Scalded to Death in a Spa


Scalded to Death in a Spa - by Tom Boster and Tom Braun
		The purpose of this paper was twofold: 1) To answer the question in the scalding death of a young child in an overheated spa: Was the high temperature produced by a faulty heating element and control system or was it created by powerful pumps and the resulting heating of the spa water by direct conversion of mechanical energy into heat? 2) To inform designers of any spa or hot tub that one must take into consideration the temperature increase when water is pumped by virtue of the mechanical equivalent of heat and to take the necessary safety precautions to prevent the generation of high water temperatures even when the normal heating mechanism is not operating or is turned off.
In order to answer these questions, the following steps were accomplished: The heating unit and the control system were tested over a period of time by several engineers and found to operate with no malfunction. It was determined that the well-insulated 500 gallon spa was left at a temperature of approximately 105° F and covered with the four inch thick spa cover with insulating skirt along the side for further prevention of heat loss. The 2.6 horsepower and 1.5 horsepower electric pump motors were left on by mistake. There was no automatic timer to turn the pump motors off and they ran continuously for approximately three days. At this time a mother and the young child opened up the spa cover and the young child jumped into the spa. It was determined that the spa water temperature was approximately 168° F when the young child jumped in. She died as a result of the scalding. We demonstrated through a simple calculation that the powerful pumps will create approximately 750,000 BTU of energy over a three-day period. This is more than enough to elevate the spa water up to a temperature of approximately 168° F even with a high percentage of heat loss. It was not possible to conduct an actual test on the subject spa to determine water temperature as a function of time. It would have been interesting to measure the conversion efficiency of the pumps to determine the precise amount of energy that was created by the low speed working pump relative to the high speed jet pump. The elevation of spa water temperature by direct sunlight and heating from the electric motors that were enclosed under the wooden frame of the spa were considered negligible. It was not possible to determine if the water had reached equilibrium temperature after three days of pump running time. However, since the spa 1) had a very tight cover with no visible gaps or openings, 2) was covered with expanded foam approximately six inches thick and 3) was then enclosed by a wooden frame, it is estimated that additional running time could produce spa water temperatures in excess of the 168˚ F measured shortly after the unfortunate accident. Conclusions: Dangerously high levels of spa and hot tub water temperature can be generated by the direct conversion of mechanical pump energy into heat. For this particular problem the following design considerations are suggested: Design the spa electrical system of lights, heaters, pumps and motors with a single power turn-off switch. This safety feature will allow users to completely shut down the spa by using one conveniently located turnoff switch. Design the spa with a manual timer that will turn off all power to the spa. While there should be some range of selection on the timer, a thirty minute maximum time is recommended. Design the spa with a manual temperature cut-off switch that is wired to the heater and all pump motors. This feature is a backup system and will protect users should the normal thermostat fail or should another malfunction occur. It is imperative that this high temperature cut-off switch be manually reset if a malfunction occurs and that it contain a warning to require immediate inspection and repair should the systems fail.