The 25tn blast door to Cheyenne Mountain military installation. Designed to withstand a 30 megaton nuclear detonation and able to filter out ABC contaminants. After this door, there is another like it. :
Bunker like hi-res stock photography and images - Page 4 - Alamy
Making a Nuclear-Resistant Air Filter - YouTube
L 15 3 Bunker Belüftung ABC Filter Schutz Anlage Frischluft in Bayern - Regenstauf | eBay Kleinanzeigen
Bunker Air-Filter WWII - 3D Model by KangaroOz 3D
NBC Air Filtration | Safe Cell | American Safe Room
L 15 3 Bunker Belüftung ABC Filter Schutz Anlage Frischluft in Bayern - Regenstauf | eBay Kleinanzeigen
PLATH at the underworld - Career at PLATH Group - Solutions for COMINT and EW
Bunker Air-Filter WWII - 3D Model by KangaroOz 3D
Bunker Air-Filter WWII - 3D Model by KangaroOz 3D
NBC Air Filtration | Safe Cell | American Safe Room