Fake fire with fabric and compressed air

[Florple]

The show is "The Princess Bride"
The scene is "The Fire Swamp" were flame bursts randomly out of the ground.
The Theater is in a public school so not so much as sparklers...
My plan includes a semi-translucent, fabric, wind-sock like thing, hidden in the floor.
The challenge is to create the powerful current of compressed air that will send it bursting into existence.
Edit: The effect I need is for it to burst out of the floor with a short powerful blast of the air, then immediately flop back down again.
Edit: already tried: electric cfm high static pressure fan. It looked like a real fire once it got going, but it took too long. the effect we are looking for is a sudden explosion of flame that is gone as quick as it appeared.
Already tried: 8 people backstage blowing into garden hoses that link into one. The sock didn't deploy much, and half of them got their mouths blown off their hose, and a mouthful of hot moist air. bleck!
The air will have to come from some sort of compressed gas container, with a valve and a hose.
Or perhaps some kind of bellows? Lots of Bike pumps?
So, where i got stuck was finding the right materials.
1:The container:
I know i can get large co2 paintball canisters at wall-mart, and those would be quite fun, and i could get one for every night so we always get the highest pressure.
Or i could look for a place to rent a compressed oxygen container? That would probably hold so much that the pressure would stay constant for how we would use it.
2: how to attach it to the valve and hose
Depends on the container, but i am especially eager for a link to where you can get hookups for paintball stuff.
3: The valve and hose?
what should they be? wheres a good place to look? The valve has to be just right. Instant-on, hold for a second or two, instant-off.
Solutions are great, but a point in the right direction is great to.
Thanks. love. lol.

 

[cprted]

Unless you know what you're up to, I would advise against any kind of compressed gas.

Remember the KISS principal. Have you thought of using an electric fan?

 

[MPowers]

Compressed air will give you short powerful blast that will sound like a fire extinguisher going off and move the fabric for a single instant. What you need is high static pressure, high cfm fans. Reverse pitch squirrel cage are perhaps the most efficient but can be noisy depending on what else is going on that may or may not be a problem. Take a look at some articles I wrote on stage fire. Fire on Stage and see if they help.

My first use of this technology was a tour of Jack and the Beanstalk where the bean stalk and the Giants castle were both fabric inflatables. Today you can see the same thing with inflatable yard displays for the holidays. All use high volume (CFM) high static pressure fans for the constant flow of air. Don't use a propeller blade type of fan, the blade forms a vortex that will spin and tangle your fabric flames.

 

[Florple]

Compressed air will give you short powerful blast that will sound like a fire extinguisher going off and move the fabric for a single instant.

That is exactly what i am looking for it to do.
Its supposed to burst out of the floor so fast that it startles people, then immediately flop down again.
As for the safety of compressed air, ive worked with it alot before. At the theater of a nearby college (Smith college), they have compressed air tubes run throughout the walls for various applications. Ive used that system many times while interning for them, hooking it up so it sprays off sawdust, with the nailgun, and to "sweep" the stage with little gusts of air (their idea not mine). Also, this thing won't be as big as you might be thinking, the longest strip of the fabric being like, 3 feet long, so the pressure won't be dangerously high. Not half as much pressure as at Smith seems like enough to me. My first thought was a 12-gram Co2 cartridge like we used in our racing cars in shop class. we used to just break the seal and let them go through photo-gates to see who was most aerodynamic.
I have no love lost for static pressure fans though. In Hamlet our ghost was projected onto a 20' tall by 5' wide strip of muslin held up by one of those fans so it billowed like crazy. But when the fan was turned on, there was a second or two we had to cover with some lighting effects while the fan sped up, and the fabric looked like the blob coming out of the floor.
I don't know how our lead "Buttercup" is going to act frightened of fire that comes up like that.

 

[MPowers]

The right tool for the job. As you describe the FX in your last post, compressed air, much like a confetti cannon, sounds like a good choice. Most of us think of "flames" as a sustained gag, not instant on and off, which is why our initial reaction to the compressed air method.

