Carbon Dioxide Filters
Carbon Dioxide Scrubbers are added to underground shelter systems when there is a threat from smoke or other compromises to the air supply. A hardened NBC shelter should have the capability to shut down the outside source of air for a period of 6 hours, for sealed shelter operation. During the first hours of a nuclear attack, smoke, carbon monoxide, and radiation particles could overcome the ventilation and filtration systems. It is assumed, after this 6-hour period, that carbon monoxide levels from the smoke outside would have dissipated. However, carbon dioxide (CO2), which is an internal threat, builds very quickly in occupied sealed areas. A concentration of CO2 over 3% in the sheltered area is unacceptable.
Each person will produce about .67 cubic feet/hr of CO2. Plan your shelter space to accommodate each person with enough room to breathe safely and comfortably for that 6-hour period. Each person needs 88 cubic feet of free air volume to shut down for 6 hours. Design your shelter with double that volume, to accommodate for furniture, food, water and other supplies. A 10 ft. x 32 ft. shelter will accommodate 14 people and supplies in a ‘shut down’ mode for 6 hours.
It would appear from this example that the shelter could be rather small. However, it should be noted that the air space for breathing must be totally empty space. You must, therefore, add about 5 cubic feet for the mass of each person. You must also add additional space for food, water, supplies and furniture. A good rule of thumb would be to multiple the required air space by a factor of 2.5; and for the example above, the volume of the shelter should increase to 2100 cubic feet. Our 10 x 32 ft. shelter (7 feet of head space, 3 feet of storage below the floor, and 32 running feet) would meet the criteria nicely.
If you plan to accommodate more people than your shut down mode can accommodate, you should purchase our carbon dioxide scrubber, or purchase compressed air tanks. Do not store oxygen tanks inside your shelter. They pose too much of a danger.