DataBasics

An explosion on October 13, 2002, propelled large fragments of debris offsite, some landed near crude oil storage tanks. Three people were injured, but fortunately, no fatalities occurred.

Steam leaking through manual block valves heated crude Mononitrotoluene (MNT) inside a vacuum distillation column, which was shut down and thought to be isolated. The column contained about 1,200 gallons (4.5 m³) of MNT, an energetic and reactive material which can decompose violently when heated. The material decomposed over several days, resulting in a runaway reaction and explosion. Debris from the explosion caused a storage tank fire and numerous smaller fires both onsite and offsite.

Low product demand delayed start up, but the MNT column was kept in total reflux, until the plant-wide shutdown was completed. A fire elsewhere caused operators to isolate heat sources to all columns including the MNT column by closing manual steam block valves and control valves. However, the valves on the MNT column were leaking through, and the temperature of the material in the MNT column did not drop but continued to rise, exceeding 450°F (232 °C) in about 8 days. There was no alarm, and there is no evidence that Operations personnel actively monitored the column temperature control system.

© AIChE | Sponsored by ioMosaic (www.iomosaic.com)

The rupture of a 145-foot-tall distillation column (C-501) used to refine mononitrotoluene (MNT) caused the October 13, 2002, explosion and fire at the First Chemical Corporation (FCC) facility in Pascagoula, Mississippi. The column was thought to be isolated and in standby mode at the time of the explosion (approximately 5:25 am) though it contained a significant amount of MNT.

Debris from the explosion, including metal fragments and packing from the column, was scattered throughout the facility and propelled offsite. One large fragment of the distillation column punctured a nearby para-MNT storage tank and ignited its contents, which burned for almost 3 hours. A 6-ton column segment was hurled 1,100 feet and landed near a crude oil storage tank at a refinery across the highway. Flying glass injured three FCC employees, who were in the unit control room at the time of the explosion. All three employees received first-aid, and one required additional medical treatment.

The FCC fire brigade fought the onsite fires, including the large para-MNT storage tank fire and numerous fires initiated by burning material on ejected column packing. Local community emergency responders provided backup and firefighting support for numerous small fires outside the facility. The sheriff’s department provided traffic control. FCC personnel, the U.S. Environmental Protection Agency (EPA), and the U.S. Coast Guard monitored the air around the facility.

KEY ISSUES:
• EVALUATION OF REACTIVE HAZARDS
• APPLYING LESSONS LEARNED
• LAYERS OF PROTECTION
• WORK PRACTICES
• FACILITY SITING
• COMMUNITY NOTIFICATION

ROOT CAUSES:
1. The FCC Pascagoula facility did not have an adequate system for evaluating the hazards of processing mononitrotoluene (MNT) in its continuous process and did not apply lessons learned from hazard analyses conducted on similar processes in the plant.
2. FCC did not have a system to ensure that the #1 MNT column (C-501) was equipped with sufficient layers of protection to prevent a catastrophic release.
3. The Pascagoula facility had no effective system for ensuring consistent work practices when isolating equipment.
4. FCC did not have an adequate program to prevent leakage from isolation valves in the steam line connected to the #1 MNT column (C-501).

Image Credit: CSB