The Chemical Safety Board investigated the incident, issuing their final report in 2013. The CSB found that stress corrosion cracking had occurred, unnoticed, in one of the crystal-growing autoclaves, leading to the catastrophic failure. They also found that NDK management had been warned multiple times over the years that the dangerous levels of hot sodium hydroxide inside the vessels would corrode the steel walls. However, NDK management insisted buildup of byproducts from the crystal-growing process would form a protective layer against the corrosion. Furthermore, during the factory's construction, the local government had been made aware that NDK's crystal-growing vessels were in violation of several state codes; when confronted, NDK had persuaded them to grant a special exception, and to hitherto allow them to conduct their own onsite inspections without outside interference. However, the vessel that ruptured had never been internally inspected to test the "byproduct buildup" theory, during its many years of service. After a smaller leak occurred in January 2007, NDK was warned about safety concerns again, this time by insurance investigators, who were ultimately ignored. Finally, the CSB determined the method for growing crystals used at NDK's Belvidere facility was prohibitively dangerous in the first place, pointing out such methods had been already abandoned by other crystal-growing facilities in favor of safer, lower-pressure and lower temperature processes.
The Chemical Safety Board investigated the incident, issuing their final report in 2013. The CSB found that stress corrosion cracking had occurred, unnoticed, in one of the crystal-growing autoclaves, leading to the catastrophic failure. They also found that NDK management had been warned multiple times over the years that the dangerous levels of hot sodium hydroxide inside the vessels would corrode the steel walls. However, NDK management insisted buildup of byproducts from the crystal-growing process would form a protective layer against the corrosion. Furthermore, during the factory's construction, the local government had been made aware that NDK's crystal-growing vessels were in violation of several state codes; when confronted, NDK had persuaded them to grant a special exception, and to hitherto allow them to conduct their own onsite inspections without outside interference. However, the vessel that ruptured had never been internally inspected to test the "byproduct buildup" theory, during its many years of service. After a smaller leak occurred in January 2007, NDK was warned about safety concerns again, this time by insurance investigators, who were ultimately ignored. Finally, the CSB determined the method for growing crystals used at NDK's Belvidere facility was prohibitively dangerous in the first place, pointing out such methods had been already abandoned by other crystal-growing facilities in favor of safer, lower-pressure and lower temperature processes.