Article Archive
Extreme Measures
After an explosion in November, an oil refinery near Salt Lake City remains voluntarily closed based on a U.S. Chemical Safety Board recommendation. At issue are pipe thickness readings that have proven to be incorrect.
Volume 25, No. 1

Everyone at the headquarters of the South Davis Metro Fire Agency in Bountiful, UT, felt the concussion when high-pressure hydrogen gas escaping from a ruptured pipe exploded at a local refinery in November, said Fire Chief Jim Rampton.

The immediate problem after the blast was determining which of three local refineries was involved.

"A power outage caused by the explosion knocked two other refineries off line," Rampton said. "I could see major headers of black smoke from three different locations. I'm thinking the world is coming to an end."

At 9:11 a.m. on November 4, 2009, a 12,500 barrel per day oil refinery in Woods Cross, UT, near Bountiful, experienced the catastrophic failure of a 10-inch pipe off the bottom of a reactor in the mobile distillate dewaxing unit. The unit was undergoing a special operation to regenerate a catalyst by a process that involved circulating hydrogen gas heated to 800 degrees Fahrenheit at a pressure of 630 pounds per square inch.

Almost simultaneous with the release was an ignition. A fireball rose an estimated 100 feet above the refinery. A blast wave, directed east toward a housing subdivision, damaged more than 100 homes, at least several of which were subsequently condemned.

Miraculously, no injuries were reported. However, surveillance video revealed that refinery employees missed becoming part of the disaster by only the narrowest of margins.

The November incident was the second major response by South Davis to the same refinery in 10 months. On January 12, 2009, two refinery operators and two contractors suffered serious burns when a vapor cloud release extending more than 200 feet from a tank containing light naphtha ignited.

Both the January and November incidents remain under investigation by the U.S. Chemical Safety Board (CSB). Preliminary results from the November investigation have already had a dramatic impact. Pipe thickness readings throughout the refinery taken as part of its mechanical integrity program prior to the November explosion have been called into serious question, said CSB lead investigator Don Holmstrom.

Specifically, in 2007 the thickness of the pipe that failed on November 4 was documented to be nearly one-half-inch. Measurements following the accident show that the pipe thickness was only one-eighth inch.

"The goal of a mechanical integrity program is to ensure that process equipment is fabricated from the proper materials of construction and is properly installed, monitored and maintained to prevent failures and accidental releases," Holmstrom said. "Because of the hazardous nature of the materials in a refinery -- and the high temperatures and pressures that are frequently used -- a robust mechanical integrity program is essential to safe refinery operations."

On the recommendation of CSB Chairman John Bresland, made in consultation with state and federal OSHA officials, management at the damaged refinery shut down its five processing units until further notice.

"This is the first time we've experienced anything like this where we've actually asked a refinery or a chemical plant to cease operation because of the hazard," Bresland said. "We are very thankful that they agreed to do that."

As of late December, the refinery remained shut down.

"The damage to the refinery will cost far less than the cost of the shut down," Bresland said.

TRIP TO BOUNTIFUL

Rather than a traditional fire district, the South Davis Metro Fire Agency functions by means of interlocal agreements among six communities with a combined population of about 90,000 in south Davis County, Utah.

Operating as a paid department, South Davis consists of about 60 career firefighters supported by another 40 part-time responders who work fulltime as well in neighboring jurisdictions. On an average day, 19 responders divided among five fire stations are on duty. Each station is equipped with an engine and an ambulance, Rampton said.

"Typically, on any structural fire call, we have a two-and-one assignment, meaning two engines, a ladder truck and a battalion chief," he said.

South Davis covers four oil refineries and several tank farms north of Salt Lake City. South Davis firefighters often attend corporate fire training schools conducted by the refineries. In addition, the refineries maintain a mutual aid organization, the Refinery Mutual Aid Group.

"It's not as often as we'd like, but we do train with the mutual aid group," Rampton said. "We do fairly extensive drills a couple of times a year." A mutual aid drill conducted in November built around a fictional fire in a 160-foot diameter storage tank drew 125 responders.

That drill took place after the very real November 4 explosion in Woods Cross. Rampton was at his desk at Station 81 when the blast occurred about 2? miles away.

"My first thought was that someone had crashed a fire truck into the building," he said. "I walked down to the bay and there were no bricks on the ground. By then, the radios started going off."

