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