BURFs PAIL and VAIL labs have many redundant fail-safe systems. Imagine the designers were clinically paranoid geniuses who know every apocalyptic outbreak scenario in print and film by heart. These people designed the PAIL/VAIL lab.
The only direct connection between the primary BURF facility and VAIL is an 800+ metre conduit from the fusion reactor to the VAIL room. Oh, and it's completely filled with dry ice. If the dry ice sublimates (because of a fusion reactor failur, for example) the sublimating dry ice will suffocate anything aerobic in the VAIL. The vast vacuum chamber bored out of the rock directly above the VAIL is just another fail safe. If power is cut or the protocol is triggered, this huge vacuum chamber is opened to the much smaller VAIL below it. The final pressure in the VAIL is about the same as what is found at about 150Km above the Earth's surface.
...I didn't mention the subcritical fusion pile, did it?
Yeah, so the Moonscape protocol also drops a beryllium-encased subcritical plutonium core into the room. The dropping action closes the beryllium sphere, causing the core to go critical, and unleash a blast of radiation that makes the air flash blue. The walls of the facility light up with phosphorescence when this happens, and the core ends up being sucked up into the vacuum chamber along with anything not tied down. The vacuum chamber seals up with the plutonium core still inside.
Three minutes later a ventilation shaft is opened to the surface, allowing a pile driver of air to blast into the VAIL and the irradiated vacuum chamber. The critical core is dropped, shattering it into subcritical pieces, and the long process of evacuating the chamber begins again. The ventilation shaft - only 10cm in diameter - is resealed with 100m of granite.
Hey, there's a reason it took a while to open the shaft! Moving a steel-cased granite pillar 100m requires time.
The granite shaft reveals the ventilation pipe quite quickly, but it takes nearly an hour to be moved back into it's original position.