The blast blew the top off a distillation tower that was approximately 145 feet tall and propelled tons of fiery debris in the air, raining down onto adjacent industrial facilities and narrowly missing nearby hazardous chemical tanks. The investigators' report said that plant operators were unaware that a dangerous chemical reaction was taking place inside the tower.
The process involved mononitrotoluene or MNT, a chemical related to TNT that can be explosive when exposed to high temperatures. Operators thought the process had been shut down weeks earlier, with all sources of heat removed. The valves used to shut off steam to the tower had deteriorated, and steam was leaking through the shut-off valves, heating the 1,200 gallons of MNT in the column to a critical temperature of over 450°F. A violent reaction was initiated as the material decomposed.
The tower exploded at 5:25 a.m. on Sunday, Oct. 13, 2002. Three plant employees were injured when glass windows shattered into the control room where they were working. The CSB report said the room was located too close to the MNT tower and was not reinforced to withstand blast pressure. A projectile from the explosion pierced an MNT storage tank some distance away, igniting a fire that burned for almost three hours. Other debris landed a few feet from a large cylinder of anhydrous ammonia without doing serious damage.
Area residents were directed to seek shelter in their homes, though the CSB learned at a public meeting later that this direction was not effectively communicated to them. Additionally, residents were not aware of the appropriate action to take while they sought shelter.
Board member Dr. Gerald Poje, chair of CSB's meeting to accept the investigator's report, said, "We are very fortunate that shrapnel from the tower did not cause a greater chemical release or a more damaging fire. This accident underscores once again the vital importance of properly managing dangerous reactive chemicals and the processes that use them."
He added that when the board voted last September to recommend that EPA and OSHA strengthen their regulations to reduce such dangers, members "hardly imagined such a dramatic demonstration of the need would occur just three weeks later."
Stephen J. Wallace, CSB lead investigator, noted the First Chemical plant did not have adequate systems for evaluating the hazards of processing MNT. He added, "First Chemical had learned of the instability of MNT during a safety analysis of a similar unit in 1996 but had not applied those safety lessons to the process that exploded a root cause of the blast."
Wallace also noted that the facility did not have an effective program for maintaining critical process equipment like the steam shut-off valves.
The report further found that the plant did not have adequate systems to warn operations personnel of unexpected temperature increases, one sign of a runaway chemical reaction. Nor were there systems to automatically bring the process back to a safe state. Column C 501 the tower used to distill MNT had no temperature alarms, no automatic shutoff of the heating source, and no adequate system to relieve pressure build-up and mitigate the effects of an explosion.
The report proposes several recommendations be directed to the Pascagoula facility and the DuPont Corp., which purchased First Chemical after the accident. CSB recommends the facility:
- Improve its hazard analyses
- Conduct process safety audits
- Install appropriate warning devices
The report recommends DuPont Corp. track the facility's progress. In addition, the report recommends Jackson County improve its community notification system for such emergencies.
The CSB also recommended that the American Chemistry Council (ACC) and the Synthetic Organic Chemical Manufacturers Association (SOCMA) improve their industry management code, known as Responsible Care, under which member companies agree to comply with various safety policies.
The report found that First Chemical Corp., a SOCMA member at the time of the accident, had earlier asserted to SOCMA that it was following those agreed-upon safety policies including performing hazard analyses even though no evaluation had been done for the MNT unit.