Nowadays in developing country like India, Bomb blast and other means of explosions are increasing day by day. There are three major types of explosions with which investigators usually are involved: atomic (nuclear), mechanical and chemical. An explosion is classified either as a low-order or high-order explosion. Explosion leads to several types of injury due to its various effects like blast pressure effect, shrapnel (fragmentation) effect, thermal effect and seismic effect. An explosive is any chemical compound, mixture, or device whose primary purpose is to function by explosion. Explosives are mainly classified as Low or Deflagrating and High or Detonating. Post blast scene investigation is very important to determine the type of explosion, intensity of explosion, type of explosive materials used, number of victims injured or died and nature of explosion means either accidental or some terrorist attack. In this paper we discussed about types of explosions, orders of explosions, effects of explosions, factors controlling explosion effects, types of explosives and crime scene investigation.