Stop. Don't Do Any Of This.

Seriously, if you have any concerns whatsoever about the safety or advisability of working with compressed gases, fire, or other dangerous things, just leave it to the professionals. While there's nothing here that's intrinsically more dangerous than deep frying a turkey (and a lot of the parts are the same), if you're not the careful type, don't attempt this at all. Fire art is not for people with a "let's just get 'er done and we'll work out the details later" attitude.

With that said...

Maybe you've gone to Burning Man, or The Crucible in Oakland, and you've thought to yourself, "I'd like to make fire shoot out of things, but I just don't know how to get started." This primer is for you. I'm going to give you a basic framework for designing "static" fire art displays that you can elaborate on to build your own custom effects. I'm going to walk you through some basic safety as well to prevent you from burning your face off, or worse. Note that this does not cover "dynamic" effects such as poofers. These are both more dangerous and require a lot more work.

If you're more serious...

A plug for Dave X's fire art workshops. He's forgotten more about fire art than I'll ever know.

Things you'll need

A tank of liquid propane
A crescent wrench or two
A vice grip is often helpful with the plumbing
A drill or drill press. We're going to do this with a hand drill, but if you want to go for precision, a drill press or an upright mill will serve you better.
A 1/16 - 1/8" carbide drill bit
A center drill
A piece of schedule 40 pipe
A pipe cap
Yellow teflon tape
Various bits of plumbing, to be described
Safety goggles
Fire retardant gloves
Fire extinguisher
A plastic spray bottle filled with soapy water, for detecting leaks

Step 1: Interfacing With a Propane Tank

You'll need a typical 20lb propane tank, of the type you can get at the gas station, or your local hardware store. Interfacing with the tank requires some specialized plumbing. You'll typically need:

A fitting to interface with the LP tank
A regulator, to ensure a specific, constant pressure feed from the tank
An emergency shut-off valve
An LPG hose for attachment to the effect
Optionally, a needle valve for fine adjustment of the flow rate

At room temperature, the gas pressure of propane is about 120PSI. The regulator brings this down to a safer level, typically 10 - 30 PSI for flame effects.

For beginners, I highly recommend the "fire pit kit" from Form and Reform of Oakland. It comes with everything you need above, except the emergency shut-off valve. (Note that if you're building effects for Burning Man, the emergency shut-off valve is a requirement.)

If you want to get fancy, you can use an adjustable LP regulator and experiment with different pressures. For this, having a pressure gauge helps, so you can see what pressure you're dialing up.

Safety tips:

Wrap all connections in yellow teflon tape or pipe dope to prevent leaks. See below for details.
Do not use plain rubber hose of any sort. Most rubbers aren't chemically compatible with propane, and will degrade and leak.

Step 2: Creating a Simple Flame Pipe

We're going to make regularly spaced holes in a short piece of schedule 40 pipe. Note that you probably actually want to avoid using galvanized pipe, as zinc is pretty toxic when it's heated. But, for small prototype projects, it's not going to kill you in the short term, if used outside. (However, never weld galvanized pipe. Welding gives off a lot of gas and particulate.)

A drill press or upright mill will allow you to do this with great precision, but it's hardly necessary. For this project, we'll use a cordless drill and a 1/16" carbide bit. You can use larger sizes, which will create differing flame effects.

Start by marking out where you want to drill at 1/4" to 1/2" spacing, and then drilling a quick divot with a center bit. This is critical for using small-diameter drill bits.

Next, use your 1/16" bit to drill the holes. The key to drilling steel by hand with a 1/16" bit (or with a drill press for that matter) is patience. Drill at low speed, and apply very little force. Use cutting oil if you have it. If you drill too fast, or apply too much force, you can easily bend and break the bit. A good indicator that you're drilling at the right speed is that you're getting nice long chips. If you're seeing powdery chips, drill slower.

Step 3: Assemble the Effect

A bit more plumbing is required to connect the hose to the effect. The hose should have a 3/8" male flare fitting. Flare fittings are great because they're self-sealing and don't require any teflon. We need a couple of adapters to attach this to our effect. See the image for details.

