Two students detonated a homemade explosive device in the middle of Ridgewood Quad earlier this month, Director of Public Safety Ed Callahan said.Callahan said an officer on duty in the nearby Ziv Commons Oct. 11 first heard a loud explosion and then found two plastic bottles filled with dry ice and water in the residence quad. Dry ice and water are explosive when enclosed in objects such as the bottles.

The Waltham Fire Dept. was called in to safely detonate the two remaining bottles, Callahan said.

"This was obviously a safety concern," Callahan said. "There were 75 people in Ziv Commons. Projectiles could have flown into someone's face."

Callahan would not name the two students involved.

A woman answering the door at the suite where Callahan said the two students lived said two of her suitemates who were involved in the incident no longer live there and are not permitted to attend classes until a University judicial hearing is held.

"I question the motivation of these students if [they are] doing this kind of thing," Callahan said. "It's a serious offense."

Last week's Police Log said the two will face judicial charges and possible criminal charges, but Callahan said he could not discuss any pending judicial action.