In the fourth project, when the nuclear explosion comes, the lives are burnt, people cannot survive, they lose food, water, and living environment, and the lives of people who are exposed to nuclear radiation will also be short-lived. 
 
After the explosion, the sensing device of the building on the ground sensed that the nuclear radiation exceeded the value and activated the entire device, causing the building to slide underground to ensure people's safety. After the building is slid into the ground, there will be a sliding passage of building modules to connect with the rooms of the underground building. There are also passages on the wall of the underground building to other shelters so that different shelters can communicate with each other.