There is a law in the USA (and Canada) requiring
that you call for underground utility locations
before you do any excavation.
The pictures below are a result of a farmer using
a post hole digger without calling for "locates"
and he hit an underground, high-pressure cross
country gas pipe.
Had to be one of those gas powered augers, either free-standing or on a tractor.
Supposedly there was no trace of the farmer or his equipment...
It also took out 2 homes...
Take a look for yourself...
Thanks to GTcars
for the pics