Outside, black smoke rose from not one but three neighboring refineries. Even though radio traffic soon identified the affected refinery, Rampton dispatched equal resources to all three to be certain that all potential emergencies were covered.

"We were kind of stretched thin there," he said. "If there had been injuries, we would have been overwhelmed."

Fortunately, the cluster of refineries is roughly equal distance from three South Davis fire stations, including Station 81. One significant difference between the January incident and the November incident was the level of response by the refinery's own fire brigade, Rampton said. At the time of the January explosion, the small refinery was already in the process of improving fire protection by upgrading its internal fire brigade.

"They were at a very beginning stage of a fire brigade," he said. "Since then, they've gotten better equipment, including a fire truck, and turnout gear for everyone. They've put in some effort toward training."

Video surveillance of the refinery captured the moment of the explosion. A white cloud believed to be hydrogen escaping from the rupture pipe was briefly seen, followed by a rapid ignition. An open-flame furnace was located near the ruptured pipe.

Four workers near the process unit at the time of the blast were knocked to the ground but not seriously injured. A worker had been taking a reading next to the pipe that failed less than two minutes before the explosion. The surveillance camera recorded a pickup truck slowly driving past and out of view only moments before the blast. A train cleared a nearby rail line that handled both freight and commuter traffic just prior to the explosion.

Rampton was among the first South Davis firefighters to arrive after the blast.

"I could see they were applying water to what looked like a furnace when I got there," he said. "The plant responders were in their turnouts applying water from fixed sites."

Compared to the fire following the January explosion, firefighters were able to make quick work of the fire after the November blast. After 30 minutes of intense flames, the emergency was brought under control. Because the fire was relatively brief, the Refinery Mutual Aid Group was not asked to respond, Rampton said.

"It's my understanding that they injected nitrogen into the line to evacuate the flammable hydrogen," he said.

Then reports of damage to the nearby residential area started coming through, Rampton said.

"Initial reports were that we got some damage to homes," he said. "We sent some police over to look at it. Then the reports just kept getting worse. There was talk about condemning houses and one blown off its foundations. However, most of it was cracked windows or buckled garage doors."

Area police, city workers and several teams organized by the refinery joined firefighters in inspecting the residential damage, Rampton said.

"Our biggest challenge was having to physically inspect each one of these homes to assess the damage and make sure no one was hurt," he said. "It was very time consuming for us."

In a story common nationwide, the refinery in Woods Cross had dealt with a host of new neighbors in recent years. Property development outside the refinery was as close as several hundred feet to the blast.

"In the last five to 10 years this area has seen major growth," Rampton said. "The refinery has been there for more than 50 years, most of the time with nothing much around it. Homes and businesses began encroaching on the refinery in the last decade."

As to the cause of the November explosion, the CSB investigation continues to focus on "serious deficiencies" in the refinery's mechanical integrity program, Holmstrom said.

"Prior to May 2009, mechanical integrity inspections -- including thickness monitoring of pipes and vessels at the refinery -- were completed by a contract company," he said. "The refinery later replaced this company with a second outside inspection company, which remains active at the site."

Thickness monitoring at large refineries is usually conducted inhouse. However, smaller refineries such as the one in Woods Cross often resort to outside contractors for such inspections.

Witness evidence indicated that various thickness readings taken by the prior contractor at the affected refinery were questionable, Holmstrom said. As a result, the refinery turned to a new contractor, asking that previous inspections be redone.

"So this activity has actually been ongoing since May 2009," Holmstrom said. "There have been problems that developed. Pipes had to be replaced in the facility. The company was making an effort to improve their mechanical integrity."

Specifically in question is the discrepancy in the thickness reading of the pipe that failed.

"A likely explanation is that the 2007 thickness measurement was inaccurate," Holmstrom said. "This and other recent measurements call into serious question the pipe thickness readings obtained by the prior contractor."

Evidence further indicated that a significant percentage of the pipe and vessels had no documented thickness readings at all, Holmstrom said.

Refinery managers have acknowledged that minimum thickness values for piping and equipment throughout the refinery have been miscalculated, he said.

"These are the thicknesses at which the equipment must be retired from service due to the potential for failure," Holmstrom said. "Specifically, the refinery has been using what are known as ultimate tensile strength values, rather than the industry-recommended stress tables."

The result of these miscalculations is that these minimum thickness values may be three-to-four times too low, he said. Some of the minimum thickness values may be too low for safe operation of the equipment.

