DENVER (AP) — A Denver school chemistry teacher who was fired after four students were burned in a science experiment gone wrong now faces a criminal charge.

Prosecutors filed a third-degree assault charge, a misdemeanor, against 22-year-old Daniel Powell on Wednesday. Powell couldn’t be located for comment.

School officials say a fire erupted in Powell’s classroom at the Science, Math and Arts Academy charter school on Sept. 15 while he was conducting a demonstration with methanol.

It marked the second time in a month that a fire linked to methanol in a science demonstration caused injuries. Thirteen people, many of them children, were hurt in a flash fire at a Reno, Nevada, museum on Sept. 3.

The Denver school said this month that three students are back in class and the fourth student continues to improve.

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