Can you smoke or allow smoking within how many feet of a vehicle containing Class 1 explosives, oxidizers, or flammables during loading?

Federal rules prohibit smoking within 25 feet of a motor vehicle that contains Class 1 explosives, Division 2.1 flammable gas, Class 3 flammable liquid, Class 4 flammable solid, or oxidizer. The same rule applies near tanks containing these materials and at loading/unloading sites. The 25-foot distance prevents a lit cigarette or match from igniting flammable vapors that may have escaped into the air around the vehicle. Cell phones with batteries that could spark, open electrical devices, and matches are all banned by extension. The rule is regularly violated by complacent operators and just as regularly produces serious fires. Even after unloading, vapors may persist for an extended period.