ICE DAMAGES EQUIPMENT DUE TO ANAMALOUS EXPANSION - ANOTHER INCIDENT

Water exhibits "anomalous behavior" because it expands when cooled from 4°C to 0°C, unlike most substances which contract when cooled. 

On December 24, 2022, at approximately 10:55 a.m., an accidental release of approximately 1,400 pounds of light straight-run gasoline (flammable hydrocarbon) occurred within a hydrotreating unit at a refinery. The release formed a vapor cloud that ignited, resulting in an explosion and fire. One operator was seriously injured due to thermal burns. The company estimated $40 million in property damage. 

From June 17, 2022, until the day of the incident, a steam turbine-driven pump and the surrounding equipment associated with the unit were a temporary dead-leg (a section of piping with no flow). During this period, the pump was locked out for maintenance by closing the inlet and outlet valves to isolate the equipment and piping from the process flow. As a result, the process fluid (hydrocarbon and water) within this equipment was stagnant for 190 days before the incident.

The chemical release occurred during a partial shutdown of the plant due to the severe cold weather. The ambient temperature dropped below freezing between December 21–24, 2022, freezing the water within the isolated pump’s piping (the dead-leg). On December 24, 2022, the daytime temperature increased, and the ice began to melt. At 10:40 a.m., flammable hydrocarbons escaped from the flange of an ice-damaged valve. This release quickly created a flammable vapor cloud, which drifted toward a fired heater (furnace), where it most likely ignited. Simultaneously, two operators, wearing their everyday flame-
resistant coveralls, were performing emergency response tasks in the fired heater area and were engulfed in the colorless and odorless portion of the vapor cloud. The two operators were injured when the vapor cloud exploded.

Probable Cause
Based on the company's investigation, the CSB determined that the probable cause of the incident was the release of flammable hydrocarbons through the flange of an ice-damaged valve. A nearby fired heater most likely ignited the flammable hydrocarbon vapor cloud.
Contributing to the incident was the company's dead-leg identification and management program, which did not identify and protect the temporary dead-leg created during maintenance activities. As a result, the water in this piping froze and expanded during cold weather.
Also contributing to the severity of the incident was the company's emergency response procedure, which allowed the operators to respond to the flammable vapor cloud to “eliminate any source of ignition if it can be done safely.” Under these circumstances, the operators relied (in part) on their senses to determine when and where it was safe to perform emergency response tasks near imperceptible portions of the vapor cloud. The company could have reduced the severity of the event by establishing clear policies and training its operators to respond to the flammable vapor release without putting themselves in harm’s way.

 Source: CSB.gov