Gunpowder explosion. Fireball from the detonation of gunpowder (also called black powder) during research into explosives. Instruments around the fireball measure its thermal output. Each red and white marking on the poles around the explosion is one metre long. Gunpowder is a mixture of about 75% potassium nitrate, 15% charcoal and 10% sulphur. It burns rapidly, generating large amounts of gas and heat which cause a sudden increase in pressure. This explosion was created with 23 kilogrammes of gunpowder. Photographed during research conducted by the Health and Safety Laboratory in Britain.