Mitchel the BOP failed. It did not close and seal the well. An acoustic switch is not a not a wellhead valve. It is a communications device to actuate the wellhead valve. It is used in tandem with or instead of a dead man switch. To simplify-it is a wireless switch. If you want to learn a little about it check this site
"Acoustic Switch" Would Not Have Saved BP Well - The Daily Hurricane
It also has some interesting comments.
On producing wells there is no BOP. There are surface safety valves and sub surface safety valves valves. These valves do not have to shear drill stem. They are fail close valves that automatically close when control pressure is lost. Totally different setup.
BP has an abysmal safety record. They and companies like them should not receive permits to drill in American waters. If BP had not cut corners...If they had operated according to industry standards this would not have happened. I am for offshore drilling. Drill baby drill. But do it by the rules and responsibly. Make safety performance a key requirement. Put teeth in the laws for those who intentionally violate the rules. And remove the cap on liability limits. It adds incentive for safe environmentally sound operation if a company stands to loose everything if they are found negligent.
Sbl I agree there is some nasty stuff that comes to the surface with hydrocarbons. The fisheries will be decimated. They will recover maybe in our lifetime if we are lucky.