English subtitles for clip: File:Updated BP Texas City Animation on the 15th Anniversary of the Explosion.ogg

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March 23rd, 2005.
The BP refinery in Texas City, Texas.

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Several units at the refinery had been shut down
for lengthy maintenance projects,

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which required nearly a thousand contractors to be on site,
along with BP employees.

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BP had positioned a number of portable trailers, close to process units,
for the use of contractors, and other maintenance workers.

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Over the period of months, BP had located ten trailers for workers
servicing the Ultracracker Unit,

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including a double-wide, wood frame trailer, that contained eleven offices,
and was regularly used for meetings.

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Though these trailers were located near the Isomerization Unit (ISOM), the occupants were not warned the ISOM unit was about to start up,

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a potentially hazardous operation.

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At 2:50 am, on March 23rd,

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overnight operators began introducing flammable liquid hydrocarbons,
known as raffinate, into 170 ft (52 m) tall raffinate splitter tower,

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used to distill and separate gasoline components.

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Near the base of the tower, there was a single instrument
that measured how much liquid it was inside.

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It transmitted this information to both the Satellite Control Room,
and the Central Control Room, located away from the ISOM unit.

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But this level indicator was not designed to
measure liquid above the 9 ft (274 cm) mark.

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During normal operation, the tower was only supposed to contain
about 6 and one half feet (200 cm) of liquid.

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But during startups, operators routinely deviated from written procedures,
and filled the tower above the 9 ft (274 cm) mark,

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concerned if the liquid level fluctuated too low,
it would case costly damage to the furnace.

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At 3:09 am, as the liquid neared the 8 ft (244 cm) mark,
a high-level alarm activated, and sounded in the control rooms.

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But a second high-level alarm, slightly further up the tower, failed to go off.

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By 3:30 am, the level indicator showed the liquid had filled the
bottom 9 ft (274 cm) of the tower, and the feed was stopped.

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The CSB later estimated that the liquid
was in fact at the height of 13 ft (396 cm).

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The operators could not know the actual level,
because the indicator only measured up to 9 ft (274 cm).

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The Lead Operator had been overseeing the startup
from the Satellite Control Room within the ISOM unit.

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At 5:00 am, he briefly updated the Night Board Operator in the
Central Control Room, about the startup activities.

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The Lead Operator then left the refinery early,
an hour before the end of the shift.

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A new Board Operator arrived in the control room around 6:00 am
to start his 30th day in a row working on 12-hour shift.

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He spoke briefly with the departing Night Shift Operator
and then read the logbook to prepare for the startup.

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But the logbook did not clearly indicate how much liquid
is already in the tower and the equipment,

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and it left no instructions on routing of the
liquid feed and products when the startup resumed.

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Instead the Control Board Operator only found
a one-line logbook entry, that said:

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"ISOM – Brought in some raff to unit, to pack raff with."

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At 7:15 am, the Day Shift Supervisor have arrived.

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Because he was more than an hour late, he received no formal briefing
from personnel on the night shift about conditions in the ISOM unit.

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At 9:51 am, operators resumed the startup.

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They began recirculating the liquid feed,
and adding more liquid to the already overfilled tower.

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As new feed was added, startup procedures called for regulating the
liquid level in the tower, using the automatic level control valve.

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But the board operators and others has received conflicting
 instructions on routing the product.

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As the result, this critical valve was left closed for several hours,
blocking the flow of liquid from the tower.

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A few minutes later, operators lit burners on the furnace to
begin heating up the feed, part of the normal startup process.

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While the startup was underway, the Day Supervisor left the refinery on short notice,
just before 11:00 am, to attend to a family medical emergency.

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Contrary to BP's own procedures,
no experienced supervisor was assigned to replace him.

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This left a single control board operator,
now without a qualified supervisor,

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to run three refinery units, including the ISOM unit,
which needed close attention.

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The refinery had eliminated a second board operator position,
following corporate budget cuts in 1999, after BP acquired Amoco.

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As the startup continued, the tower steadily filled with liquid,
reaching a height of 98 ft (30 m), shortly before noon.

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More than 15 times the normal level.

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But the improperly calibrated level indicator told operators in the control room
that the liquid was 8.4 ft (256 cm), and gradually falling.

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Furthermore, the control panel was not configured to clearly
warn operators of the growing danger.

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It did not display flows into and out of the tower on the same screen,
nor did it calculate the total liquid in the tower.

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Meanwhile, the maintenance contractors,
who were not involved in the operation of the ISOM unit,

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left their work trailers to attend a company lunch,
celebrating a month without a lost time injury.

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At 12:41 pm, an alarm activated there's a rising liquid
compressed the gases, remaining in the top of the tower.

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Unable to understand the source of the high pressure, operators opened
the manual chain valve, to vent gases to the unit's emergency relief system.

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A 1950s era blowdown drum that vented
vapor directly into the atmosphere.

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Operators also turned off two burners in the furnace,
to lower the temperature inside the tower,

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believing this would reduce the pressure.

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Nobody knew, the tower was dangerously full.

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The operators did become concerned about
the lack of flow out of the tower,

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and began opening the valve to send liquid from the
bottom of the tower to storage tanks.

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But this liquid was very hot.

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As it flowed through the heat exchanger, it suddenly raised the
temperature of the liquid entering high up the tower by 141°F (61°C).

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It was now about 1:00 pm.

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Contract workers, unaware of the startup and the looming danger,
returned from lunch, and began a meeting in the double-wide trailer,

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in the corner room, closest to the blowdown drum.

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Over the next few minutes, the hot feed entering the tower
caused the liquid inside to start to boil, and swell.

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Liquid filled the tower completely, and began spilling into the overhead vapor line,
exerting great pressure on the emergency relief valves, 155 ft (47 m) below.

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At 1:40 pm, the three emergency valves opened, sending nearly 52 000 gallons (197 000 liters) of flammable liquid

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to the blowdown drum on the other end of the ISOM unit.

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Liquid rose inside the blowdown drum, and overflowed
into a process sewer, setting off alarms in the control room.

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But the high-level alarm on the blowdown drum failed to go off.

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None of the operators knew of the catastrophe
unfolding in the ISOM unit.

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As flammable hydrocarbons overfilled the blowdown drum,
operators nearby saw a geyser of liquid and vapor erupt from the top of the stack.

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The equivalent of nearly a tanker truck full of hot gasoline fell to the ground,
and began forming a huge flammable vapor cloud.

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The vapor cloud expanded in just 90 seconds,
engulfing the unit, and the nearby trailers full of workers.

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About 25 ft (8 m) from the base from the blowdown drum,
two workers were parked in a pickup truck with the engine idling.

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As flammable vapor entered the air intake,
the diesel engine began to race.

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The two workers fled, unable to shut off the engine.

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Moments later, witnesses saw the truck backfired,
and ignited the vapor cloud.

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Powerful explosions swept through the area.

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The blast pressure wave accelerated through the ISOM unit,
causing heavy destruction, and igniting fires.

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The workers in the trailers were right in the path of the explosions.

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The fires continued to burn for hours.

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12 of the 20 occupants of the double-wide trailer were killed,
along with 3 workers in the trailer nearby.

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180 workers were injured, many with serious burns, fractures,
or other traumatic injuries.

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The wooden-metal frame trailers were blown apart from the blast.

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Firefighters struggled to rescue the injured, and recovered the victims.

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15 large chemical storage tanks were damaged,
and the ISOM unit remained shut down for more than two years.

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The disaster at BP Texas City was the most serious
refinery accident ever investigated by the CSB.