"In other words, there is the potential that multiple pieces of equipment have been operating at below the required thickness for safety and creating the potential for other serious accidents," Holmstrom said.

During a press conference in November, a reporter asked if the CSB would broaden its investigation to including the contractor that made the measurement now in question. Bresland said that decision was somewhere in the future.

"We are in the very early stages of the investigation, but obviously we will be looking at the results as they develop and comparing them with the results from the current contractor," Bresland said.

Concern about the safety of the refinery forced preliminary action by the CSB, Holmstrom said. Because the investigation is ongoing, CSB chose not to release the name of the contractor whose work is being reexamined, he said.

FLASHBACK

By comparison, the January explosion involved multiple injuries and a major response by the mutual aid organization. At about 5:20 p.m. on January 12, a 65-foot diameter storage tank containing about 440,000 gallons of light naphtha released a vapor cloud from atmospheric vents on the west side of the tank.

"On the day of the incident, tank 105 was receiving up to three different streams of hydrocarbon liquids from the refinery, including 'light' or low-boiling substances," Holmstrom said. "The primary feed into tank 105 had been sent from the No.1 crude unit pre-flash accumulator for approximately three weeks prior to the incident. Feeding tank 105 directly from this unit was a recent process change and the feed from this unit had undergone a different form of processing. Workers were also purging equipment with nitrogen to remove flammable liquid, with the intent to pressure the liquid into tank 105."

In mid-November, witnesses reported that the tank was venting gas before and after the maintenance activities, Holmstrom said.

"We subsequently have identified the hydrocarbons in the tank were much more volatile than we previously anticipated," he said. "There was lighter hydrocarbon in the tank than we would have otherwise expected and that may have contributed to the release."

As opposed to the November explosion, issues leading to the January blast may have been operational rather than mechanical, Holmstrom said. Under investigation is the possibility that nitrogen was used to pressurize the liquid in the tank, increasing the amount of gas released.

"We're going to be modeling that activity based on the conditions at the time of the incident," he said.

The ensuing flash fire spread almost 230 feet west of the tank farm. Aside from the tank, two structures were damaged -- a shed and a lab facility located about 140 feet and 160 feet from release, respectively. Two refinery operators and two contractors at the shed were engulfed by the flame front and suffered serious burns, particularly inhalation burns. None of the injured were wearing protective gear, Rampton said.

South Davis EMS responders immediately occupied themselves with packaging the injured for transport -- two by ground and two by helicopter. Meanwhile, firefighters arrived to find fire burning from the eyebrow vents 360 degrees around the tank, Rampton said.

"This overwhelmed us pretty quickly," he said. "I called for mutual aid right off the bat. We called in the Salt Lake City Fire Department and the Farmington Fire Department." The Refinery Mutual Aid Group was also asked to respond, bringing high capacity portable monitors.

At that time, the refinery involved was not a member of the mutual aid group.

"They responded at my request," Rampton said. Subsequent to the January explosion and fire, the refinery joined the mutual aid group.

Even with mutual aid assistance, extinguishing the tank fire required a half day of effort, Rampton said.

"We were able to get into the eyebrows and put enough water in there," he said. "It was a very tricky situation, figuring out how much water to put in there without sinking the interior floating roof. It really didn't take a huge amount of water."

Confusion resulted when the decision was made to voluntarily evacuate residents within a quarter-mile of the refinery during the fire. Initially, people were asked to report to a Mormon ward or church just outside the evacuation perimeter. Later, when that perimeter was expanded to one-half mile, residents were told to go to the Woods Cross High School. Adding to the confusion, the city's reverse 911 telephone system was notifying residents outside the evacuation zone that they had to leave.

Rampton later told city officials in Woods Cross that keeping the reverse 911 system updated is difficult. If a resident moves but keeps the same telephone number, the system may mistakenly notify him. As an alternative, Davis County is installing an AM radio station that can be activated in an emergency to keep the public informed.

Holmstrom said a CSB report on the January 2009 explosion and fire is expected to be released in the first quarter of 2010.

LOCAL CONCERN

Repairing the refinery after the November explosion is one thing. Repairing the refinery's reputation with the community after the revelations following the November blast is something else. Consultants hired to get the refinery working again are also working to rebuild confidence in the safety of the operation. This includes a recent briefing of the Woods Cross city council.

Public concern about the troubled refinery remains high, Rampton said.

"It's one of those things where everybody in the area can remember where they were when they felt the explosion."

 
 

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