Investigations with findings related to mechanical integrity and preventive maintenance:


Incident Description


ExxonMobil Refinery Explosion (Torrance)

Incident Description:On February 18, 2015, an explosion occurred in the ExxonMobil Torrance, California refinery’s Electrostatic Precipitator (ESP), a pollution control device in the fluid catalytic cracking (FCC) unit that removes catalyst particles using charged plates that produce sparks—potential ignition sources—during normal operation. The incident occurred when ExxonMobil was attempting to isolate equipment for maintenance while the unit was in an idled mode of operation; preparations for the maintenance activity caused a pressure deviation that allowed hydrocarbons to backflow through the process and ignite in the ESP. The CSB found that this incident occurred due to weaknesses in the ExxonMobil Torrance refinery’s process safety management system. These weaknesses led to operation of the FCC unit without pre-established safe operating limits and criteria for unit shutdown, reliance on safeguards that could not be verified, the degradation of a safety-critical safeguard, and the re-use of a previous procedure deviation without a sufficient hazard analysis that confirmed that the assumed process conditions were still valid.

Chevron Refinery Fire

Incident Description:On August 6, 2012, the Chevron U.S.A. Inc. Refinery in Richmond, California, experienced a catastrophic pipe failure in the #4 Crude Unit. The incident occurred from the piping referred to as the “4-sidecut” stream, which was a carbon steel pipe with low silicon concentrations. The pipe ruptured, releasing flammable, hydrocarbon process fluid which partially vaporized into a large vapor cloud. Testing determined that the pipe failed due to thinning caused by sulfidation corrosion, a common damage mechanism in refineries.  Inspection of sufidation corrosion for carbon steel components containing low silicon concentrations is challenging. Rather than switching to an alloy with higher chromium content for high temperature areas susceptible to sulfidation corrosion, Chevron management denied recommendations to replace the 4-sidecut line as data gained primarily from high silicon pipe-fitting components, on which they relied, but did not reflect the corrosion rates of the lower-silicon components of the 4-sidecut piping.

Carbide Industries Fire and Explosion

Incident Description:Two workers were killed and two others injured as a result of a fire and explosion that occurred at the Carbide Industries facility located in Louisville, Kentucky, which produces calcium carbide products. Post-incident examination revealed recurring water leaks in multiple zones of the furnace cover. Rather than replacing the furnace cover, the company directed workers to attempt repairs. The investigation found that the company would inject a mixture of oats and commercially available “boiler solder” into the cooling water, in an effort to plug the leaks and keep the aging cover in operation. Water leaks into the furnace interfere with the steady introduction of lime and coke raw materials, through an effect known as “bridging” or “arching”. In a carbide-producing electric arc furnace, this can result in an undesirable and hazardous side reaction between calcium carbide and lime, which produces gas much more rapidly that the normal reaction to produce calcium carbide itself. Industry literature described the phenomenon as early as 1965, and an independent CSB analysis confirmed that operating conditions at Carbide on the day of the incident could have resulted in this effect, causing hot materials to be expelled from the furnace. The company continued operating the furnace despite the hazard from ongoing water leaks.  The accident was a case study into the tragic, predictable consequences of running equipment to failure when repeated safety incidents over many years warn of impending failure. When control room windows blew out during previous furnace incidents, the company reinforced them, rather than moving the control room farther from the furnace and investigating why the smaller furnace overpressure events were happening in the first place.

Hoeganaes Corporation Fatal Flash Fires

Incident Description:Three combustible dust incidents over a six month period occurred at the Hoeganaes facility in Gallatin, TN, resulting in fatal injuries to five workers. At the third incident on May 27, 2011, the trench involved contained many pipes including nitrogen and hydrogen supply and vent pipes for band furnaces. In addition to housing the pipes, the trench also acted as a drain for cooling water used in the band furnaces. At the time of the incident, this water came out of the furnaces how and drained directly onto the pipes and into the trench. Hoeganaes did not regularly inspect the pipes in the trench. The design and maintenance of this trench, should have addressed the issue of slow corrosion over time caused by the hot water runoff and solids accumulation. Hoeganaes did not have a procedure to inspect piping within the trench to ensure that corrosion had not compromised the piping systems which would allow an uncontrolled release of hydrogen.


