The Vivos complex incorporates extensive nuclear, biological and chemical (NBC) air filtration systems that pre-filter all air before it enters the shelter. This system includes HEPA filters to remove all physical particles down to the .03 micron level, an activated carbon filtration system to remove radiation particles, a TEDA carbon system to remove chemical agents, and an ultraviolet system to further kill biological agents. Additionally, all intake valves are automatically controlled to seal the entire facility during any actual contamination event. There are a number of air shafts that provide air to the facility.  The shaft openings are hardened and designed to prohibit intrusion or blockage by any outside force, with a number of security measures.  However, should for any reason outside air not be available, or unable to be filtered and circulated, then a closed air system is activated that re-circulates all air within the complex.  All air vents and openings leading into the shelter also incorporate water proof gates and hatches that seal the shelter from submersion for the typical duration of a tsunami wave that may wash over the surface.  While this is considered unlikely due to the strategic locations of each shelter, it is a concern that has been planned for. The surface defenses would make it extremely difficult for any intruder, or force to approach and tamper with the air shafts.  Keep in mind that if a Vivos shelter is sealed due to outside contamination, or an environment that makes surface life unsupportable, then people would not be free to roam on the surface.