system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How do films and shows make people appear on fire without causing injury?
gpt
If you ever visit one of the Universal Studios parks, they demonstrate this technique as part of their special effects/stunt shows.  It's a little surreal watching a guy literally on fire 10 feet in front of you, but they explain a lot of the methods used to make it safe.

Basically, the stuntpeople are wearing as much heavy, fire-resistant clothing as possible for the scene and cover every bit of exposed skin in a protective jelly.  They use a fuel with a very low burn point so that they can burn at a temperature that won't hurt them, and they hold their breath during the stunt so that they aren't inhaling any fire.  And there's a team of assistants with fire extinguishers on standby, keeping an eye on everything.

Once all that is covered, a trained stuntperson can handle 10-20 seconds of burning without any ill effects.  They'll have a safety signal (like a raised hand or something) that means "extinguish me RIGHT NOW," but otherwise, they'll just do the few seconds of action needed for the scene and be immediately extinguished as soon as the director yells "cut."  It's a very realistic effect and is often way cheaper than paying a team of digital artists to render a good-looking flaming person.