System Purge

The System Purge, also called "The Purge" or "The Carnage", was an event used by the Organization in the film Cabin in the Woods as a desperate security measure when Marty Mikalski and Dana Polk unleashed all the monster in the glass rooms into The Facility. This was accomplished with a button in the control panel marked "System Purge".

During the Purge, each and every one of The Facility's monsters are let out in waves, eight at a time. The monsters end up killing off most if not all of the Facility Staff, including every named member.
 * The first wave of monsters included (from left to right) the Dragonbat, the Angry Molesting Tree, the Zombies, the Dismemberment Goblins, the giant rattlesnake-cobra, the Killer Robot, a Witch and the Werewolf.
 * When it came to the second wave, Fornicus, the Alien Beast, and the Dolls were seen emerging while the other creatures that emerged at the time weren't identified during the massacre of the second wave of security.

System Purge
Why the facility had the need for a System Purge is unknown, but it is likely that this is a reference to the eleventh-hour deus ex machina that is a common trope in the horror genre.

Ironically, being such an advanced corporation, the Facility was very ill-prepared for the purge. The only reinsurance of safety was on security, but, even they weren't able to fend off the attacks.

It can be safely assumed that the Facility had never faced a problem like this in the past, or a mere possibility stands that they hadn't faced such a problem like so in a while, but even if this stood true, there at least would have been stronger security. But, during the event, many futile attempts to contain the outbreak were attempted in Command. But, it can be assumed when Marty and Dana were wiring access to the elevator, that the wires they cut were important to the system's security access and procedures. This assumption is even more plausible once you remember that the tunnel didn't collapse when it was supposed to because according to demolition staff member: "there was a glitch - a power reroute from upstairs".

Trivia

 * The other name of the System Purge is also the name of the titular event of the futuristic thriller film The Purge.
 * The infamous scene of the first batch of monsters escaping their cells has been parodied in Scary Movie 5, with mutated apes taking over their role.