1994 EPA Terra Chemical Accident Investigation Report

The Incident:
At approximately 0606 hours on December 13, 1994, an explosion occurred in an ammonium nitrate plant.

The Consequences:
Four persons were killed as a direct result of the explosion, and 18 were injured and required hospitalization. The explosion resulted in the release of approximately 5,700 tons of anhydrous ammonia to the air and secondary containment, approximately 25,000 gallons of nitric acid to the ground and lined chemical ditches and sumps, and liquid ammonium nitrate solution into secondary containment. Off site ammonia releases continued for approximately six days following the explosion. Chemicals released as a result of the explosion
have resulted in contamination of the groundwater under the facility.

The Causes:
The investigation team concluded that the explosion resulted from a lack of written, safe operation procedures at the Terra Port Neal ammonium nitrate plant. The lack of safe operating procedures resulted in conditions in the plant that were necessary for the explosion to occur. The significant conditions that caused the explosion were:
1. Strongly acidic conditions in the neutralizer and rundown tank;
2. Prolonged application of 200 psig steam to the neutralizer nitric acid spargers;
3. The creation of bubbles and low density zones in the neutralizer;
4. Lack of flow in the neutralizer and rundown tank;
5. The presence of chlorides in the neutralizer and rundown tank; and
6. Lack of monitoring of the ammonium nitrate plant after the plant was shut down with the process vessels charged.

No process hazards analysis had been completed on the ammonium nitrate plant, and interviews with Terra personnel indicated that they were not aware of many of the hazards of ammonium nitrate. The two conditions identified by Terra personnel as concerns were oil contamination of ammonium nitrate and excess heating of ammonium nitrate. No one engineer was assigned responsibility for overseeing operation of the ammonium nitrate plant and reviewing operating procedures in the plant or procedures that might impact the ammonium nitrate plant.

Information gathered during the investigation indicated that overall communications and working relationships were poor between operations and engineering personnel. In the months preceding the explosion, the ammonium nitrate plant was converted to a distributed control system, (DCS). The engineers involved in hooking up the DCS communicated very little with most operators, and some of the operators felt very uncomfortable with the new system once it was up and running. They stated that they had received very little training on operation of the AN plant with the DCS system.

In the days and weeks just prior to the explosion, the equipment failures and maintenance problems were chronic. The pH probe in the neutralizer rundown line appeared to be malfunctioning and there were no spares in stock. Both the ammonium nitrate product pumps which transports ammonium nitrate to storage were leaking or otherwise malfunctioning. There were numerous problems in the nitric acid plant, and maintenance was having a hard time keeping up with the repair requests.

From interviews with Terra employees, no one believed that oil contamination could have gotten into the ammonium nitrate plant and sensitized the ammonium nitrate, even though large amounts of oil had been lost upstream in the ammonia plant. Terra did not monitor ammonium nitrate feedstreams for contaminant presence. Chloride contamination of the nitric acid had not been analyzed since 1980; although the nitric acid plant is a logical source of chloride contamination. Terra did not periodically monitor feed streams into the ammonium nitrate unit for contamination.

The Lessons Learned:
The investigation team developed recommendations to reduce the likelihood of future similar occurrences in ammonium nitrate plants.The detailed information that led to these recommendations is included in the report. The recommendations are that facility management, with the involvement of engineers, operators and maintenance personnel:

1. Conduct a thorough, formal process hazard analysis (PHA) of the ammonium nitrate process according to industry guidelines and practices. Current process safety information including piping and instrumentation diagrams, plant drawings, process chemistry, chemical hazard information and expertise in the technique used are necessary to conduct this evaluation. The findings and recommendations generated by the PHA should be promptly addressed and resolved and should address modifications, safeguards or controls to eliminate, reduce or manage chemical and process hazards.

2. Establish safe operating parameters for all activities in the ammonium nitrate process based on the PHA. Parameters for this plant should at least include pH, temperature, and acceptable contaminant levels.

3. Develop, implement and keep up-to-date written safe operating procedures for all operations and activities, including normal startups, normal and emergency shutdowns or idling and routine operation of the ammonium nitrate unit. These written procedures should be based on the PHA and require that critical process parameters identified above be monitored and specify actions to be taken when parameters deviate from acceptable ranges.

4. Develop a management of change process for all changes in process equipment, procedures and operating parameters or ranges in the ammonium nitrate unit. A pre-startup safety review should be conducted prior to operation using changed equipment, procedures or parameters.

5. Develop a program to maintain the on-going mechanical integrity of the ammonium nitrate unit. Facility management should consider use of predictive failure analyses and aggressive preventive maintenance systems as part of their mechanical integrity program.

6. Develop and implement training programs on operating and maintenance procedures for operators and maintenance personnel involved in the ammonium nitrate unit.

7. Ensure that management, engineers, operators and maintenance personnel develop lines of communication to ensure that these recommendations are implemented and maintained. The investigation team further recommends that corporate management monitor facility performance in implementing these programs and conduct periodic audits to ensure program effectiveness.

8. Share information on the hazards of the substances handled, the prevention measures in-place or planned to prevent accidental releases and the emergency response measures to be taken for the ammonium nitrate unit with the State Emergency Response Commission (SERC), Local Emergency Planning Committee (LEPC), first responders, and the public surrounding the facility.

These recommendations reflect accidental release prevention requirements contained in the OSHA Process Safety Management (PSM) regulations and in current industry guidelines and practices for prevention of chemical accidents and emergencies. EPA also intends to build on the OSHA PSM requirements and is currently considering how best to capture these recommended practices in the Risk Management Programs for Chemical Accidental Release Prevention rule to promulgated in March 1996.

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