How do they handle the exhaust from vehicles inside the mines? I've seen cases where they only allow electric vehicles with no exhaust inside facilities like this.
A common "standard" for mines/tunnelling is:
3 Cubic meters/minute per worker
4 cubic meters/minute per diesel HP (calculated on the max power output of the engines)
Electric vehicles (battery powered) are usually not considered as they normally represent a fraction of the power involved in the construction/digging.
The large machines that are electrically powered (via cable/wire) are not included as they do not produce exhaust fumes nor particles/vapours, but they may be considered in some cases for the amount of heat they produce.
OT: Recently the fire department called me because the carbon monoxide detector in one of my buildings alarmed. That was mysterious since in the summer the furnaces are not used. Eventually we discovered that the cleaning crew was using propane-driven buffers on the floor! We're not going to allow that anymore. It's a 6000 sq ft office that is mostly carpeted; they certainly don't need to use dangerous equipment that was designed for large buildings like sports stadiums.