Came across a good PDF from FEMA that outlines the different classifications of safe rooms and how to make one in your home for protection against chemical, biological and radiological (CBR) threats.
This is a single chapter from a larger document, and begins:
“A CBR safe room protects its occupants from contaminated air outside it by providing clean, breathable air in two ways: (1) by trapping air inside the room and minimizing the air exchange (an unventilated safe room) and (2) by passing contaminated air through a filter to purify it as it is supplied to the room (a ventilated safe room).
Unventilated safe rooms that are tightly sealed cannot be occupied for long periods without the risk of high carbon dioxide levels. This constraint does not apply to ventilated safe rooms, which can be designed to provide filtered and conditioned fresh air at any desired rate. Ventilated safe rooms can therefore be used on a routine basis, although most are designed as standby systems, not for continuous, routine use.
Obtaining protection from an unventilated safe room can be as simple as selecting a relatively tight room, entering it, and closing the door. This procedure is commonly referred to as expedient sheltering-in-place. In this simple form, a safe room protects its occupants by retaining a volume of clean air and minimizing the infiltration of contaminated outdoor air. In practice, however, a safe room is not perfectly tight. The natural forces of wind and buoyancy act on small, distributed leakage paths to exchange air between the inside and outside.
As contaminated air infiltrates a safe room, the level of protection to the occupants diminishes with time. With infiltration in a sustained exposure, the concentration of toxic vapor, gas, or aerosol in the safe room may actually exceed the concentration outdoors because the sealed safe room tends to retain the airborne contaminants when they infiltrate. Once contaminants have entered, they are released slowly after the outdoor hazard has passed. To minimize the hazard of this retention, an unventilated safe room requires two actions to achieve protection.”
It then continues on by describing how to go about adding CBR protection to your safe room.
Overall, it’s a great reference document if you plan on making a safe room in your home.
You can download the PDF of this chapter here: CBR Threat Protection.
Or, if you’d like to see the entire document, you can find in on this FEMA webpage: Safe Rooms and Shelters – Protecting People Against Terrorist Attacks.