The probable technical cause of the accident in the yard of the Talvivaara Sotkamo plant, which resulted in the death of an employee, was a reaction caused by limestone slurry pumped into a pre-neutralisation storage tank. As a result, carbon dioxide and hydrogen sulphide were released into the yard. The accident investigation conducted by the Finnish Safety and Chemicals Agency (Tukes) detected several safety deficiencies.
A Talvivaara Sotkamo employee died in the yard of the plant during a sampling round on 15 March 2012. The cause of death was exposure to a high concentration of hydrogen sulphide. According to the investigation findings, a valve on the limestone slurry line had been left open in the plant hall on the morning of the accident. The slurry that had spilled onto the floor from the open valve ended up in the floor drain, from where the slurry was pumped by an auto-start pump into the pre-neutralisation storage tank located outside. The reaction of the storage tank solution and limestone slurry produced high levels of carbon dioxide which, while discharging from the tank, also caused a discharge of hydrogen sulphide from the gas space of the tank. In the windless conditions, the hydrogen sulphide levels remained high and the employee, who had been performing a sampling round without a respirator or gas meter, died. The pumping of limestone slurry from the floor drain into the storage tank had not been identified as a risk factor in risk assessments.
The investigation team also noted other emission sources, as a result of which employees had recorded raised hydrogen sulphide levels in the area on previous occasions. Moreover, deficiencies were found in the maintenance and planning of the process equipment. The organisation’s handling and notification of hazardous situations were inadequate. Several deficiencies detected during the investigation have already undergone corrective measures.
Tukes ordered Talvivaara Sotkamo Ltd to take corrective measures before restarting operations after a maintenance shutdown in April, shortly after the accident.
The investigation team recommends the following measures to prevent similar accidents:
Process safety risks and their management
- The significance of process safety must be understood as it is a key issue in accident prevention and continuity of production.
- The risks of a new technology must be identified in advance, using the best possible expertise and systematic risk assessment.
- Process planners and the operation and maintenance personnel must be included in risk assessment.
- Maintenance of safety-critical equipment must be included in preventive maintenance.
- The safety significance of operational disturbances must be assessed and efforts must be made to investigate such disturbances.
Safety responsibilities and flow of information
- The management’s perspective on safety issues must be clear. In addition to providing guidelines, it is important to listen to employees and set an example. The management must take part in the handling of issues that are significant in terms of safety.
- Responsibility for safety must not be separated from the operational organisation. Process safety development requires knowledge of the production technology and the risks related to hazardous chemicals.
- The operator must have a clear means of providing information in the event of hazardous situations so that information about the hazard is disseminated quickly and reliably to all those in the area at the time.
- Responsibility for decision-making about process shutdowns due to hazardous conditions must be assigned and guidelines should be drawn up. At major accident hazard installations, the primary nature of safety in decision-making must be emphasised.
- The processing of safety observations must have a follow-up procedure that motivates the employees to make such observations.
Tukes supervises large-scale industrial handling and storage of hazardous chemicals and mine safety in Finland, among other supervisory duties and tasks.
Investigation report abstract (pdf, 80 kb)
Päivi Rantakoski, Director, Plant Surveillance Group, tel. +358 10 6052 359
Heikki Penttinen, Senior Inspector, Chairman of the Investigation Team, tel. +358 10 6052 413, firstname.lastname@example.org
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