Of the many time-honored traditions in higher education, this may be one of the least appealing of all: Around exam time, the number of campus bomb threats spikes, presumably from Joe or Jane Student hoping for a postponement. A quick Web search reveals a fair number of colleges and universities with policies designed to combat just this eventuality.

But the exam-time bomb scare took a slightly more ominous turn at Diablo Valley College on Tuesday, as local police officers blew up a student locker on the California community college's Pleasant Hill campus, after two sets of bomb-sniffing dogs led police to identify it as a "possible threat location."

Officials at Diablo Valley, part of the Contra Costa Community College District, in the San Francisco Bay area, shut the two-year institution's main campus for the day, and announced late Tuesday that it would remain closed today.

"You can always put up a new building, but it's hard to replace people," Lieut. Thomas Sharp told the San Francisco Chronicle. "Our No. 1 concern right now is the safety of the students, faculty and staff."

An alert from the Contra Costa district's police department said that local Diablo Valley officials had received two  "anonymous, unspecified" threats late Sunday and early Monday, which led them to increase the presence of officers and guard dogs. Late Monday, college officials said the campus would open as planned Tuesday.

But early Tuesday morning, officers and bomb-sniffing dogs did a sweep of the campus, and identified two possible threats. A second team of dogs confirmed the threats. "The dogs did indicate there was something on campus we should be concerned about," Chrisanne Knox, a spokeswoman for Diablo Valley, told the San Jose Mercury News. That led college officials to close the campus.

Police officers then detonated the suspicious locker, which was located outside the bookstore. News reports indicated that the locker had been empty.