Chernobyl is an example of people violating very clear safety rules, "Do not pull out the control rods past this point!"

(It's a lot more complicated than that, but it is most certainly not a "normal accident" like the BP one: http://en.wikipedia.org/wiki/Chernobyl_disaster .)

BP was too. The blowout preventer was damaged in a previous accident. The Transocean contractors wished to stop and get the well under control, but they were overruled by the BP manager at the site. Is it any wonder that when you continue drilling while the blowout preventer is damaged, there's a blowout?