Sorry, then. In my defense, that was just my opinion (also i'm obviously german) and I find the topic of regulation of manhole covers not that novel (that stuff is abundant over here and the DIN number is imprinted in each of them). PS: the concrete filling is to increase its weight (apparently not enough in the below incident) on the cheap compared to using steel.I once whitnessed how during a heavy storm a sewer surge pushed one of these out of its hole at the bottom of a hill and what serious hazard that created for motorists in the middle of that main street. You're right that this stuff is rather nerdy and that standards around it are interesting.