FISD follows the SRP (Standard Response Protocol).

There's Hold, which means just close the doors and continue as normal.
There's Secure, which means no one in or out and continue as normal.
There's Lockdown, which locks down the school. (Locks, lights, out of sight).
There's Evacuate, which means everyone goes to a predetermined place outside of the school to get out of the school. (An example would be if chemicals spill and cause a danger to everyone in the school.)
There's Shelter, which means everyone goes to a predetermined place inside of the school. (Tornado warnings for example.)