It is a reinforced concrete structure, with a thickness of approximately 30 centimeters. Soils, walls and roof are made of this material, with steel rods that run through it, so that it is completely compact and closed, as if it were a shoebox. The rods are specially designed, since they are the ones that make it a rigid box, with a lot of resistance.
It should be noted, however, that the minimum surface per person is one square meter.
Access to the cabin is made by a rather peculiar door, with the same characteristics as the emergency with which the shelter must also be provided. They are made of reinforced concrete. Its weight is two tons, although they can be opened with a finger. For the seal to be hermetic, instead of fitting into the fence, the door is larger. Thus, it protrudes from the gap, and the adjustment is produced by rubber weatherstripping.
Also, the doors are not located at random. If one of them is located so that the access from the house is simple and as fast as possible, the other has exit outside the area of collapse of the property, free of the debris area, since these could prevent the exit.
There is a closed area - just inside - where the air that can enter when opening the door is cleaned, so that even if it penetrated there, it would not reach the interior of the main passenger compartment. In this space are also located toilets.
This lock expels the contamination with a simple mechanism: it collects the air from outside, it passes through a filter that cleans it and it ends up breathing in the interior.
In addition, there is a pressurization of the passenger compartment above the ambient pressure to avoid, in case of leaks of the structure, air access from the outside. That is, the inner air is at greater pressure than the exterior, preventing the contaminated can enter by cracks, gaps or any hypothetical opening.
Other essential elements for the construction of a safe haven are ventilation and filtration systems, passenger compartment cooling air, generator set for energy supply and oil tank.
On the other hand, there are the appropriate facilities to house the equipment and to be able to live comfortably in the interior for the necessary time.