Switzerland built an extensive network of fallout shelters (mainly through extra hardening of government buildings such as schools) of a scale to protect and feed the entire population for two years after a nuclear attack. This nation has the highest ratio of shelter space to national population of any country. All these shelters are capable of withstanding nuclear fallout and biological or chemical (NBC) attacks but the blast-proof requirement varies depending on the size of the building. The largest buildings usually have dedicated shelters tunneled into solid rock. Similar projects have been undertaken in Finland, which requires all buildings with area over 600 mē to have an NBC shelter, and Norway, which requires all buildings with an area over 1000 mē to have a shelter[1].
