There is a rod that contains the broken spring. If an installed spring were to break when the door was open the most likely cause of danger is a few hundred pounds of garage door coming down on whatever was under it, so wait for the door to fully open before driving through.
What gets you as I understand it is that the turning handles for the springs. If you lose your grip on them its a rod of steel that's going to flung around at high speed with enough force to counter-weight an entire garage door.
