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Survey raises possibility of expanding area of black rainfall

by Uzaemonnaotsuka Tokai, Staff Writer

On January 25, the results of a survey conducted by Hiroshima City and Hiroshima Prefecture revealed the possibility that the black rain which fell in the aftermath of the atomic bombing of Hiroshima may have covered an area roughly three times the size of the area set by the Japanese government. The city will use the survey results to make a request to the government that the "Health Examination Special Designated Area," which is described in the Atomic Bomb Survivors Relief Law as the "heavy rain area," be expanded.

The survey was distributed to 36,614 people, mainly A-bomb survivors and those exposed to the black rain, in and around the city from June to November 2008. The respondents were asked to fill in the survey forms and send them back. Among the responses from 27,147 people, the data of 1,844 respondents which included mention of the times and locations of the black rain were analyzed.

The results show that the black rain began to fall immediately after the atomic bombing, or after 8:15 a.m., in the western part of the city and covered the largest area between 10 a.m. and 11 a.m. Regarding the distribution of those who were exposed to the black rain, the respondent in the northernmost location was in former Tudani Village (now, Kitahiroshima Town), the respondents in the westernmost location were in former Sagotani Village (now, Yuki Town in Saeki Ward) and in the former Hatsukaichi Town (now, the city of Hatsukaichi), and the respondent in the easternmost location was in former Mita Village (now, Shiraki Town in Asakita Ward).

The rainfall area that has emerged as a result of this survey is about six times larger than the "heavy rain area," which was defined on the basis of a 1945 survey, and about three times larger than the "heavy rain area" and the "light rain area" combined. A further possibility about the rainfall has also arisen. One response to the survey indicated that the black rain fell for more than four hours in former Minochi Village (now, Yuki Town), about 20 kilometers northwest of the hypocenter, a part of which is defined as a "light rain area."

Regarding the black rain's impact on human health, 16 percent of those exposed to the black rain in the "heavy rain area" answered that they suffered from diarrhea or hair loss, while 10 percent of those exposed to the black rain in the other areas also suffered from diarrhea or hair loss. These figures are substantially higher than the 3 percent of those who were not exposed to the atomic bombing or the black rain but still suffered from such symptoms.

On January 25, the survey results were released at the meeting of the Hiroshima City Investigative Research Study Group on the Actual Situation of the Atomic Bomb Damage, comprised of researchers and employees of Hiroshima City and Prefecture. Kenji Kamiya, chair of the study group and director of Hiroshima University's Research Institute for Radiation Biology and Medicine (RIRBM), explained, "This is the largest survey ever conducted and provides useful data for illuminating the actual circumstances of the A-bomb damage." The group will compile its final report by the end of March.

Keywords

Black rain
The black rain, which is believed to have contained radioactive fallout, fell immediately after the atomic bombing. In 1945, meteorological technicians at the Hiroshima District Meteorological Observatory interviewed 118 local residents and checked the area of the black rainfall. In 1976, the Japanese government defined an oval area stretching northwest from the hypocenter for about 19 kilometers from north to south and for about 11 kilometers from east to west as the "heavy rain area" and designated the area as the "Health Examination Special Designated Area." Those who were in the area at the time of the atomic bombing are provided with health checkups in line with the Atomic Bomb Survivors Relief Law. Concerning the area stretching northwest from the hypocenter for about 29 kilometers from north to south and for about 15 kilometers from east to west, which includes the above-mentioned "heavy rain area," the Japanese government defined the other area of the oval as the "light rain area" and did not include it in the "heavy rain area."

(Originally published on January 26, 2010)

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