My concern would actually be the ventilation. It looks like the access hatch goes straight down from the floor of the workshop. He often seems to have various machinery in there and I'd be concerned that a gas leak could flow into the tunnel and push out the oxygen, making it an asphyxiation risk.

I hope he's mitigated this because there are documented cases of unaware first responders trying to save those in enclosed spaces and themselves asphyxiating.