NDK Crystal Inc. Explosion with Offsite Fatality

Incident Description:On December 7, 2009, State Special Vessel No. 2, under an operating pressure of 29,000 psig, suddenly and violently ruptured, 120 days into a 150-day operating cycle. A white cloud of steam and debris rapidly expanded outward from the facility, traveled onto the interstate, and dissipated within seconds. The sudden release of superheated liquid caused an eight-foot tall by four-foot wide vessel fragment, weighing approximately 8,600 pounds, to travel through two concrete walls and finally land about 435 feet from the NDK building. The fragment skipped across a neighboring facility parking lot and slammed into the wall of an adjacent business office. The force of the impact pushed the wall inward causing furniture to shift and ceiling tiles to fall. One person working near the wall was injured. The thrust from the escaping liquid caused the base of the vessel to violently shear away from its foundation and blew pieces of structural steel out of the building into the parking lot of a nearby rest stop gas station, known as the Illinois Tollway (I-90) Oasis. One piece of structural steel struck and killed a truck driver at the rest stop. An employee at Grupo Antolin, an adjacent automotive supply company, received minor injuries because of the impact from the 8,600-pound vessel fragment against the exterior wall of the office area. Emergency medical services evaluated and treated the Grupo Antolin employee on-scene. The NDK production facility sustained major damage. The neighboring facility, Grupo Antolin, also received damage.

Tesoro Refinery Fatal Explosion and Fire

Incident Description:An explosion and fire led to the fatal injury of seven employees when a nearly forty-year-old heat exchanger catastrophically failed during a maintenance operation at the Tesoro refinery in Anacortes, Washington. The CSB’s investigation found an immediate cause of the tragedy to be long-term, undetected High Temperature Hydrogen Attack (HTHA) of the steel equipment, which led to the vessel rupture. Tesoro, like others in the industry, used published data from the American Petroleum Institute (API), called the Nelson Curves, to predict the susceptibility of the heat exchangers to HTHA damage.  The CSB found these curves unreliable because they use historical experience data concerning HTHA that may not sufficiently reflect actual operating conditions. For example, a CSB computer reconstruction of the process conditions in the exchangers determined that the portion of the carbon steel exchanger that failed likely operated below the applicable Nelson curve—indicating it was “safe.”  The CSB found that recommended practices of the API do not require users to verify actual operating conditions in establishing operation limits of the equipment or to confirm that the materials of construction selection will prevent the damage.  An inspection strategy that relied on design operating conditions rather than verifying actual operating parameters contributed to the accident.  The CSB determined that inspections for such damage are unreliable because the microscopic cracks can be localized and difficult to identify.  The CSB noted that while API has identified high- chromium steels that are highly resistant; these were not installed by Tesoro.

Silver Eagle

Incident Description:On the evening of January 12, 2009, two refinery operators and two contractors suffered serious burns resulting from a flash fire at the Silver Eagle Refinery in Woods Cross, Utah. The accident occurred when a large flammable vapor cloud was released from an atmospheric storage tank, known as tank 105, which contained an estimated 440,000 gallons of light naphtha. The vapor cloud found an ignition source and the ensuing flash fire spread up to 230 feet west of the tank farm. On November 4, 2009, a second accident occurred at the Silver Eagle Refinery in Woods Cross, Utah, when a powerful blast wave, caused by the failure of a 10 inch pipe, damaged nearby homes. The CSB investigation team found that the examination of the ruptured pipe segment and adjacent piping clearly indicated wall thinning had occurred in the piping component.  The elbow adjacent to the pipe segment that failed was noted to have an original thickness of 0.719-inch.  A 2007 thickness measurement of the elbow indicated a wall thickness of 0.483-inch, indicating years of thinning had taken place.  The adjacent straight-run segment that failed was found to have a wall thickness as low as 0.039-inch and there were no records of any previous inspection.  The CSB found that in this investigations, as with other refinery investigations, mechanical integrity programs at refineries repeatedly emphasize inspection strategies rather than the use of inherently safer design to control the damage mechanisms that ultimately cause major process safety incidents. 

