Collective protection for civil defense
A nuclear, biological, and chemical (NBC) safe room protects the occupants from inhaling harmful or deadly airborne toxins such as very fine particles of radioactive fallout, biological toxins, and chemical agents. In the past, the United States Government has poured extensive resources into providing the best information for the protection of its citizens from NBC warfare agents. This is not the case today.
For protection of the U.S. population we have the government website: www.ready.gov. It suggests duct tape and plastic, then wait for further official instruction. Although the tape and plastic method would offer some immediate short term protection from low level toxins at low concentrations, it would be, at best, a short term solution. Most governments tend to only recommend emergency procedures that can be afforded by all their citizens.
As a contrast to most governments, both Switzerland and Israel require, and subsidize the cost of, NBC safe rooms and blast shelters in residential dwellings and commercial buildings. They have strict standards in place governing both the construction of the room and the ventilation equipment protecting the room.
For protection of some of our military personal and government officials, the U.S. Department of the Army - Corps of Engineers has standards by which NBC airborne toxic free areas must comply. These standards dictate the differential pressure (overpressure) in the safe room (protected space) as well as the design of the NBC filter/ventilation system.
The main reasons why an un-pressurized room will not protect the occupants for very long is that the room "breaths" - in other words, it leaks air both in and out through the cracks as the external atmospheric pressure fluctuates - due wind or other atmospheric variables like temperature, and barometric pressure swings due to approaching weather fronts. Air constantly tries to normalize its pressure and temperature between different variants - as it does this, it brings with it whatever that air contains. Also, in a sealed room, there is no accommodation to replenish oxygen and expel the exhaled carbon dioxide of the occupants.
In order to create and maintain overpressure as well as give the required air exchanges to support the air supply needs of the sheltered occupants, a safe room must be equipped with true positive pressure NBC filter/ventilation unit and a means of a metering the exhaust air out of the protected space.
American Safe Room filter/ventilation equipment and related components are designed and manufactured specifically for this purpose.
The safe room
A safe room consists of an envelope (a room) that has a true NBC filtration/ventilation system installed that will maintain more air pressure inside the room than outside of it (overpressure) in order to constantly keep air blowing outward from the protected space. This will not allow airborne toxins from migrating back into the room and your lungs.
With the right equipment, standard residential construction - homes and apartments - can be a perfectly suitable envelope to keep out airborne toxins. Absolute sealing of the room is not necessary - as long as you have achieved and maintain overpressure.
Even if you are inside a hermetically sealed container, you need true ventilation - air in and air out. This ventilation continually removes moisture, heat, and carbon dioxide that is exhaled by the occupants while bringing in a fresh supply of oxygen-rich air.
This air must be filtered in order to make it safe and breathable. The best filter combination is a bank of pre-filters, an individually DOP scan tested nuclear grade HEPA for radioactive fallout and a nuclear grade carbon adsorber that will adsorb radioactive iodine.
Room selection - inside rooms offer more distance (one component of protection) from radioactive fallout, but outside rooms offer more surveillance of outside your safe room. You may have visitors. Incorporating a bathroom in a protected space is a good idea, but bathroom fans must be sealed up so you maintain overpressure. If you cannot seal it, place the NBC filter as far away from the bathroom as possible and seal up everything else. The bathroom fan duct will be your air outflow.
Room size in volume - we like to see at least one air exchange per hour. The 60 CFM Safe Cell will do that in a space up to 3,500 cubic feet. The 120 CFM Safe Cell will do it in up to 7,000 cubic feet.
The number of anticipated occupants - the 60 CFM Safe Cell is rated for up to 12 occupants using the ASHRE standard of 5.0 CFM per occupant and 17 occupants using the Israeli standard of 3.5 CFM per occupant. The 120 CFM Safe Cell doubles these occupancy ratings.
How well the room is sealed - if the room is well sealed, then the air needs some way of being returned from where you get it. An overpressure valve over a penetration (hole in the wall or ceiling) is the best solution
What pressure the air is that is being drawing into the room - is it being drawn from static air or from a central forced-air system? Static air is best. The airspeed through the carbon be must be engineered to ensure it has the proper residency time in the carbon. Speeding up the air before the filter may reduce this residency time below the quarter-second specification issued by the US Army Corps of Engineers.
What you do if the power fails? The Safe Cell has an onboard automatic battery backup system, and for extended power outages - see the emergency hand pump page for more information
American Safe Room provides free air filtration and component blast protection shelter consultations. Contact our Sales Manager at 541-459-1806 or send a plan view drawing of your shelter to sales@AmericanSafeRoom.com or FAX it to 503-212-6695.