The division between left and right Solid Rocket Boosters was roughly equal. Each instance of thermal O-ring distress was accompanied by a leak path in the insulating putty. The leak path connects the rocket's combustion chamber with the O-ring region of the tang and clevis. Joints that actuated without incident may also have had these leak paths. At time of launch, it was cold enough that water present in the joint would freeze.
Tests show that ice in the joint can inhibit proper secondary seal performance.
A series of puffs of smoke were observed emanating from the 51-L aft field joint area of the right Solid Rocket Booster between 0.678 and 2.500 seconds after ignition of the Shuttle Solid Rocket Motors. The puffs appeared at a frequency of about three puffs per second. The puffs were seen to be moving upward along the surface of the booster above the aft field joint. The smoke was estimated to originate at a circumferential position of between 270 degrees and 315 degrees on the booster aft field joint, emerging from the top of the joint. The leak was again clearly evident as a flame at approximately 58 seconds into the flight.