Park Soon-kwan, the CEO of the battery maker Aricell, had been charged under the country's industrial safety law, which subjects senior executives to prison terms of more than one year when found guilty in the event of fatal accidents.

Park's son who is a senior company executive was also sentenced to 15 years in prison, a public affairs judge at the Suwon District Court said by telephone.

Park, the chief executive, failed to ensure safety measures were in place and that the fire was "not an unpredictable" accident under the conditions the company was operating in, the judge cited the court's ruling as saying.

The lawyers for the Parks could not be immediately reached for comment.

South Korean media said the longest sentence previously given under the law was two years.

Investigators have said the company operated without proper safety protocol or training for its workers, many of whom were hired on a temporary basis, and failed to address signs of dangerous quality defects in products in a rush to meet supply deadlines.

Park has previously apologised but denied the allegations of safety lapses at the factory, which is located in the city of Hwaseong south of Seoul.

South Korea President Lee Jae Myung has said not enough was being done to protect workers from being killed or injured on the job despite introducing the law aimed at holding the employer accountable with criminal prosecution in 2022.

Last year, 589 people died in job-related accidents, according to government data.