Vault blast door

Unlike internal doors, Vault blast doors are designed not only to keep contaminants and radiation out, but also to protect the occupants from danger. These massive doors are one of the iconic elements of a Vault, their gear design instantly recognizable in the wastelands.

These Vault doors had a projected 2% failure rate, in case of a direct hit by a nuclear missile. The only known vault to have been hit by a nuclear weapon is Vault 87 and the blast damaged the door beyond repair.

Seal-N-Safe Vault Door Model No. 343
The No. 343 was the basic Vault door model, first used in the demonstration Vault. The efficiency of the design led to it being used in numerous Vaults, including Vault 8, 12, 13, 15, and other installations. They were usually shipped assembled and installed whole.

The central element of the assembly is, of course, the gear-shaped door. Four yards (3.6m) thick at its thickest point and made out of heavy duty steel, they are designed to withstand a lot of punishment. The twelve cogs of the door lock into recessions cut into the frame, providing stability and support for the massive frame. The door was shaped like a cork, using friction wedge design to plug the door frame and and create an excellent seal.

When the right password was input, the door would be removed from the frame by a hydraulic press, placing it on the external track. A separate mechanical arm would extend from the external assembly, lock into the recessions placed on the back of the door, and smoothly slide it into a reinforced container on the side.

An integral component of the door is the airlock, overpressurized to keep the contaminats out of the Vault. This long hallway's floor was covered in grating, coupled with a series of wall-mounted vents for decontamination. It terminates in a security door leading into the Vault. Unlike other models, this one opened sideways, with interlocking steel plates on both sides and a slab of lead sandwiched between them for added protection.

Advanced Vault door
Vaults also used superior models, like the advanced Vault doors. Thinner and with nine cogs instead of twelve, it was fitted into the door frame snugly and was opened inwards, rather than outwards, by a large hydraulic arm suspended from the ceiling inside the airlock. The door had a clearance of 4.52 meters (14 feet and 10 inches), allowing easy entrance and exit. The door ensured that the airlock would remain overpressurized and keep contaminants out of the controlled environment of the Vault.

When activated, the airlock would initiate a purge cycle, equalizing pressure through the door-mounted valve. The safe distance for anyone in front of the Vault door was 10 meters (33 feet). Once the cycle was completed, the door would be engaged by the mechanic arm, pulled back onto the internal track, and rolled sideways. The mechanism relied entirely on the mechanical arm, rather than a hydraulic press as in the No. 343 model.

The airlock was also different. People entering the Vault would do so through a trench flanked with railings, observed from the control station by security personnel. The airlock was equipped with ceiling-mounted sprinklers, for easy decontamination. The advanced model could also be further reinforced, with the resulting fortified Vault door offering top notch protection against assailants trying to get into the Vault.

Dome elevator
The dome was an additional protective measure designed for Vault 111. Placed on the top of the hill overlooking the neighborhood, the dome would protect the interior of the Vault by causing the blast wave to pass over it, without concentrating in any one point. In the center of the dome was a secondary blast door that protected the lift leading inside the Vault. Notably, it appears that the dome has an emergency interface panel, which allows the blast door to be open manually using a crank and a wheel.

Blast door
Vault 8 was one of the few Vaults equipped with an additional door built into the side of a mountain. Embedded into a concrete wall reinforcing the slopes, the massive door was designed to seal the access corridor to the internal Vault door. The circular reinforced concrete frame provided additional protection and ensured an equal distribution of weight in case of a natural catastrophe. Vault 76 had a similar design.

Behind the scenes
An interesting thing to note is that No. 343 model would protect better against a nuclear blast. The nine cog model rests in its recessions without mechanical stops to prevent it from collapsing inward under the shockwave. By comparison, the No. 343 has a friction wedge and stops for the cogs. As a result, the shockwave would press it harder against the frame and complete the seal, unless the entire door frame fails. However the newer model would allow the door to be opened even if rubble had fallen near the door on the outside.