CSB Publishes Last Catchup Investigation Report for 2022

Yesterday, the Chemical Safety and Hazard Investigation Board (CSB) announced the publication of their final investigation report on the 2018 explosion and fires at the Husky Superior Refinery in Superior, Wisconsin. This was another incident at a fluid catalytic cracking (FCC) unit at a refinery that used hydrofluoric acid as the catalyst in such a unit. There was no HF release in this incident, but major precautionary civilian evacuations were conducted near the refinery because of the proximity of the HF storage tank to the incident.

The incident occurred during startup after a turnaround of the FCC unit. The initial explosions occurred in two vessels of the Gas Concentration unit. The report describes some anomalies noted just prior to the explosions but does not provide an explanation for the possible cause of the explosions (sometimes the root cause just cannot be determined). The main item of interest, however, is that debris ejected from the unit by the explosions punctured a very large asphalt storage tank. The hole in the tank was large enough and low enough to cause a stream of liquid asphalt (@ about 320 degrees F) to pour out over the top of the containment berm that surrounded the tank and spread throughout the FCC unit area. While not technically a flammable liquid (flash point in excess of 200 degrees C), the material was hot enough that it eventually ignited, spreading flames throughout the unit. The ignition source was not apparently determined either.

There are a number of interesting mini discussions about a wide variety of process safety topics throughout the description of the incident. For example, on page 49, there is a look at the internal discussions during the incident about putting water on the very hot asphalt to slow its spread and prevent fires.

The publication of this report completes the CSB’s 2022 schedule for catching up on the backlog of inspection reports. The most recent version of that schedule shows that the CSB intends to publish six additional investigation reports (dating back to 2019) in the first six months of 2023.