From the Introduction: "'Active shooter' events in a healthcare setting present unique challenges: a potentially large vulnerable patient population, hazardous materials (including infectious disease), locked units, special challenges (such as weapons and Magnetic Resonance Imaging (MRI) machines (these machines contain large magnets which can cause issues with firearms, or remove it from the hands of law enforcement), as well as caregivers who can respond to treat victims. There is no single method to respond to an incident, but prior planning will allow you and your staff to choose the best option during an 'active shooter' situation, with the goal of maximizing lives saved. The best way to save lives is to remove potential targets from the shooter's vicinity. We address some difficult choices that will need to be made in this document."
U.S. Federal Bureau of Investigations [FBI]: http://www.fbi.gov/