Puzzle: Account of an Unusual Investigation

"When you eliminate the impossible, whatever is left, however improbable, must be the truth." These words come from Arthur Conan Doyle, creator of the world's most famous detective. While forensic engineers rarely demonstrate the deductive powers associated with the great Sherlock Holmes, our investigations may sometimes resemble detective work. If we're methodical, observant, thorough, and perhaps most-especially lucky, we may unearth the truth. Once our clients' needs have been met, in a case where the circumstances were unusual or the results perhaps surprised us, we may be left with interesting stories. This paper presents a particularly challenging investigation; one with enough twists to test the consultant's knowledge of engineering and his powers of reasoning. In this case, electrical transformers that were buried beneath a sidewalk exploded and burst into flames. Happening within a block from the State Capitol, the local news trucks found it easy to cover this event and so it even made the evening news. The media coverage showed flames coming out of the sidewalk and the fire department hosing down the adjacent house. Measurements made later show that the steel grates covering these transformers were 40 and 50 inches away from the basement wall of the adjacent house. There was no immediate evidence of cracking or other vibration damage and the owner didn't notice any damage for a few weeks. That's when he called his insurance company. The insurance adjuster called me. In this and other investigations, the facts at first seemed confused and even contradictory. The owner noted that he had felt the explosions but he did not observe any damage. Weeks later, however, he noticed bulging siding, nails popping, and significant movement in the cladding on a timber-framed wall. Although the wall appeared damaged, this wall is supported by a centuries-old stone foundation that has no visible cracks. Immediately behind the damaged exterior, the owner noticed water stains and paint peeling from the plaster wall that follows a curving staircase. Throughout our investigation into this case, the actual causes of the visible damage emerged only after the "obvious" and expected causes were eliminated. In the end, this investigation tested imagination as much as knowledge, casting doubt on our initial reactions, constantly challenging assumptions, and forcing me to question myself at every turn. Many investigations are puzzles, and for me, success — when and if it comes — always owes a debt to instinct, persistence, and deliberation, but especially to a healthy dose of luck.