It was designed by engineers and deemed sufficient. Several people signed off on it.

In a company with failing engineering quality, what typically happens is that, of all the engineers qualified to sign off, management over time tend to choose the ones who are more willing to sign off. The more careful engineers who refuse to sign off, or attempt to negotiate harder for safety before signing off, are not promoted over the less careful engineers. The result is that the engineers in a position to sign off increasingly comprise the less careful ones.

Who is to blame in this case: the management who drive the process that selects the less careful engineers, or the less careful engineers?