Case Study: BP Texas City Explosion 23 March 2005
The Texas City Refinery is BP’s largest and most complex oil refinery with a rated capacity of 460,000 barrels per day (bpd) and an ability to produce about 11 million gallons of gasoline a day. It also produces jet fuels, diesel fuels and chemical feed stocks. The refinery has 30 process units spread over a 1,200 acre site and employs about 1,600 permanent BP staff. At the time of the incident there were approximately 800 additional contractor staff on site for significant turnaround work. This section is a bit long, but the seeds for this disaster were sown years prior to the accident and it is hard to understand that properly without getting an historical perspective. The key thought to keep in mind is this: no one came to Texas City Refinery on 23 March 2005 expecting to die or maliciously planning to be unsafe, and yet a terrible tragedy (because these kinds of problems are preventable) did ensue.
Isomerization (ISOM) Process Description
The Raffinate Splitter tower was a vertical distillation column with an inside diameter of 12.5 feet and height of 170 feet with an approximate liquid-full volume of 154,800 gallons. Pre-heated, liquid raffinate feed was pumped via an automatic flow control valve (adjusting the feed rate) into the tower near the tower’s midpoint. The splitter tower was equipped with a level transmitter, which provided a reading of liquid level in the tower to the control room board operator. The transmitter measured the tower’s liquid level in a 5-foot span within the bottom 9 feet of the 170-foot tall tower. The splitter tower also had two separate alarms that indicated high liquid level; one was programmed to sound when the transmitter reading reached 7.6 feet in the tower. The second, a redundant hardwired high level switch, was designed to sound when the liquid level reached 7.9 feet in the tower. The splitter had a level sight glass, used to visually verify the tower level, but it had been reported by operators as unreadable because of a buildup of dark residue; the sight glass had been nonfunctional for several years (ERROR).