Quarantine zone (location)
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A quarantine zone surrounded the Library of Installation 05. The zone was surrounded by an enormous structure known as the Sentinel wall. The Sentinel wall, along with the containment shield it projected, had kept much of the Flood from spreading during the eons-long outbreak on Delta Halo, allowing Sentinels to contain the violent parasitic force. The shield's deactivation by Arbiter Thel 'Vadamee during his search for the Activation Index in 2552 ultimately allowed the Flood to overwhelm the Sentinels' defenses and thus move freely about the ring.
The area was guarded and patrolled by various Forerunner constructs, ranging from the small but necessary Constructors, to the standard Sentinels and Sentinel Majors, to the titanic Enforcers. The Quarantine Zone was apparently kept starved of all life by the Sentinels, of which more were produced by local manufacturing plants. The only signs of past life, besides the Flood, were dead trees and it was constantly snowing. It seems that the Sentinels or some other systems have caused this climate change in order to prevent life from growing and/or existing in this area, therefore denying the Flood of any possible sources of energy. It is unlikely that the change in climate was enacted by 2401 Penitent Tangent as the Monitor had not sent the requested "security detail" after approximately 287 years since the initial request for one. Likewise, the presence of trees at all indicates that it was not always such a cold climate, and is instead a response to the Flood outbreak.
Upon arrival within the Quarantine Zone, Covenant forces stumbled upon a four-way fight between the Flood, Sentinels, and the recently arrived United Nations Space Command forces. After the Arbiter had lowered the shield, more and more Flood had begun to spread into other sections of the Sentinel Wall and would conquer vast territories on the ring.
As Covenant and UNSC forces deployed mechanized forces from their ships, the Flood were able to overwhelm their occupants, infect them, then operate these machines in order to turn them on their foes. Their forces would grow to accumulate Ghosts and Warthog reconnaissance vehicles, and even Scorpion and Wraith tanks. The Flood's access to highly-mobile, and heavily armed and protected vehicles greatly multiplied their combat effectiveness on Installation 05.
Following the crash-landing of High Charity on Installation 00 during the final battle of the Human-Covenant War, the Flood were able to begin spreading their influence across the installation, with the Gravemind even managing to extend its tentacles into the installation's Citadel. However, under the guidance of the Installation's Monitor, 000 Tragic Solitude, the Flood were contained within a quarantine zone around the wreckage of the city, with the surrounding Refugia modified to prevent and inhibit the development of any life form to ensure the Flood would not be able to survive. Approximately three hundred meters around the quarantine site, all plant life stopped growing - blackened, charred and chopped down - and all animal life stopped living, with no sound audible from birds or insects. A battalion of Sentinels was additionally kept on a permanent patrol of the area around the quarantine zone to both prevent the flood escaping and intruders breaching the site and potentially letting the Flood loose. Unlike Installation 05's quarantine zone, the zone established on Installation 00 seemed to rely more on energy shields for containment than physical structures like the Sentinel Wall.
Following Tragic Solitude's destruction in Operation: FAR STORM, the Sentinel defenses on the Ark - like those of Installation 05 - were only able to enforce the quarantine measures already in place. This would allow the Flood within the city's ruins to fester over the course of several years, producing a variety of hitherto-unseen Flood forms created specifically for the purpose of escaping the quarantine and infecting the Ark.
Several months into the protracted Second Ark Conflict, High Charity's quarantine zone would become the target of reconnaissance and - in the case of the latter group - salvage operations by UNSC forces of the UNSC Spirit of Fire and Banished. Due to a close encounter with a Forerunner ship, James Cutter deployed teams to watch over several potential hotspots of activity throughout the Ark including the wreck of High Charity while Jiralhanae brothers Pavium and Voridus were tasked by Atriox to salvage the area around the quarantine zone for potentially salvageable Covenant equipment. These orders were followed with an explicit instruction to, under no circumstances, enter or breach the quarantine zone. However, many soldiers of the Banished, including Voridus, believed the tales of High Charity's fall and the end of the war to be mere Covenant propaganda, and thus ignored these instructions. Voridus was able to use his Infused Scarab to burn a hole through the quarantine shield. A small squad of Jiralhanae were sent into High Charity to scout out the entrance way, but re-emerged as infected combat forms. These combat forms were soon followed by a swarm of Pod infectors, Abominations, Spawner forms and many other new Flood forms to quickly spread across the Ark. However, this threat was ultimately contained thanks to Pavium and Voridus' timely reactivation of the Ark's defense grid, with Sentinels proceeding to swarm the area and presumably completely sterilize it.
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