Pyro : Fireball blaster

Here is a picture of my fireball blaster going off at BurningMan '99 (click for a much larger image). The little person in the metal hat is me. I had three blasters and put on a 2 hour show on Saturday night.

About

I had seen a fireball blaster go off at BurningMan '96 but hadn't gotten a good view of the actual mechanism. Also while at BurningMan I saw someone use a pneumatic gun to launch a spray of water on people. I simply added things up.

The week before Burningman '98 I constructed my first fireball blaster (FireBlaster v1.0).

Design

The system is basically a remotely fired pneumatic air gun, that instead of launching a solid projectile it launches about a gallon of gasoline. This giant spray of gasoline goes by an ignition system (FireBlaster v1.0 simply used a big torch) which causes the spray to erupt into a giant ball of fire and gnurl into the sky.

What is described below is the simplest (reasonably safe by my un-expert oppinion) incarnation of the blaster. I have taken the design MUCH farther than what is described here by adding MANY safety features (I suggest that if you build you're own you do the same). The first change I made was to use a remote pressurized air cylinder, regulator, air hoses, and connectors to be able to presurize the gun without being near it. I strongly reccomend this change.

BEFORE EVEN THINKING OF MAKING A BLASTER AND USING IT THINK ABOUT THIS:
IT IS INHERRENTLY UNSAFE - IT LAUNCHES A 20 FOOT DIAMETER BALL OF FIRE FOR CHRISSAKES!!!!!!!!!!!!!

The gun is basically two parts: a pressurized chamber and a barrel coneected to each other by a solenoid sprinkler valve (an electric on/ off valve).

To fire the gun you merely open the valve. The sudden change of pressure shoots just about anything out the barrel.

Components

These should all be avaialbe from your local hardware store:

• The gun has a barel made of galvanized 2" pipe that is 3' long.
• The barrel is open ended at one end (obviously) and has a 2" to 1" reducing bell housing at the other.
• The bell housing is connected to a 1" one way catch valve and drain plug. The valve and drain plug prevent gasoline from washing back to more delicate plastic parts that would melt is the presence of harsh chemicals like gasoline.
• The catch valve is connect to a electric sprinkler valve (FireBlaster v1.0 actually uses two). The valve is closed by default, until current is applied to its solenoid. The wires for the solenoid are extended 30 feet to three 9v batteries in series. Closing the ciruit causes the valve to open and the gun to fire (if there is pressure in the pressure chamber).
• The sprinkler valve is connected to the pressure chamber via a PVC 3" to 1" reducer.
• The pressure chamber is made of 3" PVC pipe that is 3 feet long. It is capped to form a closed space. Attached to the pressure chamber is a standard pressure valve (like those on most bicycle tires and automobiles). Also attached to the pressure chamber is a pressure gauge , allowing you to actually know the pressure inside the chamber. I addition the pressure chamber has a safety pressure release valve (in case the batteries get low on power and only partially open). I used a bicycle pump to fill the chamber up to 140 PSI (which is completely adequate for launching about a gallon of gasoline).
• The ignition system is a 12 foot pole and some Kevlar wicking (available from juggling suppliers).

Performance

1. Set up in an absolutely safe and legal area.
2. Make sure the area is completely clear of any people or other flamable objects.
3. Place the gun upright (use a stand of some sort). Make sure that the gun is at a slight angle (~15 degrees) from completely vertical, so that the opening or the barrel faces slightly away from the wind. This way any fuel will not fall back on the blaster.
4. Perform a firing test:

   I've had some problems in the past with the PVC getting brittle and then cracking when transported, so always do a pressure test before any firings.

   1. Fill Barrel with water.
   2. Go to remote location.
   3. Fill the pressure chamber with air at 140 PSI.
   4. Close circuit to open valve, thus firing.
   5. If all goes well continue (never use broken or failing equipment).

5. Fill Barrel with kerosene (or gasoline).
6. Place a lit torch (using kevlar wicking) about 10 feet up (on a metal pole) away from the opening of the barrel. The torch should be a separate structure from the blaster (this way any fuel dripping down it will not touch the blaster). DO NOT use a material that can drop ashes (like cotton) into the barrel. Take extra special care to make sure that the flame of the torch does not come close to the barrel. A better design would be to have an electirc ignition arc at the end of the pole.

   There is are two good reasons for having the ignition so high up:

   • The fuel doesn't start burning close to the ground, so slow moving droplets do not get ignited and do not fall burning to the ground. In practice I found that when I had the torch only a foot or two away that some burning material made it to the ground, but when I put the torches higher that NONE of the burning fuel made it to the ground - even in a strong breeze.
   • By allowing the spray cloud to disperse you get a stronger fuel are effect, this makes the fireball ingite all at once which is more impressive and aesthetically pleasing.

7. Go to remote location.
8. Make sure the area is completely clear of any people or other flamable objects.
9. Fill the pressure chamber with air at 140 PSI.
10. Make sure the area is completely clear of any people or other flamable objects.
11. Announce "Fire in Hole" and give a 10 second countdown (making sure to keenly watch the area for wandering fools).
12. Close circuit to open valve, thus firing.
13. Watch huge ball of fire erupt into sky.