AUSTIN, Texas – Thousands of people streamed off three college campuses Friday after bomb threats prompted officials to issue evacuation orders for schools in Texas, North Dakota and Ohio.

The campuses of the University of Texas at Austin and North Dakota State University in Fargo had been deemed safe by early afternoon, and authorities were working to determine whether those threats were related. A third evacuation order for much smaller Hiram College in northeast Ohio was issued hours later and remained in effect Friday evening.

Hiram spokesman Tom Ford said the school had received an emailed bomb threat that it was taking seriously. Crews with bomb-sniffing dogs were checking all buildings on the campus about 35 miles southeast of Cleveland, where about 1,300 students are enrolled, he said.

The threats on the much larger campuses in Texas and North Dakota ended as false alarms after tens of thousands of people followed urgently worded evacuation orders, one of which some worried didn’t come fast enough.

Both of those campuses emptied at quick but orderly paces Friday morning, though students acknowledged an air of confusion about what was going on. The threats coming as violent protests went on outside U.S. embassies in the Middle East also stirred nervous tension among some students, and Texas officials acknowledged global events were taken into account.

The first threat came around 8:35 a.m. to the University of Texas from a man claiming to belong to al-Qaida, officials said. The caller claimed bombs placed throughout campus would go off in 90 minutes, but administrators waited more than an hour before blaring sirens on the campus of 50,000 students and telling them to immediately “get as far away as possible” in emergency text messages.

Authorities said they started searching buildings for explosives before the alert was issued. UT President Bill Powers defended the decision not to evacuate sooner.

“It’s easy to make a phone call the first thing we needed to do was evaluate,” Powers said.