Hotter Water Needed to Prevent BacteriaI am writing in response to the article entitled, "Scald Burn Risk and Energy Conservation," by D. Bynum, Jr. in the July 2001 issue. Dr. Bynum's analysis and conclusions are right on target as far as they go; however, it must be noted that ASHRAE, ASPE and others in the industry recommend that the minimum water heater storage temperature be 140 degrees F to eliminate (or at least greatly minimize) the possibility of Legionella bacteria developing in the water. The risk and potential liability associated with Legionnaires' Disease is potentially greater than the risk of scalding by hot water. I am all in favor of reducing risks and saving energy, but not at the expense of creating another problem. Our office standard is to design all domestic water heating systems for 140 degrees F storage, with a thermostatic mixing valve to reduce the supply to the fixtures to 110 to 120 degrees F. There are obviously exceptions, such as process hot water systems or kitchen hot water systems, which are generally higher temperature requirements.
Thomas M. Long, P.E.
Gannett Fleming, Inc.
Dr. D. Bynum Jr.'s response: You say that your practice is to use 140 degrees F hot water storage, then use a thermostatic mixing valve set at 110 to 120 degrees F. But what have you accomplished, since legionella can replicate at 110 degrees F? I believe you have eradicated Legionella in the water heater, but have made a home for the disease in the pipes and fixtures, and especially in dead end piping, after the hot water leaves the water heater. I do agree with you that point of source thermostatic mixing valves should be used, though.
Bacteria Prevention More Important than Scald RiskI am a plumbing engineer with over 20 years experience in designing plumbing systems, including hot water systems. I recently read an article titled, "Scald Burn Risk and Energy Conservation," by D. Bynum, Jr. in the July 2001PME, and I feel I must address many things in his article that are in error and are misleading.
Mr. Bynum is recommending to turn the water heater thermostat down to prevent scalding. This obviously comes from his past exposure to litigation related to scalding that he refers to in the article. I'm sure he was probably an expert witness in a scalding case, and after being exposed to the pictures, I can understand why he would want to crusade for protecting people from being burned from scalding water. While his intentions are good, his advice is bad.
His recommendation to turn down the thermostat probably had many people rushing to their mechanical rooms to turn down the thermostat on the water heater and create a condition that will incubate waterborne pathogens and bacteria. When someone runs out of hot water, there can be scalding when the thermostat is turned back up. According to the book, Legionellae Control in Health Care Facilities, it is estimated that of the 2.4 million people that die of pneumonia each year, 10,000 to 100,000 of them die from Legionellae. These statistics are with predominately 140-degree domestic hot water storage systems. It is quite likely that Mr. Bynum's recommendation could lead to many more people dying from Legionella, and people will still be scalded with the 120-degree system.
I have also been an expert witness in scald cases, where a system was designed exactly as Mr. Bynum recommends, with the water heater set at 120 degrees. I saw the horrible pictures of a child scalded with no skin left from his waist down. The water heaters were turned down to 120 degrees to prevent scalding. After running out of hot water on one occasion, the maintenance person turned up the thermostat on the water heater and did not re-adjust the maximum temperature limit stops. The scald problem returned, and the child was severely burned. What that system needed was a master mixing valve, not a thermostat adjustment on the water heater. Mr. Bynum also did not address Legionellae or master mixing valves, which are more appropriate to use when dealing with scalding than the thermostat on the water heater.
He seemed to be so concerned about scalding and energy efficiency that he did not take everything into consideration. I am quite sure the cost savings in energy between the two different sized heaters at different temperatures is so insignificant that it cannot really be used as an argument.
For example: consider that the water heater designed for 120 degrees storage temperature needs to be almost twice the size as the water heater with 140-degree water, so there is much more surface area for heat loss. I have also dealt with systems where the water heater thermostat was turned down, and in the wintertime, it required over 80% of the mixed water temperature to be hot water. This caused severe pressure drops in the already smaller domestic hot water piping to the point where cold water at a much higher pressure was crossing over into the hot water system at several mixing valve locations, and there were numerous other problems with the system.
