A lot of nonsense is written about uncontained engine failures. Anything that comes loose will be blown out the back of the engine so is uncontained in that limited sense. The containment design problem refers to loss of a fan blade. In that event the fan case is designed to contain the blade so that it does not fly sideways and penetrate the cabin for example. But such a failure produces a lot of debris that will escape to the environment through the back of the engine.