Explosion of flammable gases at the hydrocracker reactor of a refinery

A section of effluent piping ruptured on the hydrocracker reactor of a refinery. A mixture of light gases (methane, butane), light and heavy gasoline, gas oil and hydrogen was released from the pipe and instantly ignited upon contact with air, causing an explosion and fire.

The pipe ruptured because of too high temperature (over 760°C) stemming from the catalyst bed. The excessive heat generated in a catalyst bed was initiated by a reactor temperature excursion that began with a hot spot in another bed (most likely caused by poor flow and heat distribution within the catalyst bed) and spread through the other beds.

An operator who was checking a field temperature panel at the base of the reactor was killed; 46 employees or contractors were injured, 13 hospitalised.

The INITIATING CAUSE was a reactor out pipe rupturing due to excessive temperature (over 760°C) in the reactor.

Accident and consequence were caused by a poor design of the and lacks in safety management. The temperature excursion could not be not brought under control because the reactors were not depressurised and shut down as required. The written operating procedures prescribed the reactors to be shutdown when their temperatures exceeded the temperature limit of 426°C.
However, operators did not activate the emergency procedure because they were confused about whether a temperature excursion was actually occurring. The alarms system was poorly designed: there was no additional audible high temperature alarm and fluctuating readings obliged an operator to go read the temperature under the reactor.

Effluent piping from a Hydrocracker Reactor of a Refinery.

An operator who was checking a field temperature panel at the base of the reactor was killed; 46 employees or contractors were injured, 13 hospitalised.

The environmental protection agency investigated the case and pointed out poor safety design and lacks in management:

1. Inadequate operating conditions.
2. Poor design of the Reactor Temperature Monitoring System: 3 different instrumentation systems were used to obtain temperature data, access to the most critical monitoring points located underneath the reactors, alarm system allowing one alarm to be received at a time, no distinction between emergency alarms and other operating alarms. Hydrogen purity analysis data available to operators lagged seven minutes behind the actual time of the analysis and provided misleading information to the operators.
3. Inadequate supervisory Management. No communication of incidents to management, no comprehensive operator training, including refresher training, had been No management of change program was implemented to address mechanical changes or operational changes.
4. Inadequate Operational Readiness and Maintenance : the temperature monitor in the control room unreliable and/or out of service, radio communications unreliable and/or not functioning, emergency depressurization system was not tested to ensure its reliability when needed.
5. Inadequate operator training and outdated or incomplete procedures. Recommendations from several incidents were not incorporated into procedures.