If you have a non-conductive flammable liquid and you are passing them through a filter, the hazard associated with static electricity generation can be up to 300X greater. This actually goes with any type of obstruction in the pipe/hose (orifice plate, partly opened valve, flow probe, etc). If you must have a filter/strainer in your delivery system, “relaxation time” becomes critical! This means that we need to put the filters early in the delivery system and NOT at the end before the liquid enters a container. Here is what NFPA 77, the authoritative standard for controlling static electricity.
8.4.5.1.2 To prevent the charges described in 8.4.5.1.1 from entering the receiving vessel, the filter should be placed far enough upstream so that the charge can decay to the magnitude it would be in the pipe flow. Common industry practice is to provide 30 sec of residence time in the pipe or conductive hose downstream of the micro filter, especially if the conductivity of the liquid is not known. For nonconductive liquids that have both very low conductivity (i.e., less than 2 pS/m) and high viscosity (i.e., greater than 30 centistokes) at the lowest intended operating temperature, longer residence times might be appropriate. In those cases, a residence time of up to three times the relaxation time constant of the liquid should be considered.