That was the day the Deepwater Horizon oilrig exploded in the Gulf of Mexico, killing 11 workers and injuring 17 more.
The rig experienced an initial blowout releasing an uncontrollable flow of oil and gas from the well.
Hydrocarbons then ignited, causing the explosion and fire.
It caused a massive offshore oil spill of over 4 billion barrels and is considered the largest environmental disaster in U.S. history.
British Petroleum was the main operator responsible for the well design.
The drilling contractor, TransOcean owned and operated the rig.
A handful of smaller companies were also involved.
While company and governmental officials initially argued the explosion was unforeseeable and then subsequently blamed each other, there were warning signs in the months leading up to the explosion.
Multiple equipment failures, design deficiencies, poor preventative maintenance, bad engineering decisions and a chase for profits that emphasized low worker injuries at the expense of process safety, all combined to create the disaster.
As well, regulations and standards enforcement were weak in an almost totally deregulated industry.
One phrase used by investigators to characterize the explosion was the Normalization of Deviance.
From workers, to managers to executives, none saw the explosion coming.
There were dozens of contributing factors as the Chemical Safety Board investigation noted.
They listed 57 key technical, human and regulatory factors in their 2016 final report.
However, engineers had raised concerns about the potential failure of key equipment.
Workers were sensitive to the fact they could be fired for raising safety concerns that delayed drilling.
BP was found ultimately responsible and racked up over $70 billion in fines, clean up and settlement costs.
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