For good / breathable air, maybe some of that flex pipe you were talking about & connect a fan up top that pushes fresh air down & in. Run a bell connected to a string so you can alert someone if you have any serious problems. Def. get a battery powered flashlight + a backup for when # 1 dies. I think in the tool thread you are on Ryobi? I'm sure they have some decent ones. At any point are you going to go wider? Do we have any geologists around here that can discuss how deep (on average) he will need to go & then the soil / dirt / whatever changes to something softer or possibly even more difficult than what is currently being encountered? & what if you go... maybe 20 ft. deep... any possibility for going sideways? My 2nd favorite thing about Hogan's Heroes - # 1 was always the tunnels - # 2 was when they would pop up from a fake tree stump. I would gladly donate to a fake tree stump fund, however the stump has to be maybe 50 feet away (or more) from where this current hole is, furrher awY from the building... otherwise it's just an access point for this existing hole. Made of a decent steel or whatever it is they use @ Disney to make fake rocks that don't turn to shit over time. So, yeah. Fake stump secret exit hatch thingy.