Reading Mr. Bynum's article, I wondered if he was aware that most people with a basic knowledge in the industry know you should store the hot water at 135 to 140 degrees to prevent Legionellae bacteria growth in the water heater. In fact, the American Society of Plumbing Engineers has published a research paper and issued a Board of Directors position statement that recommends storing hot water between 135 and 140 degrees Fahrenheit to control Legionella growth in the water heater.
What Mr. Bynum's article failed to address is, to control scalding you should use a master mixing valve conforming to ASSE 1017, point of use scald prevention devices conforming to ASSE 1016 on shower valves, and maximum temperature limit stops on faucets and shower valves. There are also several manufacturers promoting new anti-scald devices that shut off the flow of water to a faucet or showerhead when the water temperature exceeds 120 degrees.
Mr. Bynum also states a water heater should be horizontal, not vertical. In the ASPE Hot Water Design manual, every water heater manufacturer and most plumbing engineers will disagree with Mr. Bynum when it comes to efficiency and tank orientation. A water heater should be vertical, not horizontal. A vertical installation with the outlet piping from the top and the inlet piping at the bottom allows the water to stratify and you have more usable hot water from the heater. A horizontal tank promotes mixing of the hot water in the tank and a lower blended temperature, causing the horizontal tank to run out of hot water earlier and causing the thermostat to come on more often.
His energy calculations did not justify lowering the storage temperature of a water heater. It would create a breeding ground for waterborne pathogens, and the increased cost of the larger water heater required does not pay for itself in energy savings from a 20-degree temperature difference over a larger surface area.
The ASPE Data Book references a major study on burn research done by A. R. Moritz and F.C. Henriques, Jr. at Purdue University. They both show a table for time/temperature combinations producing skin damage. The skin damage was defined as "first degree" burns. The report also shows the normal threshold of pain is 118 degrees Fahrenheit. I can recall entering a hot tub at the local health club and checking the floating thermometer to find it was at 110 to 111 degrees Fahrenheit. It was hot, but not painful. I question what kind of research was done to determine his comments of the "threshold of pain" being 103 degrees and the "scream point" being 105 degrees. (I am visualizing lab rats being dipped in hot water, and the ones dipped in 103 degree water screamed). Maybe it could be that Mr. Bynum has thin skin. Not everyone will be uncomfortable in 103-degree water, but some would be very comfortable. I would be interested in hearing more information and background on the "scream point."
He also said you should buy a 75-gallon water heater when you design a system for his recommended 120-degree system, in lieu of the industry standard 140-degree system. He said a 40-gallon water heater costs $146, and a 75-gallon heater costs $399 dollars. I hope he calculates the difference in installed cost in his energy savings calculation. He will find with the same efficiency and the overall installed cost, the larger water heater will not pay for itself in energy savings over the five- to seven-year life expectancy of the water heater. I wondered why he did not suggest purchasing two 40-gallon water heaters for $146 each. He would then have 80 gallons of hot water for $292.
I also wondered why the only reference material he cited was the two articles he wrote.
Michigan Plumbing Designer
Dr. Bynum's response: Regarding the comments by the Anonymous Michigan Plumbing Designer:
1. Correct, I have worked on a large number of scald burn cases, for the Plaintiff, the Defense and for the Ad Litem. And yes, I want to crusade for protecting you, the children, the elderly, the infirm and ill people from serious or fatal burns that could and should be prevented. The required burn treatments are horrible, and the problems that third-degree burn survivors suffer last for the rest of their lives.
2. I agree that Legionella is also terrible and should be eliminated so far as is possible. But I question the Legionellae morbidity stats he cited. And according to the NEISS stats in the 1989 CPSC Summary Report, an estimated 10,495 children, all less than four years of age, were treated in U.S. hospital emergency facilities for hot water scald burns in that year!
3. I do not agree with the 120 degrees F system. Actually, my recommendation is that the hot water at the draw should not exceed 115 degrees F, for justifiable reasons too numerous to mention here.
4. He discusses a case where the maintenance man turned the thermostat too high, causing scald burns to a child. That was clearly a lack of training of the maintenance man, and the owner should have to pay for lack of training and for not putting a lock on the water heater room.
