A CATastrOphic failure 0r CATO is defined as:
A motor failure, generally explosive, where all the propellant is burned in a much shorter time than planned.
This can be a nozzle blow-out (loud, but basically harmless), an end-cap blow-out (where all of the pyrotechnic force blows FORWARD which usually does a pretty good job of removing any internal structure including the recovery system)or a casing rupture which has unpredictable, but usually devastating, effects. Another form of CATO is an ejection failure caused by either the delay train failing to burn or the ejection charge not firing, but the result is the same: the model prangs. from the Model Rockets FAQ, by Wolfram von Kiparski.
Obviously, a manufacturing error can cause the CATO. These motors will fail brand new, right off of the hobby sales shelf, and should be reported to the manufacturer. There is a website, MESS Reports, the Malfunctioning Engine Statistical Survey (MESS) a joint organization program that
allows NAR Standards & Testing, Tripoli Motor Testing and the CAR Motor Certification Committee to track field trends in the reliability of sport rocket motors. Old and new motors, that are not stored properly, cycled from hot to cold and back again will tend to fail occasionally. This temperature cycling can cause the propellant to crack inside the casing. CATO’s could start a fire so always be ready, you never know when they will occur.