This is where the case becomes very difficult. First of all, there were a total of three electric blankets in the room: one on each twin bed, and another folded away in the closet. (Luckily, the blanket in the closet could be eliminated.)

Though the debris had been carefully sifted through to find components from the electric blankets, there was not much to go on.

Fine burned wire of the heating elements... ...two melted plastic controllers like the one seen here... ...and three thermostats, about 1
Only the fine burned wire of the heating elements... ...two melted plastic controllers like the one seen here... ...and three thermostats, about 1" x 1 ¼ " long, are recovered.

In the construction of electric blankets from this vintage (Anderson’s engineers were able to determine the approximate manufacturing date of the blankets), 9 separate thermostats were woven into each blanket. After the fire, only three were recovered for examination: three out of eighteen.

Anderson Engineering had two problems to solve. First, the attorney wanted to know who manufactured the blankets. Then, the attorney needed to know which blanket failed, and how.

The engineers determined that at the time of the blankets’ manufacture, there were only two companies manufacturing electric blankets: Fieldcrest Cannon and Sunbeam. By the shape of the two controllers and by the type of the remaining blanket components, Anderson determined one bed had been covered with a Fieldcrest Cannon blanket, and the other with a Sunbeam blanket.

The Sunbeam blanket was the more deteriorated of the two, a strong indication that it had caused the fire. However, the attorneys put both sides on notice, essentially telling both manufacturers: “We’re almost certain one of these blankets started the fire.”

Experts from both companies provided useful information: two of the surviving thermostats were manufactured by Sunbeam, the remaining one was from Fieldcrest Cannon.

Now forensic science comes fully into play. The fire at the foot of the blanket suggests a failure of connection where the electrical cord meets the blanket – a common failure in electric blankets. However, neither a cord nor a connector survived the fire. These crucial parts weren’t recovered.

What Anderson Engineering did have in their possession was a thermostat contact which showed indications of pitting – deterioration resulting from the small arcing events that occur every time the thermostat opens/closes under electrical load. This suggests that the blanket was overheating and the thermostat was having trouble opening. If the thermostat doesn't open properly, the circuit would continue to provide power to the heating element within the blanket. The heating element would continue to operate even though localized temperatures would normally have been hot enough to open the thermostat and stop the heating process.

The attorney had his case.

  • Expert Witness Testimony