The gas in the effect is actually at atmospheric pressure, because it's venting through the holes, by design. As such, teflon on the fittings isn't actually required. But it's good practice to teflon wrap all your connections. Tips for teflon wrapping the joints:

Use plenty of tape, 3 - 4" per connection. It should wrap around a couple of times at least.
Wrap the tape against the direction of rotation of the male part. In other words, think about the direction you'll be rotating the male part to screw it in, and wrap the teflon in the opposite direction, so that when you're done wrapping the "tail" of the tape is pointing away from the direction of the rotation. This will ensure that when you start screwing it in, the tape will tighten with the threads, instead of being loosened by them.
Wrap the tape with about 1/8" overlapping the end of the joint, and smooth it out with your fingers a bit before screwing in the joint.

If you've done it properly, you can screw in the joints hand tight and not have an leaks.

Once you're done assembling the effect, wrap it in steel wool, and tie it around with wire. I've used single stranded copper wire, which I have lying around my electronics bench, but bailing wire works fine as well. As we'll see, the steel wool will help prevent blowouts by maintaining a flame close to the effect at all times.

Step 4: Safety, Safety, and More Safety

I told you this would be about safety. It's right there in the title.

Safety precautions

Go outside. Don't play with fire effects indoors. Don't do it on a wooden patio. Use your common sense.
Fire extinguisher. Have one that is charged, and know how to use it.
Goggles. Wear them.
Fire retardant gloves. These won't protect your hands from intense radiant heat, but they will prevent you from burning your fingers if you accidentally touch a part that has been heated by the flame. And, because they're flame retardant, they won't catch on fire accidentally.
Wear natural fibers. Don't wear polyester. It will melt onto your body if it catches fire, and it will cause third degree burns.

Checking for leaks

Make sure the safety valve and needle valves are shut.
Open the main shutoff valve slowly.
If you have an adjustable regulator, slowly raise the pressure to around 10PSI.

At this point, use all your senses:

Do you hear the hiss of gas escaping?
Do you smell gas? LP has odorants added to make it easy to detect.
Use your spray bottle to spray around the joints, and look for soap bubbles (see the photo above for an example.)
If you see, smell, or hear a leak, shut off the main valve, disassemble the offending joint, rewrap with teflon, and try again. Don't proceed until your plumbing can hold 30 PSI without leaking.

Step 5: Work Holding

Often you want to test effects before they're mounted to their final place. Be smart about your workholding. Use only metal, and make sure it's clamped down and can't flop around if something happens causing gas to escape at high pressure. Here, I've used a metal TV stand and a vice grip. It's not fancy, but it's safe. Under no circumstances should you use plastic zip ties or plastic of any kind for holding the parts.

Step 6: The Moment of Truth

Open the main shutoff valve, and the emergency shutoff valve.
Dial up the pressure if necessary.
Slowly open the needle valve until you can hear a low flow of gas from the effect.
Use a long lighter, and standing at arm's length from the effect, ignite the effect. You will want to light the lighter a foot or two away from the effect, and then slowly bring it close to the effect: the local concentration of propane near the effect is too high to support combustion, and will sometimes prevent the lighter from igniting.

As demonstrated in the video above, after we've ignited the effect, we can shut off the emergency shutoff and then turn it back on, and the effect will self-ignite because of the steel wool. This is our blowout-preventer. Even in moderately windy conditions, it will stay lit, although it will affect the aesthetic of the effect if it's not wind shielded at all.

When you're done, close the emergency shutoff valve. Then, always close the main shutoff valve when you're done before you put the tank back in your garage or wherever you're going to store it. At this point, re-open the emergency valve to vent the gas that remains in the line.

Congratulations! You've built a small flame effect without killing yourself! Now you're ready to experiment with expanding it, adding electronic valves and pilots, building it into metal sculptures, or whatever you can imagine.

If you're interested in following my work, you can see it here at Flaming Icosahedron.