Explosive is a material that produces a rapid, violent reaction when acted upon by heat or a strong blow. During the reaction, explosives give off large amounts of gases at high pressure. The enormous power released during an explosion gives explosives many commercial and military uses. Explosives enable construction workers to clear land of tree stumps and boulders in order to build roads or buildings. They are used in excavating (digging) mines and to loosen the flow of oil deep beneath rock in oil wells. They blast tunnels through mountains. In war, explosives are used to damage cities, destroy ships and airplanes, and kill enemy troops.