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Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
ok, first and foremost I am doing this legally - no explosives are used (so no license from the ATF), I have the Fire Marshal's consent, I am not doing this for an audience or for a group of more than 50 people (which by law is an audience even if not intended and means that I do not need Flame Effects License).
UPDATE (2/7/10): I have put the videos on my YouTube Page - clthe car flame shots will have car in the title, and yes on one of them another camera is in frame because the angle shifted on us
UPDATE: amazingly, I will not have to use bursting bottles! - While testing a new barrel for the directional shots (it was a seven foot 3/4" iron pipe to hold more liquid) I also found amazing amount of dispersion that even a camera a decent distance away perceived it as a fireball of epic proportions (should I have had the alcohol loaded in instead of water lol) - I will use this pipe for the car explosion, and just snake the pipe through the missing rear to fire it out the front towards the unmanned camera, giving greater effect - I wwill post pics as soon as I can, I am off now to film - wish me luck!
EDIT!!:I have decided against the Dry Ice Method and instead will use a similar principal but instead of dry ice bursting the bottle I will use the Air Cannon pumped through a pipe or hose to burst it - ignore the rest of this!
Second: DO NOT ATTEMPT WHAT I DESCRIBE HERE!! - I have had years of experience in safety measures, and do numerous tests of various components to every thing I do involving fire etc to make sure everyone stays safe. i consult with the fire department when flames are involved, I use blast shields made from Bullet Resistant Material One Inch Thick!, All things are done remote that can be, and in this case water temperature is monitored and each bottle is measured to ensure that it does detonate only after ample time to run has been allowed, and the all items in question, including the car, have been prepared to ensure there is no shrapnel or uncontrolled fires!!!
I started out with a pneumatic cannon that propels a stream of Isopropanol into a pilot light for the Flame Thrower in my Indie Film (Isopropanol is used because unlike regular alcohols, Iso-alcohols have the abnormal alcohol OH placement in the molecule, so it naturally has an orange flame without needing any colorants and it is available in large amounts at a local hardware store in very pure form). This flame thrower effect was very successful and is on my youtube page: here
My new scenario is to make a fireball for the Car explosion scene (it does not have to be that big, as camera trickery can do quite a bit when multiple takes are used). normally, Hollywood uses gasoline or alcohol in a frangible container that has a Black Powder Charge in the center. However, I cannot use black powder even though I can buy it at a gun store because I will not be using it in a gun, and therefore would need an ATF license. I thought, what could make a decent burst that would not use explosives, not need a complex nozzle on my air cannon, nor, use difficult to use materials. I had a moment of genius today: a Dry Ice Bomb.
The idea is simple, and practical from many points: the alcohol is in a frail plastic bucket, with a water bottle dry ice bomb put into the container with weights to make it sink. A series of pilot lights made using Fire Paste from a camping store will ignite the dispersed liquid. All sounds simple, well it might just be too simple and I found out why.
My question is: will the reduced temperatures caused by the dry ice bring the Isopropanol below a point at which it will ignite? The alcohol will be outside the water bottle but I still wonder if it will drastically affect anything, as I have built a cloud chamber and know it can have bizarre properties. Also, I thought that if it will not affect the isopropanol too much, I might fill the water bottle itself with it so that I can have a better effect by having a couple of smaller bursts placed in the small cramped areas too big to place an open container with the bottle inside (like tossing one in the engine compartment and lowering the hood.
I also thought about trying other liquids such as kerosene, however I am trying to avoid using something like that at all costs due to the more intense burn, the solvent properties, and other reasons.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
rp181 wrote ...
Dry ice bomb legality varies from state to state, but as far as I know, it is only legal in Utah. I would check that first.
the law they can be filed under are "destructive devices" - they make exemptions in some cases for things like potato cannons as long as they are not used in a destructive fashion such as destroying mailboxes or doing it in a residential area - in this case, however, I have checked with local authorities of jurisdiction and they cleared it for the giver circumstances
and to clarify things a little: this is not a big soda container, this is a small water bottle and it is a controlled case with various safety measures in place, such as a valve I am fitting onto the lids to prevent pressure build-up while handling.
also a side note, while typing this I my mind kind of wandered off (amazing how easily mine does while still performing the task at hand) and I realized I could actually use my air cannon and a pipe to burst the bottle - this would make things a lot more efficient as I can "dial in" the pressure required and it only needs a strait section of pipe.
I think I'll go with the air cannon - I may have got the clearance from the local authorities, but I will try out the cannon mod and see how it works
I love ADHD - I get a lot of Aha moments thanks to the constant chain-of-thought going through my head.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
I don't think you need to worry about the DIB significantly chilling a whole bucket of alcohol.
A practical problem with DIB's is the unpredictable bursting delay and pressure. That was a consideration over 15 years ago when I used them in a (steel) pneumatic cannon. A series of remedies: 1. To DIB bottle cap, connect a long 1/4 inch OD plastic hose (such as for drip irrigation). At the other end of hose you can monitor pressure with a gauge, and vent the DIB if a safety hazard arises while you wait. (If DIB is accelerated with internal water, venting through hose might be insufficient to prevent it from bursting, esp. if water goes into the hose). 2. Skip the dry ice, and pressurize bottle through the hose. I used a 20 lb CO2 cylinder with a needle valve and 2 pressure gauges, but no regulator. 3. Induce bursting at a known pressure, less than the minimum spontaneous-burst pressure. An electrically heated wire (parallel to axis of bottle, because that's the direction it wants to rip) served well.
