CSB Safety Video: Explosion at BP Refinery

Incident Overview - Isomerization Unit Overfill and Explosion

Initial Operations and Equipment Malfunction

• At approximately 2:00 a.m. on March 23, 2005, operators began introducing flammable liquid hydrocarbons into the rapenet splitter tower, which should normally contain only about 6.5 feet of liquid at the bottom.

• A level indicator was in place to measure the liquid inside the tower; however, it was not designed to accurately measure levels above 10 feet, leaving operators unaware of dangerous conditions.

Alarm Failures and Liquid Overflow

• A high-level alarm activated but a second redundant alarm failed to trigger; by 3:30 a.m., operations ceased with the indicator showing only 10 feet of liquid when it was actually overfilled to about 13 feet.

• By around 9:50 a.m., operators mistakenly circulated more liquid into an already full tower while the outflow valve remained closed, leading to rapid filling beyond normal levels.

Escalation of Conditions

• By approximately 10:00 a.m., heating burners were lit without realizing that the tower continued to fill rapidly, reaching an alarming height of over 20 times its normal capacity (138 feet). The level indicator falsely indicated lower levels.

• At around noon, pressure alarms activated; attempts to manage pressure through manual venting were made as conditions worsened with hot liquid exiting through heat exchangers causing further temperature increases in the feed entering the tower.

Catastrophic Failure and Explosion

• By about 1:10 p.m., overflow began from the top of the tower into vertical piping, creating significant pressure on emergency relief valves located below. Emergency valves opened shortly after but did not prevent flooding in other areas like blowdown drums.

• A geyser-like eruption occurred from the blowdown stack due to complete filling; this led to a large vapor cloud formation that ignited at approximately 1:20 p.m., likely triggered by nearby vehicles. This resulted in multiple explosions and extensive destruction within the facility.

Aftermath and Impact

• The explosion caused severe damage including fatalities among contract workers; video footage captured ongoing fires post-explosion as hydrocarbons continued emitting flames from damaged structures like blowdown stacks.