing methods (at the highest thermostat setting with higher (3 gpm) flows) minimize the stacking effect that can occur.  

In real-world conditions, the temperature differential from the thermostat set-point to the water heater outlet can be much greater.

The model plumbing codes dictate that the maximum safe temperature limit for water flowing from bathtub spouts and showerheads to prevent scald injuries is 120 F. Currently, there is no safe temperature limit in the codes for water other than that flowing from bathtub spouts and showerheads, excepting a few other fixtures such as lavatories, in some cases, and bidets.  

I have participated in all the model code and plumbing product standard committees relating to temperature controls. Every committee referred to the data from the studies conducted by Drs. Moritz & Henriques to determine that 120 F was the maximum safe temperature to allow a person to get out of harm’s way before an irreversible scald burn injury occurs.  

Actually, 120 F is uncomfortably hot; most people would find water at this temperature to be too hot. At that temperature, an adult male will receive scald burns in about four to eight minutes. Women, children, the elderly or those with illnesses or disabilities have thinner skin than an adult male and will receive scald burns in less time and at lesser temperatures.  

However, this temperature limit of 120 F is not achieved from the setting on the water heater thermostat dial. With respect to storage-type, gas-fired water heaters, when the thermostat is set to a mark corresponding to 120 F, the outlet temperature can reach much higher, permissibly by the tolerances allowed in the standards. Therefore, when a thermostat is set to 120 F, the outlet temperature can be 150 F, permissibly, and a scald burn can occur in less than one second.

The inherent risk of scald burn injury within the tolerance for accuracy in the standards is demonstrated in a chart I developed (Figure 2) based on the graph presented by Doug Bynum Jr., P.E., at the 1993 ASSE annual meeting seminar (Figure 1).

With respect to water heater labels, danger warnings and water heater manuals, I’ll just say that I have read many. Even though a label or manual may tell a reader that water hotter than the thermostat dial can be produced, and even that mixing valves are available, this written information does not make the water heater any safer for users.

Manuals are dense; they contain a lot of information written for the knowledgeable person or professional, such as installation instructions, on the front-end, and manuals imply that the thermostat dial setting controls the outlet temperature. The thermostat of storage-type water heaters (gas or electric) should never be used to control the maximum hot water temperature at the fixtures.  

Dr. Feldman

However, returning to the discussion of the CPSC proceedings, the document that started the official response by the CPSC consisted of a two-page letter with several attachments. The letter, dated June 26, 1978, was signed by Gordon Vickery, superintendent of Your Seattle City Light. The letter was titled “Reduction of Tap Water Scalds,” and it directed the CPSC to “send all correspondence to the attention of Kenneth W. Feldman, M.D., The Odessa Brown Children’s Clinic.” The attachments to the letter included:

• Two pages of signatures of supporters;

• A Sept. 27, 1977, letter from The Proctor & Gamble Co. to Dr. Ken Feldman;

• A May 31, 1978, letter from the National Sanitation Foundation to Feldman.

Feldman was an active advocate for the prevention of scald burn injuries in children, according to David Hemenway’s book “While We Were Sleeping: Success Stories in Injury and Violence Prevention.” He had been engaged with industry representatives before Vickery’s letter was sent to the CPSC. Feldman, the driving force behind the letter, was not a plumbing engineer or plumbing product design professional; he was a medical doctor, and with respect to his concern with pediatric scald burn injuries, his focus was on hot water usage temperature.  

Like many lay-persons and some plumbing industry professionals who still advocate for a lower thermostat setting, Feldman apparently believed that the water heater thermostat controlled the outlet temperature and, therefore, the usage temperature. I would not expect him to have understood, nor is there any evidence that he understood, the following:  

• Because of the manner in which gas-fired, storage tank-type water heaters are designed to function — cold water is brought into the bottom of the water heater, where the internal thermostatic probe is located — there will always be thermal layering and stacking in a water heater. This is associated with short, intermittent draws of hot water, which cause the burner to cycle on continually. The burner cycling raises the temperature of the outlet hot water above the set-point of the water heater thermostat.

• The water heater combination gas control (thermostat) was never intended to accurately control the outlet temperature; it is merely a burner control. Thermostat manufacturers have confirmed this.

• Water heater sizing guidelines are typically based on a storage temperature of 140 F to have sufficient capacity of hot water to meet peak demands. When hot water temperatures are arbitrarily turned down, the result is often a shortage of hot water in installations with more people in a household. We now understand that a higher storage and distribution temperature is necessary to control the growth of Legionella bacteria.

