The blowout preventer can seal off an oil or natural gas well being drilled or worked on. If underground pressure forces oil or gas into the wellbore, operators can close the valve remotely (usually via hydraulic actuators) to forestall a blowout, and regain control of the wellbore. Once this is accomplished, often the drilling mud density within the hole can be increased until adequate fluid pressure is placed on the influx zone, and the BOP can be opened for operations to resume.

The Deepwater Horizon blowout preventer is a 50 foot - 300 ton assembly manufactured and supplied by Cameron International for the Macondo Exploration Well on Canyon 252 Block. The BP wellhead had been fitted with BOP, but it was not fitted with remote control or acoustically activated triggers for use in case of an emergency requiring a platform to be evacuated. It has a dead man's switch designed to automatically cut the pipe and seal the well if communication from the platform is lost, but it was unknown whether the switch was activated.

The BOP was raised and taken to NASA抯 secure facility in Michoud, Lousiana in August for forensic examination. DNV has utilized its forensic investigation expertise from the Columbus, Ohio office and its subsea equipment (BOP) expertise from the Houston, Texas office in the project.

BOEMRE/U.S. Coast Guard (USCG) Joint Investigation Team announced that it would hold a seventh session of public hearings the week of April 4, 2011. The hearings, which will focus specifically on the forensic examination of the Deepwater Horizon blowout preventer, are scheduled to take place at the Holiday Inn Metairie, New Orleans Airport, 2261 North Causeway Blvd., Metairie, La.

The forensic examination is one aspect of the much broader comprehensive investigation into the causes of the Deepwater Horizon explosion, loss of life, casualty loss, and the subsequent oil spill. Although the full investigation report is not expected to be released until sometime this summer, a report on the BOP and other matters is scheduled to be issued within the next month.

Lawyers for Cameron and BP rejected DNV's findings and said there was no data to support its conclusions, as the report was based on computer modeling and not studies of the actual blowout preventer salvaged from the seafloor.