ratified the treaty, including the US and China. France, Russia, and the UK have ratified the CTBT. The technology for detecting underground tests has significantly improved since the 1950s and 1960s, with monitors detecting tests down to 1 kiloton with a high degree of confidence. Violations and accidents Early compliance with the PTBT was believed to be good, but there have been a number of accidental releases of nuclear debris into the atmosphere by parties to the treaty. Additionally, "venting" of underground tests by the US and the Soviet Union also continued to release radioactive debris into the atmosphere. Fully contained underground tests were not wholly "clean" either. Underground testing reduced the risk caused by radionuclides with short half-lives, such as iodine-131, and is generally safer than other forms of testing. However, underground testing may also cause long-lived radionuclides, including caesium-135, iodine-129, and plutonium, to seep into the ground. A notable atmospheric release of radioactive gas followed the Soviet Chagan test of 15 January 1965 in present-day Kazakhstan. Roughly 20% of the radioactive debris produced by the 140-kiloton detonation was released into the atmosphere, with some fallout occurring over Japan. The US complained to Moscow, but no subsequent action was taken. On 25 April 1966, the Pin Stripe underground test in Nevada (part of Operation Flintlock) experienced a venting malfunction and produced a radioactive plume headed towards the Midwestern United States; the AEC determined that the test did not threaten human health. Another accidental release occurred following the Baneberry shot at the Nevada Test Site on 18 December 1970 (part of Operation Emery). The 10-kiloton underground detonation produced a fissure in the ground, which allowed radioactive gas to escape into the atmosphere. Radioactive material released by the fissure reached an altitude of and exposed 86 workers to radiation but none at excessive levels. The incident has since been described as one of the "world's worst nuclear disasters." Declassified US documents indicate that the US may have violated the PTBT's ban on atmospheric testing in 1972 by, at the instruction of Henry Kissinger, monitoring and collecting data on French atmospheric tests over the Pacific Ocean, which may have amounted to co-operation with the French program. Declassified documents also indicate that the US and the UK circumvented the prescribed verification system in 1964–65 by establishing a series of additional control posts in Australia, Fiji, Mauritius, Pakistan, and South Africa. The 1979 Vela