HAVE YOU IDENTIFIED ALL POSSIBLE SOURCES OF CORROSION?

On October 1, 2020, at approximately 9:00 a.m., approximately 554 pounds of chlorine gas were accidentally released at a facility in Louisiana. Exposure to the toxic chlorine vapors seriously injured one employee.

At the time of the incident, four workers (two employees and two contractors) were trying to stop a chlorine leak (described by as a fugitive emission) from a drain valve in the company’s methyl diisocyanate production plant. Because a chlorine leak was detected, the company assumed that at least one of the drain valve’s connections in its flanges or bonnet was loose.
The four workers had a safe work permit to retighten the bolts using hand tools. However, the leak persisted after the bolts were retightened by hand. One of the contractors then tried to retighten the bolts using an impact wrench, a power tool designed to tighten and loosen bolts with short bursts of high torque. The vibrations from the impact wrench caused the connections on the drain valve’s bonnet to fail catastrophically, forcefully disconnecting the top half of the drain valve (closing element, stem, and handle) from the bottom half (body and seat) and releasing the toxic chlorine vapors.
The workers were wearing supplied air respirators to perform the job. After the chlorine release, they evacuated the area. However, one employee did not switch to the “escape bottle” for their respirator before detaching the respirator from the stationary air supply source during the evacuation. The subsequent lack of supplied airflow in the respirator caused the employee to remove their respirator mask during the evacuation, resulting in the employee being exposed to the toxic chlorine vapors. The employee was transported and admitted to a hospital for medical treatment.
The company's investigation found that the drain valve was severely corroded. Over time, chlorine being released from the drain valve had reacted with condensed water that had accumulated in the piping system’s insulation blanket, creating hydrochloric acid that had corroded the valve and deteriorated the bolts in the valve’s bonnet. After the incident, the company discovered that three other valves were similarly corroded.

The investigation also revealed that one of the contractors tried to use their stop work authority after seeing the dilapidated valve. The contractor brought concerns to one of the employees. While the  employee went to get a supervisor’s opinion, there was a miscommunication between the two parties about whether or not to continue working on the corroded valve. As a result, the work continued, ultimately leading to the chlorine gas release.

Probable Cause
Based on the company's investigation, the CSB determined that the probable cause of the incident was the catastrophic failure of corroded bolts in the drain valve’s bonnet. The corrosion was caused by prolonged exposure to hydrochloric acid, created by the reaction between chlorine and condensed water.
Contributing to the incident was the company's mechanical integrity program. Had the company  inspected the valve before authorizing this job, the extent of the corrosion could have been identified, and a shutdown could have been initiated to replace the drain valve instead of attempts to repair it. Contributing to the severity of the incident was the company's respiratory protection program, which did not ensure its workers could effectively transition to the escape bottle during an emergency. Had the company effectively trained its workers to switch to their escape bottles during an emergency, the employee should have not been exposed to the chlorine.

Source: CSB.gov

DISTILLATION TOWER COLLAPSE DUE TO INTERNAL FIRE

On September 5, 2023, at 11:50 a.m., a distillation tower (“Tower”) collapsed (Figure 1) at a Petrochemical in Texas. The collapse was the result of a fire inside the distillation tower. The incident resulted in approximately $194 million in property damage.

A few weeks before the incident, the company shut down its Pyrolysis Gasoline unit, including its extractive Tower. The company followed its procedure to remove solvent and hydrocarbons from within the Tower to prepare for maintenance work. On the day of the incident, a maintenance crew began opening manways to prepare the Tower for entry. At 9:30 a.m., temperatures with the Tower’s stainless steel structured packing beds began to rise. The company sounded an emergency alarm at 10:44 a.m. after smoke and flames showed a fire within the Tower. Personnel were evacuated after adding nitrogen and trying to stop air from entering the Tower. At 11:53 a.m., the Tower folded over (collapsed).
The company investigation found that the Tower fire resulted from a chain of undesired reactions. About a month before the unit shut down, equipment leaks in another area of the process allowed water to enter the extractive distillation unit, leading to internal corrosion that removed iron from the metal walls. This iron formed iron sulfide (a pyrophoric material) from hydrogen sulfide that is usually present in the process equipment. When the Tower’s manways were opened, oxygen (air) entered the Tower, starting an exothermic iron sulfide oxidation reaction. The company concluded that the heat from this iron sulfide oxidation reaction resulted in localized heating (1,300 to 1,800 degrees Fahrenheit) within the structured packing that weakened the Tower’s walls and ultimately caused the Tower to collapse.
In addition, The company’s investigation found that a 2016 incident had revealed the potential for iron sulfide to accumulate within the Tower. The investigation team determined that this knowledge had not been effectively transferred to the existing site personnel. Had the site’s operations team known about the potential for iron sulfide within the Tower, changes to the procedure to remove solvent and hydrocarbon could have been made to mitigate the heating from the iron sulfide oxidation.
During the incident, approximately 160 pounds of sulfur dioxide and an unknown amount of other reaction and combustion products were accidentally released.
Probable Cause
Based on The company’s investigation, the CSB determined that the probable cause of the fire was smoldering iron sulfide oxidation within the structured packing of the Tower. Contributing to the incident was that the company did not effectively maintain its knowledge from its 2016 incident finding that iron sulfide could accumulate within the Tower.

