According to my now deceased father-in-law, diesel disolves or washes off the galvanizing, which may be why they specify plastic.
Static: Static electricity builds up in plastic fuel cans and dissipates very slowly if at all. The movement of gasoline over the plastic creates the charge, so the charge is created by filling it, movement as it sloshes around and when pouring it out the spout. Don't know about diesel, but it is probably similar.
Anyway, a detailed article in Sport Aviation magazine several years ago described a study in which they were able to measure the charge in the plastic cans and it was in the thousands of volts. They found that leaving the can sit for a couple weeks did not reduce the charge. They could completely dissipate it, however, by wiping the can with a wet cotton towel, which they recommended be done prior to fueling an aircraft from a plastic can. They also said that a metal can is the worst for a potential spark unless the can was grounded to the aircraft prior to pouring fuel. A grounded metal can was the safest.
Once in awhile I see references to tractors that burned; how the fire started I don't know. May or may not have been from fueling, but I do know aircraft fires do start occasionally from fueling from plastic cans.
Diesel is not explosive, so I have heard. What about the fumes coming off the stuff? I don't know. I do know that you sometimes hear about diesel rigs burning up, so at least a fire started somehow.
What do I do? I wipe down my plastic cans with a wet towel before fueling my plane, but just pour the diesel straight in to my tractor without any concern. But my airplane is in a hangar with 10 other planes and my tractor is usually outside and is worth only about a fifth of what my plane costs.
