According to the Himeji City Board of Education, the class was conducting an experiment to generate hydrogen by mixing zinc and hydrochloric acid when the gas ignited and shattered the flask.

One male teacher in his 50s and 15 students sought medical attention, reporting cuts to the forehead and hands as well as ear discomfort from the blast. Of those, six people, including the teacher, were confirmed injured.

The Himeji City Board of Education said it “sincerely apologizes for causing concern to students, parents, and residents,” and added that it will reinforce safety measures and ensure strict adherence to proper procedures for science experiments.

Source: YOMIURI