That stinks

[Timelord]

If you can find access tunnels of that sort that provide you with an emergency route or temporary shelter - (not during rainfall at the location or on higher ground out of sight), then that is an excellent facility to your preps. Please be aware that many people believe and refer to gas masks as being able to preserve you from toxic gases. This is not true. If the concentration is high, then there will not be enough oxygen and you will suffocate. The same is true for a smoke filled environment or any similar instance. In those scenarios you would need a rebreather of an alternative air supply. If you do find yourself in this situation, then GTFout or have some hastily created expedient air reserve. Your life is in your hands with this one though. Safe travels, TL.