It's pretty epic to capture the details of fire onto a camera. It is also not as difficult as it seems to be. In a short snippet, here's how to shoot fire breathers.
1/1000 sec at f/ 4.0, ISO 800
1. Safety First (most important step!!!!!)
First of all, make sure your fire breather knows what he is doing!
If he or she isn't a professional, I wouldn't recommend doing this at all. However, this is the Internet and people will definitely try it themselves if they are really curious. So if that is the case then at least learn the ropes. Instead of starting off with a fuel, start off with corn starch. It is non-flammable. It teaches you how to spit correctly so you don't burn your face. This isn't a tutorial to learn how to breath fire so you can definitely find more information through local fire performance groups.........or through YouTube (not recommended).
Second, make sure you have a fire extinguisher with you or a wet cloth to pat down anything caught on fire, whether it is yourself, your model, your fire breather, your assistant, your equipment, or the environment around you. Also, don't wear flammable clothing. 100% cotton is recommended. Polyester will melt into your skin.
Third, steer clear of flammable environments. A bad idea to do this is in the middle of a forest, or indoors, especially if the air is very dry. An exception to this is if it just rained outdoors. If things are covered by water, it is very difficult for anything to catch fire. However, passing pedestrians, patrol, or your neighbors might harass you. Personally, for me, I would only do this in urban environments.
Fourth, if possible, have fire performance insurance. A monthly fee of two hundred bucks can cover you if, worst case scenario, you burn down a million dollar property.
2. Judge where the wind is blowing.
DO NOT for any reason blow fire at the direction that the wind is hitting you. You want to blow it towards the same direction as the wind to send the projectile far away from contacting your face.
3. In regards to shooting, fire breathing requires safe combustibles with a high flash point (such as paraffin oil).
High flash point means that it gets REALLY bright. The iso and the f-stop can be adjusted. However, shutter speed has to be high. 1/200 is the absolute minimum. The flames will be kind of blurry. If you want super sharp flames, aim for 1/1000 or faster if it is possible. The faster the shutter, the texture on the flame will be crisper. There is no magic number so experiment, experiment, experiment.
4. Every split moment when the flame comes out requires different exposures.
As it travels out the mouth, the exposure quickly goes from extremely bright to dark. Wait a split moment for the flames to cure itself, exposing its awesome texture. Look at the difference in exposures from the ignition at his mouth to the outskirts of the flame.
1/200 at f/ 4.5, ISO 800 (If I had a little higher shutter speed, that over exposed section wouldn't have happened)
5. It is okay for the photograph to be completely under exposed.
If the flame is overexposed, the detail will be lost. Underexposed photographs can be recovered extremely well these days. The dynamic range on most cameras, especially on raw files is extremely impressive.
6. If you want to add flashes to your photographs, throw on an orange CTO gel.
The white balance with the flash doesn't correlate with the color balance of the flame's light. If needed, layer the CTO gel one or twice.
1/200 at /f 3.5, ISO 800 - one external flash with double layered CTO gel is place to the left of the camera
The rest is up to you to experiment. Good luck!
I thank Benjamin Von Wong for throwing tips and pointers towards my direction. If you are curious, check out his work!