FEMA 453 Design Guidance for Shelters and Safe Rooms

stainless steel cables connected with a shock-absorbing device
to an aluminum box section, which is attached to the jambs,
the underside of the header, and topside of the sill. The energy
absorbing characteristics allow the catch systems to be attached
to relatively weakly constructed walls without the need for additional
costly structural reinforcement. To reduce the possibility
of slicing the laminated glass, the cable may either be sheathed
in a tube or an aluminum strip may be affixed to the glass directly
behind the cable.
2.5.2.3 Internal Partitions. Unreinforced masonry walls provide
limited protection against airblast due to explosions. When subjected
to overload from air blast, brittle unreinforced CMU walls
will fail and the debris will be propelled into the interior of the
structure, possibly causing severe injury or death to the occupants.
This wall type has been prohibited for new construction where
protection against explosive threats is required. Existing unreinforced
CMU walls may be retrofitted with a sprayed-on polymer
coating to improve their air blast resistance. This innovative retrofit
technique takes advantage of the toughness and resiliency
of modern polymer materials to effectively deform and dissipate
the blast energy while containing the shattered wall fragments.
Although the sprayed walls may shatter in a blast event, the elastomer
material remains intact and contains the debris.
The blast mitigation retrofit for unreinforced CMU walls consists
of an interior and optional exterior layer of polyurea applied to
exterior walls and ceilings (see Figure 2-16). The polyurea provides
a ductile and resilient membrane that catches and retains
secondary fragmentation from the existing concrete block as it
breaks apart in response to an air blast wave. These fragments, if
allowed to enter the occupied space, are capable of producing serious
injury or death to occupants of the structure.
Structural deSign criteria
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