Miami Township, OH, Aug. 24, 2004 - The U.S. Chemical Safety and Hazard Investigation Board (CSB) today issued a Case Study examining the causes of a Sept. 21, 2003 nitric oxide leak and explosion which occurred at a high-technology biochemical products plant in Miami Township, Ohio, near Dayton.
The accident occurred at the Sigma-Aldrich Corporation-owned Isotec facility about 12 miles south of Dayton, Ohio and destroyed a 300-foot tall nitric oxide (NO) distillation column, installed below ground. The explosion happened as company operators worked to shut down the system after a nitric oxide leak, which occurred about 7:30 a.m. A large steel panel from a blast containment structure was blown off, striking a 52,000-pound carbon monoxide (CO) storage vessel. Leaking CO gas ignited and burned for more than an hour. Authorities ordered a one-mile radius evacuation out of concern that the carbon monoxide vessel could blow up.
The blast also destroyed other nearby plant structures, and blew out windows in the main office building about 140 feet from the explosion. Glass shards lacerated the hand of an Isotec employee. No other people were injured. Small chunks of concrete and metal shards were propelled as far as 1,000 feet and fell on adjacent property. Three houses north of the facility were struck by debris causing minor damage.
The company distilled nitric oxide liquid to separate and extract nitric oxide molecules that contain stable isotopes of nitrogen. Stable isotopes are non-radioactive atoms. These isotopes are used in medical and scientific applications, including magnetic resonance imaging (MRI) and drug screening chemicals.
The CSB incident analysis noted that nitric oxide is a toxic, nonflammable gas at room temperature. In its liquid form (chilled below -241 °F) it may be susceptible to detonation if it is exposed to any kind of shock force or concussion. The extensive destruction of the distillation system prevented identifying the exact cause of the nitric oxide leak and source of the concussion that caused the explosion.
The study concluded that a hole developed somewhere along the more than 2200 feet of pipe in the distillation column, releasing nitric oxide liquid into the vacuum jacket, a high-efficiency insulating container similar to a thermos bottle. The study cited two potential sources of the concussion that caused the nitric oxide to detonate: pressure that had built up in the vacuum jacket might have crushed a heater at the bottom of the column; or rapid boiling of the nitric oxide liquid flowing at very high velocity through the damaged pipe may have caused the pipe to vibrate.
CSB lead investigator John Vorderbrueggen pointed to several findings related to the violent explosion. Primary among these was a determination that the company's process hazard analysis was incomplete. The CSB found that Isotec managers knew about the explosive properties of nitric oxide, but did not thoroughly evaluate their system to minimize the possibility of a failure and to properly design appropriate explosion shields.
The study found that Isotec had experienced two earlier incidents in similar distillation columns in 1995 and 1998. Both involved piping failures that allowed nitric oxide to leak into the vacuum jacket. One involved a small explosion belowground. But the CSB determined that the company's investigations into these incidents were deficient in that they did not identify causes or establish appropriate corrective actions to prevent recurrence.
CSB Board Member John Bresland said, "The company had two previous incidents involving nitric oxide distillation system malfunctions at the Benner road facility. Both involved piping failures that released nitric oxide. One involved a small explosion. Our study found that these incidents were not reviewed adequately and did not result in appropriate corrective actions that might have prevented this larger explosion. The accident once again shows the importance of conducting thorough hazard studies so that every conceivable scenario, and actual events are considered." The report notes that the Isotec plant was once surrounded by farmland and that over the years, zoning changes did not adequately consider potential dangers at the plant.
The CSB study reported problems within the emergency planning and notification systems: the urgency of directives to evacuate varied among police; some residents were only told to evacuate by other neighbors; and some residents were unclear about where to go or what shelters were available.
Under "Lessons Learned," the CSB Case Study urges zoning, planning, and permitting authorities to evaluate public risks from pre-existing chemical facilities. It calls on governing authorities to use public awareness campaigns to inform communities of actions to take in an emergency, and to train emergency responders in evacuation plans. The study said the company should thoroughly investigate all incidents to identify causes and to implement correction actions.
The Chemical Safety Board is an independent federal agency charged with investigating industrial chemical accidents. The agency's board members are appointed by the president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in safety management systems.
The Board does not issue citations or fines but does make safety recommendations to plants, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA. Further information about the CSB is available at www.csb.gov. For more information, contact Sandy Gilmour (Public Affairs Contractor), 202-251-5496 (cell) or Kara Wenzel, 202-261-7642 and 202-577-8448 (cell).