blasting, shattering, breaking, or splitting of rock or other material by the discharge of an explosive placed within or in contact with it. It is a necessary part of many engineering operations. An ancient method of breaking rock consisted of heating the rock by fire and then pouring water on it, the sudden contraction resulting in shattering or cleavage. Modern methods of blasting involve four operations: drilling the holes to receive the charge, placing it, stemming the hole (i.e., filling the hole above the charge with earth or clay), and igniting or detonating the charge. The location, size, and number of holes drilled depend upon local conditions and the nature of the work. The holes vary from 1 to 3 in. (3–8 cm) in diameter and from a few inches up to 20 ft (6 m) or more in depth. The charge is made up of some explosive, such as dynamite or ammonium nitrate; black powder, the oldest known explosive, is rarely used today. Multiple charges are sometimes set off, either simultaneously or in sequence.