What Does Down the Hole Hammer (DTH Hammer) Mean?
A down-the-hole hammer (DTH hammer) is a tool that can be attached to the end of a drill string and inserted into a bore. It's a small jack hammer used to break hard rock into small particles that can be flushed away by the DTH hammer's air exhaust.
Trenchlesspedia Explains Down the Hole Hammer (DTH Hammer)
A down-the-hole hammer provides a solution to the problem of removing hard rock barriers encountered in a bore. The DTH hammer resembles a small jack hammer. It screws onto the end of a drill string like a section of drill pipe. Like the jack hammers used above ground, it's air-powered with a high cyclic rate; unlike jack hammers above ground, it combines its fast-action hammer with a rotary, drilling action. This combined action rotates its chisel-like tip as it drives into the rock, breaking it into chips and dust. Because the DTH hammer is pneumatically powered, it has an air exhaust, which blows the chips and dust from the bore.
Small portable rigs equipped with a DTH hammer are reputed to drill through rock as quickly as large truck rigs.