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Flame Forks

Discussion in 'Special Effects' started by egorleski, May 3, 2006.

  1. egorleski

    egorleski Member

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    Alright heres another question for you all. If you have read Bernard Wilkie's book creating special effects for tv and video then you may remember reading about this device. A flame fork is essential metal tubing connected to a propane tank. the metal tubing can either have holes drilled in it or just be connected to multiple tubes to resemble a fork. This can be used to give the illusion of burning furniture, or if you use copper pipe that is easily bent could feasably be used to add some flare to a set when warrented. Besides the obvious safety concern that the area must be clear, only use this effect if the person who will operate it can see the area where flames will come out so that they are sure it is clear before the effect goes. I know from welding that you have flashback arrestors and the like because the gas may travel back to the tank. And it seems that most propane tanks dont really but out a whole lot of pressure which would make me think the likelyhood of a flashback would be greater.

    So has anyone ever tried this effect? Any ideas on safety precautions necessary? I would probably stick a flashback arrestor on just to be safe rather than sorry but maybe im wrong and theres somthing about propane that it wont flashback?
     
  2. koncept

    koncept Active Member

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    i would have several "kill switches" one at the tank, a spotter in the line, and on the handle for a user. i would not recomend building this but it is probably do able, best is to probaly use the jets from a propane grill
     
  3. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Yes, I have used flame forks (we call them flame bars).

    YES, you must have a flash arrestor.

    YES, you must have a regulator.

    YES, these are dangerous and should not be used unless the theatre owner and manager allow it and the fire marshal approves of its use.

    YES, someone must man the bottle at all times so that they can shut off the gas. This is especially important in a flame out. In an ideal situation you would have a solenoid to open the gas line and a flame sensor to shut it of automatically if the flame dies.

    NO, I do not recommend using copper pipe. Steel pipe is the only material that I have seen used or have used myself.

    NO, I do not recommend using these unless you have appropriate training and experience in using them.

    Warning – Dave might decide to close this topic due to the risk of someone making up a set with Daddy’s welding set and some old copper pipe. These things do create a good look but can be very dangerous and I am considering closing down this topic myself.
     
  4. egorleski

    egorleski Member

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    Yea understandable if he decides it is best to close the topic. Pritty much all the possible dangers i suspected. I wonder then if there are any more safe alternatives? I think i have seen advertised flame bars made specificaly for use in theatres. Any other devices that get a similar result but more safely?
     
  5. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Not that I can think of. Video projection maybe or gobo would be the only alternative that I can think of but that will never capture the same effect of a live flame.
     
  6. nez

    nez Member

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    sounds fun got any pics?
     
  7. saxman0317

    saxman0317 Active Member

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    With propane, there is a fair amount of pressure in the tank, but id put a supresser on it anyways, just to be sure. Also, i wouldnt use the valve on the tank to operate it, or even going directly from the tank in the first place. It may be safer to have a smaller tank with a check valve that is filled by the main tank and only holds as much as your going to need, then running your system off of that so you only have the few ounces of gas you need and dont run the risk of something going wrong and having to burn the whole 26 pds in a typical 40 pd tank. Also, use some sort of valve that can be operated fast, without a locking open position, such as a gas rated buterfly or something. Make sure that you have some type of burner/nipple at the end and a air/gas mix chamber though to get a combustible mix or you can get liquid gas dripping onto the ground (yes, this does happen, and its darn cold and flammible, just ask anyone who fills tanks it hurts alot to get on ya)

    personally...i wouldnt try building this myself for an indoor show...or any show
    i may do something like it on my own somewhere, but not anywhere where theres going to be people, and i doubt that this would fit fire codes in about 99% of the cities around here unless you are a HUGE venue with alot of lincensing. buy a rig and hire a pro...insurance companies like that better and less credibility on you in a lawsuit
     
  8. egorleski

    egorleski Member

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    I think it fits well with movies, which is where the device is from. From all the input it sounds like people in any proximity=bad. in most movies when you have a burning sofa there probably aren't going to be actors on the sofa and if there are then it being a camera you can have the flames way back and make it look like its on fire still. With a stage comes limitations and these limitations make it very hard to use a device exactly like what i started the thread talking about. There are profesionaly made flame bars that you can by that would get you around that whole insurance thing. I have never used one of these to know what sort of fuel it uses and how effective it is but it sounds interesting. I think the most interesting "semi-homemade" method for this effect and probably safest other then buying someone elses- would be the grill disection method. A grill has a tank of gas that goes through a regulator and then into a tube that goes to metal pipe where it enters another pipe that on each end has gratings to introduce air. In this pipe there are holes that allow the flames to come out. my grill has many thus reducing the size of the flame as there is so little propane going to each outlet. My question is how come theres no flashback arrestor? Ive never seen a grill with one on it. Is this a function of the way it is designed its not necesary? is there really one but its hidden somewhere? or is there somthing special in the regulator that comes with the tank?
     