5. Using 80% hot water in a mix is a very good idea. But, if hot water is then drawn from a second fixture, the pressure drop in the hot water will cause the percent of hot water in the initial mix to decrease at both fixtures, not increase.
6. I completely agree with the reader that ASSE 1016 and 1017 valves should be used at the point of source. Then you can sometimes safely set the water heater thermostat to higher temperatures. But, I worked on one particular child burn case caused by a malfunction of a tempering valve that did not fail-safe. Another problem is that residential hot water heaters are not ever factory fitted with these needed valves, not even as an option to the consumer.
7. Some of the reader's arguments against horizontal heaters is nonsense. Agreed that the vertical installation allows more stratification or layering, but that is exactly what you do not want!
8. The noteworthy and unusual research work done by Moritz and Henriques was reported in five separate papers in the Journal of Pathology in 1947. Unusual because the authors and several volunteers placed glass stems on their arms and backs, then made small burns at various places at different temperatures, which is the basis for most, if not all time-temperature burn charts.
9. But, as you might expect, the Moritz tests on their own skin and on porcine skin were limited to the determination of skin reddening, sunburn (first degree, in epidermis), blisters (second-degree, begin dermis burn), and minor necroses (third-degree, partial dermis burn), but none of the more serious burns.
10. Using their data and meager heat transfer property data available for human tissue, we are presently trying to calculate the time-temperature relations for the more serious burns, i.e. fourth-degree (burn completely through the dermis), fifth-degree (burn through the subcutaneous tissue), sixth-degree (burn through muscle or ligament), seventh-degree (burn through the periostium), and eighth-degree (bone burn). To validate this work, this is a call for volunteers willing to incur fourth- through eighth-degree burns on various small areas of the body.
11. Neurologists formerly conducted hot bath tests on MS patients to measure the number of neurological deficits (signs) as the water temperature was gradually raised from 105 to 110 degrees F in 10 to 15 minutes. The practice ceased in about 1980 because of the severe trauma incurred by the patients.
12. I have worked on lot of cases involving severe burns caused by excessively hot temperatures for a large number of reasons. Some of these were epileptics having grand mal seizures in the shower or other types of seizures (a normal body response is to "black out" in severe trauma, such as getting a leg very slowly cut off without anesthesia or shower burns), or MS patients, etc. When the body core temperature of people with MS rises only 0.5 to 2.5 degrees F degrees, they can lose their vision, become mute and even paralyzed. In one severe case, an elderly gentleman incurred sixth- and seventh-degree burns to both legs, which had to be amputated, and then he died from sepsis within a week due to the contamination of the deep exposed tissue while in the bathtub. Looking at photos of burns to the bone are not pretty pictures.
13. I do not believe the writer's reported experiences--he should buy a new floating thermometer for his health club if he thinks 110 to 111 degrees F is not painful. Also, a sudden immersion in a 102 degrees F hot tub can cause heart fibrillation if you have any latent heart problems.
14. Regarding pain threshold, the State of California requires that the hot water temperature in all showers in jails and prisons not exceed 105 degrees F. This is so that two prisoners could not grab another prisoner's arms and torture and/or scald the guy under the shower. Prison/jail max hot water temp is 110 degrees F in Texas and also 110 degrees F in Michigan.
15. I do not believe that the normal life expectancy for water heaters is only five to seven years, as was stated. Show me where it is so. In my former residence, my water heater lasted about 15 years, and my understanding is that the average heater life expectancy is about 12 years.
16. The premium cost of a 75- vs. a 40-gallon heater from Lowe's prices is about ($399-146) /12, or about $21 per year or about five cents per day, a lot less than about $20,000 per day for costs of severe third-degree scald burn treatment and care for about 30 days of hospitalization in the first three months after the burn occurrence.
17. I only cited three (not two as was stated) references, and those were my previously published articles, because I thought these were most pertinent for my "crusade." I wanted to cite another 1,000 or more references but did not think the editor would go for it.
Hot Water UsageRegarding Chart 11, Energy efficiency, in the article on scald burn risk from Dr. D. Bynum in the July issue, the calculations assume that the same amount of hot water is used per day, no matter what the temperature. However, in reality, the user or a hot water regulating valve will use smaller amounts of hot water at 165 degrees than hot water at 115 degrees to mix with cold water to obtain the water temperature the user needs. Therefore, the energy savings will be much lower than indicated. The savings will be solely due to the reduced heat losses from the tank and increased efficiency of the heater.
