I'm involved with The Beltane Fire Society and run the local Fire Club every Monday.
First off - fire safety. If you are close to fire make sure you are wearing natural fibres - wool or cotton. I don't let anyone play with fire if they are not suitably clothed. That goes for being close to performers too. Clothing melting into your skin is not pleasant.
When I'm taking pictures and not playing
the best option is low ISO (100 or 200) aperture about f10 or f11 and shutter speed around 1/2 a second.
I adjust aperture and shutter speed to account for differences in flame temperature and performance speed.
Some props burn brighter than others- it's a case of trial and error.
Performance speed - some performers move their props faster so fire trails can be captured at shorter shutter speeds. I probably wouldn't go faster than 1/4 second though.
Too high an ISO overexposes the fire, but cooler props might require a slightly higher ISO maybe up to 320 or 400.
The fun starts when you are trying to balance ambient light with fire prop light
Trial and error again. In my examples below it was pointless raising ISO too high as there was no ambient light to speak of - I had my other camera set to 6400, I think, for non fire / no flash photography.
That's the first part of your exposure!
On to flash (just treat as seperate exposure).
I generally use manual flash for Fire Club, rear curtain sync, set to 1/4 or 1/8 with some compensation to get it right and depending on the distance. I'm used to taking pics from a certain distance and everyone knows me so performers are used to facing me and know they and I are safe.
At Beltane it was different as distances vary so much between performer and photographer. It's best to use TTL for flash in this case.
When you edit your images just lift the shadows and then maybe the exposure. Highlights can be brought down if the fire is a bit too white.
I tend to shoot a bit wide most of the time and crop in. Peformers and props move as in first example - I didn't expect her to go that high!
A couple of examples from Beltane
Beltane 2019 by
Ken, on Flickr
Beltane 2019 by
Ken, on Flickr
Another thing to look out for is when a fire trail covers the performer's face - it happens a lot! Just something you (mainly) get used to. Watching a performance gets you used to where the fire trail will be. Adjusting your shooting height from kneeling to standing can give you a clear shot depending on the performance or performer's height.
One from Fire Club.
Fire Club by
Ken, on Flickr
Hope this helps.
Edit: looking back at my first efforts is embarrassing, but I'm getting better