Sha @ fire workshop (shooting tip below)
When shooting a fire performer, you have two choices for exposure.
On the top image, it is a typical quick shutter speed (eg. 1/125) to capture movement and lighting was mainly from the fire, but some off camera light to help illuminate the performer's body.
The lower images is a long exposure (bulb setting with remote trigger) with a single strobe/flash (triggered manually and then close camera's shutter right after) toward the end of the shot to light the face. The long exposure captures the movement and the flash keeps the face in focus.