For this achievement, you have to beat the first stage without dying. I would recommend sticking to the high ground and hitting the mortar with the flame at a distance in the starting point. Then, avoid the mines after the mortar. After this, continue sticking to the top of the carriers. Once you have reached the end, I recommend you conserve all 3 of your shots for the end of the stage. I say this because, in the end, there are 3 waves coming from a truck. When a brown, unarmed, soldier is about to get you, unleash your first flame. Then when a second unarmed soldier is about to get you, repeat. For the third close henchman, unleash your final flame.