At 8:14 pm, a process vessel containing 350 kg of hydroxylamine (HA) exploded during distillation phase of the first commercial batch to be processed at a new chemical facility.
HA (chemical formula NH2OH) is usually handled as an aqueous solution (up to 50%) or as salts in the semiconductor manufacturing industry, but also in the manufacture of nylon, inks, paints, pharmaceuticals, agrochemicals, and photographic developers. The concentrated base (over 80 %) is susceptible to explosive decomposition.
The production process involved four steps : reaction, filtration, 30-h distillation, and ion exchange purification. The distillation started on the 15/02; it was shut down in the evening of the next day for maintenance when it was determined that water had leaked into the charge tank through broken tubes in the heater column. The necessary repairs were made by the 18/02 afternoon, and the distillation process was restarted. On Friday, February 19, a 38 mm feed line to the heater column was replaced with a 50 mm line, which delayed start-up until later in the morning. The concentration of liquid solution in the charge tank steadily increased throughout the day. Between 7:00 and 7:15 pm, the concentration of liquid solution in the charge tank was recorded as 86 wt-percent HA, reaching dangerous concentrations. According to their procedures, the personnel called the manufacturing and engineering supervisor and tried to wash away the formation of explosive crystals using a 30% HA solution when the decomposition explosion occurred, triggered either by heat of friction in the process.
Four employees and a manager of an adjacent business were killed. Two employees survived the blast with moderate-to-serious injuries. Four people in nearby buildings were injured. Six firefighters and two security guards suffered minor injuries during emergency response efforts.
The production facility was extensively damaged and the explosion also caused significant damage to 10 other buildings in the Industrial Park and shattered windows in several nearby homes. Estimated property damage in was $4 million.
A crater approximately 1,8 m wide, 8 m long, and 40 cm deep was found in the concrete floor directly below where the charge tank had been located, thus indicating an explosive force equivalent to 363 kg of (TNT).
The US CSB conducted an investigation and found out that due to inadequate collection and analysis of process safety information, the operator’s process safety management systems were insufficient to properly address the hazards inherent in its HA manufacturing process and to determine whether these hazards presented substantial risks. Basic process safety and chemical engineering practices–such as process design reviews, hazard analyses, corrective actions, and reviews by appropriate technical experts–were not adequately implemented.
Furthermore, the existing system of siting approval by local authorities allowed a highly hazardous facility to be inappropriately located in a light industrial park. A similar HA explosion occurred 16 month later in Japan (ARIA 17922).