Extremely Hard Design (50 PSI) Rating, Includes:
Design Assumptions/Must Withstand:
1: 2 1/2 miles from 20 megaton blast
2: 1000 Miles per hour wind
3: 40 G shock wave
4: high velocity debris
5: Intense radiation, heat and electromagnetic effects

Design Criteria/Stats:
1: Below grade construction with 2 ft concrete walls and a minimum of 4 ft of earth over cover
2: Shock mounting on communications equipment to reduce excelleration to 8 g's
3: Metal shield completely enveloping structure (-80 db at freqs above 10 Khz)
4: Provisions for flexing of incoming cables at entrance points
5: Above ground structure (microwave and troposcatter antennas) require at least two thirds of the
structure to be below grade to prevent tilting or rotation
6: Microwave antennas require tilting to shed debris, beryllia window to resist over pressure, flame sprayed aluminum finish to reflect heat and concrete filling for weight.

Typical Structures/Areas/Locations:
1: Buried cable 4 ft deep i.e.: L-4
2: Military locations with troposcatter and line of site microwave
3: L-3 and L-4 main stations less than 5 miles from a potential target
4: L-3 and L-4 repeater and equalizing stations (18" earth over cover)

P.S. This typical structure is less than 5 miles from Downtown Detroit, which is a potential target due to Detroit being a major city.

Although this has an Extremely Hard Design (50 PSI) rated AT&T Long Lines Facility, it also has windows, which could be a weak point for the building. However, these windows are small, only at the first floor level, & seem to have a size of around 2X1 feet, being 2' wide & 1' tall.