FEMA 453 Design Guidance for Shelters and Safe Rooms

2.1 OVerVieW
Structural deSign criteria
Structural deSign criteria 2
this chapter discusses explosive threat parameters and
measures needed to protect shelters from blast effects.
Structural systems and building envelope elements for
new and existing shelters are analyzed; shelters and FEMA model
building types are discussed; and protective design measures for
the defined building types are provided, as are design guidance
and retrofit issues. The purpose of this chapter is to offer comprehensive
information on how to improve the resistance of shelters
when exposed to blast events.
2.2 explOSiVe threat parameterS
A detonation involves supersonic combustion of an explosive material
and the formation of a shock wave. The three parameters
that primarily determine the characteristics and intensity of blast
loading are the weight of explosives, the type of the explosives,
and the distance from the point of detonation to the protected
building. These three parameters will primarily determine the
characteristics and intensity of the blast loading. The distance of
the protected building from the point of explosive detonation
is commonly referred to as the stand-off distance. The critical
locations for detonation are taken to be at the closest point that
a vehicle can approach, assuming that all security measures are
in place. Typically, this would be a vehicle parked along the curb
directly outside the facility, or at the vehicle access control gate
where inspection takes place. Similarly, a critical location may be
the closest point that a hand carried device can be deposited.
There is also no way to effectively know the size of the explosive
threat. Different types of explosive materials are classified as High
Energy and Low Energy and these different classifications greatly
influence the damage potential of the detonation. High Energy
explosives, which efficiently convert the material’s chemical
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