Before he championed the petition to the CPSC, Feldman contacted various appliance industry representatives about his ideas to lower the temperature of water produced by water heaters. He seemed to have support:

• Feldman contacted The Proctor & Gamble Co., they wrote a letter to him, confirming the “recent telephone conversation regarding the temperature of water in home automatic dishwashers,” stating: “It is true that automatic dishwashers do specify 140 F (at the water heater); however, the average water temperature actually delivered to the equipment is approximately 130 F in most cases.”  

• Feldman contacted the National Sanitation Foundation, and they wrote a letter to him, stating that: “Domestic-type dishwashing machines do not rely on hot water for sanitization or drying. Instead, they rely on heat usually generated from an electric calrod unit in the dishwashing machine compartment to elevate the temperature for drying.”  

• The Association of Home Appliance Manufacturers (AHAM) also was contacted, but apparently, the conversation was misunderstood. In a letter dated Sept. 11, 1978 (after the letter was received by the CPSC), AHAM’s Technical Director Walter H. Blanck Jr., wrote a letter to Harry Wall, an associate mechanical engineer with Seattle City Light, stating:  

“… It was apparent that there was some confusion on your part regarding any temperature drop from the water heater to the tap. You indicated that the intent of the petition was to have 130 F temperature at the tap and not to restrict the water heater thermostat to a maximum setting of 130 F.

“This letter in no way indicates a position by AHAM on behalf of its members but is to make a record of our understanding regarding your telephone conversation with me and to indicate the possibility of a faulty petition in view of the fact that you stated that you were not going to correct the petition until the CPSC acted upon it.”

CPSC Response

Vickery’s letter and the attachments were received and docketed by the CPSC on June 30, 1978. On July 6, 1978, the Office of the General Counsel (OGC) advised:

“The submission from the Department of Lighting, City of Seattle should be treated as a petition under section 10 of the CPSA [Consumer Product Safety Act, 15 U.S.C. sections 2051-2089 (1972)] requesting the issuance of a consumer product safety rule for new gas or electric residential water heaters to require such heaters to have a maximum thermostat setting of 130 F and to require that the heaters display warning labels describing the hazards of hot water and instructions for setting water heater temperatures.”

The OGC also advised that the “120-day period for granting or denying” the petition (under section 10 of the CPSA) began to run from the date it was received, or June 30, 1978.  

Thereafter, the CPSC issued a petition, which says: “This action is brought to the attention of the Consumer Product Safety Commission under Section 10 of the Consumer Product Safety Act.” Among other things, the petition sought whether the CPSC should “require that water heaters be fabricated with a maximum thermostat setting of 130 F.” It was based on its understanding of Vickery’s request in his letter.

The CPSC did not reach out to Feldman before writing the petition, as he lamented in a letter after he was provided with a copy of the first staff briefing packet (which is a consolidated report from the various staff departments of the CPSC and provided to the five-member commission for a decision on the petition).  

At this juncture, I find it important to reiterate briefly, as discussed in the August column I wrote about the CPSC proceedings, that prior to the CPSC’s receipt of Vickery’s letter, the CPSC was involved with the plumbing industry in the development of several product standards for anti-scald devices at the point-of-use, and was already leaning toward deference to voluntary standards (as it is required to do so by statute) rather than the issuance of a new consumer product safety rule.

Nonetheless, the CPSC authored the petition in such a manner that, if granted, would require water heater manufacturers to redesign their product to perform a function — control of the outlet temperature to within a few degrees of the thermostat set-point — which, to this date, cannot be technically accomplished.  

Within the ensuing letters and document exchanges between the CPSC and appliance associations and manufacturers, there is imparted to the commission both information and acknowledgment that water heater thermostats cannot accurately control outlet temperatures to a set temperature. This information should have triggered action on the part of the CPSC to scrap the petition or at least return to the drawing board, so to speak.

Noteworthy is the fact that in no staff briefing packet provided to the commission does the CPSC staff advise the commission that there is currently no technology that allows water heaters to “be fabricated with a maximum thermostat setting of 130 F.”

Quite obviously, a diversion was needed. And, that diversion was found in the requested maximum temperature limit of 130 F, which temperature was plucked by Feldman, as he later explained, as a concession to allow for adequate dishwashing. Thereafter, the focus of the petition wallowed into an exploration of the temperature of hot water necessary to activate detergents in order to clean dishes and clothes.  

