Homeland Security Active Shooter How to Respond Guide
Active Shooter situations are often over within 10 to 15 minutes, before law enforcement arrives on the scene, individuals must be prepared both mentally and physically to deal with an active shooter.
Below is a link to the U.S. Department of Homeland Security "Active Shooter How to Respond" guide.
https://www.dhs.gov/xlibrary/assets/active_shooter_booklet.pdf