Dr. Bynum's response: I agree that the same amount of hot water at the different prescribed temperatures given in Chart 11 of my article were used in each case. For people taking one-hour-long showers, you are right, and then the calculations could and should be adjusted. But I do not know the U.S. average time for shower time, and even if we had that data, it would be approximate to use for only a small percent of general calculations.
I have two associates that tell me a one-minute shower is a "long time" for them. And without frequent use of the shower, it would require about a minute for pipe heating to then get your higher water temperature. And, in this case, my calculations are quite valid and appropriate.
If you have a single 180-degree turn handle on a mixing valve in the shower, then with your 165 degrees F hot water, and assuming 50 degrees F cold water, you then need 43.5% hot water in the 100 degrees F mix, which corresponds to 78.3 degrees (78.3/180 = 0.435) of handle rotation. If the water heater was stacked, then the mix may suddenly turn scalding hot.
When a person accidentally bumps the handle to, say, 128 degrees open, then the mix temperature suddenly becomes 132 degrees F. This temperature will cause third-degree burns in 30 seconds for an adult or 15 seconds for a child or the elderly, and second-degree burns in 15 seconds for an adult or about seven seconds for a child or the elderly.
Factoring in panic delay time when escaping by children or the elderly, then severe scald burns with 165 degrees F hot water are inevitable. Delivered hot water at 165 degrees F makes it easy for lawyers to sue, and they love it.
Controlling Bacteria Growth Must Be Considered, TooThe "Scald Burn Risk and Energy Conservation" article in the July 2001 issue reminded me of the conflict that sometimes occurs between energy conservation and safety or health concerns. The energy crunch of the 1970s resulted in tighter buildings that drastically reduced the amount of outside air per person. Poor indoor air quality was the consequence. We saved energy, but got "Sick Building Syndrome" in the process. Fortunately, this has been corrected.
The water heater temperature issue is similar to the outside air problem. Turn back the thermostat on the water heater and save energy and help prevent scalding, both desirable results. What this fails to address is the pervasive presence of Legionella bacteria. Legionella can be found in almost all city and well water systems in this country. The bacteria typically survive chlorine disinfection treatments. The immune system of a healthy person can normally fight off the Legionella bacteria. However, the elderly, smokers, and immuno-suppressed persons are more susceptible. The bacteria thrive between the temperatures of 68 degrees F and 122 degrees F. It feeds on the biofilms or slime found in water heater sediment and scale. Water heaters, therefore, become amplifiers of the Legionella bacteria.
According to OSHA Technical Manual, Section III: Chapter 7, domestic hot water should be stored at a minimum of 140 degrees F and delivered at a minimum of 122 degrees F. OSHA's guidance pertains to the workplace and not to residences, and it does not distinguish between sizes. The PME article compared various water heaters with less than 100-gallon capacity and focused on energy efficiency. This is generally the range of most residential water heaters, but this size can also be found in many commercial and industrial places where people work. OSHA's guidance focuses on the control of Legionella growth. The question then becomes what's more important, energy efficiency and scald prevention or the risk of a Legionella case? We may be able to save some precious energy but is it worth getting "sick plumbing syndrome" in the process? Raising water heater temperature to 140 degrees F will increase heat loss and ultimately cost more to own and operate. But, in most cases, human health and safety is more important than the incremental energy cost of this higher setting.
Charles A. DePase, P.E., C.E.M.
U.S. Army Garrison, Aberdeen Proving Ground
Directorate of Public Works
Aberdeen Proving Ground, MD
Dr. Bynum's response: 1. I do not see a conflict between water and energy conservation, and health. If, for example, water conservation was not important, why was the w.c. flush volume decreased?
2. In "Sick Building Syndrome," you failed to mention the two primary causes. The first cause was improper ventilation design in "tight" buildings, which was not a problem in "leaky" buildings. The second problem was vapors emitted from incomplete polymerization in plastic products (curtains, flooring, carpet, etc.) when plastics first began to be widely used.
