With the Aurora theater shootings still in most people’s minds, I want to point out that such situations—mass killing sprees—are extremely rare. You’re more likely to die in traffic or falling in the tub than to get killed in a movie theater or a restaurant by a lone gunman.
One situation where this might happen is in your workplace.
Here’s what OSHA (Occupational Safety and Health Administration) has to say about workplace violence at their website:
Workplace violence is any act or threat of physical violence, harassment, intimidation, or other threatening disruptive behavior that occurs at the work site. It ranges from threats and verbal abuse to physical assaults and even homicide. It can affect and involve employees, clients, customers and visitors. Homicide is currently the fourth-leading cause of fatal occupational injuries in the United States. According to the Bureau of Labor Statistics Census of Fatal Occupational Injuries (CFOI), of the 4,547 fatal workplace injuries that occurred in the United States in 2010, 506 were workplace homicides. Homicide is the leading cause of death for women in the workplace. [More…] However it manifests itself, workplace violence is a major concern for employers and employees nationwide. (U.S. Department of Labor, http://www.dol.gov.)
Domestic violence can easily spill over into the workplace. In my city a few years ago, a woman who worked at a local business was shot and killed—at work—by her estranged husband, who then turned the gun on himself. He easily could have killed or wounded her coworkers.
I’m one of those people who makes an escape plan everywhere I go; it keeps me entertained while I’m standing in line somewhere to imagine what I will do if the zombie apocalypse suddenly begins while I’m there. In 1980, the McDonald’s shooting in San Ysidro, CA woke me up. To this day, I won’t sit with my back to the door in a restaurant.
Am I afraid? Not exactly. I’m cautious, yes. Personal safety is a pet cause of mine. I firmly believe that if you are prepared to handle a situation, no matter how remote it might seem, that when it does you will react appropriately.
This video, called Run-Hide-Fight, was posted on Facebook by my local news. It is a disaster-preparedness video with a very simple strategy on how to react to a shooting incident. In the illustrative case, it’s at the office.
WARNING: While not graphic, the video is very intense.
Your boss or HR professional may not be able to tell you if someone is in a situation that could turn violent, or your coworker might have kept it a secret. They should, however, have safety strategies in place, and so should you.
There are always signs of impending violence. Unfortunately, if you’re in a situation like the Aurora or San Ysidro incidents, you won’t see them until the shooter acts.
Security expert Gavin de Becker, in his excellent book, The Gift of Fear, lists pre-incident indicators (PINS) that may be a sign someone is not to be trusted. You can find them summarized in this Wikipedia article.
de Becker says many people use these tactics every day, especially men who are trying to talk to women, and they’re not necessarily sinister, but they should give you pause.
Another handy acronym de Becker uses is JACA, which stands for four elements in the perception of a person contemplating violence:
(Perceived) Justification: can the person justify using violence to solve the problem?
(Perceived) Alternatives: is there any other alternative to violence?
(Perceived) Consequences: are they intolerable, or can the person live (or die) with them?
(Perceived) Ability: does the person have the ability to carry out the violence? 
Knowing how a perpetrator thinks goes a long way in risk assessment. You can apply the JACA elements to a lot of situations, de Becker says, even on a global scale. I think it should be required reading in business and human resource courses especially.
Read the book. I have owned two copies, my current one, and the first, which I gave to someone who was on the verge of being stalked. No, I’m not an affiliate and I don’t have any connection to Mr. de Becker. I think he’s on the ball and I want you to be safe.
None of this means you have to be in a low-grade panic all the time. Whether it be wearing a seat belt or getting first aid/CPR training for a job, advance preparation can save your life.
Some resources you might want to check out:
How to interpret the news: https://www.gavindebecker.com/resources/article/media_fear_tactics/
Hans Zimmer scored all three Nolan Batman films. His composition, Aurora, is a lovely and moving requiem for the shooting victims, containing the Batman theme. You can download it at the link below. Yes, it’s legit.
 de Becker, Gavin. (1997). The Gift of Fear and Other Survival Signals that Protect Us from Violence. New York, NY. Published: Dell Publishing, a division of Random House, Inc.