[maple_leaf_eh]

I can't comment on the safe distance, but it might be a good test to fire a few blanks in zero wind on an open field with a couple of decibel meters in an array at 90-deg and then spaced along the line of "fire". If anyone lays a complaint, you would have some sort of definitive proof of the sound's decay.

Several years ago I was involved in a complaint at a rifle range. Someone griped that a "30 caliber" bullet had hit their house and lodged in the bathtub, a long way down but outside the danger template. The homeowner knew instantly the differences between the 6.5 Swedish, French 7.5, NATO 7.62x51 and Russian 7.62x54, and someone's German 8mm. The volume from the Chief Provincial Firearms Officer and the Ontario Provincial Police was intense. Eventually the complaint was settled with some amateur forensics with a cleaning rod through the holes and a stern lecture to the complainant about public mischief. (I figure he shot his own house to try to get the range closed.)

There is no end to the idiocy that passes for public knowledge. Forewarned is forearmed.