In my day, a failure was either contained or uncontained. Binary.
Today I hear words like "high energy" and "low energy" uncontained failure.
Pieces of airfoils penetrating the case (and almost certainly the cowl) are regarded "low energy", thus unlikely to bring down the aircraft.(*)
But a rotor disc burst results in chunks with the mass and velocity of a cannonball, putting the enterprise in jeopardy.
* Debris blown out the tailpipe, while not penetrating the case, can possibly damage the tail feathers, and is worrisome from that aspect.
