A few years ago I was canoe camping during the Victoria Day weekend in Nova Scotia with three friends. We had set up camp on an island in Ponhook Lake on the Friday evening intending to move on the next day but weather kept us there an extra night. The same fire place had been being used to prepare Friday supper, illuminate the evening yack, and then Saturday breakfast. Dinner was a non-cooked affair but the fire was relit to make the steaks for Saturday supper and tended to a nice bed of coals. The steaks were put on and had just been flipped once when the bomb hit.
I heard a loud crack like a rifle shot, felt and saw a shower of glowing fragments explode all around me, some bouncing off me, followed by a low clanging as the light metal grate I was using skidded sideways to a stop beside the fire. All four steaks were lying on the ground.
After we extinguished the fall out, picked the surprised ants and pine needles off the steaks, and put things back together, supper proceeded as it was supposed to. We did find something interesting though. The explosive effect had come from a small rock, roughly oval in shape, about 5 inches long, 3 inches wide, and 1.5 inches thick. One half of it (presumably the part that moved the grate) had been broken into pieces but the bottom half was intact. We recovered enough of the fractured part to recreate the crime and find that there had been a sizeable cavity in the middle of the rock. The rock hadn't been put there by us so was apparently in the underbed of the fireplace we had built well above the signs of highest water level. We guessed that it was porous enough to release pressure for a while but exposure pushed it past the limit.
We stayed the night and the fire burned still more. Much dark rum and good steak calmed our nerves so we've all moved on since then.
