FEMA 453 Design Guidance for Shelters and Safe Rooms

CBR ThReaT pRoTeCTion
Figure 3-
Task 3. Determine the Level of Safe Room Positive Pressure
Required
For a safe room of this height, buoyancy pressure is significant,
and both wind pressure and buoyancy pressure must be considered
in determining the safe room operating pressure. As a corner
stairwell, it has two exterior walls. The pressure requirement is defined
as the velocity pressure of a 20-mph wind plus the buoyancy
pressure that occurs against ground-level doors and other points
of leakage at winter design conditions. With a height of 140 feet,
the maximum buoyancy pressure at the lowest level of the stairwell
is calculated at 0.11 iwg for a 60-degree Fahrenheit indooroutdoor
temperature differential. Adding the maximum wind
pressure of 0.2 iwg for a 20-mph wind yields a design pressure of
0.3 iwg. At an internal pressure of 0.3 iwg, the force required to
a blower door test on the selected safe room aids
in estimating the size of air-filtration unit required
and in identifying air leakage paths.
SoURCe: BaTTelle
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