DOES YOUR LOW FLOW TRIP OF FIRED HEATERS TAKE CARE OF ALL PASSES?

 On August 19, 2022, at approximately 3:45 a.m., about 4,000 pounds of a hydrogen and hydrocarbon mixture was accidentally released into the firebox of a fired heater, where it ignited, creating a large fire at a refinery in Texas City, Texas. Estimated that the property damage from the incident was $10 million.

On the morning of the incident, the company restarted a fired heater that had been offline for approximately 12 hours due to a compressor shutdown caused by a malfunction of a pressure transmitter in the lube oil system. During the startup, it was essential to flow process feed through all four passes of the fired heater’s tube system. However, only two of the four passes in the tube system had sufficient flow through them when the burners were ignited. Although the minimum flow was eventually established in another tube pass, there was no flow through the fourth pass.
Company investigation of the incident found that without the fluid flowing through the fourth pass to remove heat, the tube’s metal wall temperature reached 1,500 degrees Fahrenheit (℉), which exceeded the design temperature limit. After the operations supervisor noticed the high temperature, field operators were sent to inspect the heater tubes. The field operators reported that some tubes were “glowing red hot,” and consequently they manually turned off two of the fired heater’s eight burners. The field operators then reduced the flow through the first three passes to help drive feed material into the fourth pass. Although operators reported hearing material flowing in the fourth pass, the meter indicated no flow. The operations team concluded that the flow meter was malfunctioning.
Less than an hour later, a convection section tube in the fourth pass ruptured due to short-term, overheating  releasing a flammable mixture of hydrogen and hydrocarbons into the firebox. Flames from the gas-fired burners ignited the mixture, resulting in a large fire.

During its investigation, the company discovered that the startup procedure for the fired heater, which required maintaining a steady flow through all four tube passes before lighting the burners, was not used. This procedure was “conditional,” however, and was only necessary if the firebox temperature had cooled below 400℉. At the time when the burners were lit, this temperature was slightly below 400℉.
Additionally, the company found that the fired heater lacked engineered safeguards to prevent the burners from being lit before establishing flow in each of the four passes. In response to the incident, the company modified its automated burner controls to help ensure that the flow rate through every pass exceeds a predetermined minimum flow rate before operators can ignite a burner.

Probable Cause
Based on the company investigation, the CSB determined that the probable cause of the incident was a ruptured fired heater tube from short-term overheating. Flames from the fired heater’s gas-fired burners ignited these flammable chemicals, resulting in the fire. The lack of automated safeguards that did not prevent the burners from being ignited before the minimum flow was established through each of the four tube passes contributed to the incident. Had the company had such automated safeguards in place, this incident likely could have been prevented.

Source:CSB.gov

ARE YOU CLEARING YOUR TANKS COMPLETELY AND ENSURING NO FLAMMABLE / TOXIC VAPOURS ARE PRESENT BEFORE HANDING OVER TO MAINTENANCE?

On July 29, 2022, at 7:45 a.m., an explosion and fire occurred at a facility in Mississippi. The explosion and subsequent fire fatally injured one employee and seriously injured five other employees 

The facility separates crude oil condensate (flammable liquid hydrocarbon) from salt water through a series of four tanks. After the crude oil condensate is recovered, the saltwater waste is pumped into a saltwater disposal well. Two of the tanks used in the disposal process were replaced with new tanks shortly before the incident occurred, but two tanks were not replaced.
The company's investigation found that although most of the liquid was removed from the two tanks that were not replaced, some salt water, residual hydrocarbon material, and air remained inside these tanks. At the time of the incident, seven employees were completing the tank replacement work, which included installing an elevated walkway between the tanks and finishing piping and structural connections. While welding piping between the two middle tanks, one of the employees opened a valve to the older tank that contained residual crude condensate material, likely releasing some hydrocarbon vapors into the new piping being welded. The flammable vapor ignited, and flames traveled back into the tank, resulting in an explosion and fire that ejected the top of the tank. In addition, the blast launched and forcefully propelled an adjacent tank approximately 80 feet into the woods 

As a result of the explosion and fire, six of the employees were transported and admitted to the hospital, where they received treatment for their burn injuries. One of these employees died at the hospital six days later.
The company's investigation found that no work permits were written for the welding work associated with the tank replacement task. An investigation by the federal Occupational Safety and Health Administration (OSHA) found that the tanks involved in the explosion had not been thoroughly cleaned, which allowed flammable material to remain near the welding activity at the time of the incident.

Probable Cause
Based on the company's and OSHA’s investigations, the CSB determined that the probable cause of the incident was the presence of flammable vapors near a welding activity being performed. Not thoroughly draining, cleaning, and purging the tanks to remove the flammable material before starting construction contributed to the incident. Had the tanks been thoroughly drained, cleaned, and purged prior to the commencement of construction, this incident likely could have been prevented.

Source:csb.gov

ARE YOUR PROCEDURES CLEAR AND WARN OF DANGERS?

On July 2, 2021, at approximately 9:15 p.m., approximately 700 pounds of a mixture of vapors, including chlorodifluoromethane (“R22”) and perfluoroisobutene (“PFIB”), were released a facility in Alabama . Exposure to the toxic mixture of vapors fatally injured two operators and seriously injured another Daikin operator.

