Silver Eagle Refinery explosion: Surveillance video released
19 November 2009
The CSB has released a dramatic surveillance video that underscores the seriousness of the November 4th accident at the Silver Eagle refinery and its potential to cause even more harm had the circumstances been slightly different.
Silver Eagle Refinery explosion: Surveillance video released
Investigators arrived in Woods Cross on the evening of November 4th and have been actively investigating there ever since.
Based on preliminary findings about the conditions in the refinery and in consultation with state and federal OSHA officials, the refinery was shut down temporarily to correct potentially serious safety problems that had come to light. Silver Eagle management responded rapidly and positively to this suggestion.
This decision will obviously cost Silver Eagle some revenue in the short run, but it is the right action to protect the long term interests of the company, its workforce, and the community which gives it license to operate.
At 9:11 am on November 4th, 2009, the refinery experienced a catastrophic failure of a 10-inch pipe off the bottom of a reactor in the Mobil Distillate Dewaxing Unit. The force of the rupture has caused a section of the pipe to wrap itself around a steel support.
At the time, the unit was undergoing a special operation to regenerate the catalyst. This operation involved circulating high-pressure hydrogen gas inside the piping, at a temperature of 800 degrees Fahrenheit and a pressure of 630 pounds per square inch, or psi.
The refinery operated a surveillance video camera, which was pointed directly at the unit where the failure occurred.
The video shows a truck passing directly past the unit a few seconds before the blast. There’s a release and almost instantaneously the gas ignites in large fireball, which is estimated to be 100 feet high. The hydrogen contents of the reactor continue to be released through the pipe, which is now open and pointing directly east toward the housing subdivision next to the refinery.The fire burns for a number of minutes while responders arrive.
The video in slow motion shows briefly a white cloud, which is the hydrogen escaping the ruptured pipe, and then the very rapid ignition. An open-flame furnace near the pipe was a likely ignition source.
There were four workers near the process unit at the time of the explosion. They were blown to the ground but were not seriously injured. Another worker had been taking readings next to the pipe that failed just 1-2 minutes before the release.
In addition there are commuter rail lines that frequently carry passengers on routes that are immediately adjacent to the refinery. Fortunately there was no train present during the blast.
Clearly this explosion had the potential to cause deaths or serious injuries had it occurred even a few moments earlier or later in the day.
The CSB investigation to date indicates that the Silver Eagle refinery was operating with a mechanical integrity program that had serious deficiencies.
The goal of a mechanical integrity program is to ensure that process equipment is fabricated from the proper materials of construction and is properly installed, monitored, and maintained to prevent failures and accidental releases.
Because of the hazardous nature of the materials in a refinery – and the high temperatures and pressures that are frequently used – a robust mechanical integrity program is essential to safe refinery operations. It is also a regulatory requirement for refineries and chemical plants under the OSHA Process Safety Management standard, enacted in 1992.
So it was a very positive development that the refinery agreed to a voluntary shut down to try to address these important issues.
Prior to May 2009, mechanical integrity inspections -- including thickness monitoring of pipes and vessels at the refinery -- were completed by a contract company hired by Silver Eagle. The refinery later replaced this company with a second outside inspection company, which remains active at the site.
Witness evidence indicates that various thickness readings taken by the prior contractor are of questionable validity. The refinery is now in the process of revalidating those readings.
Specifically, witnesses report that in 2007 the prior contractor documented the thickness of the pipe that failed on November 4th to be nearly one-half-inch. But measurements following the accident show that the pipe thickness was only one-eighth of an inch. A likely explanation is that the 2007 thickness measurement was inaccurate. This and other recent measurements call into serious question the pipe thickness readings obtained by the prior contractor.
The evidence further indicates that a significant percentage of the pipes and vessels have no documented thickness readings at all.
Refinery managers have now acknowledged to CSB investigators that minimum thickness values for piping and equipment throughout the refinery have been miscalculated. These are the thicknesses at which the equipment must be retired from service due to the potential for failure. Specifically, the refinery has been using what are known as ultimate tensile strength values, rather than the industry-recommended stress tables.
The result of these miscalculations is that these minimum thickness values may be 3-4 times too low; some of the minimum thickness values may therefore be too low for the safe operation of the equipment. In other words, there is the potential that multiple pieces of equipment have been operating at below the required thickness for safety – and creating the potential for other serious accidents.
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