  9. soundlight

    soundlight Well-Known Member

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    I wouldn't do this unless I was properly trained, had the proper safety equipment, and had the fire marshall THERE on the site at the time of use. But, of course, I'm just a safety freak. But I do think that anyone who reads this topic shouldn't just go out and set one of these up, and I would be concerned that someone would get a propane tank blown up in their face. So don't do it.

    Yes, it's cool. No, it's not safe for anyone but trained professionals, and I am not one of those. And I am a strong opponent to using any flame except for possibly a candle (but we even use electric candles) in high school theater.
     
  10. egorleski

    egorleski Member

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    Yea and i wouldn't even just trust a firemarshal. Im going to build one, after having plans looked at by both a firemarshal and a physics teacher. Then i will have the built one inspected by both those guys again. Then at least the first time i use it have the firemarshal there. And at least the initial try theres no reason not to be extra careful and you could put the propane tank in a hole in the ground or something. The biggest problem in my mind is that while you can take all these precautions in a controlled test setting and can get the device working perfectly like that, who knows what will happen in a live theatre situation where anything can happen. A draft of wind blows some fog and the fog leaves a residue on the pipes in the flame fork and who knows what that would do. While i think in theory this could add an amazing element to a scene, at what cost? saftey definantly should be the number one concern. While if you wanna make one on your own and assume responisiblity to do it safely thats fine, but i would never put others in danger with somthing i made.
     
  11. Chris15

    Chris15 CBMod CB Mods Premium Member

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    I thought that household gas was piped in copper?
     
  12. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Yes - but is the copper pipe on fire in a household situation? The burners on your stove or BBQ will be steel or cast iron. It would probably be ok but I would worry about the holes/slots melting or blowing out over time.
     
  13. Chris15

    Chris15 CBMod CB Mods Premium Member

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    I guess it is the same as the fact that we carry gas in pressure rated PVC hose, but it will melt without too much effort.
     
  14. jwl868

    jwl868 Active Member

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    If you are working with propane, then use materials and equipment rated for propane. You need either a licensed-contractor (possibly a plumber, or other heating, ventilation, and air conditioning [HVAC]) or a professional engineer with HVAC experience to design this properly. The fire marshal may know the code. And with all due respect, your physics teacher is not the technically correct choice to check this design.

    You are dealing with fire in a theater, not a back yard, not a sound stage, not a back lot. To say the least, the stakes are much, much bigger. Safety is the issue.

    In the USA at least, household natural gas is at a surprisingly low pressure – well below 0.5 psig. (The big gas transmission lines are at a higher pressure, but that is let down for community distribution.) So the copper pipe and tubing works well for transmission. Propane’s vapor pressure at room temperature is about 122 psig and at 100 F, the vapor pressure is 190 psig. Can’t compare this to natural gas.

    And you mention a "controlled" test setting - that is all well and good to see if it works, but the next step is a true test is as close to actual operating conditions as possible. If you think there are drafts, then you had better be simulating those in any test.

    Joe
     
  15. kingfisher1

    kingfisher1 Active Member

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    I read somewhere about air propelled fog. maybe throw so red light onto it and it'll look good, idk.
     
  16. saxman0317

    saxman0317 Active Member

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    Grills do have a reg on them that stops flashback.. They are an induction regulater. They only let gas out as its being burned and at a pressure so that it is always being forced away. Also, the gas isnt mixed with air untill it is right near the burners so that it wont burn back anyways for lack of air thus cutting off the fire tetraheydrian.
     
  17. egorleski

    egorleski Member

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    i talked to a guy who specialises in fire fx and we chated about flame forks among other things. he showed me his flame for rig. basicaly he has a solenoid just for better remote control and then a regulator rated for propane and then black pipe with slits cut in it and an end cap. when working with gas make sure u use flare fittings and other than that its not complicated. like is said above the fire cant really go back because no oxygen. he me some sweet effects but figgured i would follow up on this.
     

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