Ventilation Systems
"AndAir AG" Switzerland.
VA-150
How often and for how long the air handling unit should be operated depends on the size of the shelter, the number of occupants, and the capacity of the unit.
Air Volume
Assuming a family of six in a 3700 cubic foot shelter, they may wish to operate the air system for an hour every six hours or so to freshen the shelter atmosphere. This schedule is not very close to the level of desperation, but it does maintain good morale and comfort for shelter occupants.
In order to maintain acceptable air quality in a shelter housing twenty to thirty occupants, the ventilator should be run for twenty minutes and then rested for twenty minutes. Fifty occupants is considered the absolute limit with a single VA-150 and would require continuous operation to support life.
This assumes a steel or concrete shelter with un-insulated walls that will absorb body heat and keep temperatures under control. The combination of insulated walls, lots of occupants, and inadequate ventilation will cause temperatures to soar to intolerable levels in a short period of time.
With this many people in a shelter, there will be a larger number of volunteers to operate the system (imagine the consequences of losing power with an electricity-dependant air handling unit under these conditions). The “ventilation officer” will also have the job of listening to the radio (perhaps on headphones) to stay informed about an ongoing situation. For this reason, we suggest that you position the radios near the ventilation unit.
Shelter Closures
ANDAIR specializes in concrete filled shelter closures. Exterior Civil Defense shelter doors should fit against the wall facing the potential blast. A proper blast door should never fit into the frame of the shelter opening. During blast or earth movement, shelter openings can bend and could block the entrance.
Our most popular model, the VA-150, comes standard with a 1 bar (15 psi) explosion protection valve/pre-filter assembly, air pump, exhaust over-pressure explosion protection valve, hoses, clamps, and GF150 Gas Filter. In peacetime, the system bypasses the gas filter and delivers 177 cubic feet per minute (cfm). With the gas filter connected, the recommended air rate is 88 cfm to allow for complete scrubbing of the outside air.
War Gases
Andair AG Gas Filters protect against the following war gases:
Gas filters do NOT protect against carbon monoxide and dioxide. A separate filter is available for scrubbing carbon dioxide from the shelter atmosphere during a period of time when outside air is not suitable. This could occur if burning debris is too close to the air intake vent.
Carbon Dioxide
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 multiply 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.
If there is a need to accommodate more people than your shut down mode can accommodate, you should purchase our carbon monoxide scrubber, or purchase compressed air tanks. Remember, however, it is not so much a matter of depleted oxygen, as it is a matter of too much carbon dioxide. Do not store oxygen tanks inside your shelter. Nor should you ever use propane in a bunker or shelter. They pose too much of a danger.