The snow began early on Sunday, February 16, continued all day, and was piled high on the rooftops and in the streets when, around midnight, Steven Johnson, director of facilities, got the call from the security company telling him that something had set off the sprinkler system at Baltimore’s B&O Railroad Museum.

Johnson drove through the nearly deserted city to the building. When he went inside, he saw that two sections of the roof had collapsed, there was about four inches of water on the floor, and he smelled gas. The falling roof had severed the pipes. At considerable danger to himself, in view of subsequent events, Johnson got a flashlight from his car and went back in to shut off the water and gas.

Alerted by Johnson, Courtney B. Wilson, the museum director, soon arrived. There were two more roof collapses, separated by several hours, on Monday morning. In all, eleven sections fell in, exactly half of the lower roof of the B&O Passenger Car Shop, commonly known as the roundhouse …