Certainly the systems are designed to. But over the operational life, things happen. Systems degrade, maybe maintenance lapses a bit. Maybe, for example, a mec

Certainly the systems are designed to. But over the operational life, things happen. Systems degrade, maybe maintenance lapses a bit. Maybe, for example, a mechanic tired of trouble shooting an issue replaces the 9th blown burst disc in a row with one he just cut from the mud flap on his shop truck. NBD, the system was only running 5% over pressure anyway and he wants to go home. Later, this overpressure state backs up through the system and overheats a pump which, considering that it is pumping liquid explosives, isn't ideal. Maybe this trips a temperature sensor and the jury rigged burst disc is discovered. Maybe it doesn't, or the sensor was bypassed or silenced, and the pump explodes. I'm rambling, but this is a real world example. My point is that these various factors: designed safety monitors like sensors or fail-safes play hand in hand with over-engineered systems as well as the security of the control systems. Any one part of the system should not be allowed to lapse or be less secure with the idea that another level of the system will catch the problem before it becomes life endangering.