SECTION 10: RECOMENDATIONS
The investigation team concluded that the conditions that caused the explosion existed primarily because of the lack of safe operating procedures in the Terra Port Neal ammonium nitrate unit. Most of the operating procedures that were used in the AN plant were not written. The investigation team further concluded that the lack of written safe operating procedures:
1. Would have made development and evaluation of training programs difficult.
2. Would have made enforcement of operating procedure use difficult.
3. Would have made evaluation of the operating procedures for deficiencies and improvements difficult.
Effective safe operating procedures can only be written and evaluated after completion of a comprehensive process hazard evaluation. The investigation team could find no evidence that Terra had conducted such an evaluation of the ammonium nitrate unit. This resulted in a low pH in the neutralizer after shutdown, the unknown presence of contaminants in the neutralizer, the lack of monitoring when the plant was shut down with the process vessels charged, the lack of flow in the neutralizer, the introduction of high temperatures through the nitric acid spargers, and the introduction of low density zones in the neutralizer.
Terra employees assumed that the DCS in the ammonium nitrate unit was not capable of operating in automatic or cascade mode because of a part shortage. A lack of clear communications between operations, maintenance and engineering caused the unit to operate without a pH probe from November 27 through the time of the explosion. pH probe suppliers indicated that a viable pH probe could have been provided in a few days if one had been ordered. Operators were performing maintenance tasks, because maintenance was busy in other parts of the facility.
To avoid the conditions described in Section 9 of this report that resulted in the explosion in the ammonium nitrate plant and to minimize the chance of a similar event occurring again, the investigation team developed the following recommendations for ammonium nitrate manufacturers.
1. The investigation team recommends that engineers and operators conduct a thorough process hazard evaluation of ammonium nitrate plants. This should include a thorough literature search to identify materials and conditions that increase the hazards of producing AN solutions. This evaluation should be conducted periodically to ensure that the most recent information is always available to the engineers and operators conducting process hazard evaluations. This activity also requires current piping and instrumentation diagrams, unit drawings, materials of construction, equipment histories, and safe operating procedures. Many of the hazards listed in this literature can be avoided through procedural changes. The engineer responsible for the AN unit should head the evaluation team.
2. The investigation team recommends that engineers and operators establish safe process operating parameters for the ammonium nitrate unit. Operating parameters should include at least pH, temperature and the presence of contaminants. This should include a program to monitor feed streams for the presence of known contaminants on a periodic basis as well as periodically reevaluating operating parameter ranges.
3. The investigation team recommends that engineers and operators develop written, safe operating procedures for the ammonium nitrate unit. Procedures should be developed for activities conducted in the AN plant in all modes of operation, including periods when the unit is shut down and the vessels are charged. These procedures should require that process parameters be monitored and should specify actions to be taken when parameter values deviate from acceptable ranges. Management roles in this process include ensuring that these procedures are used and that procedures are appropriate for conducting tasks safely.
4. The investigation team recommends that engineers and operators complete a management of change procedure for all operating parameter range changes. This should include approval to operate the unit outside of approved parameter ranges by the engineer responsible for the AN unit, and documentation of these activities. The engineer responsible for the AN unit should be included in all changes in the facility that could change feed streams or conditions in the AN unit.
5. The investigation team recommends that maintenance, operations and engineering personnel develop a maintenance program that anticipates problems in the AN unit. This program should include predictive failure analyses and an aggressive preventive maintenance program. The maintenance program should be periodically evaluated by this group by at least utilizing maintenance records and equipment histories.
6. The investigation team recommends that engineers, operators, and maintenance personnel develop and deliver training programs that include complete, written safe operating procedures. The training programs should contain specific performance and knowledge goals for participants and the procedures that will be utilized to evaluate participant competence.
7. The investigation team recommends that plant management ensure that engineers, operators, and maintenance supervisors and managers develop lines of communication to ensure that these recommendations are implemented and maintained. Facility management should be responsible for conducting periodic audits of these programs to ensure that they are adequate. The investigation team further recommends that corporate managers conduct periodic audits of facilities to ensure that these programs are utilized and that communication between corporate facilities supports these programs at a corporate level.