Russian environmental supervisory body Rostechnadzor has found that technical and operational failures were to blame for the collapse of a Nornickel diesel tank in May, rather than melting permafrost.
The tank collapse near Norilsk in northern Russia, on 29 May 2020, spilt more than 20,000 tonnes of fuel into the surrounding land and waterways, and the clean-up is still ongoing. Nornickel, whose subsidiary Norilsk-Taymyr Energy Company (NTEC) originally blamed melting permafrost, later admitted that poor construction had been a factor in the collapse, as the tank supports did not rest on the bedrock, but said that this had been exacerbated by melting permafrost. However, operating director Sergei Dyachenko claimed that following repairs in 2018, state inspections had passed the tank as safe.
Rostechnadzor has now published its preliminary findings into the accident, which found errors in tank construction and operational violations. It also found that the piles did not rest on rock, leading to an uneven distribution of load, but its investigators found no evidence of melting permafrost. Further, it found that state supervision of the tank ended in 2015 when it was taken out of service for repair in 2015, and that the regulatory authorities were not notified when it came back into service in 2019, and that Nornickel did not observe industrial safety requirements, including failing to carry out periodic technical and geotechnical surveys of the foundation, and failing to implement sufficient maintenance procedures on the tank.
‘In addition, after major repairs, during the hydraulic test, miscalculations were made, and, as a result, almost half of the total number of piles in the base of the tank received loads exceeding the bearing capacity,’ Rostechnadzor says in a statement.
The investigators also found that the tank developers did not fully analyse the compliance of the tank design with the as-built documentation for the pile foundations, or the documents certifying the quality of the structures and materials. Additionally, filling levels of the tank were increased by a quarter.
Nornickel has yet to comment on the findings. The investigating commission will hold a final meeting on 13 November 2020 to formally approve and sign the conclusions of the report.