One thing that you could do is to composite and explosion over what you've filmed (I'm not trying to talk you out of it, I've played around with some explosions myself), but if you go to www. detonationfilms.com they have some royalty free explosions that can be composited over what you've filmed, I've used them a bit, and they look good.

i have a very gritty/handheld filming style (eg Brotherhood/Assembly) and iv checked Detonation films and the explosions are okay, but alot of the time against a black backround which is hard to key. my shots are often full of depth and placing a 2D explosion will not look good at all, iv considered it, tried it with a previous war film i made and it looked awfull.

im thinking of attaching a banger to the end of a standard wire, and the other end to my switch board (conected to a car battery). water proofing the banger with a smakk plastic bag or somthing, placing the banger inside a white spirit bottle with the wire coming out. sealing the opening so its water tight, and burying it under lots of cork blocks painted brown.

does anyone know of any super market product which will give more of a kick the white spirit?

Again, not trying to dissuade you from blowing stuff up, but depending on the editing software you're using (I use final cut pro) you can composite images by simply right clicking the video on the timeline, selecting composite mode, and a list will pop up. You can experiment with different modes, they will take out all of the black or white or whatever, and almost flawlessly incorporate it into the image. If you have a handheld, gritty style, you could move it using keyframes. But it sounds like you know what you're doing with explosions, so whatever works best I guess.

I agree with filmmaker. I use detonationfilms and after effects... it kind of depends on the background scenery, but you can make it look pretty realistic.

"There's no point in living if you can't feel alive"

the problem with using AE explosions is that dirt + debree does not interect with with surrounding scenery, ie dirt falling on actor + ground + the lighting affect on surroundings, for this reason AE explosions are only really suitable for far away explosions.
i want to make a gritty war film (Brotherhood,Assembly, we were soldiers, band of brothers i love, they are all fairly gritty war film, they all use lots of real explosions) btw im not using real explosions because 'thats how its meant to be done', i just think to 'spear head a film' with AE will nearly always result in the AE being noticable.

as for the saftey issues, anything that could remotly harm an actor, i practice on myself a gazilion times until im 100% confident in its reliablility.

the explosions im trying atm are under ground level, dig a hole, a 2 litre bottle of petrol, rigged to a car battery, put dirt on top, boom. like i said before, practice it to perfection.

I don't know if you get the Discovery channel where you are, but the program "Mythbusters" recently did a segment on dust explosions. They greated an IMMENSE fireball using nothing more than a flare, some compressed air (like a shop compressor will work) and non-dairy coffee creamer. You might be able to access the segment on the Discovery channel website to see it.

Pondweed you are right that the CGI blasts don't interact with the people and things and thus look fake, but it doesn't have to be that way.

You could rig something to launch dirt in the air combined with a bounceboard covered in crinkled aluminum foil to project a flash of light on the actor as the explosion happens. Then when the CGI blast is put in you could have it right ontop of the actor in total safety.
Also if the blast is not in center frame, but instead partially out of frame it will probably look better. If you can rig something to yank your actor off his feet as the blast hits it will look better still but I don't know how to do that safely (although a mannican, face covered in blood and dirt, yanked back and possibly losing his legs might look really nice).

This works even better if you use real explosions for some other, safer, blasts to set the stage and then if at all possible have one of those blasts in front of a green screen so the composited blast is actually a real one and not a particle-generated one.

So imagine, your guys are low-crawling across a field. Blasts in the distance. Flash and noise off camera and dirt indicate some are closer the soldiers are near the trees. One freaks and runs for the treeline. The second follows. The first runs out of frame, the second is near the center of the frame. Bam. Dirt, flashed light, sound. The first (actor offscreen and safe is now replaced by a mannican in similar uniform) blasts back, nearly landing ontop of the second. Then you cut to closeups in which the first actor is back with his legs buried in the dirt and an artificial torn lower torso attached.

Now you've got the great character moment of soldier two's reaction (whtever it is). Probably muffle the sound to indicate damaged ears (and because quiet is eiree and it's awesome when the sound pops back on).

I think it could be a very effective blast without anyone being at risk.

RJSchwarz

Oh, and a reliable source has informed me that it you don't really see flames in an explosion of the type you might find on a battlefield. Short of napalm or an actual fire most blasts knock the air out of the area and thus flame doesn't last. They are very anti-climactica. a Puff of cottony smoke and a lot of dirt.

RJSchwarz

interesting rjschwarz, im definatly gonna try that, see what it looks like.

as for the point you made about flames. im not really after a firball explosion. just a band of brothers style debris/dirt explosion.
so probably a 2 litre bottle of petrol would not be a good idea, as the heat danger could harm actors.

i might start experimenting with gunpowder, seeing as i want a shockwave explosion to make dirt fly.
if i was to dig a hole, put a gunpowder charge at the bottom, and make sure that the dirt i put back in has no rocks/stone/ or any lumps of dirt.

i suppose a big danger now would be the eyes, so ill avoid a 180 degree 3 meter zone in front of the actor. or if i do, film it from the back so the actor can wear some goggles.
gunpowder seems pretty cheap to make, so ill start of experimenting with small amounts.

considering what iv said in this thread, im actualy a very safe person. i think the main reason behind most pyrotechnic related accidents is, people dont know the full capability/ variables of the pyrotechnics/ techniques they are using. so with enough practice explosions etc beforehand, i will know to take the neccessary safty precausions.

its a pity there is not much i can do with compressed air, as it seems to be out of my budget range. (other than combining gunpowder with a deodrant can, but that would send shards of metal in all directions, so nooooooooo).

You could always try using a model. I know this sounds hard and will look unrealistic but it could work (depending on your scene) I recently had a scene where a man ran out of a room, past a wall and dives on the floor as a massive fireball came out of the room and above the man as he dived on the floor.
What i did was take a photo (with a very good camera) of the scene from where i would put the camera. I then printed it out and cut it out. I stuck it to piece of wood (so it would stand upright I also cut out the wall seperately and stuck it to another piece of wood (so it would be further forward and look more 3D). I then took a deodrant can and a match and sprayed a fireball through the gap between the two pieces of paper. I then shot the actor running forward and diving against a greenscreen and then put it all together in post.

Rob - UK

there seem to be some really interesting techniques everyone is posting up, thanks, does anyone have any examples of these on youtube etc.
id quite like to see the results

What is a banger?

an English sausage that goes well with mash potatos. (c;

RJSchwarz

so you exploded a sausage?