SRB (Solid Rocket Booster) - O-ring Failure Issues, Pg 1

This memo, discussing SRB (Solid Rocket Booster) Critical Items, reports on concerns about O-ring failures.  On the cause of a failure mode, the memo notes:

Leakage at case assembly joints due to redundant O-ring seal failures or primary seal and leak check port O-ring failure.

NOTE:  Leakage of the primary O-ring seal is classified as a single failure point due to possibility of loss sealing at the secondary O-ring because of joint rotation after motor pressurization.

Failure Effect Summary:  Actual Loss - Loss of mission, vehicle, and crew due to metal erosion, burnthrough, and probably case burst resulting in fire and deflagration.

The memo was written a bit more than three years before Challenger's fatal mission. 

Credits

NASA memo online, courtesy NASA.