Is this what a pyromancy flame +20 looks like?

I'm going to assume, using my pitiful knowledge of science, his entire arm is covered with copious amounts of some flammable gel, as liquid versions would attempt to soak the skin instead of just sitting on top as gels would, such as your everyday hand sanitizer. Thus, when ignited, the gel will burn before the skin; However, the fire must be put out in a short amount of time, as the fuel (the alcohol in the sanitizer) burns quickly, and the fire will seek another source of fuel, aka the skin.