Oslo-Yara International ASA said Jan. 14 that the five-person team investigating the explosion at one of the two NPK plants in Porsgrunn has concluded that the serious incident that occurred Dec. 3 was caused by the decomposition of liquid in the NP buffer tank. “High temperature and low pH in the tank resulted in gas formation and overpressure,” said Plant Manager Jan Petter Fossum. “Following the explosion, fire erupted in electrical cables and a mixture of oil and wax from an adjacent tank.” The plant had been shut down three days before the incident and steam was added to keep the tank above crystallization temperature. But a leaking valve led to gradual increase in temperature, followed by water evaporation and finally a chemical reaction with heavy gas formation and consequent rupture of the tank. “Yara management takes this very seriously and nominated a team of specialists to investigate the accident,” said Fossum. “The investigation found weaknesses in the technical design as well as in the operating procedures. The plant has now been modified, taking full account of the recommendations from the investigation and was started up again 10 January.” The main reason for the accident was the unawareness of the risks involved when the plant was shut down. This was not identified in Yara’s technical standards, nor ever experienced in the 40 years of operation of the plant. All persons in the facility at the time of the accident were evacuated before the explosion. Five persons received medical attention, but only minor injuries occurred. The accident resulted in a loss of 110,000 mt of complex fertilizers (NPK) and 40,000 mt of calcium nitrate production capacity. The property damage is estimated to NOK 50 million for repair of the building and replacement of the tank and cabling.
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