You get this achievement in Chapter 6 Carla. I don't know if this achievement is missable or not because I got it without even realizing what was happening.
Anyway, Barry is in the room where you have to turn off the fire blocking your path with a valve. You will notice a person that is throwing molotov's at you. This is Barry and if you sit under the walkway he is on, he'll throw a molotov right by him and catch himself on fire. After he burns up, the achievement should pop.