The ECD 60 is a 60 ft diameter x 22 ft tall clamshell 40 psi dome. It is shown here as a stand-alone underground structure. It is designed as a two story structure with almost 5000 ft2 on two levels. It can have any floor plan and is usually used to protect 10-50 people. The spiral stairwell has a 2500 gallon diesel tank on the bottom with a hydraulic hatch at ground level. This structure is usually equipped with two 6 kw diesel generators and two MCAS 600 units allowing a shelter duration up to five years. The secondary exist is shown opposite the spiral stairwell.