Many years ago, there was a catastrophic nuclear explosion. You escaped to a fallout shelter where you have been surviving with basic equipment and rations. You’ve heard that radiation levels have returned to normal, and it is finally safe to leave shelter. Not a minute too soon, supplies are running low, the air is stale and you’re feeling strangely breathless. Excitedly you begin to unbolt the door, but it won’t budge to your abject horror you find it is jammed you’re locked in. The CO2 monitor is reading dangerously high levels, you only have 60 minutes to escape before this situation becomes deadly.