The stunning tragedy at Virginia Tech is, fortunately, a rare event. A few days later, however, a NASA employee, apparently disturbed by a performance review, came to work with a gun and killed the manager and himself. It's happened before, not again, not a common occurance as it still makes news. No, if one works in health care, the risk of a violent incident is mostly found in mental health situations, the ED and clinics that do abortions. Health care workers, according to the OSHA, have a significantly higher risk of workplace violence than does the general workforce.
At the basic level, access to your office should be somewhat restricted. For example, the general public can enter and leave through one door, and a person must pass the receptionist to do so. An emergency system, even using the phone, for help in an exam room covers not only a dangerous situation but, more commonly, when help is needed immediately for a medical problem. Personally - and I know there are many who disagree - I would not allow staff to carry guns into the office. Police officers have extensive training in working in such a situation and in using their weapon - civilians don't.
If you are concerned about an employee, meet with them and be prepared to refer them to a counselor who can help them. A second person in the room, particularly if you have an HR person, is helpful for all concerned. In short, if you need help to deal with a problem employee - get it.
Most police departments will give a free security review for you, and there are private companies who can be hired when you have a more extensive operation or unique circumstances.
John Gilliland of the Indianapolis law firm of Gilliland, Markette and Milligan, summarized the OSHA publication "Guidelines for Preventing Workplace Violence for Health Care and Social Service Workers (OSHA 3148)". The document itself is available online here.
Some resources here at All Business include:
1. Handle with Care HR magazine
2. Breaking Point HR Magazine
3. Training the Supervisor to Prevent Workplace Violence Supervision magazine