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CHANGES CAUSE AN INCIDENT

 On August 29, 2024, at 6:45 p.m., flammable vapors were accidentally released from a reactor at a refinery in Houston, Texas, resulting in a fire at the facility. The incident resulted in $16.8 million in property damage.
At the time of the incident, employees noticed flames coming from the head of a reactor in the fluidized catalytic cracking unit (“FCCU”). The flammable vapor released from the reactor likely caught fire from autoignition because the reactor operated at 960 degrees Fahrenheit (℉), which is above the autoignition temperature for most of the hydrocarbons released. Unit operators put out the flames with a fire extinguisher. The company reported that over 400 pounds of flammable vapors were released during this incident.

The company’s investigation determined that the flammable chemicals were released through an 8-inch crack in the wall at the top (head) of the reactor. Additionally, the company found other cracks in the reactor that were up to 67 percent of the wall thickness. The cracks were created by a damage mechanism known as corrosion fatigue. Corrosion fatigue is caused by cyclically applied stress under corrosive conditions. Internal cracks formed at the top of the reactor, an area that was consistently exposed to sulfur-containing chemicals commonly found in petroleum refining. This sulfidation corrosion was coupled with temperature swings over 200℉, which applied stress to the vessel through expansion and contractions of the metal with the temperature changes. The company found that there had been more than 50 temperature cycles since 2011. Additionally, platform supports were added to the reactor head in 2001, contributing to the cracking by increasing the stress exerted on the vessel. Stress-assisted preferential sulfur penetration is the specific type of corrosion fatigue responsible for the 8-inch crack.

The investigation also revealed that the company was not inspecting the reactor’s walls for cracking because the site’s mechanical integrity program did not identify corrosion fatigue as a potential damage mechanism. The company attributed this gap to following industry standards that did not identify corrosion fatigue as a common FCCU reactor damage mechanism.

Probable Cause
Based on the company’s investigation, the CSB determined that the probable cause of the accidental release was an 8-inch corrosion fatigue crack through the wall at the top of the reactor. Adding platform supports to the top of the reactor contributed to the incident by increasing the stress exerted on the vessel during the temperature changes. The company’s mechanical integrity program contributed to the incident by not identifying corrosion fatigue as a potential damage mechanism for its FCCU reactor.

Source: CSB.gov

HUMAN FACTORS CAUSED A FURNACE TUBE RUPTURE

 On July 12, 2024, at 7:00 p.m., a mixture of nitrogen and benzene was accidentally released into the firebox of a fired heater. The benzene ignited, causing a fire at a facility in Texas. The company estimated that the incident resulted in $9.8 million in property damage.

The incident occurred while employees were restarting the fired heater after Hurricane Beryl damaged offsite power systems, disrupting water availability and causing a shutdown of the facility on July 8, 2024. Process fluid should circulate through the fired heater’s tubes during the unit startup. The company's investigation found that the process flow through the fired heater was reduced because two misaligned valves (open valves that should have been closed) allowed some of the flow to bypass the heater.
Without enough fluid flow to remove heat, the tubes reached temperatures as high as 1,900 degrees Fahrenheit, far above the safe operating temperature. The high-temperature condition weakened the tubes in the upper portion of the fired heater and caused some of them to rupture, likely from short-term overheating.

The company reported that the ruptured tubes released approximately 16,000 pounds of nitrogen and 630 pounds of benzene into the firebox. The operating burner flames ignited the flammable benzene, resulting in a fire.
The company's investigation reviewed the company’s process hazard analysis and determined that the existing instrumentation safeguards did not protect against low-flow or high-temperature conditions in the fired heater during startup. The investigation also found that human factors caused valve alignment errors that allowed some process flow to bypass the furnace. These included vague radio communications, multitasking due to a high startup workload, stress from the major hurricane, perceived time pressure from delays, and implementing an unfamiliar startup, which was infrequently conducted.
After the incident, the company provided its operations team with fired heater startup simulator training and improved the company’s instrumented safeguards for the fired heater. These instrumentation upgrades included an alarm and a safety interlock to protect the equipment when the temperature difference between any individual tube pass temperature and the combined process fluid temperature exiting the furnace indicates that there is insufficient process flow through the tubes.

Probable Cause
Based on The company's investigation, the CSB determined that the probable cause of the incident was ruptured process tubes in a fired heater. Short-term overheating likely resulted in the tubes rupture, releasing nitrogen and benzene into the firebox. The flames from the fired heater’s operating burners likely ignited the benzene. Human factors resulted in two valve misalignments that contributed to the incident by creating a low-flow condition through the tubes, which increased the temperature in the tubes. A lack of instrumentation safeguards to protect the fired heater from low-flow and high-temperature conditions also contributed to the incident.