The documents show that, even before the petition was issued, the CPSC had an ongoing relationship with home appliance associations and manufacturers (such as water heaters, dishwashers and clothes washers). It reached out to these industry representatives for early advice on the request presented in the petition. The following letters were exchanged ahead of the first meeting of the five-member commission on Nov. 9, 1978:

• July 25, 1978: Letter from CPSC to Whirlpool;

• Sept. 12, 1978: Letter from the Gas Appliance Manufacturers Association to CPSC;

• Sept. 13, 1978: Letter from AHAM to CPSC;

• Sept. 20, 1978: Letter from State Industries to CPSC;

• Sept. 20, 1978: Letter from Underwriters Laboratories to CPSC;

• Oct. 31, 1978: Letter from the American National Standards Committee to CPSC;

• Nov. 2, 1978: Letter from Consumers Institute/General Electric to CPSC.

Industry response

Not surprisingly, appliance manufacturers and industry associations rejected the request in the petition, and they set out to counter it by proving that scalding hot water was necessary for sanitation (sometimes rejecting contrary evidence). For example, in a letter dated Sept. 13, 1978, AHAM’s Vice President of Engineering Herb Phillips wrote to CPSC’s Director of Voluntary Standards Donald R. Mackay with his concerns about the petition:

• He wrote that “consideration must be given to those households where hot water is required for dishwashing and clothes washing.”  

• He wrote that the currently available dishwashing detergents require temperatures of 140 F or higher.

• He pointed to a final rule for the Department of Energy, dated Aug. 8, 1977, regarding test procedures for dishwashers, in which it was stated that “[u]nder present technology no dishwasher detergent exists that is effective at a temperature of 130 F.”  

• He pointed to the January 1977 study prepared for the CPSC by the A.D. Little Co., “The Feasibility of Lowering Water Heater Temperature as a Means of Reducing Scald Hazards,” for the proposition that lowering thermostat settings only benefits homes with children 4 years of age or under. That only accounts for about 25 percent of all homes, forcing “families with older children … to supplement or upgrade water heating capability to meet quantity requirements.”  

AHAM also commissioned a study by Thomas Kaneko and J.W. Compton of BASF (Wyandotte, Mich.) to study the effects of water temperature on dishwashing detergents. The study was published in the August 1978 issue of Soap/Cosmetics/Chemical Specialties. The study concluded that “satisfactory performance results could be obtained from four of six major brands of dishwasher detergents at a water temperature of 100 F.”  

Dissatisfied with the results of its own commissioned study, AHAM, through its technical director, Walter Blanck, spoke with Peter L. Armstrong of the CPSC and indicated that he thought the study was flawed. However, there is no evidence that this was brought to the attention of the authors of the study or their employer, BASF Wyandotte.

Instead, AHAM actively involved its membership in taking a position on the petition, writing in a Nov. 17, 1978, mailing: “It is apparent that a strong industry position is needed to support the need for 140 F water at the water heater to assure [sic] satisfactory performance of [clothes washers and dishwashers].” Member responses were summarized in a letter and sent to CPSC’s Mackay on Feb. 13, 1979.  

The letter also summarized the results of a consumer survey that AHAM, through the Chicago Consumer Sounding Board, sent to 99 families in the Chicago area, asking select consumers to weigh the cost-benefits of energy savings vs. scalding. It concluded:  

“It is strongly requested that the enclosed information be given due consideration. There is a strong possibility that if consumers are faced with hot water shortages and unsatisfactory performance of appliances, the tendency might be to set water heaters higher than necessary and increase the tap water scalding hazards. The consumer education program and labeling program must be conducted very carefully in order to prevent tap water scalding from becoming an even greater problem.”

The CPSC proceedings were not a review of water heater design, and there has never been a public review on water heater design to make them safer with respect to scald burn injuries. In my August column, I discussed the statutory authority of the CPSC to issue a consumer product safety rule, which requires the CPSC to defer to voluntary industry standards, and that standards for bathtub and shower valves to control the maximum (mixed) hot water temperatures at the point-of-use were in development at the time of the CPSC petition.  

I also discussed how the CPSC proceedings became focused not on water heater design but on the hot water temperatures necessary to activate detergents for automatic dishwashers and clothes-washing machines.  

As a final note on water heater design, I have advocated, and I strongly am of the opinion, that it is technically and economically feasible to incorporate into the design a mixing valve on the outlet of a residential water heater, similar to the incorporation of the pressure relief valve that comes with every water heater.  

It will make water heaters safer as it will stabilize outlet temperatures with respect to scald burn injuries at the fixtures (i.e., taps), where hot water contact with human skin is not only anticipated but expected.  

However, a safe domestic hot water system relies upon a good design, including piping layout and selection and placement of equipment, such as master mixing valves and, especially, point-of-use mixing valves and maximum temperature limit-stop adjustments. A water heater is just one part of the overall domestic hot water system.

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Original post: https://www.phcppros.com/articles/14195-the-continuing-scald-problem-in-plumbing-systems-part-2?oly_enc_id=7354C5924023F5Q