4-2-0 2-0-1-0 (April 20, 2010)

* 7 am – BP cancels a recommended cement bond log test. Conducting the test would have taken 9–12 hours and $128,000. By canceling the cement test BP paid only $10,000. Crew leaves on 11:15 am flight.[11] BP officials gather on the platform to celebrate seven years without an injury on the rig.[20] The planned moving of the Deepwater Horizon to another location was 43 days past due and the delay had cost BP $21 million.[21]

* 9:45 pm CDT – Gas, oil and concrete from the Deepwater Horizon explode up the wellbore onto the deck and then catches fire. The explosion kills 11 platform workers and injures 17 others; another 98 people survive without serious physical injury.[23]

* 9:49 pm CDT - Block 252, Mississippi Canyon Andrea Fleyras had been monitoring the dynamic positioning system on the bridge of the Horizon when she felt a jolt. Before she could make sense of it – a rig shaking shock that came out of nowhere – magenta warnings began flashing on her screen. Magenta meant the most dangerous level of combustible gas intrusion.[22]

And the rest is history: