One of the main reasons that I chose to go to school in Middle-of-Nowhere, Missouri is that my school offers pyrotechnics classes down at the “on-campus” experimental mine. It was during one of these classes (the very first day, actually) when I got a second-degree burn by wearing pants with too much spandex in the blend.
From staring at the dime-sized burn, it was only natural to wonder: “How do I avoid this happening next time?” and then it was a hop, skip, and a jump to, “How do stunt people set themselves on fire without injury?” And so I present:
Full Burn Film Stunts
To start off, this is one of the more dangerous stunts that professionals do: you should not try this at home.
With that said, a full body burn is all about the set up.
Before the Stunt
First, an undershirt, long underwear, and a hood is soaked in a specially-formulated gel. This gel is the key part of what protects the performer and is made with a (trade-secret) compound which absorbs a ton of water. The water is held in the gel as tiny droplets, with millions of droplets in a glob of gel.
Water has a high latent heat– it takes a lot of energy for water to change from ice to liquid, or from liquid to vapor. Like ice cream on a hot day, as long as you eat it quickly, you can enjoy your frozen treat. In stunts, as long as the burn is performed quickly (before the water has had time to boil off), movie-goers can enjoy the finished effect.
The underclothes are no ordinary material either. They are usually made from Novex or Kevlar which are fabrics that firefighters wear. If heat is applied to Kevlar for more than a few seconds, it will start to burn. If that heat is taken away, the flame will extinguish itself within a few seconds. Novex doesn’t burn at all but will simply char and flake away. As both are impregnated with the no-burn gel, they are highly unlikely to catch on fire.
The next trick is that all parts of the stunt- clothing, gel, and performer- are kept as cold as possible, for as long as possible. This is to prevent the water droplets in the gel from boiling off early, either due to energy from the sun or heat from the performer’s body. Clothing and gel are kept on ice, and the performer is shooed into the shade.
The performer next slides into the gel-soaked clothes and proceeds to slap no-burn gel on all exposed skin. Any skin not covered with the thick gel risks being burnt. A costume made of only natural fibers is then worn on top of the Nomex and gel.
Meanwhile, other crew members have prepared the set- putting down a fire blanket or wet furniture blanket where the performer will be ending their stunt, and gathering and testing fire extinguishers. CO2 fire extinguishers are often used and, as they put out the fire by starving it of oxygen instead of removing the heat, a water hose is often nearby for if skin was accidently left un-gelled and heat needs to be quickly removed (the high latent heat of water in use again!).
During the Stunt
Finally the time has come, the fire extinguishers have been manned, and the performer gets into position. As the performer has just spent a fair amount of time becoming inflammable, burn gel is now applied to them so that something is able to catch on fire. Burn gel (or burn paste or any other mixtures used) have one main trick: they burn at a lower temperature than fires usually experienced in life. This allows the no-burn gel to last longer and for stunts to be more elaborate.
The burn gel is applied, the performer is lit, and the rehearsed movements are acted. One less-obvious safety consideration is practiced here: the performer is almost always moving forward. This keeps both flames and (more importantly) hazardous smoke out of their face. If the performer is asked to stand still for a shot, they hold their breath, and the length that the stunt can be safely performed is greatly reduced.
After the Stunt
At the end of the take (or if the performer is feeling unsafe), they go to the prepared blanket and drop to their knees. This is the signal to those manning the fire extinguishers, and the flames on the performer are quickly smothered.
The director examines the footage that was just shot as the stunt coordinator checks in with the performer, with medics hovering nearby. If the performer is fine and the director asks for the shot to be done again, the performer applies more gel and re-does the action. Once the director is happy with the footage, the performer retires from scene to go take a long hot shower.