wycome5 Posted January 8, 2006 Share Posted January 8, 2006 I want to create the effect of an explosion in/on water (like you see when a ship gets attacked and the water sprays up in the air). I want to acheive it with pyro rather than air. If I put a theatrical flash in a bag (fully waterproofed with tape etc) and fired it (it would float on the surface because of air in the bag) would this create the effect? Link to comment Share on other sites More sharing options...
Simon Lewis Posted January 8, 2006 Share Posted January 8, 2006 My fast fading chemical knowledge suggests that you will possibly get a much bigger bang than you anticipated... Pyros are relatively safe because a) the gases produced are not constrained and b) the burn velocity is relatively slow. When you place a pyro in a tank of water, the rapidly expanding gases are constrained, and the effect of the explosion is magnified. I believe the Mali nightclub bomber used a layer of water over the explosive device to increase its impact. The mitigating issue would be whether there was sufficient oxygen available in the mixture or in the surrounding atmosphere in the bag to ensure complete combustion. Also, a floating bag may arguably just pop and not do as much damage than if it was submerged So, I'm no pyro expert, but having caused quite a bit of damage experimenting, I'd suggest that using air would be a potentially safer alternative. Simon Link to comment Share on other sites More sharing options...
mike Posted January 8, 2006 Share Posted January 8, 2006 Good evening sir.... My gut instinct is NO! having looked at your profile, it leads me to think you are not a stranger to these kind of things, so I'm sure I'm safe to suggest that you seek some serious professional advice on this one. Pyro's and explosives are one thing - but water adds a new dimension all together. For example, an amount of gunpowder, or similiar explosive, will have 10 times the effect in water, than it does 'on land' - water as a medium for explosives is less forgiving than our own dear atmosphere!!!!so, get help test fully and stay safe good luckmike Link to comment Share on other sites More sharing options...
wycome5 Posted January 8, 2006 Author Share Posted January 8, 2006 Thanks for your sensible advice guys. I should point out that this was only an idea I had been thinking about and I don't plan on doing it. How were the effects created in Peral Harbour (movie)? I know it wasn't air as I saw it on the DVD extras that they used pyro but not what/how. Link to comment Share on other sites More sharing options...
ChrisD Posted January 8, 2006 Share Posted January 8, 2006 If you've seen Pearl Harbour, you may also have seen another film (possibly one of the impossible missions) in which explosives are inserted into a safe, followed by water, to blow the door off. I recently watched a documentary on this very scene and it explained that because water is denser than air, it doesn't absorb the explosion. Link to comment Share on other sites More sharing options...
mac.calder Posted January 8, 2006 Share Posted January 8, 2006 I know it wasn't air as I saw it on the DVD extras that they used pyro but not what/how. it could have been pyro-powered water cannon - ie a pyro is fired, pushing a platform upwards rapidly, and atop the platform is water... it would of course be enclosed. Then again, with a budget like pearl harbours, they could afford experts to calculate exact ammounts and custom make the pyro device - and using camera angles, the explosion could be further away than it looks Link to comment Share on other sites More sharing options...
Andrew C Posted January 8, 2006 Share Posted January 8, 2006 The focusing effect of water on explosions was used to great effect by the Dambusting bomb designed by Barnes Wallis. Water doesn't compress as air does, so the force is all applied to the target. In your case there is no target; and the blast would all be upwards. In less H&S fixated times, I would have enjoyed trying that... Link to comment Share on other sites More sharing options...
robert morley Posted January 9, 2006 Share Posted January 9, 2006 for an even more intense BLAST of water, could you not have a pipe capped at one end. Have the open end pointing up a few feet below the water and some how put a pyro device in that. I suppose that would help with the h & s aspect of it all as well because the blast would be controlled not just fired anyhow. Just a suggestion anymore? :) Link to comment Share on other sites More sharing options...
Guest lightnix Posted January 9, 2006 Share Posted January 9, 2006 I just found this with :) HSE Entertainment Information Sheet No.16: Special or visual effects involving explosions or pyrotechnics used in film or television productions. Please note that the document......does not cover the issues associated with physical effects or organised firework displays......but does carry a further reading list, including the ABTT's CoP, Pyrotechnics and smoke effects. It does contain a lot of food for thought, however and makes the following point about underwater explosions...Diving and explosives in water A specialist dive contractor and extraordinary controls will be required for all work involving underwater explosions or where, in the event of a misfire, explosives could finish underwater.This advice is repeated on this page of BBC H&S requirements regarding visual effects in general - possibly some more to think about in there. Can I also just make a polite request, to ask members to post from a postion of (preferably qualified) knowledge and experience when replying to questions in general and this forum in particular. As with many (nay, all) things pyro, this is starting to look like a job for a professional contractor. Link to comment Share on other sites More sharing options...
AndrewR Posted January 9, 2006 Share Posted January 9, 2006 As pointed out, a professionals advice would be a very sensible course of action. Even if they just give you a very simple answer/plan it covers you to a degree. (and as to putting a pipe (cannon!) underwater and firing a pyro at the bottom. Read the other posts! Water tamping (to give it a technical name) is very well understood and very effective, if you get it wrong then your pipe would disintegrate, violently.) Speak to someone who has done this before, and can give you a safe method. (Pearl harbour almost certainly used submerged explosive charges, set by pro's, as at a safe distance they are relatively harmless, and very effective)But there are good reasons why most small scale effects like this use compressed air. (which can be used for surprisingly large effects) All that said, you may well find that a professional gives you the ok, as a floating pyro may well be a common ploy. But get the advice! By the way, whats it for? I'm intrigued Link to comment Share on other sites More sharing options...
wycome5 Posted January 9, 2006 Author Share Posted January 9, 2006 I did already post above that it was only an idea that I had been wondering about for a while, if it was possible, I might have worked it into a furure SFX show, no show currently exists but when it came planning time for one I may have used it. Link to comment Share on other sites More sharing options...
Rich newby Posted January 9, 2006 Share Posted January 9, 2006 Has everyone not been to universal studios (I think)? in Florida. They do a sort of pearl harbour re-enactmet of a small part. A torpedo racing towards a small ship (still the size of a fishing boat, about 10-15m long), That is using air, and then they use some form of air chamber, to blow the water into the air. I know this doesn't answer your question, saying you said you don't want air systems. But I think this will be cheaper. Why do you specifically want pyro? Whats wrong with the fresh stuff?! :) Rich Link to comment Share on other sites More sharing options...
wycome5 Posted January 9, 2006 Author Share Posted January 9, 2006 I wanted pyro because I presumed it would be cheaper and easier as there would be less to install. Also that is at MGM in Walt Disney World Florida, a part of The Backlot Tour trip (pre-show). Link to comment Share on other sites More sharing options...
Rich newby Posted January 9, 2006 Share Posted January 9, 2006 Yer that's the one, I knew a Tour was involved somewhere in the title! I suppose for a few blasts pyro would be cheaper, but in the long run, if you use it quite alot, you could make a ring with a £50 compressor, and keep it in stock, always handy! Rich Link to comment Share on other sites More sharing options...
wycome5 Posted January 9, 2006 Author Share Posted January 9, 2006 Could you explain how I would do that? Link to comment Share on other sites More sharing options...
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