An investigation report has been released about the fire that broke out in Nanjing's Xiyuan community on Feb 23, which resulted in the loss of 15 lives and 44 injuries, according to Jiangsu Fire and Rescue on Wednesday afternoon.

The investigation, led by the provincial government, concluded that the fire was triggered by thermal runaway in an illegally modified electric bicycle's oversized lithium-ion battery.

The report stated that the battery, parked in a building's open-air space, overheated and caught fire. The flames quickly spread to nearby bicycles and flammable materials stored illegally in the courtyard.

The resulting chimney effect allowed toxic smoke and intense heat to penetrate residential units, leading to casualties.

The investigation also revealed that the bike owner had illegally modified the vehicle and purchased an oversized battery from unregulated online sources. The manufacturer and retailer of the electric bicycle were found to have violated national safety standards.

Contributing factors included poor maintenance of firefighting equipment and the property management company's failure to quickly detect the fire, evacuate residents or take effective emergency measures.

As a result of the investigation, 10 individuals, including the bike owner, unlicensed battery sellers and the property management company's executives, have been placed under criminal investigation.

Seven companies involved in electric bicycle production, sales and property management face penalties from regulatory authorities.

Liu Boqian contributed to this story.