[edit] 2-liter DIBs in the early 1990's had a median burst pressure of about 170 psig. As I recall, the thermodynamic energy was about 2000 joules. CO2 is significantly more energetic than air, not only because of its higher gamma, but because the adiabatically-expanded temperature is so low that that a significant fraction of the gas condenses & release phase-change heat.
For converting gas pressure energy to mechanical work, it's hard to beat the efficiency of a piston in cylinder (a.k.a. a gun). At venues such as my back yard, where it was unsafe to launch anything solid, the DIB (not really) -powered mortar could shoot a 6 x 36 inch slug of water to make quite a plume. In the field, it could make a 16 lb concrete slug fly for more than 5 seconds, and a 4 lb pumpkin fly for more than 9 seconds.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
Klugesmith wrote ...
I don't think you need to worry about the DIB significantly chilling a whole bucket of alcohol.
A practical problem with DIB's is the unpredictable bursting delay and pressure. That was a consideration over 15 years ago when I used them in a (steel) pneumatic cannon. A series of remedies: 1. To DIB bottle cap, connect a long 1/4 inch OD plastic hose (such as for drip irrigation). At the other end of hose you can monitor pressure with a gauge, and vent the DIB if a safety hazard arises while you wait. (If DIB is accelerated with internal water, venting through hose might be insufficient to prevent it from bursting, esp. if water goes into the hose). 2. Skip the dry ice, and pressurize bottle through the hose. I used a 20 lb CO2 cylinder with a needle valve and 2 pressure gauges, but no regulator. 3. Induce bursting at a known pressure, less than the minimum spontaneous-burst pressure. An electrically heated wire (parallel to axis of bottle, because that's the direction it wants to rip) served well.
[edit] DIBs in the early 1990's had median burst pressure of about 170 psig. With cold CO2 that corresponds to about 2000 joules. At venues such as my back yard, where it was unsafe to launch anything solid, the DIB-powered mortar could shoot a 6 x 36 inch slug of water to make quite a plume. In the field, it could make a 16 lb concrete slug fly for more than 5 seconds, and a 4 lb pumpkin fly for more than 9 seconds.
thanks for the information - before I realized that I could use my air cannon and a hose, I actually had constructed safety devices for said DIBs - it was a valve assembly on the bottle cap, it remained open while everything was secured. and readied - when everything was set, a small cord is pulled to close the valve (or, the valve would be closed by hand as there is always some lag between sealing and detonation due to the need for pressure build up, unless extreme mixes of dry ice and water are used - in this case a small amount of cold water is used to accelerate the reaction). Also, since the bottle is submerged the environmental pressure around it is greater and therefore the pressure needed to burst is greater as well
anyways, my plan is basically the same - the difference is to use my air cannon as a compressed gas tank and use it to burst the bottles in the same way the dry ice would. I don't know why I didn't think of it before, it's so simple! Plus, with the cannon it will have an even larger volume of air and therefore it will be able to propel more of the alcohol because it can apply pressure over a longer period of time.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
I'm glad you seem to have given up on the rather unpredictable dry ice bomb. Anyway the flash point of IPA is quite high so if you cool it down below about 10 or 15 degrees it won't burn very impressively. Just in case someone else reads this and decides to try it, it won't work very well. It will start a fire but I don't think you will get the "Hollywood" fireball you are after.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
I tested DIB liquid dispersion without the alcohol (just to see the burst pattern on my high speed camera) - it would have made an omnidirectional effect, but it would not have gotten enough liquid out for a car sized flame unless some changes were made - I could have made those changes, but decided to not use a container bursting method, as today while I was testing my Air Cannon for other flame effects, I saw an incredible amount of dispersion from a new, longer barrel I installed for running the air through the compact car - so I went with that, and the results (having just gotten home from shooting) were pretty good considering that we had to cut down the effect severely (long story short, the owner of the car couldn't get it out to the open space planned, so we had to just shoot the fireball out of the back of the car - hopefully I can fix it a little in post to make it look more broad, but it isn't as good as it should be and we only had one shot per owner's request, so we had to leave it as is)- If I had found a few metal "Y" fittings to get a better and more even spread I could have done a true 1/2 hollywood fireball, I say one half because the alcohol won't go backwards out of the air cannon.
I'll let you guys now when I upload today's footage!
-Jimmy
p.s: I was surprised at how fuel efficient my first cannon was, and was doubly surprised at how fuel efficient the larger bursts were - I only went though about one and a half bottles of 915 Isopropanol from the Drug Store for the effect... Now, if I had time to load the barrel completely full we could have had some fun!
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
main post updated with video link
I think I am done with this device until a month or so, when my uncle's house goes down... this cannon would be much more suited for that because it would only be to burst out the windows, rather than try to achieve a very broad fire ball
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Isopropanol Flame Device
