I don't recommend idling anything at a gas station. I'd possibly consider it okay at diesel only lanes but it's not a habit I'd get into.
The biggest fire I've personally witnessed was caused when a diesel engine ran away on gas fumes and blew. We were cleaning sludge out of a tank when the engine on the vac truck ran away. When it was all said and done about 30,000 barrels of crude had burnt destroying the whole facility. Talk about emissions...
I can picture the same thing happening with an idling diesel and a gasoline spill when the yoyo on the other side of the pump jams a coke bottle in the handle and walks away trusting the automatic shutoff to always work...