This file was made for the game engine. It is a simple example of a starting file (I do not want to recreate an explosion from scratch for each new explosion -- I want to eventually build about 10 different kinds of explosions). The default camera, though in the scene, is not connected to any controllers. Place your cursor in the 3d window and press the "p" key to play the explosion. The explosion will only occure once; press the "esc" key to stop the game engine.
What you see and why: The falling block is a Riggid Body and will fall and tumble when it hits other objects, just like a hand grenade. After a few seconds the cube disappears and is replaced with an expanding shock object and a central bang object. The Sphere object is located in the second layer. It presently has a material set with the transparency turned on, and which is set low enough to allow the sphere to be seen. The Bang object is located in the third layer. It consists of three planes to which the same image has been UVed. The image has an alpha channel, which is the transparency color, with transparncy set to max. There is another sphere in the fourth layer, with an Ipo animation, but you should note that it is not active (it can be used to carry either an expanding "smoke" texture and/or a collision wave).
The sphere object in the secon layer can also be made into, and probably will be made into, the collision object.
I intend to update this some time this week and put in some more textures and the collision properties (so the wave actually knocks stuff outward).
[Edit: 2.59 file was replaced; forgot to pack the textures before I zipped it! All fixed )