Allied Terminals Fertilizer Tank Collapse

Incident Description:On November 12, 2008 a two-million-gallon liquid fertilizer storage tank collapsed at the Allied Terminal distribution facility in Chesapeake, Virginia. The incident critically injured two contract workers, who were hospitalized. The CSB found that the collapse of Tank 201, which contained an aqueous solution of urea and ammonium nitrate fertilizer, likely resulted from defective welds on the tank wall. The welding was performed in 2006 as part of a project to strengthen four fertilizer tanks that were constructed around 1929 by replacing vertical riveted seams.

DuPont Corporation Toxic Chemical Releases (Belle)

Incident Description:On January 23, 2008, there was a release of highly toxic phosgene, exposing a veteran operator at the DuPont facility in Belle, West Virginia and resulting in his death one day later. A braided steel hose connected to a one-ton capacity phosgene tank suddenly ruptured, releasing phosgene into the air. The phosgene hose that burst in front of a worker was supposed to be changed out at least once a month, but the hose that failed had been in service for seven months. The CSB found the type of hose involved in the accident was susceptible to corrosion from phosgene.

Valero Refinery Propane Fire

Incident Description:On February 16, 2007, a propane fire erupted at the Valero McKee Refinery in Sunray, Texas. The fire occurred in the refinery's propane de-asphalting unit, which uses high-pressure propane as a solvent to separate gas oil from asphalt; gas oil is used as a feedstock in other gasoline-producing refinery processes. The propane leaked from an ice-damaged piping elbow that is believed to have been out of service since the early 1990s. Unknown to refinery personnel, a metal object had wedged under the gate of a manual valve above the piping elbow, allowing liquid to flow through the valve. Piping above the valve contained liquid propane at high pressure, and small amounts of water were entrained in the propane. The elbow was part of a dead-leg formed when the piping was taken out of service. The section of piping that remained connected to the process was not intended to have any flow of liquid through it. Dead-legs can pose special hazards in refineries that should be carefully managed. The refinery, then owned by Ultramar Diamond Shamrock, did not identify hazards arising from the dead-leg when it was created in the 1990s and did not implement safeguards, such as removing the piping, isolating it from the process using metal plates known as blinds, or protecting it against freezing temperatures.

BP America Refinery Explosion

Incident Description:At approximately 1:20 p.m. on March 23, 2005, a series of explosions occurred at the BP Texas City refinery during the restarting of a hydrocarbon isomerization unit. Fifteen workers were killed and 180 others were injured. The explosions occurred when a distillation tower flooded with hydrocarbons and was overpressurized, causing a geyser-like release from the vent stack.  The investigative team found a number of problems with the facility's preventative maintenance program that were causally related to the March 23 accident. The CSB concluded that BP supervisory personnel were aware of the equipment problems with the level transmitter before the March 23 startup but still had signed off on equipment checks as if they had been done, which the report said reflected the prevalence of production pressures at the refinery.  The day of the incident, a blowdown drum vented highly flammable material directly to the atmosphere. The drum was never connected to a flare since its construction in the 1950s. The previous owner of the refinery, Amoco Corporation, replaced the ISOM unit blowdown drum in 1997 with identical equipment; Amoco refinery safety standards recommended connecting the drum to a flare when such major modifications were undertaken, but this was not done.


Technic Inc. Ventilation System Explosion

Incident Description:On February 7, 2003, an explosion ignited a fire inside a vent collection system (VCS) at Technic Inc., a plating chemicals manufacturing and research facility located in Cranston, Rhode Island. One employee was critically injured. Eighteen other employees were transported to Rhode Island Hospital for medical evaluation. The vent collection system was severely damaged, and plant operations were interrupted for several weeks. In addition to evacuating plant employees, the Cranston Fire Department (CFD) ordered an evacuation of residents and businesses within 0.5 mile of the facility because of concern that cyanide salts and acids stored in the plant might combine to create toxic hydrogen cyanide gas. According to witness testimony, the incident likely began when an employee—suspecting the plastic ventilation duct to be clogged—tapped on it with a small hammer. The resulting explosion severely injured his eyes and face. Subsequent to the explosion, a fire involving accumulated combustible materials broke out inside the main vent header duct. The fire propagated through the main header duct to the branch ducts on mezzanine 1 and eventually consumed a plastic acid hood.

