A section of buckled drill pipe lodged in the blowout preventer on BP PLC's ill-fated Macondo well prevented the emergency equipment from stopping the flow of oil and gas that gushed into the Gulf of Mexico for months last summer, according to a federal investigation of the subsea device.

The Interior Department today released a lengthy forensic report about the blowout preventer that says its blind shear rams -- the equipment's final line of defense against a gusher -- could not seal off the well as designed because the pipe had buckled in the initial blast.

"The primary cause of failure was identified as the [blind shear rams] failing to fully close and seal due to a portion of drill pipe trapped between the blocks," the report says. "The buckling most likely occurred on loss of well control."

The forensic examination of the blowout preventer comes as part of the Interior and U.S. Coast Guard joint investigation into the April 20, 2010, accident that killed 11 rig workers, destroyed Transocean's Deepwater Horizon rig and sparked the nation's worst oil spill. Interior and USCG commissioned Det Norske Veritas, a company headquartered in Norway that assesses the risks involved in projects around the world, to examine the 60-foot-tall equipment and write the report.

The 300-ton blowout preventer was raised from the seafloor last September, and Det Norske Veritas conducted the probe at a NASA facility in New Orleans from October through early this month.

The report details the circumstances that led to the pipe buckling and calls for a series of industry studies into the nearly 90-year-old accident-prevention technology. Specifically, the study urges examination of conditions that could lead to loss of well control and how those conditions would affect pipes in the wellbore, the inability of the blind shear rams to cut through the buckled pipe and the vulnerability of other backup control systems, among others.

The two federal agencies will discuss the report's findings during a public hearing in Louisiana early next month.

Democrats in Congress are already calling for a closer examination of the technology's effectiveness.

"A blowout preventer is like a car's airbag. It can't prevent the car accident, but it is supposed to deploy and prevent fatalities," Rep. Ed Markey (D-Mass.) said in a statement. "It isn't clear from this report that blowout preventers can actually prevent major blowouts once they've started."

Click here to read the report.