BEIJING, Feb. 14 (Xinhua) -- Dereliction of duty was blamed for a laboratory explosion at Beijing Jiaotong University that killed three students in December, local authorities said Wednesday.

The explosion happened on Dec. 26 when students were conducting experiments in a laboratory of the university. The three students were killed at the scene, according to the Beijing Emergency Management Bureau.

An investigation showed the hydrogen generated in the experiments was ignited by a spark caused by metal friction in the mixer and exploded. That caused the magnesium dust nearby to explode and the surrounding combustibles to burn.

The investigation said the risky experiments were conducted against relevant regulations. Dangerous chemicals were illegally purchased and stored in the lab and the university failed to oversee the safety of the laboratories.

Li Desheng, director of the research project, and Zhang Qiong, manager of the laboratory, will be investigated for criminal negligence, according to public security authorities.

The Ministry of Education and Beijing Jiaotong University also punished 12 officials from the university.

All universities in Beijing have been ordered by local authorities to strengthen safety inspections, improve the safety management of laboratories and enhance personnel training to prevent future accidents.