I know "accountable", "responsible" and "answerable" are used in the following way in English,
The engineering team is accountable for this failure of the system.
The terrorists are responsible for this attack to the train station.
He is answerable for the accident.
But I have a confusion that I'm not sure if those words imply that people who are responsible are one of the causes of the problems and deserve punishment, i.e., blameable ? I am confused because in my mother language (Chinese) we distinguish two cases,
The first case is, someone held the duty of doing a job and he did it as best as he could. Unfortunately something bad happened which was impossible to be stopped (e.g. blackout of the whole city and backup power didn't work for no reason). In this case, the investigators of the problem think he was in charge of the job and should give his explanation (be accountable ?) to the problem to help identify the cause. If the investigators determined, after necessary examinations and questions, that the problem was indeed caused by something impossible to stop, then we think he should not be blamed. It is a tragedy but no one should be blamed.
The other case is that it is for sure that someone did something bad accidentally or on purpose to cause the problem, then he is blamable.
So my question is whether the words "accountable", "responsible" and "answerable" can tell the difference between the two cases ? If not, how can we use English to distinguish the difference ?
Can we say "He is accountable for this accident but not blamable", or "He was involved in the accident but not accountable/responsible/answerable for it" ?