Campbell McKay, of Ridgway School, asks :-
How do they make the special effects on TV like when a shop blows up just as someone is leaving it?
Anthony Lealand, a pyo-technic scientist who formed The Fireworks Display Company of Christchurch and who regularly devises special effects for orchestral productions, celebrity openings, advertisements, movies and TV programmes, responded.
Real explosions are actually quite boring looking things.
There is a fast flash, objects fly about so fast you wouldn't see them on video and generally there is only a small puff of black smoke. This is because an explosion is the result of a very fast chemical reaction and most explosives are carbon rich. In other words there is not enough oxygen to burn the carbon in them.
However this is too boring for television and film. For these explosions we use low explosives, such as gunpowder and nitro-cellulose, which are very slow and which therefore do not generate a supersonic bang. These are triggered by electrical ignition so the sequence of explosions is under the careful control of the explosive expert and/or his/her computer. For example, as an actor runs from a building a whole sequence of explosions can be initiated.
For effect, these explosives are placed inside bags or drums of fuel which ignite to give the glowing fireball effect. Frequently other pyrotechnics effects are added, such as mines or mortars or cannons that will blow out white stars or titanium powder to form white sparks. The procedure is messy, dangerous and frightening to rig because the liquid fuels could be ignited by chance sources of ignition. This can go horribly wrong unless one has had considerable experience.
The whole effect is a comic book explosion totally unlike a real explosion but fully satisfying the visual demands of television and film.