OPEN TOP TANKS CAN BE DANGEROUS!

On February 6, 2023, at 8:15 a.m., a release of a hot sodium hydroxide and water solution (“caustic slurry”) seriously injured two employees at an aluminum refinery in Louisiana

 On the morning of the incident, a team of operators was assigned to drain hot caustic slurry, at a temperature of approximately 195 degrees Fahrenheit (℉), from a tank with an open-top design. The operators closed the tank’s steam injection control valve before beginning the draining operation. During their initial attempt to drain the tank, the operators determined that the drain piping was blocked. They used compressed air to blow through the drain piping to clear the blockage. However, when they directed the air into the piping, caustic slurry erupted from the tank’s open top. The hot, corrosive liquid splashed onto two of the operators. After they washed off in a safety shower, the two operators were transported to a hospital, where they were admitted for treatment of their burn injuries. It was reported that approximately 80 gallons of caustic slurry had been released during the incident.
The company’s investigation revealed that bauxite ore had accumulated in the tank and blocked the drain piping. Additionally, although the steam control valve was closed, it was leaking, which resulted in the tank’s contents being heated beyond the target temperature of 180℉. The investigation also found that no isolation device was installed to prevent the air injected into the drain piping from entering the tank. Furthermore, it was noted that some operators were not wearing the required chemical suits while clearing the pipes. Among the injured operators, one wore the required chemical suit, goggles, and rubber gloves, while the other wore goggles and rubber gloves but not the chemical suit.

Probable Cause
Based on the comapny's investigation, the CSB determined that the probable cause of the incident was flowing compressed air into the bottom of an open-top caustic slurry tank. The air created a geyser-like eruption of hot (195℉) caustic slurry that sprayed onto two operators, resulting in serious burn injuries. The lack of an isolation device between the tank and the air injection location, as well as the lack of an effective procedure to clear the drain piping, contributed to the incident