Leave level boundaries hint
Note: Make sure you create a class with the following: Perk 1-Marathon, Perk 2 - Lightweight, Death Streak-Painkiller. With a Tactical Insertion, go on a map with radiation and get near it. Then, plant your tactical at the edge and die. Repeat this three times to activate PainKiller. Once you spawn back, start running and your extra health will allow you to break through and be free to explore.