(WIBC.com file photo: Mike Corbin)

Saturday's explosion on Indy's south side blew two houses to smithereens, but even pieces that tiny can be enough for investigators to determine a cause.

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Fires or explosions start somewhere. Ivy Tech fire safety instructor Rick Palmer explains eyewitness reports, starting with whoever calls 911, may offer an idea of where that starting point was. Even if they can't, the wreckage will radiate outward from the point of origin.

Even the size of the fragments left behind tells investigators something about what happened. Palmer says the larger the pieces, the lower the rate of the explosion. Those clues help investigators distinguish a natural-gas explosion from a bomb blast or other causes.

Palmer isn't involved in the Richmond Hill investigation, and spoke generally about investigative procedures. He says once investigators zero in on where a fire started, they focus on debris closest to that point, and hope the chunks are big enough for a lab to determine whether an appliance malfunctioned or something else happened. But he notes some cases end up unsolved.