In the event of a shooting, you have 3 options:
Run - The amount of time you have to get out of the building or facility is extremely limited, try and exit within the first few seconds.
Hide - In a situation that requires you to hide, turn off the lights and silence your cell phone. This includes sending text messages.
Fight - As a last resort, fight and follow through.
Resist the temptation to use your cell phone and get out of the building as quickly as possible.