Source: CSB.gov

TANK OVERPRESSURE INCIDENT

On June 22, 2023, at about 9:10 p.m., a 5,200-gallon polyethylene storage tank (“tank”) ruptured at a facility in North Carolina. The rupture fatally injured one employee.
At the time of the incident, the tank needed to be refilled with aluminum chloride; however, sulfuric acid was added instead. Approximately 80 gallons of 93 percent sulfuric acid were added to the 60 gallons of aluminum chloride remaining in the tank, resulting in a reaction that caused the tank to rupture. The tank rupture fatally injured the employee who was refilling the aluminum chloride tank.
The company's investigation appeared to focus on the incorrect reaction rather than a reaction scenario consistent with the available evidence. Its research materials pointed to the reaction between sulfuric acid and aluminum metal that generated hydrogen gas. The company concluded that the hydrogen gas was released at its autoignition temperature (over 1,000 degrees Fahrenheit (°F)) and ignited, triggering an explosion. Post-incident photographs of the damaged tank do not appear to support a scenario where the internal tank temperature reached 1,000 °F, however. The melting temperature of the polyethylene is approximately 260 °F. Therefore, the company’s reaction scenario appears inconsistent with the available evidence.
The CSB concluded that the reaction most likely generated hydrogen chloride vapors. The more likely scenario was that the reaction between aluminum chloride and sulfuric acid produced enough hydrogen
chloride vapor to increase the pressure within the polyethylene tank, likely resulting in an overpressure that separated the tank’s body from its base.
The CSB estimated that approximately 130 pounds of hydrogen chloride vapors were accidentally released.
Probable Cause
Based on the factual information from the company's investigation, the CSB determined that the probable cause of the overpressure was the increase in the tank’s internal pressure resulting from the hydrogen chloride vapors created by the reaction between sulfuric acid and aluminum chloride.

Source:CSB.gov

A SELF ACCELERATING DECOMPOSITION REACTION KILLS AN OPERATOR

On May 4, 2023, at about 12:40 a.m., a pressure Nutsche filter vessel (“vessel”) exploded at a facility in  Massachusetts. The explosion and fire fatally injured one operator and caused approximately $48 million in loss from property damage, which led to the permanent closure of the facility.

At the time of the incident, the plant was producing a substance called Dekon 139 (“Dekon”). The Dekon had already been synthesized, and excess liquid from the production process had been removed from the solid product (“cake”) within the nitrogen-inerted vessel. The plant used an agitator to smooth the cake and remove lumps that formed during drying to remove the liquid from the cake.                                                                                                                                                                            In post-incident testing, the plant determined that Dekon could undergo exothermic, self-accelerating decomposition when heated to 280 degrees Fahrenheit. The plant learned that Dekon decomposition releases flammable gases, including hydrogen, methane, and carbon monoxide.
In its incident investigation, the plant determined that leading up to the incident, the agitator had loosened and was rubbing a plate at the bottom of the filter dryer vessel, generating heat from friction. The friction likely caused an area of high temperature (“hot spot”) in the Dekon, which likely reached the temperature
necessary for the Dekon to begin decomposition. The decomposition reaction released energy, which increased the temperature of the material in the vessel and caused more Dekon to decompose.                                                                                                                                
The gases produced by the reaction rapidly increased the pressure within the vessel, causing the vessel’s discharge door to open. The released flammable materials (gas and Dekon dust) mixed with atmospheric oxygen and ignited, causing an initial weak explosion. Shortly after that, the vessel’s rupture disc opened, and a second larger explosion occurred when the vessel failed.
One operator was unable to escape the area and was fatally injured.
The CSB estimated that approximately 600 pounds of Dekon decomposed into flammable gases that were consumed during the incident.
Probable Cause
Based on the company's investigation, the CSB determined that the probable cause of the explosion and fire was a self-accelerating decomposition reaction of Dekon, which produced flammable gases and released combustible Dekon dust that ignited upon release. Contributing to the incident was the company's incomplete knowledge of the hazards associated with Dekon, including its ability to undergo a self-accelerating decomposition reaction capable of rupturing the reaction vessel.

