'Baneberry' on 18 December 1970, an underground test
that vented large amounts of radioactive debris

18 December 1970 - the Baneberry incident

Fallout from the Baneberry test. Source – www.260press.com

On 18 December 1970, the Unites States conducted the Baneberry underground test at the Nevada Test Site. Although the 10 kiloton device was detonated at 270 metres below the surface, a large cloud of radioactive dust was released into the atmosphere.

For the first time since the Partial Test Ban Treaty (PTBT) had driven nuclear testing underground in 1963, a nuclear testing cloud could be observed as far away as Las Vegas, 120 kilometres from the test site. According to a report (PDF) by the National Cancer Institute, Baneberry released 80,000 curies of radioactive iodine-131 into the atmosphere - more than any other U.S. underground nuclear test and comparable to a smaller atmospheric nuclear test. The radioactive dust reached a height of around three kilometres, from where it was carried by winds into several adjacent U.S. states. Read more on the effects of U.S. nuclear testing.

The highest exposures … were received by two security guards and were about 30 percent of the Federal Radiation Council’s quarterly guide for the whole body and about 37 percent of the guide for thyroid exposure.U.S. Atomic Energy Agency Commission report
The Baneberry Vent: A Geologist Remembers, by Larry Ramspott

The fallout also rained down locally, affecting 86 workers at the test site. Although the U.S. Department of Energy stated that none of them had been harmed, two of the workers died four years later from leukaemia. Their widows subsequently filed lawsuits against the U.S. government. In a 1996 ruling, a U.S. Court of Appeals found the government to have acted negligently, but concluded that the Baneberry test did not cause the cancer.

After the Baneberry incident, nuclear testing at the Nevada Test Site was suspended for six months pending investigation. The official report (PDF) issued by the U.S. Atomic Energy Agency Commission concluded that the primary cause of the venting was “an unexpected and unrecognized abnormally high water content in the medium surrounding the detonation point.”

Treaty status of the 44 'nuclear capable' States listed in the CTBT whose ratification is precondition for entry into force. Click to enlarge.

The United States continued conducting underground nuclear tests for over 20 years until the ‘Divider’ test on 23 September 1992. In 1996, it was the first country to sign the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which bans all nuclear explosions. The United States is one of the few countries that has yet to ratify the Treaty for it to become global law. The last one to have done so is Indonesia, who ratified the CTBT on 6 February 2012.


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Next featured nuclear test:

27 January - the first nuclear test at the Nevada Test Site in 1951