Chronology: Pump collapse, leak caused Venezuela refinery blast

(Reuters) - State-run oil giant Petroleos de Venezuela's PDVSA.UL 645,000 barrel-per-day (bpd) Amuay refinery is struggling to recover from a 2012 explosion that killed 47 people in one of the world's worst refinery disasters in decades.

Firefighters work to extinguish a fire at a storage tank at Amuay refinery in Paraguana August 28, 2012. REUTERS/Miraflores Palace

A year after the mishap, the precise cause of the explosion is still under study and has become part of the ongoing political battle between the government and the opposition in the highly polarized country.

Refinery output in Venezuela - which has the world’s largest oil reserves - plummeted after the accident, prompting the country to greatly increase its imports of gasoline. Those imports have hurt the country’s external accounts.

Average production at the refinery was down by 170,000 bpd at 310,000 bpd after the fire until repairs were completed in April. It is now running around 435,000 bpd, or 68 percent of capacity.

The socialist government of President Nicolas Maduro, who was elected this year after the death of his longtime political mentor, Hugo Chavez, released a report on Monday blaming sabotage for the deadly explosion and saying that several bolts had been intentionally removed from a gas pump.

A separate technical report done by the Center for Energy Orientation in Venezuela (COENER), which was commissioned by opposition lawmakers, agrees with the government that a massive leak of propane that lasted almost 70 minutes caused the accident, but COENER attributes it to poor maintenance.

COENER estimates that the total damages caused by the explosion to Amuay’s facilities represent $1.84 billion - 67 percent more than the government’s calculation of $1.1 billion - including the losses caused by the refinery’s shutdown for almost a week and the shuttering of the CDU for eight months.

The following is the reconstruction of the events leading to the explosion, according to the COENER report and details given by Venezuela’s Energy Minister Rafael Ramirez:

- June 2012: A pump known as P-200 in a storage area of the Amuay refinery in Venezuela’s Paraguana Refinery Complex develops a leak and is fixed. COENER says the same pump eventually failed twice, but the government said pump tied to the explosion was different than the one that failed in June.

- August 24, 2012, morning: Hundreds of people near the Amuay refinery complain of a strong “rotten egg” smell. That is usually a sign of the presence of hydrogen sulfide (H2S) and mercaptans (RSH). They are components found in olefins - propane, butane and isobutane.

- August 24, noon: The neighboring Puramin C.A. lubricant plant orders its workers to evacuate because of a high concentration of hydrogen sulfide. A gas detector inside the Puramin plant also finds a high concentration of methane.

- August 24, 11:30 p.m.: The neighboring 310,000 bpd Cardon refinery reports that the pumping of propane from a storage area of the Amuay refinery known as Block 23, which holds gas spheres, had lost concentration of hydrogen sulfide.

- August 25, midnight: The Cardon refinery reports a total loss of pressure during the pumping of olefins from Amuay.

Two operators at the Amuay refinery take the unusual step of leaving an isolated control booth to go outside and visually inspect the pump number 2601. They detect a hydrocarbon cloud around it that turned out to be propane.

They realize they cannot stop the leak, call to warn firefighters, and one of them runs looking for a fire-proof suit. Investigators think he wanted to return to try to manually shut off the valve of the propane sphere.

Workers at the Puramin plant, a half-mile away, report that they can see the vapor cloud at the Amuay refinery. Investigators think heavy rains during the day prevent the cloud from rising and keep it close to the ground.

The cloud continues to grow until 1:07 a.m., wafting through the Amuay facilities, a military post, a storage patio, Puramin’s buildings and the nearby neighborhoods.

The petroleum ministry says a total volume of 3,570 equivalent barrels of olefins leaked massively and abruptly through a 2.9-inch hole in the pump, releasing around 22 percent of the propane in its spherical storage tank.

A military vehicle leaves the post after being warned about the leak. Its engine - allegedly powered by diesel - could have become the ignition point for the explosion at 1:07 a.m. Alarms designed to warn people of emergencies never rang.

The explosion and fire completely incinerate the military post, the Puramin plant, part of a neighboring hydrogen plant, several residential areas, several storage areas for fuels and gases, and LPG facilities.

The fire rapidly expands to 11 storage tanks containing isobutane, butane, crude, naphtha, alkylate and vacuum gasoil. The tanks release 1.54 million barrels of fuels, a release of 500,000 metric tonnes of carbon dioxide, equivalent to the total emissions from vehicles in the capital city of Caracas over two weeks.

Several pumps, pipelines and other facilities are also affected. Automated water spray systems do not work properly.

In addition to storage spheres and tanks, a critical 185,000 bpd crude distillation unit is severely damaged.

As many as 3,400 houses, restaurants, schools and others structures were destroyed or damaged.

Within hours, firefighters extinguish the flames at 9 of the 11 tanks. They spray water over two tanks still on fire to cool them down.

Houses are evacuated and 35 injured people are taken to hospitals. Dozens of people are reported as disappeared.

Hours later, PDVSA combines the water with foam. The combined use of these two is not recommended by firefighters.

- August 27 - The heavy volume of foam and water directed at the storage tanks causes the dome of one tank to collapse, causing a fire to break out on a third tank.

- August 28 - Firefighters finally quash the last of the flames, some 96 hours after the explosion.

Additional reporting by Deisy Buitrago and Eyanir Chinea in Caracas; Editing by Erwin Seba, Terry Wade and Jim Marshall