A refinery hydrocracker effluent pipe section ruptured and released a mixture of gases, including hydrogen, which instantly ignited on contact with the air, causing an explosion and a fire. Excessive high temperature, likely in excess of 1400°F (760°C), initiated in one of the reactor beds spread to adjacent beds and raised the temperature and pressure of the effluent piping to the point where it failed. An operator who was checking a field temperature panel at the base of the reactor and trying to diagnose the high-temperature problem was killed. A total of 46 other plant personnel were injured and 13 of these were taken to local hospitals, treated, and released. There were no reported injuries to the public.

Property damage included an 18-inch (46-centimeter) long tear in the reactor piping, heat/fire damage to ladders/scaffolding/platforms around the rupture area and a nearby light pole, and damage to a large fire water piping. Approximately 13 pounds (5.9 kilograms) of friable asbestos insulation from the damaged piping and equipment was released into the air as particulates, but subsequent testing found asbestos levels below the detection limit and below the OSHA standard. Damage is shown in Attachment 1 (Figures 1 to 5).

The high temperature that caused the pipe rupture was not brought under control because the operators did not activate an emergency depressurization of the reactor when some internal reactor temperature readings reached 800°F (427°C) because they were confused about whether a temperature excursion was actually occurring. Their confusion was due to a variety of factors, including: fluctuating temperature readings, a discontinuation of makeup hydrogen flow to one of the reactor stages, a misleading recycle hydrogen purity analysis, and the absence of additional audible high-temperature alarms after the first high-temperature occurrence. They were attempting to verify temperatures in the reactor by having an operator obtain temperature readings from the field panels under the reactor. Poor radio communications hampered relaying these readings to the control room. Even after the operators in the control room noticed that another reactor stage inlet temperature had increased beyond 800°F (427°C), they did not depressurize but began to take steps to cool the reactor by increasing quench hydrogen flow and reducing heat input from the trim furnace.

Incident Date
Jan 21, 1997
  • Piping/Fittings/Valves
  • Piping
  • Process Equipment
  • High-Pressure Reactor Cell
When Incident Discovered
Lessons Learned

1. Management must ensure that operating decisions are not based primarily on cost and production. Performance goals and operating risks must be effectively communicated to all employees. Facility management must set safe, achievable operating limits and not tolerate deviations from these limits. Risks of deviation from operating limits must be fully understood by operators. Also, management must provide an operating environment conducive for operators to follow emergency shutdown procedures when required.

2. Process instrumentation and controls should be designed to consider human factors consistent with good industry practice. Hydroprocessing reactor temperature controls should be consolidated with all necessary data available in the control room. Some 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. Supervisors need to ensure that all required procedures are followed. Supervisors should identify and address all operating hazards and conduct thorough investigation of deviations to determine root causes and take corrective action. Equipment and job performance issues related to operating incidents should be corrected by management.

4. Facilities should maintain equipment integrity and discontinue operation if integrity is compromised. Hydroprocessing operations especially need to have reliable temperature monitoring systems and emergency shutdown equipment. Equipment should be tested regularly and practice emergency drills should be held on a regular basis. 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. For hydrocrackers, this should include training on reaction kinetics and the causes and control of temperature excursions. Operators need to be trained on the limitations of process instruments and how to handle instrument malfunctions. Facilities need to ensure that operators receive regular training on the use of the emergency shutdown systems and the need to activate these systems.

6. Management must develop written operating procedures for all phases of hydrocracker operations. The procedures should include operating limits and consequences of deviation from the limits. The procedures should be reviewed regularly and updated to reflect changes in equipment, process chemistry, and operation. As appropriate, the procedures should be updated to include recommendations from process hazard analysis and incident investigations.

7. Process hazard analysis must be based on actual equipment and operating conditions that exist at the time of the analysis. The analysis should include the failure of critical operating systems, such as temperature monitors or emergency operating systems. A Management of Change review should be conducted for all changes to equipment or processes, as necessary, and should include a safety hazard review of the changes.

More information on management of change can be found in the Lessons Learned Corner and also in the Hydrogen Safety Best Practices Manual.