The typical steam system runs about 2 psi. There is nothing that could hit the ceiling, but the air vent on the side of the radiator can have stripped threads and it could then fly sideways and hit a wall. Steam at 2 psi would then flow from the 3/8" diameter hole and scald someone standing near it. But the steam would not come out in "jet" like it would on a high pressure system. Steam temperature is a function of its pressure so at 2 psi it would be about 218 degrees. At 5 psi it would be 227 degrees and at the maximum 15psi for a low pressure steam system it would be 250 degrees. Above that pressure it becomes a high pressure system and they do not have air vents that can blow off or any other item that could.