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What Caused the Explosion in Shell Co. in Deer Park, Texas


Quiz Questions

1. The JCAIT determined that the immediate cause of the accident was the internal structural failure and drive shaft blow-out of a 36-inch diameter pneumatically-assisted Clow Model GMZ check (non-return) valve. The valve was located on a high-pressure light hydrocarbon gas line installed in the process gas compression (PGC) system of Olefins Plant Number III (OP-III). The check valve’s failure started a large flammable gas leak. The escaping gas formed a vapor cloud and eventually ignited, resulting in an unconfined vapor cloud explosion.
True
False

The JCAIT identified the following root causes of the accident:
2. The Clow Model GMZ check valves installed in the OP-III process gas compression
system were not appropriately designed and manufactured for the heavy-duty service they were subject to in OP-III. This resulted in the valves being susceptible to shaft blow-out during normal use.
True
False
3. Lessons learned from prior incidents involving Clow Model GMZ check valves installed at Shell facilities and at Saudi Petrochemical Company (a Saudi facility partly owned by Shell) were not adequately identified, shared, and implemented. This prevented recognition and correction of the valve’s design and manufacturing flaws at OP-III prior to the accident.
True
False
4. The process hazards analysis (PHA) of the process gas compression system was
inadequate; the PHA did not identify the risks associated with shaft blow-out in Clow
Model GMZ check valves, and consequently no steps were taken to mitigate those risks.
True
False
5. Measures necessary to maintain the mechanical integrity of Clow Model GMZ check valves installed in OP-III were not taken. This resulted in undetected damage to and eventual failure of critical internal valve components.
True
False
6. Operating procedures for the start-up of the PGC system did not specifically instruct operators to re-verify the position of pneumatically-assisted check valves before restarting the compressor following unexpected automatic compressor trips; consequently, operators did not re-verify the position of the valve that failed. Re-verification might have enabled operators to observe possible indications of the fifth stage suction check valve’s imminent failure on June 22, 1997.
True
False
 

The JCAIT identified the following factors that contributed to the accident:
7. The lack of clear and immediate indications in the control room of a hydrocarbon leak contributed to the severity of the accident by significantly delaying operator action to shut down and depressurize the PGC system.
True
False
8. Inadequate communications practices during the accident contributed to its severity by hindering the timely flow of information to control room operators.
True
False
9. Figure E-7: Photograph of blast damage to buildings and structures in the vicinity of the explosion. Note the buckled metal walls of the storage building in the center and the panels missing from the cooling tower on the right. These buildings were located approximately 500 feet north of the blast center.
True
False
10. Figures E-9 and E-10: Photographs of two views of the disassembled subject 36″ Clow check valve. The pneumatic actuator assembly can be seen in both views. In the lower photograph, the hole directly below the 12-inch ruler formerly contained the valve’s drive shaft. This is where the shaft blow-out and flammable gas release occurred.
True
False

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