Officials say they still don't know what sickened people at a Villanova University chemistry lab, prompting evacuation of the building and sending 29 people to the hospital.

Officials at the private Catholic school in suburban Philadelphia say one student became ill and left during an experiment at about 2:30 p.m. Tuesday at the Mendel Science Center. Other students then reported feeling ill, prompting the evacuation and decontamination procedures. The building reopened Wednesday.

Radnor Fire Chief Dan Kincade told The Philadelphia Inquirer (http://bit.ly/Vc3wbJ ) that the student who initially fell ill has asthma and could have had a reaction to a vapor released during the experiment. He said hazmat crews found no vapors in the lab, but the building's ventilation system would have cleared the air by the time they arrived.

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Information from: The Philadelphia Inquirer, http://www.philly.com