God gave Noah the rainbow sign, no more water, the fire next time." So goes the old gospel song that suggests fire is a more severe punishment than water. I'm not so sure that applies to property damage: water can cause terribly expensive damage.
Scene of the Crime
The scene: an upstairs storage room in an elegant old Boston restaurant: the time, the wee small hours. A heat-sensitive ceiling sprinkler tripped and spewed water until it was discovered the next day. The water poured through the ceiling of the bar and main dining room creating a horrific and very expensive mess. There was no sign of a fire, so why did the sprinkler go off? I was called in by the attorneys for an insurer to solve the mystery.
The Investigation
Some people are surprised to learn that alloys may melt at a lower temperature than any of the components. A 50-50 copper-nickel alloy melts hundreds of degrees Celsius below either pure component and a 50-50 solution of anti-freeze (ethylene glycol) and water melts at about -40 degrees (Celsius or Fahrenheit, take your pick) which is tens of degrees below the melting point of either component. These low melting solutions are called eutectics after the Greek, eutektos, easily melted.
Proper chemistry control can produce an alloy of almost any desired melting point, from below room temperature to white heat. There are more than a hundred so-called "fusible alloys" (based largely on bismuth, cadmium, lead and tin), that melt between room temperature and about 300C. They are widely used in fire protection as fusible plugs to prevent overheating in boilers, and as low temperature solders.
The fusible metal in the subject sprinkler was supposed to melt at 165F. Since it was possible that a lower-melting alloy had been used by mistake, I did a compositional analysis in the scanning electron microscope. The fuse was found to be made of a Bi-Cd-Pb-Sn alloy with a composition corresponding to a commercial alloy that melted at 167F, so the material was correct. It was also possible that something had overstressed the fusible material, causing fracture. A scanning electron microscope study showed that the fuse surface was bumpy, as may be caused by melting. There was no sign of the dimples, characteristic of ductile failure, or the facets associated with brittle fracture. The fuse had melted, but why?
The Culprit
The fuse was located only about six inches from a 100W incandescent light, leading to suggestions that the bulb was the culprit. I investigated this hypothesis in my home. I placed the sensing end of an Instant Read meat thermometer six inches from a bare, overhead 100W bulb, to match the conditions in the restaurant. The thermometer read only 80F — not even close. I then placed the thermometer one inch from the bulb and only got a 100F reading. It was clear that mere proximity to the overhead light was not going to trip the fuse.
Then I put the thermometer inside a closed 6-inch Lightolier globe with a 60W bulb. The temperature quickly reached 190F. The 100W bulb thus generated plenty of heat if it were tightly enclosed with the fuse. The storage room where the accident happened was regularly filled with boxes piled to the ceiling. I concluded that most probably the boxes had been piled so as to tightly enclose the bulb and fuse, causing an accident.
I am sure that the restaurant's insurance people raised Cain over the proximity of the light bulb to the fuse and boxes. I never learned the outcome of this case.
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