Ft Mchenry tunnel , on I95 Baltimore area

[H. John Kohl]

[s]I believe both Harbor and Ft McHenry tunnels are propane restricted. Take the Scott Key bridge or the west route (long way)but no toll on 695. Or you can take 50/301 north across the Chesapeake Bay Bridge, Annapolis, up the eastern shore. Beautiful Drive.[/s]

This link gives the answer.
Here is excerpt
The Transport of Hazardous Materials Across our Toll Facilities

Code of Maryland Regulations (COMAR) govern the transport of hazardous materials across our toll facilities. Under these regulations, vehicles carrying bottled propane gas in excess of 10 pounds per container (maximum of 10 containers), bulk gasoline, explosives, significant amounts of radioactive materials, and other hazardous materials are prohibited from using the Fort McHenry Tunnel (I-95) or the Baltimore Harbor Tunnel (I-895). The Francis Scott Key Bridge (I-695, the Baltimore Beltway) is a convenient alternative route for crossing Baltimore's Harbor.