DPC Enterprises Festus Chlorine Release

Incident Description:On August 14, 2002, a chlorine transfer hose ruptured during a rail car unloading operation at the DPC Enterprises chlorine repackaging facility near Festus, Missouri. The CSB found that DPC lacked an effective testing and inspection program for its chlorine emergency shutdown system. Emergency shutdown valves failed to close properly once the chlorine leak had begun, greatly extending the duration and severity of the release. Investigators concluded that the valves were inoperable due to internal system corrosion, in turn caused by inadvertent introduction of moisture into the chlorine system. DPC's testing and inspection program was inadequate to uncover the faulty condition of the valves before the accident occurred.

Marcus Oil and Chemical Tank Explosion

Incident Description:On the evening of December 3, a storage tank failed catastrophically at the Marcus Oil and Chemical polyethylene wax facility in Houston. CSB investigators determined that the failed vessel, known as Tank No. 7, had been modified by Marcus Oil to install internal heating coils, as were several other pressure vessels at the facility. Following installation of the coils, each vessel was resealed by welding a steel plate over the two-foot diameter temporary opening. The repair welds did not meet accepted industry quality standards for pressure vessels. Marcus Oil did not use a qualified welder or proper welding procedure to reseal the vessels and did not pressure-test the vessels after the welding was completed.

Motiva Enterprises Sulfuric Acid Tank Explosion

Incident Description:On July 17, 2001, an explosion occurred at the Motiva Enterprises refinery in Delaware City, Delaware. A work crew had been repairing a catwalk above a sulfuric acid storage tank farm when a spark from their hot work ignited flammable vapors in one of the tanks. This tank had holes in its roof and shell due to corrosion. The tank collapsed, and one of the contract workers was killed; eight others were injured. The refinery's sulfuric acid tanks had a history of leaks but Motiva took no effective action, even when its own tank inspectors recommended full internal inspections "as soon as possible" in three successive annual reports prior to the explosion. Three weeks before the explosion, an operator submitted a formal Unsafe Condition Report noting holes in two tanks and pointing out that the hose used to blanket the tank with nonflammable carbon dioxide was improperly installed. The CSB found Motiva investigated the Unsafe Condition Report but took no action to correct the deficiencies.

Tosco Avon Refinery Petroleum Naphtha Fire

Incident Description:On February 23, 1999, a fire occurred in the crude unit at Tosco Corporation's Avon oil refinery in Martinez, California. Workers were attempting to replace piping attached to a 150-foot-tall fractionator tower while the process unit was in operation. During removal of the piping, naphtha was released onto the hot fractionator and ignited. The flames engulfed five workers located at different heights on the tower. Four men were killed, and one sustained serious injuries. On February 10, 1999, a pinhole leak was discovered in the crude unit on the inside of the top elbow of the naphtha piping, near where it was attached to the fractionator at 112 feet above grade. Tosco personnel responded immediately, closing four valves in an attempt to isolate the piping. The unit remained in operation. Subsequent inspection of the naphtha piping showed that it was extensively thinned and corroded. A decision was made to replace a large section of the naphtha line. Over the 13 days between the discovery of the leak and the fire, workers made numerous unsuccessful attempts to isolate and drain the naphtha piping. The pinhole leak reoccurred three times, and the isolation valves were retightened in unsuccessful efforts to isolate the piping. Nonetheless, Tosco supervisors proceeded with scheduling the line replacement while the unit was in operation. On the day of the incident, the piping contained approximately 90 gallons of naphtha, which was being pressurized from the running process unit through a leaking isolation valve. A work permit authorized maintenance employees to drain and remove the piping. After several unsuccessful attempts to drain the line, a Tosco maintenance supervisor directed workers to make two cuts into the piping using a pneumatic saw. After a second cut began to leak naphtha, the supervisor directed the workers to open a flange to drain the line. As the line was being drained, naphtha was suddenly released from the open end of the piping that had been cut first. The naphtha ignited, most likely from contacting the nearby hot surfaces of the fractionator, and quickly engulfed the tower structure and personnel.


Last updated July 27, 2017