LANZHOU, Nov. 24 -- Fifteen people have been punished after they were found to be responsible for a gas explosion at a dormitory in Lanzhou University in the northwest province of Gansu in July, the local work safety watchdog said Tuesday.

The blast occurred at 7:32 a.m. on July 20 at Lanzhou University in Lanzhou, capital of Gansu. In addition to the 15 fatalities, 31 were injured.

The blast was likely caused by a gas leak from damaged pipes in an adjacent building. The explosion happened while workers were demolishing the building and accidentally cracked the pipes.

The university and Gansu Provincial Ninth Construction Group Co., Ltd. started the demolition work without any formality or license.

The construction company were found to have worked illegally while the supervision company and the university failed to fulfill their safety responsibilities, according to Lanzhou Work Safety Supervision Commission.

The punishments range from fines, dismissal to administrative detention.

The construction group was fined 480,000 yuan (75,120 U.S. dollars) while the construction supervision company and the university were fined 400,000 yuan respectively, according to the commission.