A drying tower was being returned to service after it had been offline for maintenance. After the maintenance activity, this equipment contained air, and the procedure included steps to remove this air and replace it with R22. To accomplish this, the company used a two-step purge process. First, nitrogen was added to sweep out the air, and second, R22 was added to sweep out the nitrogen. The displaced vapors were released into the ambient air from an open valve about six feet above the ground for each step. The valve was aimed vertically downward, resulting in the vapors being released in a downward direction toward the area where the operators were working.
The procedure did not specify the source of the R22 material used in this purging operation. The R22 was taken from another process vessel that contained other chemicals, including PFIB. As operators performed this purging, PFIB was released into the ambient air from the open valve, exposing three operators to this toxic vapor. The operators did not immediately report any adverse effects from the exposure and went home at the end of their shift. Approximately two days later, two of the operators became ill and were admitted to the hospital. The next day, the third operator was hospitalized. Two of the operators later succumbed to their respiratory injuries. One operator died on August 10, 2021, and the second operator passed away on September 28, 2021.

After the incident, the comapny updated its procedure to warn that toxic vapors may be present and to require that its operators use supplied air respirators. In addition, the company now directs the purge vapors to an incinerator. The procedures were also updated to specify that only high-purity (non-toxic) R22 can be used in the purging procedure.

Probable Cause
Based on the company's investigation and an investigation by the federal Occupational Safety and Health Administration (OSHA), the CSB determined that the toxic PFIB vapors were likely released with R22, which was purged from equipment into the ambient air to remove nitrogen. The safety management systems, which allowed the discharging of R22, PFIB, and other byproducts into a work area, contributed to the severity of the incident. Had the company ensured that the release of these hazardous vapors was avoided or discharged to a safe location, the incident could have been prevented. 

Source:CSB.gov

ARE YOUR EMERGENCY SHUTDOWN PROCEDURES ADEQUATE TO PREVENT DAMAGE?

 On February 15, 2021, at 3:05 p.m., a hydrogen and hydrocarbon gas mixture was accidentally released into the firebox of a fired heater, where it ignited and exploded. It was estimated the incident resulted in $2.5 million in property damage.

The company's investigation found that the facility shut down multiple fired heaters when extreme cold weather from Winter Storm Uri caused several freeze-related operational issues. Due to emergency conditions that included utility losses and supplier-driven gas shortages, the company shut down its fired heaters without removing the solidified carbon deposits on the interior walls of the heater tubes (decoking).

The company's investigation revealed that further utility upsets caused the facility to stop all fuel gas supply and fully shut down the remaining fired heaters. During the shutdown, a valve between one of the ethylene unit’s fired heaters and downstream equipment remained open. The open valve allowed downstream flammable hydrogen and hydrocarbon gas to flow backward into the fired heater tubes. Approximately 30 minutes after this happened, a tube within the fired heater ruptured, allowing the flammable gas to enter the firebox. The gas accumulated, ignited, and exploded, causing extensive damage to the fired heater (Figure 2).

The company's investigation determined that the tube failure likely occurred because the fired heater tubes were shut down without decoking. Coke fouling can insulate the tube surface, resulting in local hotspots and increasing the risk of thermal shock and tube failure in fired heaters. These conditions stressed the tube’s walls when the metal cooled faster than the internal coke, breaking the tube. The company's investigation concluded that hot insulation inside the firebox likely ignited the gas (autoignition).

Probable Cause
Based on the company investigation, the CSB determined that the probable cause of the incident was a fired heater tube failure from thermal stress due to the rapid shutdown. When the tube broke, a hydrogen and hydrocarbon gas mixture from downstream equipment flowed into the firebox. Hot insulation within the firebox likely ignited the flammable gas, resulting in an explosion. Inadequate winterization of multiple valves, instruments, and control systems contributed to the incident.

Source: CSB.gov

HAVE YOU CONSIDERED FREEZING OF WATER IN INSTRUMENT AIR HEADERS DURING LOW AMBIENT WEATHER CONDITIONS?

 On February 15, 2021, at 9:53 p.m., a hydrogen and hydrocarbon gas mixture was accidentally released into the firebox of a fired heater, where it ignited, creating a fire at a facility in Texas. The estimated property damage from the incident was $5.8 million.

The company investigation determined that freeze-related operational issues due to extreme cold weather from Winter Storm Uri caused the facility’s boiler units to shut down. This shutdown decreased the supply of steam and water to an ethylene unit at the facility. A safety system automatically shut the fired heater down due to insufficient steam and water flow. Although the automatic valves closed to prevent feed from entering the tubes, the fired heater’s fuel gas isolation valve failed to close as intended. This failure allowed the burners to continue operating. Without any flow through the tubes to remove heat from their walls, the tubes in the fired heater reached excessively high temperatures. Some tubes ruptured, likely due to short-term overheating, but a metallurgical analysis was not performed to confirm the cause of the tube failures. When the tubes ruptured, hydrocarbons downstream from the fired heater were released through the broken tubes and ignited by the burner flames inside the firebox, causing a fire.

During post-incident testing by the company in temperatures above freezing, the fuel gas isolation valve successfully closed as designed. The company's investigation concluded that the fuel gas isolation valve did not close because water in the instrument air supply had frozen or ice formed on the external actuator components (related to inadequate winterization), preventing the isolation valve from closing.
Probable Cause
Based on the company's investigation, the CSB determined that the probable cause of the incident was the rupture of fired heater tubes from short-term overheating. When the tubes were broken, a hydrogen and hydrocarbon gas mixture flowed from downstream equipment into the firebox. Flames from the burners ignited the flammable materials, resulting in the fire. Inadequate winterization of flow control equipment contributed to the incident.