Last summer when a mysterious explosion leveled a former ranger headquarters at a state park in Michigan, the event made national news--primarily because it was blamed on bat guano. National humor writer Dave Barry used it as fodder for his weekly syndicated column, and radio personality Paul Harvey included the item in his noon commentary. Campers from 14 miles away were awakened by the blast, and window frames were hurled some 100 feet into the woods. The building had been vacated a month before, so no one was injured.
As has often been the case with sensational bat stories, few newspapers or other media carefully checked their facts initially or carried the follow-up, which later exonerated the bats and officially blamed sewer gas. The articles vindicating bats appeared last fall and were limited primarily to a few local Michigan papers. Most people who read the original story did not see the follow-up and were left with the impression that bat guano in buildings can cause a violent explosion, confirming the worst fears of those who already dislike bats. Such scare stories typically lead to needless war on bats.
The notion that bats caused the blast came from Detective Sgt. Walley Helmila of the Michigan State Police Fire Marshall Division. Before he had finished his investigation, he was pressed by reporters for an answer to the explosion. He rattled off a number of things that might have caused it, including a joking comment about methane gas resulting from decomposing bat guano. Bats had long been roosting in the building, and a great deal of guano had accumulated in the attic and walls. Exploding bat guano was a lot more interesting than any of the other theories, which included propane or sewer gas. The story assessing blame to bats was picked up by one of the wire services and ran in many newspapers across the country.
In the meantime, Sgt. Helmila, who has no grudge against bats, called BCI to apologize for the bad press and to explain how the unproven theory got blown out of proportion and accepted as fact. He had also discovered that he had been given some inaccurate information during his official investigation. At BCI's urging, the investigation was reopened.
Propane had been ruled out, since the propane tank had been disconnected. Foul play was unlikely; the building's insurance had been canceled two months before the blast. The explosion was clearly generated in the basement, and considerable evidence pointed to the sump pump itself. Most of the guano, however, had been in a well-ventilated attic. In any case, there is no evidence that bat guano ever produces methane. Since methane is lighter than air, it would be virtually impossible that any methane-caused explosion in the basement could have come from guano in the attic. The original news reports had stated as fact that methane is heavier than air and could have sunk from the attic, igniting when the electric pump turned on (advice Helmila had received from an "expert").
Thanks to the conscientiousness and perseverance of Sgt. Walley Helmila, the official cause of this explosion is now listed as sewer gas. There is no known case of bat guano ever spontaneously exploding in a building.