Fire in a hydro-cracking unit due to the failure of a hose

The incident occurred during maintenance works at a hydro-cracking unit of a refinery (the report does not explicitly mention the unit, but it is plausible to assume that it was a hydro-cracking and/or desulphurisation unit). A flexible hose ruptured releasing a flammable mixture containing hydrogen and hydrocarbons. The mixture ignited, resulting in a large fire at the refinery.

On the day of the incident, two company’s employees and one contractor’s employee were removing temporary equipment installed for the change of the reactor’s catalyst. The hose which failed was part of this equipment, connected to a flare system. The hose had a maximum pressure rating of 20 bar (300 psi). The workers, preparing to remove the temporary equipment, opened a valve that exposed the hose to a pressure above 120 bar (1,800 psi). The over-pressure broke the hose and approximately 2.9 metric tons (6,400 pounds) of flammable material.

According to the investigation performed by the company, its management of the change process for the temporary equipment was missing information.
The piping and instrumentation diagram did not identify hoses, and the review team assumed that piping with an appropriate pressure rating was used. However, the team responsible for the pre-startup safety review incorrectly concluded that the hose’s pressure rating was sufficient.
Another finding was that the company did not apply other management systems, including a job safety analysis, and did not develop a procedure detailing the correct order to open the valves, as they were not identified as necessary for temporary equipment.

The INITIATING CAUSE was the over-pressurisation and failure of a flexible hose used a temporary set-up during maintenance.
The ROOT CAUSE was lack of a proper management if change and the failing to execute a correct risk assessment of the maintenance and start-up operations.

hose

The plant was being restarted.

According to the CSB report, “the probable cause of the incident was the overpressure of a temporary hose. Contributing to the incident was not recognizing the potential to overpressure the hose, resulting from misunderstandings during the management of change process and an ineffective pre-startup safety review.”
The incident could have been avoided, if the company would have performed an effective hazard analysis and risk assessment of all operations occurring after the maintenance and during the pre-startup phase. This assessment would have identified the mismatch between the equipment used and the pressure present in the unit.

After the incident, among other actions, the company approved a project to install permanent piping to prevent the need for hoses during similar catalyst replacement work in the future.