BP releases Deepwater Horizon inspection report

A number of factors -- including human and mechanical failures -- ultimately led to the Deepwater Horizon oil rig explosion, according to an internal investigation report (large .pdf file) released by BP on Wednesday.

The April 20 blast that killed 11 workers occurred when hydrocarbons, found in crude oil, escaped the oil well and ignited on the rig. BP's report said no single factor caused the tragedy, and it blamed a number of work teams and companies, including Transocean Ltd. (operator of the rig) and Halliburton (provided the well's cementing services).

The report claimed:

• The cement barrier at the well failed to contain hydrocarbons.
• BP and Transocean incorrectly accepted a negative pressure test, even though well integrity had not been established.
• The Transocean rig crew did not recognize an influx of hydrocarbons in time.
• The rig's fire and gas system failed to prevent ignition of the gas that flowed into the engine rooms through the ventilation system.
• The blow-out preventer failed to seal the well on the seabed.