3. I agree that Legionella bacteria generally thrive at 68-122 degrees F and feed on slime biofilms formed in sediment and scale. And, since it is possible for the bacteria to replicate at 68 degrees F, when your water heater is indoors, maybe you should redesign your air conditioning system so that you can keep your room temperature at home to maybe 50 degrees F, or better, at 35 degrees F. The bacteria has also been found in ice machines!
4. Also, since some of the water in the pipes in the house will be at room temperature of 76 degrees F, by your reasoning, you should first heat the cold water to 140 degrees F, then cool it to 68 degrees F to avoid the 68-76 degrees F window of opportunity for the bacteria.
5. More importantly, if you, for example, found sewage in your hot tap water, I would recommend that you find and fix the source, rather than raising the water heater temperature. Also, disconnect long dead end pipes containing stagnant water.
6. You referred to the OSHA Tech Manual, Sec. 3, Chap. 7, which recommends but does not require hot tap water temperature in the workplace at a minimum of 140 degrees F storage and 122 degrees F delivery. I agree that these temperatures could apply to the workplace, but not in residences, for good reasons. The Tech Manual is a derivative of paragraph 5.a.1, the General Duty Clause, in the Williams Steiger Act, PL 91-596, 29DEC70, 91st Congress, which originated OSHA, leading to Title 29 CFR 1910 and 1926.
7. No dispute that Legionella is a cause for concern, as indicated in Sec. 3, Chap. 7, paragraph IIC of the Tech Manual, SEP99, which estimates that the over 25,000 cases of the illness each year cause over 4,000 deaths, or a morbidity rate of 16%.
8. But you seemed to conveniently ignore acceptable treatments that were also given in the same OSHA Tech Manual. These include (a) proper inspection and maintenance, (b) use of biocides such as bromine, (c) frequency of cleaning, (d) pasteurization at 158 degrees F for 24 hours, with 20-minute flushes at each outlet, (e) periodic chlorination, (f) ozonization, (g) oxidation, (h) ultraviolet radiation, (i) periodic chlorine shock treatment, etc.
9. Following your line of reasoning, if it is better to use 140 degrees F rather than 120 degrees F, then I assume that you would also agree that 160 degrees F is better and 180 degrees F is best.
Which Is the Greater Threat--Bacteria or Scald Risk?The article written by D. Bynum, Jr. was of the most in-depth reports on the subject of scald burn risk that I have ever read. Dr. Bynum is absolutely correct that this is a very serious problem. Unfortunately, when we solve one problem, we create another. One must remember that by lowering the hot water temperature stored in a vessel below 140 degrees F, we welcome the breeding environment for Legionella. Now, one must evaluate which situation poses a greater threat, wasting energy by raising the water temperature or creating a life-threatening situation. There is no solution that will resolve both issues. Presently, we design domestic hot water systems that store water in a vessel at 140 degrees F. A thermostatic mixing valve is provided that will reduce the leaving hot water temperature to either 110 or 120 degrees F. As a further safety measure, we can provide a solenoid valve with a sensor that, upon a rise in temperature above the set point of the thermostatic mixing valve, will shut the valve, preventing water distribution. (An alarm can also be provided.) Yes, we have solved the Legionella problem, and we have solved the scald problem, but we have not saved energy. Which leads back to my original question: which is more important, life or energy?
Joseph M. Smaul, P.E. NSPE
Burt Hill Kosar Rittelmann Associates
Dr. Bynum's response: I am pleased to hear that you are also using point of source tempering valves, but see my other comments attached. Your idea of installing an alarm is superb--I wish that I had thought of that. I have information on thousands, and personal knowledge on probably a hundred or more, hot water scald burn victims that occurred in the home. I am quite familiar with the Legionella vectors and their spread in commercial and industrial establishments, and in large buildings and hotels, such as those in Philadelphia. To date, I have not heard of a single case of Legionella that was home based. I would appreciate receiving any info you may have concerning contractions of Legionella in a domestic dwelling. I firmly believe that we can design water heater plumbing systems so that we can preclude severe or fatal scald burns, eradicate Legionella problems, AND conserve energy. The arguments are about how to do it all, safely and economically.