Silo Season 2: The Safeguard Explained

The following contains heavy spoilers for season 2 of "Silo."

"Silo" is one of the best sci-fi shows of the past decade, one with a compelling mystery and exquisite worldbuilding that feels similar to the constant lore drops and plot twists of "Attack on Titan."

The show takes place in a dystopian future where most of the world has been destroyed and humanity wiped out. The only remnants of civilization live in an underground silo hundreds of levels deep. The show deals with the simple idea of knowledge and how hard it is to kill human curiosity no matter how much those at the top use regulations to keep the population under control. At the end of the first season, former engineer now sheriff, Juliette Nichols (Rebecca Ferguson) left her silo (a death sentence) and actually managed to survive her walk outside, eventually finding another silo nearby.

Season 2, which cemented "Silo" as one of the best shows on AppleTV+, and reason enough to subscribe to that platform, concerns Juliette discovering that the new silo she encountered had been wiped out when the people revolted and tried to leave for the surface. Back home, however, revolution is brewing and IT systems analyst Lukas Kyle (Avi Nash) starts discovering the secret past of their own silo, until he learns about the horrific safety protocol known as the Safeguard Procedure.

Though the season 2 finale of "Silo" already did a rather expansive job explaining what the Safeguard Procedure is, some people have the inexplicable hobby of just spoiling themselves on TV shows. Whether that's you, you were watching the show with your eyes closed, or went to the bathroom when they explained what this safety protocol is, fret not. Here's your handy guide as to what the Safeguard Procedure is in "Silo."

In the penultimate episode of "Silo" season 2, Lukas Kyle dives down to the very bottom of the silo and finds a mysterious tunnel — the same one Juliette's boyfriend George (Ferdinand Kingsley) was looking into before his death in the first season. The tunnel leads to a door that is guarded by some AI-sounding voice that talks about the Safeguard Procedure that will kick into place if anyone dares cross that door or talk to anyone about what they found down there.

The Safeguard Procedure is essentially a contingency plan in case the silo revolts, and it allows some unseen entity to kill every single person in the silo via a pipe full of poison that gets distributed through the vents. This is a last-ditch effort to prevent the residents of a silo from escaping and alerting the other silos of their existence.

When Lukas learns about this in the season 2 finale, it wrecks his worldview as he realizes it doesn't matter how much the people of the silo fight or how they try to liberate themselves or learn the truth. They were always, and will always be one button away from dying horrible deaths. The fate of the people of the silos has always been out of their hands.

At the same time as Lukas learns about the Safeguard Procedure in Silo 18, Juliete over in Silo 17 hears from Solo (played by Steve Zahn, the best part of "War For the Planet of the Apes") that his parents did know about the procedure that poured poison out of a vent.

Turns out, Silo 17 had been a victim of the Safeguard Procedure when they tried to revolt. It started when a man wrote "LIES" on the outside camera when he left the silo to clean, which made everyone in the silo believe that it was safe to go outside. This prompted a revolution that led to everyone deciding to leave their silo — and die trying.

This is the crux of the season, as Juliette — knowing that everyone on Silo 18 died when they gain hoped that someone could survive outside like she has — realizes that Silo 17 is about to suffer the same fate as Silo 18. Indeed, a big part of the season's story is the aftermath of Juliette's miraculous walk outside, which sparks a rebellion that nearly tears the silo apart until Juliette comes back in the season finale.

We don't know for sure if the Safeguard Procedure can be stopped, but it seems like it can. While talking to Juliette, Solo recalls the day his silo died, and how his parents supposedly discovered the Safeguard Procedure and managed to find a way to stop it. According to Solo, his parents simply put a cap on the vent, preventing the procedure from killing everyone.

What's more, it seems people from Silo 17 managed to go outside and not die — at least not at first. Whatever Solo's parents did, it managed to make it safe to go outside. That opens up a whole can of worms that "Silo" needs to explore come season 3. So far, we have been led to believe that the one solid fact in the show's world was that the surface was radioactive or toxic, and no one could survive out there. If the poison from the Safeguard Procedure can impact whether it's safe to go outside or not, does it mean it is something from inside the silos that kill people when they leave for the surface? If that is the case and it can be stopped, we're in for a big reckoning in season 3 of this Stephen King-certified show.