Pasadena, Texas Explosion Case Analysis

Case Description

On October 23, 1989, a massive explosion took place at the Phillips Petroleum Houston Chemical Complex in Pasadena, Texas. This 800-acre chemical facility produced plastics that were used worldwide. It was a multi-level structure with the highest tower being 14 stories. The outer part of the facility was filled with heavy concrete and steel reinforced buildings.

The day before the explosion, maintenance work had begun to remove three out of the six settling legs on a reactor. The settling leg part of the plug got stuck in the pipework. A member of the team went to the control room to seek help. Shortly afterward, 85,000 pounds of a flammable mixture containing ethylene, isobutene, hexane, and hydrogen, was unintentionally released in the product takeoff system. Approximately minutes later, a flammable vapor cloud ignited. The large gas cloud was immediately formed because the system was under high pressure and temperature. The gas mixture exploded with a force of 2.4 tons of TNT and was equivalent to an earthquake registering a 3.5 on the Richter scale. Additionally, there were more explosions after the first large one due to numerous pipes and tubes that had gases trapped in them. An alarm was sounded, but the explosion occurred 60 to 90 seconds after, giving workers little time to follow the evacuation plan and just running for their lives in any direction away from the explosion.

The exact explosion source may never be known, but possible ones were located all over the plant, including ventilation fans, electrical switches, and gas burn-off flames. As a result, $715 million was lost, 23 individuals died, and another 314 injured. Metal and concrete debris were found as far as six miles away from the explosion site.

Case Investigation

Failures in engineering systems occur due to specific causes, whether foreseen or not. Many of the causes are related to specific procedures. The disaster analysis revealed that many safety procedures were not followed, particularly, the product take off valve was removed, the single-block (DEMCO) valve was open, and the lockout device was detached. These actions caused the release of the flammable mixtures, and thus the explosion. There was either a failure in the line or in the valve that carried ethylene and/or isobutane. The line was ten inches in diameter and carrying approximately 700 pounds per square inch pressure.

The polyethylene products usually settle in the settling leg and are removed from the product takeoff valve. Sometimes, the settling plug gets stuck because of a building of products, but it is fixed by maintenance. The normal and safe procedure involves closing the DEMCO valve, removing the airlines, and locking the valve. The buildings were equipped with sprinkler systems; however, the force of the explosion cut off the water supplies for the system.

At the conclusion of the investigation on April 19, 1990, OSHA issued 566 willful and nine serious violations against the Phillips Petroleum with a proposed penalty of $5,666,200. OSHA found that no process hazard analysis had been completed in the plant and as a result, many serious safety violations were overlooked. No arrangement was made for the development, implementation, and enforcement of the effective permit systems and no gas detection was located in the region of the reactors. Furthermore, the proximity of control rooms to the hazardous operation, poor separation amongst buildings, and packed process equipment contributed to the severity of the explosion. It is unidentified if the failure was triggered by a mechanical or human error. Regardless, the high-pressure line carrying flammable products created the big, explosive cloud within seconds.

Recommendations

The failures of the Phillips disaster were due to an unenforced permit to work, maintenance procedures, plant layout, warning signs, and emergency response. An effective permit to work for company employees and contractors was not enforced. That action was extremely unsafe, especially since the plant contained a lot of hazardous materials and precautions that had to be taken. The audible level of the emergency alarm was not loud enough. It was likely that individuals in certain parts of the plant were unable to hear the siren that resulted in more deaths than if all workers heard it right away [4]. It is recommended that each site include a backup emergency operations center in its emergency plan.

The accident investigation established that a single isolating ball valve was actually open at the time of the release. The air hoses to the valve were cross-connected so that the air supply that should have closed the valve actually opened it. The air hoses to the valve were supposed to be disconnected prior to maintenance work, but this task was never carried out. The site held a large inventory of flammable material under high pressure, yet it had no fixed gas detection system. Rather than relying on a single-block valve, a double block and bleeding valve arrangement or a blind flange after the single-block valve should have been used.

The location of the control room, separation distances between plant and escape routes were all at fault. Ventilation intakes of building close to the process plant were not arranged to prevent intake of gas in the event of a release. The plant should have cautiously been built further away from other hazardous buildings. There was no dedicated fire water system. Instead, firewater was drawn off from the process water system. However, the system got severely damaged by the explosion, resulting in loss of water pressure so they failed during the fire attacks. There were another three standby diesel pumps units, but one was under maintenance and another ran out of fuel.