The New York Times has published a very good technical article on Blow Out Preventers, and the BOP on the Deepwater Horizon. Thanks to Angela Summers, of Sis-Tech, for sending this to the ISA84 mailing list.
Once again, this article shows how High Impact Low Probability Events can be ignored, minimized or even discounted, since "we've drilled 33,000 wells and only had a couple of blowouts!"
The process industries are notorious for this kind of thinking, which is revealed, of course, only in the aftermath of a HILPE that actually occurred. Somehow we need to get beyond this.