From the bit of time I did working in warehouse software, all the indoors warehouses I've seen were exclusively using electric forklifts, specifically because gas/oil coulnd't be used because of the fumes.
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.
