The fissures are the “living” cracks that will chase you in different parts of the story. The first one that you actually encounter in the game will be in Episode 2. When you get the lighter, you have to blow up the car you just crashed, then go down to the end and light some wood on fire that is blocking your way. When you do that, the fissure comes after you. Run into the corner to the left of the wood you set on fire, and the fissure will chase you, run into the fire in that corner, and die.
The next one that you can burn is in Episode 3. Near the end of the episode, you have to drive a car over a jump to get the ambulance. If you check your GPS, you’ll see the static circle down a path to the right of the road. When you get to it, you’ll find a large house with a burning car outside. Go down the steps by the car to get into the basement. In the basement, you’ll find a Ratz nest and the first Root of Evil.
Once you burn the root, look behind it to find a power box that you can activate to restore power to the elevator. Use the elevator to go up to the top floor. In the first room that you enter, a Fissure will attack you, so have your gun equipped and loaded with fire bullets. Just shoot the Fissure and it will ignite, killing it and unlocking the achievement.