18F Handbook

yep, it's the federal government, there's a section on how to deal with an "active shooter".

tl;dr: bend over and kiss your ass goodbye

Threatening person with a weapon

    Stay calm and signal a coworker for help.
    Have that person call 911 and then call the Security Command Center.
    Maintain eye contact and stall for time.
    Keep talking but follow the instructions of the person who has the weapon. Never grab for a weapon.
    Watch for a chance to escape to a safe area.

Active Shooter

    Evacuate if possible. Keep your hands up and leave all belongings.
    Hide out if evacuation is not possible. Stay out of view. Lock doors and block entry.
    Take action as a last resort only when your life is in imminent danger.
        Attempt to disrupt and/or incapacitate the shooter by:
        Acting as aggressively as possible.
        Throwing items and improvising weapons.
        Yelling.
        Committing to your actions.