Back to the right tool, line. Fans can work instantly for things like fabric strip flames up to 3' or 4' long, a good example was the "flame" FX used by the Ice Capades for many years. A shallow trough surrounded the entire ice rink, several hundred feet around. It was lined with (A Lot of) squirrel cage fans. The cage fans were about 3 or 4 inches in diameter and about 3' long each similar to the cross-flow blowers here McMaster-Carr Because the fan cages were small in mass, they started and stopped almost instantly. The "flames" could rise and fall with the music, actually quite spectacular. Of course there were hundreds of MR-16 lamps in the trough as well as the fans to put a lot of varied light FX on the fabric also. Many people went away convinced the flames were real. Back to your FX, any large unit or inflatable simply follows the rules of physics. If you were trying to hold up a 20'x5' piece of flat fabric with a fan, you were pushing the limit of what can be done. Usually something that large has to be an enclosed structure like a tube or balloon or similar. For the flat fabric, situation you were trying to "fill" a volume of air about 400 cubic feet with no containment so the air was escaping almost as fast as it was being supplied. The fabric would only "grow" as fast as the fan could supply the cfm to fill the space with air. In the case of the Beanstalk Gag, we used the time lag for inflation to purposely control the growth rate of the bean stalk as it slowly rose and grew in full view of the audience.

Just curious, Smith? The one in Northampton? I helped install a fire curtain there a few years ago while I was TD at U Mass. My wife worked in the costume shop at Smith.

 

[MPowers]

Now, back to your original question. What to use and where to get it. For the valve you are looking for a high volume solenoid valve similar to McMaster-Carr The valves are electrically operated and are designed for instant on and off. The same for hoses and fittings. McMaster, Grainger, Fabco, Clippard et.al. Do some goggle for pneumatic equipment.

As for gas, The least expensive is compressed CO2, the expense is getting a proper regulator that will not freeze up, because rapidly releasing large volumes of any compressed gas also releases a tremendous amount of heat energy and can freeze up lines and valves etc.

The paint ball canister can work, just depending on the gas volume you need each time and how many times you want to have the flame appear at each location.

IIRC, the store I got paintball supplies for pneumatic FX while I was there, was on Hwy 9 about 2 miles east of the bridge over the river. It was a combination Military surplus/Paintball supply place on the south side of the road. HTH.

 

[Florple]

Yes, the one in Northampton!
Nice to meet you. My names Jared Koester and I'm the TD at Northampton High School.
But honestly sometimes this site is really great because people don't just answer the question asked, they try to help you with the whole project, and sometimes i find this site frustrating because they don't just answer the question asked, they try to help you with the whole project. Hahaha.
So i guess it might be a good idea to explain this scene in full detail huh? not skipping any parts like the instant on-off thing?
Buttercup and Westley are walking through the swamp, which for us will be a mostly empty stage, with tree cutouts in the backround, and some ropes painted like vines and roots and maybe some carpets painted to look like moss.
As they walk, Buttercup stops to talk to Westley and as they talk, he hears the bubbling noise below her feet. He knows the bubbling noise signals a burst of fire, so he picks her up and moves her away just as a jet of flame erupts where she had been standing.
Yeah, she has to stand on it....
and there is no way to put her on a platform or put any kind of dip in the stage. whatever this contraption is going to be has to hide inside a mound of moss...

The canister of gas would be hooked up to a valve, backstage, from the valve we go to a hose, which goes to the floor and, and is disguised on-stage as a root. The hose or "root" goes to a "patch of moss" which is a light piece of fabric taped to the floor on the upstage side. Under the moss, the hose connects to a 90 degree turn piece secured to the floor. and on the open end of this 90 degree turn segment, is the sock, folded up under the moss fabric.
The valve opens, and the sock explodes upward, pushing it's way through the moss flap by it's own power, and making multiple pants be shat.
My co-director and i agreed that the realism of the flames is less important to us than how well they are hidden, and how unexpected we can make them. Many people have seen the movie, and they'll be thinking, "oooh, the Fireswamp, i wonder how they are going to do this?" and we don't want them to just see a big stump with fans behind it and be expecting it. Plus the characters talk about the flames before they appear, so it won't confuse anyone. The real magic of the moment is how flames can come out of anywhere, unexpectedly, and thats what we want to show onstage.

 

[Florple]

Whoa, you totaly answered my question liked i had hoped!
but after i started typing the response to your previous above...
Nevermind then and thanks that's really helpful

 

[MPowers]

If you put the canister back stage, you want the valve as close as possible to the FX. When the valve is triggered, it first has to fill all the hose between the valve and the gimmick before the action can start and that will mean both a time lag and a loss of power proportional to the length of the hose run between the valve and the gag. Think about hiding by emphasis. Instead of making the "root" (or whatever) small, make it, and several others not involved with the gag, big enough to place the valve within a couple of inches of the gimmick. The closer you can get the valve to the "flame" the better off you will be.

