Once you’ve found a flammable spray – bug spray, medical spray, rust cleaner, etc. – simply equip it by highlighting it and pressing
. Equip your lighter at the same time and go into first-person view by pressing
. You’ll now be holding the lighter in front of the spray bottle. When you get close to a Humanz, just pull the
to fire a spray of flame at them, lighting them on fire and unlocking the achievement.
You will not receive the lighter until the end of Episode 2, when you get out of the first car in the parking garage and have to blow it up to open a new path.