History Lesson: BP's Texas City Explosion

[MrScorpio]

Texas City Refinery (BP)
From Wikipedia, the free encyclopedia

BP's Texas City Refinery in Texas City, Texas is the second-largest oil refinery in the state and the third-largest in the United States. BP acquired the Texas City refinery as part of its merger with Amoco in 1998. It has an input capacity of 437,000 barrels per day (18,354,000 gallons or 69,477,448 litres) as of January 1, 2005.

A major explosion occurred in an isomerization unit at the site on March 23, 2005, killing 15 workers and injuring more than 170 others. According to a report issued after the accident, actions taken or not taken led to overfilling the raffinate splitter with liquid, overheating of the liquid and the subsequent overpressurisation and pressure relief.

Hydrocarbon flow to the blowdown drum and stack overwhelmed it, resulting in liquids carrying over out of the top of the stack, flowing down the stack, accumulating on the ground, causing a vapor cloud, which was ignited by an abandoned white pickup truck with the ignition on. The report identified numerous failings in equipment, risk management, staff management, working culture at the site, maintenance and inspection, and general health and safety assessments.



Explosion

The U.S. Chemical Safety and Hazard Investigation Board investigating the incident found that operators had started-up the raffinate splitter tower (which separates light and heavy gasoline components) of the ISOM unit (which increases the octane rating of gasoline) and begun filling it with hydrocarbon fluid (i.e. gasoline components) without beginning timely discharge of product. The operators started the tower while ignoring open maintenance orders on the tower’s instrumentation system. An alarm meant to warn about the quantity of liquid in the unit was disabled.

Once the lack of draw-down from the tower was recognized, operators opened the discharge valve. This worsened the problem because the hot discharges passed through a heat-exchanger that pre-warmed incoming fluids. The resulting increase in temperature caused the formation of a bubble of vapor at the bottom of the raffinate tower that was already overly full and overheated. The tower burped the vapor bubble and the liquid above the bubble into the overhead relief tube of the tower.

The relief tube was connected to a disposal system for relieved discharges. The particular type of disposal system serving the raffinate tower was a blow-down drum with an atmospheric vent stack rather than an inherently safer and more environmentally sound knock-out tank and flare system. Because of the overfilling of the raffinate splitter tower and the burp of both vapors and liquids to the undersized blow-down drum with an atmospheric vent stack, a “geyser like” emission of hot flammable vapors and liquids was expelled from the vent stack.

A new white diesel pick-up truck, owned by a contractor, was parked near the blow down stack. While BP operators were running to turn-off furnace burners, to remove sources of vapor cloud ignition, the truck's owner returned to his truck and proceeded to crank the engine in an attempt to move his new truck out of the area. Due to a high hydrocarbon content above the Upper Explosion Limit (UEL), the truck would not start. As the man continued to crank the engine, operators ran to him in an attempt to get him to stop. Once the hydrocarbon content in the surrounding air came down to the UEL, the truck provided the source of ignition for the Vapor Cloud Explosion.

The people in the trailer located near the process unit's battery limit, holding a meeting, were unaware of the ISOM's unit start-up condition. The people on the side of the meeting table with their backs to the process unit were killed due to blunt force trauma. A number of people on the side of the table facing the unit survived the blast.

Aftermath

The CSB report found that BP had failed to heed or implement safety recommendations made before the blast. Among them were:

In 1991 the Amoco refining planning department proposed eliminating blow-down systems that vented to the atmosphere. But funding for this plan was not included in the budget.

In 1992 OSHA issued a citation to Amoco for unsafe design of similar pressure relief systems at the plant. However, Amoco successfully persuaded OSHA to drop this citation by relying on the less stringent requirements in API Recommended Practice 521.

In 1993 the Amoco Regulatory Cluster project proposed eliminating atmospheric blow down systems but again funding was not approved.

In 1995, a refinery belonging to Pennzoil suffered a disaster when two storage tanks exploded, engulfing a trailer and killing five workers. The conclusion was that trailers should not be located near hazardous materials. However, BP ignored the warnings, and they believed that because the trailer where most of the deaths happened was empty most of the year, the risk was low.

Despite Amoco’s process safety standard No. 6 which prohibited new atmospheric blowdown systems and called for the phasing out of existing ones, in 1997 Amoco replaced the 1950’s era blow-down drum / vent stack that served the raffinate splitter tower with an identical system instead of upgrading to recommended alternatives that were safer.
In 2002, engineers at the plant proposed replacing the blow-down drum/vent system as part of an environmental improvement initiative but this line item was cut from the budget due to cost pressures.

Also in 2002 an opportunity to tie the ISOM relief system into the new NDU flare system was not taken due to a $150,000,000 incremental cost.

During 2002 BP’s Clean Streams project proposed converting the blow-down drum to a flare knock-out tank and routing discharges to a flare. When it was found that a needed relief study of the ISOM system had not been completed due to budget constraints, the Clean Streams project proposed adding a wet/dry system to the ISOM instead.
Between 1994 and 2004 at least eight similar cases occurred in which flammable vapors were emitted by a blow-down drum vent stack. Effective corrective action was not taken at the BP plant.

As a result of the accident, BP said that it would eliminate all blow-down drums/vent stack systems in flammable service. The CSB, meanwhile, recommended to the American Petroleum Institute that guidelines on the location of trailers be made.
Legal action

On February 4, 2008, U.S. District Judge Lee Rosenthal heard arguments regarding BP's offer to plead guilty to a federal environmental crime with a US$50 million fine. At the hearing, blast victims and their relatives objected to the plea, calling the proposed fine "trivial." So far, BP has said it has paid more than US$1.6 billion to compensate victims.<1> The judge gave no timetable on when she would make a final ruling.<2>

On October 30, 2009 the US Occupational Safety and Health Administration (OSHA) imposed an $87 million fine on the company for failing to correct safety hazards revealed in the 2005 explosion. The fine was the largest in OSHA's history, and BP announced that it would challenge the fine.<3>

[Wilber_Stool]

1. Great graphic Mr. S............n/t