Post-Virginia Tech, the image of a gunman roaming colleges' halls continues to spark discussion. At the University of Michigan, a physics professor has generated discussion over a seemingly simple request: to outfit classrooms with doors that can lock from the inside.

Keith Riles, the professor, was teaching a course in a high-rise building in February 2008 when a gunman at Northern Illinois University took the lives of six people. Riles realized that if such an incident were to occur at Michigan, he and his students would be vulnerable in the classroom, he said.

"If we were to receive a campus lockdown alert, those teaching in classrooms would be unable to respond by locking anything," he said. "How do you respond to a campus lockdown if you can't lock your door?"

Starting in May, officials from the Facilities and Operations department have been researching the amount of money and time it would take to install new doorknobs. Classroom doors currently have a single lock that is part of the doorknob, and replacing them with locks on the inside would likely come at a "considerable cost," said Diane Brown, a spokeswoman for the public safety department. The campus, which serves some 30,000 students, consists of 600 to 900 classrooms, some of which have as many as a dozen doors.

To comply with Michigan fire safety code, doors to rooms that hold at least 50 people must swing outward, Brown said. The law also requires that people need only make one action to exit.

"Unlike at home, where you might have a deadbolt lock and also a door handle, you can't do that with large classroom doors," she said. "Essentially you must push your hand and also be able to get the door open. Whether you turn down a knob or push down a crash bar, you can only do one thing to get out."

While the group's research remains in the unofficial stage, with no funding attached so far, its momentum points to the self-analysis undertaken by higher education institutions in the wake of on-campus tragedies that have occurred in the last two years. At Virginia Tech in 2007, a student named Seung Hui Cho shot to death 32 students and faculty and wounded more than a dozen before killing himself, adding up to one of the deadliest shootings in American history.

In a report released by the Virginia Tech Review Panel several months after the shooting, the panel observed that the campus's classrooms did not have door locks operable from the inside. "Whether to add such locks is controversial. They can block entry of an intruder and compartmentalize an attack," the report states. It continues, "On the other hand, a locked room can be a place of refuge when one is pursued." On balance, the panel generally thought having locks on classroom doors was a good idea.

In general, doors that lock from the inside have been in place on college campuses for several years, said Jesus M. Villahermosa Jr., president of Crisis Reality Training, which advises organizations on handling emergencies. He said that while it is impossible to eliminate risk entirely, in his experience "locks absolutely work. People are able to secure themselves in rooms and shooters haven't been able to get to them." He added that it cost one institution $5 million to install locks on the inside.

"Let's say we add a lock to this door," he said. "What does it change? It changes nothing. Now students and teachers have assurance that if they need to lock down, they can."