Three Chinese engineers hired by Shandong Electric Power Construction Corp. have been arrested in connection with the collapse last year of a 330-foot chimney under construction at a 1,200-MW coal-fired power plant in India’s eastern state of Chhattisgarh, killing 41.

Around 300 workers were reportedly working on the chimney in Korba district when it collapsed on Sept. 23 last year, 135 miles northeast of the state’s capital, Raipur. The project was part of an expansion of an aluminum smelter by construction company Gannon Dunkerley & Co. (GDCL) for Bharat Aluminum Co. (BALCO), a company owned by Vedanta Resources and the Indian government.

It is still unclear what caused the accident.

The arrests on Monday were based on findings by the Raipur branch of the National Institute of Technology (NIT), an engineering and technology college, which had been asked to investigate the cause of the accident. According to the Times of India, NIT claimed that the collapse was caused by “sub-standard construction material, lack of supervision, inadequate curing time and poor soil testing.”

The investigation also reportedly found that the project did not meet Indian Standard Code and suffered faulty technical design, among other lapses.

The arrests now bring the total number of persons under custody for the accident to seven. In November, the police arrested three top officials of the Vendanta Resources of London, including the company’s vice president and power project manager, an assistant general manager, and a trainee engineer. Earlier, the police had arrested a GDCL project manager engaged in construction of two industrial chimneys for the plant.

Sources: POWERnews, Times of India