Explosion of a hydrogen/oil mixture in a refinery

The event started at the effluent pipe of one of the hydro-cracking reactors, which broke and released a mixture of hydrogen, light gases (methane, butane), light gasoline; heavy gasoline; gas oil. The mixture instantly ignited upon contact with air, causing an explosion and fire.

The explosion caused one fatality a several injuries

The pipe ruptured due to excessively high temperature, in excess of 14000 F (760 C). This high operating temperature was initiated by a temperature excursion in one of the a catalyst beds of the reactor which raised the temperature in the reactor effluent pipe. The runaway event was a consequence of the failure of initiating the shut down procedure which is foreseen by operating procedures in case the reactor temperatures exceeded the 800 F temperature limit (425 C). This procedure foresaw the full depressurisation of the reactor.
The cause of the temperature excursion was probably related to poor flow and non-uniform heat distribution.

According to the EPA report (see references), the INITIATING CAUSE was of the rupture of the effluent pipe due to excessively high temperature.

Contributing cause was the fact that the operators did not activate the emergency shutdown procedure because they were confused about whether a temperature excursion was actually occurring (difficult interpretation of the signals).

The investigators identified the following ROOT and CONTRIBUTING CAUSES:
(1) The conditions to support employees to operate the reactors in a safe manner inadequate.
(2) Human factors poorly considered in the design and operation of the reactor temperature monitoring system.
(3) Supervisory management inadequate.
(4) Operational readiness and maintenance inadequate.
(5) Operator training and support inadequate.
(6) Procedures outdated and incomplete.
(7) Inadequacy of the process hazard analysis
(8) Barriers against hazardous work conditions inadequate.

Hydrocracking unit, pipe

Of the 46 personnel injured eight were refinery employees and 38 were contractor personnel. The injuries were mainly caused by the blast from the explosion.
The materials damage was confined to the surrounding of the reactor.

Fire brigade and police evacuated the surrounding areas and set up cordons within a radius of around 500 meters, because the explosion of another even larger hydrogen tank could not be ruled out.
The nearby highway was closed in both directions and a specific area of the airspace was also blocked.

The EPA investigators developed recommendations to address the root causes of this accidents. Among those, the following ones are related to general lesson learnt:
(1) Process instrumentation and controls should be designed to consider human factors consistent with good industry practice. For example, a hydro-processing reactor temperature controls should be consolidated with all necessary data available in the control room.
(2) Backup system of temperature indicators should be used so that the reactors can be operated safely in case of instrument malfunction. Each alarm system should be designed to allow critical emergency alarms to be distinguished from other operating alarms.
(3) Adequate supervision is needed for operators, especially to address critical or abnormal situations, ensuring that all required procedures are followed.
(4) Facilities should maintain equipment integrity and discontinue operation if integrity is compromised. Maintenance and instrumentation support should be available during start up after equipment installation or major maintenance.
(5) Management must ensure that operators receive regular training on the unit process operations and chemistry.
(6) Management must develop written operating procedures for all operations. The procedures should include operating limits and consequences of deviation from limits.
(7) Process hazard analyses (risk assessments) need to be based on actual equipment and operating conditions that exist at the time of the analysis.
(8) A Management of Change review should be conducted for all changes to equipment or the process, as necessary, and should include a safety hazard review of the change.