cover" against a solid inner wall of a school, if time does not permit seeking better shelter—such as a storm cellar—during a tornado warning. The tactic is also widely practiced in schools in states along the West Coast of the United States, where earthquakes are commonplace. Ducking and covering in either scenario would theoretically afford significant protection from falling or flying debris. Earthquakes In an earthquake, which are generally of a natural tectonic plate origin (although they can be artificially generated by the detonation of a nuclear explosive device in which sufficient energy is transmitted into the ground, with an extreme case to serve as an example of this phenomenon being the Operation Grommet Cannikin test of the 5 megaton W71 warhead exploded deep underground on Amchitka Island in 1971, which produced a seismic shock quake of 7.0 on the Richter magnitude scale) people are encouraged, regardless of the cause of the quake, to "drop, cover and hold on": to get underneath a piece of furniture, cover their heads and hold on to the furniture. This advice also encourages people not to run out of a shaking building, because a large majority of earthquake injuries are due to broken bones from people falling and tripping during shaking. While it is unlikely that "drop, cover and hold on" will protect against a building collapse, in earthquake-prone areas in the United States building codes require that buildings withstand quakes up to an expected magnitude enough to allow evacuation after shaking stops. and thus a building collapse of these structures (even during an earthquake) is rare. "Drop, cover and hold on" may not be appropriate for all locations or building types, but the Red Cross advises it is the appropriate emergency response to an earthquake in the United States. See also General A Day Called X a dramatized 1957 CBS documentary following the evacuation drill of the entire city of Portland, Oregon per Civil Defense protocol, in response to the RADAR detection of an en-route Soviet nuclear bomber force. Abo Elementary School - Underground school built in the 1960s, used until the 1990s Air-raid shelter Atomic Bomb Casualty Commission - upon whose work the writers of Duck and Cover heavily borrowed. Blast shelter Civil Defense Geiger counters Comparison of Chernobyl and other radioactivity releases CONELRAD Desert Rock exercises Enewetak Atoll High-altitude nuclear explosion List of artificial radiation belts List of nuclear weapons#Soviet Union/Russia