The rules for hazardous materials are clear and unwavering. The placards remain on the transport vehicle until there is no longer a placardable amount of hazardous materials on the transport vehicle......PERIOD! These rules have nothing to do with accidents on, or off public property.
As an example, a national chemical company at their world headquarters in Midland Michigan used to do just as you are suggesting, that is, removing the placards off trailers and railroad cars on their private property while still loaded. There were 4 of us that day about 17 or 18 years ago (at that time there were about 64 of us nationwide and traveled quite extensively) that were inspecting the plant and corporate offices (as federal DOT officers we legally inspected not only railroads, airlines, river barges, motor carriers and their driver's, but consignors (shippers) and consignees (receivers) of hazardous materials as well). After our inspection of their facility (which took almost 5 full days days because of its' size), we issued a civil penalty (fine) of over $225,000.00 just for the non-placarding of the transport vehicles (a simple definition of transport vehicle is anything used to transport hazardous materials). There were other fines as well but I show this one only to rebut your statement.
If the customer wants you to take the placards off before they're supposed to be removed you should tell them that it is not proper and/or legal to do so until there is no longer a placardable amount in your trailer. You and the consignee may both be held responsible, and both may be subsequently issued federal civil penalties if caught. Some state officers also have the same legal rights as we federal officials as well, depending on how that individual states laws are written (TX, NC, and OH come to mind immediately). It would more than likely be issued to you first because under the hazardous materials rules you are responsible for the contents of the transport vehicle (trailer) until it has been unloaded. I would also suggest that this consignee does not know the rules very well if they ask you to remove the placards before backing into their dock. I would suggest that they, and you read 49 C.F.R. parts 172.500 through 172.560.
I can therefore assure you sir, that "THE DOT" does care what happens on private property because the hazard still exists in that trailer until the hazard has been removed. Federal officials would not only inspect you on private property, but the warehouse as well. That is not only DOT rules, but OSHA rules as well.
tHIS IS NOT MY WORDS BUT STATES WHAT i KNOW IS TRUE! i WILL KEEP RESEARCHING THIS TO FIND THE ACTUAL LAWS THAT APPLY TO THIS!