36 © The Containment of Underground Nuclear Explosions Photo creat Swoas met wry Blanca containmentfailure, 1988. kilotons. The first few tests after Rainier. however, were detonated at greater depths than this formula requires because it was more convenient to mine tunnels deeper in the Mesa. It was not until ““Blanca,’’ October 30, 1958, that a test was conducted exactly at 300 (yield)feet to test the depth scale. The containment of the Blanca explosion, however, was unsuccessful and resulted in a surface venting of radioactive material. As a consequence, the depth scale was modified to include the addition of a few hundred feet as a safety factor and thus became: 300 (yield)? *‘plus-a-tew hundredfeet." Today, the general depth of burial can be anpros mated by the equation: Depth = 400 (yield) ©. where depth is measured in feet and vicid in kilotons.'* The minimum depth of burial. however, is 600 feet.'5 Consequently, depths of bunal van from 600 feet for a low-yield device, to about 2.100 feet for a large-yield test. The depth is scaled to the '2**Public Safety for Nuclear Weapons Tests,"’ United States Environmental Protection Agency, January, 1984. 3The 600-foot depth was chosen as a minimum after a statistical study showed that the likelihood of a seep of radioactive maternal ly the surtse cor explostons buned 600 feet or more was about 1/2 as great as for explosions at less than 500 feet. even if they were buried at the same wane depen in each case.