The earliest shelters were built after ion storms decimated population centres, including an incident in which Dr Ignatio Mobius and his top research staff were killed by a lightning bolt striking their bunker.
Typically, shelters are located between 10 and 30 metres below ground level, but no closer than 70 meters to underground Tiberium or water deposits. Their construction includes foot thick, steel-reinforced concrete walls with integrated Sonic Emitters to prevent nearby Tiberium growth. Newer shelters include dormitories, cafeterias, medical facilities, vehicle maintenance garages, long-term power generators and redundant Sonic Emitters. In high-risk areas, some shelters have gained cultural significance as centres of social activity from sports to art and music events, gaining nicknames such as "Sector 7", "Old Blue" and "The Hatch".
Many private organisations have developed smaller shelters for corporations and individuals at exorbitant prices. On rare occasions, these private shelters link with official GDI shelters via underground tunnels. Private citizens with shelters that link to GDI Public Shelters are required by law to allow access to anyone who requests aid during Class C emergencies and above.