Source:CSB.gov

H2S LEAK KILLS ONE AND SERIOUSLY INJURES ANOTHER

On May 29, 2024, at about 3:15 p.m., several pounds of hydrogen sulfide and carbon monoxide gas were released at a facility in Colorado. As a result of the release, one employee was fatally injured and another  employee was seriously injured due to inhalation of the gases.

The company's investigation found that at the time of the incident, two employees were performing maintenance work on a pump at the facility. The workers closed an isolation valve and removed approximately half of the bolts on the connection before water began leaking from the flange onto the floor. The workers and their supervisor determined that the isolation valve was not properly seated. The two workers left the pump house to get a tool to help close the valve. While the workers were gone, hydrogen sulfide and carbon monoxide gas began releasing into the pump house (which was approximately 400 square feet and 8 feet tall).
When the workers reentered the pump house, they experienced symptoms consistent with toxic gas exposure. One of the workers lost consciousness (“Worker One”) when trying to escape up a ladder. The other worker (“Worker Two”) escaped the pump house. Worker Two explained the situation to another supervisor, and emergency responders were contacted. A third supervisor and two other employees attempted to rescue Worker One, but they realized that the area was dangerous and tried to escape. During the escape, one of the attempted rescuers (“Rescuer One”) fell, appeared to be unconscious, and could not self-rescue. An air monitoring device that was lowered into the pump house sounded an alarm for both hydrogen sulfide and carbon monoxide, indicating the concentrations of the gases were above 20 and 35 parts per million, respectively. Because of the high concentrations of the gases, employees halted their rescue attempts and waited for emergency responders to arrive.
Emergency responders with self-contained breathing apparatuses were able to rescue the two employees from the lower pump house and transport them to a local hospital for medical treatment. Rescuer One died at the hospital later that day. Worker One survived and was released from the hospital after a few days. After the incident, The company classified the lower pump house as a confined space and installed continuous air monitoring equipment.

Probable Cause
Based on The company's investigation, the CSB determined that the probable cause of the incident was the pump’s leaking isolation valve that allowed hydrogen sulfide and carbon monoxide gas to enter the pump house when the flange was opened. Not identifying or controlling these toxic gases from being released in this part of the process contributed to the incident. Contributing to the severity of the incident was that the lower pump house was not classified as a confined space, which allowed employees to enter without safeguards such as respiratory protection, air monitoring, attendants, or a rescue plan.

Source: CSB.gov

WHY OPERATIONAL READINESS MUST BE CHECKED

 On March 17, 2024, at approximately 12:50 p.m., about 250,000 pounds of hydrogen and naphtha mixture were accidentally released into the firebox of a fired heater, where it ignited, creating a major fire at a Refinery in Texas. The company estimated that the property damage from the incident was $32 million.
The company's investigation revealed that three days before the incident, on March 14, 2024, the temperature of the tubes in the fired heater exceeded 1,200 degrees Fahrenheit, the heater’s operating limit. When the alarms indicated that the temperature exceeded the operating limit, operators at the facility lowered the temperature in the fired heater by reducing the fuel gas flow to the heater’s burners.
On March 17, 2024, the day of the incident, the same fired heater reached similar high temperatures, prompting operators to respond again. The situation escalated when two tubes within the fired heater ruptured, releasing hydrogen and naphtha into the firebox. The existing burner flame ignited these flammable hydrocarbons, resulting in a major fire.
The company’s investigation found that fire blankets and insulation material (“debris”) were present inside the failed tubes. The company determined that this debris was likely left inside the equipment after the conclusion of maintenance work (turnaround) that had been done three weeks earlier. This debris restricted the flow through the tubes, causing an increase in the temperature of the metal walls and ultimately leading to the tube failures. Additionally, the fired heater was not equipped with individual pass flow instrumentation. The company’s metallurgical examination determined that the tubes ruptured because of a combination of creep damage (which results from prolonged exposure to stress at elevated temperatures) and short-term overheating.

The company’s investigation revealed that the refinery’s process for ensuring that equipment was clean before resuming operations did not include checks of piping or fired heater tubes. Additionally, The company determined that its operational readiness programs assessed only the external status of piping and valves and did not evaluate their internal condition.

Probable Cause
Based on The company’s investigation, the CSB determined that the probable cause of the hydrogen and naphtha release was that tubes in the fired heater ruptured due to a combination of creep damage and short-term overheating. Flames from the fired heater’s burners ignited these flammable materials, resulting in the fire. Reduced flow through the fired heater’s tubes, caused by debris left inside the equipment after maintenance, contributed to the incident.

Source:CSB.gov