Source:CSB.gov

Watch "Process Alarm Systems Updates to EEMUA 191 by Andy Brazier" on YouTube

 Watch "Process Alarm Systems Updates to EEMUA 191 by Andy Brazier" on YouTube

 https://youtu.be/xh62GMQ53u0?feature=shared

INCOMPATIBLE CHEMICALS CAUSE H2S RELEASE

 On March 29, 2023, at approximately 5:05 p.m., toxic hydrogen sulfide gas was accidentally released at a paper mill in Kentucky. Exposure to the hydrogen sulfide gas seriously injured one operator and injured two other operators.
At the time of the incident, three operators were tasked with circulating an acid-cleaning solution through process equipment to remove the buildup of solids impairing its performance. This task required an operator to stand directly over a tank and pour solid sulfamic acid powder into its opening.
When these operators added the sulfamic acid powder, the tank should have contained water, but a valve had been left open. This allowed a “weak wash” process stream to enter the tank before the operators added the solid sulfamic acid. The weak wash contained sodium sulfide, which reacted with the sulfamic acid, generating the toxic hydrogen sulfide gas.
Operator 1, who was standing directly over the tank opening (Figure 1), lost consciousness from exposure to the hydrogen sulfide gas that evolved from the tank. Operator 3 was able to call for help over the plant radio system but lost consciousness soon after. Operator 2 was seriously injured after losing consciousness (while trying to help Operator 1), falling to the floor, rolling through a guardrail system, and falling about 11 feet to a lower area of the structure.
Two other Domtar employees heard the distress call and entered the room to help the operators. All three operators regained consciousness. Operator 1 and Operator 3 were able to walk outside without assistance. Emergency responders transported Operator 2 to a hospital for treatment.
The company reported that about 25 pounds of hydrogen sulfide were released.

Probable Cause
Based on the company's investigation, the CSB determined that the probable cause of the hydrogen sulfide release was the reaction between the added sulfamic acid and the sodium sulfide in the tank. The company's procedure procedures did not indicate that the weak wash valve should be closed during normal operation, which contributed to the incident. Had the weak wash valve remained closed (or more robustly isolated), sodium sulfide could have been kept out of the tank, preventing the reaction that generated the toxic hydrogen sulfide.

Source:CSB.gov

"Travel Stops on Spring Supports: What Engineers Need to Know" by Piping Technology and Products

The June 2025 process safety beacon talks about an incident that I had experienced with a locked spring hanger. Read the beacon in this link https://ccps.aiche.org/resources/process-safety-beacon/archives/2025/june/english

Piping Technology and products have published a safety alert explaining  "

"Travel Stops on Spring Supports: What Engineers Need to Know"

Read it in this link

https://pipingtech.com/resources/technical-bulletins/safety-alert-installation-spring-supports/

 

 

A FIRE WATER HOSE CAUSES A PUMP TO CRACK AND INJURE A EMPLOYEE

On February 24, 2023, at 9:20 a.m., an accidental release of approximately two gallons of a sodium hydroxide and water solution (“caustic solution”) seriously injured an employee at a facility in South Carolina.
A new pump for unloading caustic solutions from tank trucks was installed at the facility the day before the incident. On the day of the incident, the company used the new pump for the first time. Employees turned on the pump to begin transferring the caustic solution from a tank truck, but the pump failed to move fluid and leaked. The employees planned to disassemble the pump to identify the operational problem.
Before disassembling the pump, it was decided to flush it out with water from a fire hose. This action was taken to prevent employees from getting the caustic solution on their hands when the pump was disassembled. An employee connected a fire hose to the pump and partially opened the valve. The pump could not handle the pressure supplied by the firewater, and the plastic pump casing cracked. Caustic solution and water sprayed out of the pump, seriously injuring one employee.

After the incident, the company modified its caustic unloading system, eliminating the need for an unloading pump.
Probable Cause
Based on the company's investigation, the CSB determined that the probable cause of the incident was the overpressure of a pump casing after pressurized firewater was introduced to the pump.

Source:CSB.gov