A Cameron Blow Out Preventer (BOP) is installed at the base of the BP leased, Transocean owned Deepwater Horizon rig. An unmanageable surge of oil led to the fire that sunk the rig and ended 11 lives.
The BOP is not preventing up to 200,000 gallons/day of oil from gushing into Gulf of Mexico. At this point, no one appears to understand why.
The Blow Out Preventer is only a very visible part of an intricate human and technological system under enormous economic pressure to deliver crude oil.
If interactive complexity and tight coupling — system characteristics — inevitably will produce an accident, I believe we are justified in calling it a normal accident, or a system accident. The odd term normal accident is meant to signal that, given the system characteristics, multiple and unexpected interactions of failures are inevitable. This is an expression of an integral characteristic of the system. System accidents are uncommon, even rare; yet this is not all that reassuring if they produce catastrophes. — Normal Accidents: Living with High-Risk Technologies