 

[ruinexplorer]

If you are using compressed CO2, then you don't really need to have the fabric. Watch this video from a Glee episode, starting at about 45 seconds in. They are using a compressed gas, probably a CO2 cannon, and just lighting for effect. If you are going for an effect like the movie, I think that this might work for you.

 

[MNBallet]

Hand Held Confetti Launcher

I've used these to put into a Nutcracker cannon. Works great every time. It depends on how many times your going to do the effect. It could get pricy doing several of these single shots, but so could a hose system hooked up to one large tank. These could work for your tube socks, or fill with red confetti.

It's a great idea and easily done. The biggest issue it really boils down to is how worth it is the effect for the time and money.

Kenneth Pogin
Production / Tour Manager
Minnesota Ballet

 

[jwl868]

Bear in mind that the pressure in compressed gas cylinders is high: carbon dioxide is around 800 pounds per square inch gauge (psig). I had trouble finding compressed breathing air cylinder information, but I think that is typically on the order of 1,000 psig. The system mentioned in post #4 sounds like a shop system that might be 100 to 200 psig. And the fans are probably less than 1 psig.

The valves and piping described in post #4 may not be suitable for safe use with high pressure compressed gas. Make sure you use a suitable regulator, and fittings, hoses, and valves with the proper pressure ratings. One must consider a regulator failure or human error.

Joe

 

[mjw56]

jwl868 is in the right order of magnitude. The Scuba tanks i worked with on co-op were filled to 2000 psig for the average tanks but we had two that could be filled to 3000 psig. We usually ran the divers airline at about 150 psi (tank fed surface supplied air system) where the diver had fine tuning on the regulator on the superlite.

 

[Van]

Let me throw in a couple of words of caution.
I would stay as far away from the use of 'Compressed' air < whether it be from a compressor or a SCUBA tank.> I would tend toward the use of high volume / moderate speed fans, perhaps even employing a venturi effect device right at the gag point.
I can expand on this more later < gotta run to staff meeting> My issue with Compressed air is the simple fact that you have a rather uncontrolable situation where actors are going to be, essentially, right in front of the discharge with no eye protection. As with any type of effect like this you have the potential for particulate contamination and with a compressed gas such as CO2 you have the potential for High speed / High energy ejection of particulates with no good way of controlling the trajectory. Ok gotta run more later.

 

[icewolf08]

Bearing in mind what Van said above, I am surprised that no one mentioned just using an air compressor. If you don't want to buy a little compressor, you can probably rent one from your local home improvement or hardware store. If you are using enough air to warrant the compressor needing to re-fill then you can probably place it backstage and just get the proper hoses or tubes to run from the compressor to the effect. This is probably the simplest way to do the effect. Buying paintball tanks from wal-mart is probably not the best idea. You have to also make sure that you have a way to safely cover any holes that you make in the deck so that you don't create a trip-hazard for the actors.

With some planning you can have the blocking of the show staged so that the actors are not near the effect when you fire it.

 

[Florple]

If you are using compressed CO2, then you don't really need to have the fabric. Watch this video from a Glee episode, starting at about 45 seconds in. They are using a compressed gas, probably a CO2 cannon, and just lighting for effect. If you are going for an effect like the movie, I think that this might work for you.

How did they do that? It looks perfect, but i have no idea how it works. I can't imagine just lights and co2 doing that

 

[derekleffew]

Likely due to The Station tragedy, the trend is away from pyro and propane effects and toward cryogenics. But CO2 and other compressed gases can still be dangerous.

Have a look around this website:

strictlyFX - Cyrogenics and CO2 Effects

 

[SHARYNF]

Likely due to The Station tragedy, the trend is away from pyro and propane effects and toward cryogenics. But CO2 and other compressed gases can still be dangerous.

Have a look around this website:

strictlyFX - Cyrogenics and CO2 Effects

what I have used is one of those emergency tire fill tanks that napa sells, you take them to a gas station fill them to about 100 lbs, you would need to modify the outlet connection to use a relay valve

I have used Dharma fabrics ultra light weight Silk for the effect, and orange and blue mr16's
flashing the lights can also enhance the speed of the effect

Sharyn

 

[CrisCole]

I've heard a lot about cryo...but never used it.

I've contact your link for some more information, but I want to know from someone who's not trying to sell me anything. Does it really work?

 

[ruinexplorer]

Here's another company that you might want to contact.

I have never used the system but only worked with those who have. I have seen it as quite an effective look when done right. The saleperson should be able to answer your safety concerns and be able to instruct in installation (as stated on this website in particular).