[wfontjr]

first i would never use air to pressurize a hydrocarbon, the only thing you are missing in the vapor space is a spark, most vessels containing hydrocarbons have a nitrogen blanket to prevent this, second its probably a good idea to ground the tank when filling tank or tractor, flowing liquids can build up static electricity, and when it discharges, boom

i have seen static discharging inside a closed vessel, the only safety was the vapor contained no oxygen