Li Lijuan, 49, a former employee of Hangzhou Yusei Machinery set fire to a company warehouse on January 1 afternoon when 193 workers were on duty.
Three firefighters died in the rescue and another three were injured. It took nearly 400 firefighters about nine hours to bring the fire under control.
The arson caused direct losses of more than 60 million yuan ( USD 9.76 million), Hangzhou Intermediate People's Court in east China's Zhejiang Province ruled.