2023 World Conference against A and H Bombs
International Meeting -- Session 1
The Significance of Hiroshima High Court Decisionon A-Bomb ”Black Rain” Lawsuit
TAMURA Kazuyuki
Professor Emeritus, Hiroshima UniversityIntroduction
The Hiroshima High Court on July 14, 2021 ordered the issuance of Atomic Bomb Survivor’s
Certificate to 84 Plaintiffs, recognizing that they all had been affected by the “Black Rain” thatfell shortly after the A-bomb explosion in Hiroshima and that they must be considered as
hibakusha as defined by the A-Bomb Survivors Relief Law.
This report presents the gist of that court decision and attempts to indicate that the decision isuseful for reflecting what should be appropriate aid and remedy to be extended to hibakusha,
the A-bomb survivors, as well as other radiation victims at large.
1. Laws Providing for the Aid to A-bomb Victims
The first laws set in place for providing relief to hibakusha included the Act for Atomic Bomb
Sufferers' Medical Care instituted in 1957 and the Law Concerning Special Measures for ABomb Sufferers enacted in 1968. In 1994, these two laws were consolidated into a single act
which is the Law Concerning Relief to Atomic Bomb Survivors, currently in effect.
The provisions of the A-Bomb Survivors Relief Law are intended for living hibakusha alone(deceased hibakusha are excluded from the law subjects) and designed to help hibakusha only
for the health damage they still suffer and that is known to be caused by the A-bomb radiation.
It is explained that these limitations are placed because the health damages hibakusha suffer are“special damage”, distinctive of other common war damages.
The A-Bomb Survivors Relief Law distinguishes four categories of “hibakusha”:
1(1) Those who were in the city zones or in the zones adjacent to them in Hiroshima andNagasaki at the time of the A-bomb explosion;(2) Those who were in the areas within 2 kilometers from the ground zero at the time of theexplosion or during the two weeks that followed;(3) Those who were in situations where they might physically be exposed to A-bomb radiation
at the time of explosion or afterwards;(4) Fetus in the womb of people who fall under the three categories above.
The definitions of hibakusha categories (1), (2) and (4) correspond very precise to concepts thatleave almost no room for discretion, while that for category (3) gives some room to discretion
and its substance is to be determined by legal interpretation. So far, most hibakusha have been
categorized as (1) or (2), whereas category (3) has been considered as a supplementary subcategory.
The number of holders of Hibakusha Certificate peaked in March 1981 with 372,264
individuals. By March 2023, their number has decreased to 113,649 and their average age 85.
The A-Bomb Survivors Relief Law provides for free health checkup, free medical care forsickness and wounds caused by the A-bombing (A-bomb disease), free medical care forsickness and wounds other than A-bomb disease (public health insurance premiums are to be
paid by hibakusha), and a few types of allowances (payment of money). At present, about 90%of the hibakusha receive some type of allowance.
Hibakusha have fought many court battles to obtain the entitlements by virtue of the A-Bomb
Survivors Relief Law, including lawsuits for A-bomb disease recognition, for the application of
the A-Bomb Survivors Relief Law to hibakusha residing outside Japan and for the issuance of
Hibakusha Certificates etc. They have won many of these lawsuits so far.
2. Hiroshima High Court Ruling on A-bomb “Black Rain” Lawsuit
As mentioned at the beginning, Hiroshima High Court decided that the people caught in the Abomb “Black Rain” should be considered as hibakusha. On that ground, it ordered that theHibakusha Certificate should be issued to the Plaintiffs. With this decision, the Hibakusha
Certificate was accorded also to those who were not the plaintiffs of the initial lawsuit but who
2could be recognized as having been in similar situations as the initial plaintiffs at the time ofthe A-bomb explosion. The number of those who have obtained Hibakusha Certificates has
already exceeded 4,000.
The ”Black Rain” is a black-colored rain containing mud or oil that fell from pyro
cumulonimbus clouds formed in the sky right after the A-bomb explosion. It contained
radioactive particles produced within the fireball created by the A-bomb explosion. Therefore,people who were showered with that rain were exposed to radiations externally. They were also
exposed internally to radiation, by taking into their bodies food and drinks contaminated withthese particles.
The area where the “Black Rain” showered following the A-bomb explosion in Hiroshimaextends to all directions around the ground zero. According to Doctor MASUDA Yoshinobu,
its longer diameter was over 50km and shorter diameter 30km (see the map of the Black Rainfall
areas). The Ministry of Health and Labor assumed that the Black Rain fell over an oval-shape
area with a little less than 30km of major axis and 15km of minor axis. But it recognized as
hibakusha of category (3) only those who were located within an oval area of 19km by 11km(heavy downpour zone), and since 1976, has issued the Hibakusha Certificates to them, bywhich they were entitled to receive official aid measures provided by the State.
For many years, those who were showered with “Black Rain” outside the heavy downpour zone
have been demanding that Hibakusha Certificates be accorded to them, claiming that theyshould fall under the category (3) hibakusha, but the Ministry of Health and Labor has turned
down their demand, saying that there was not scientific evidence to support their claim. In 2015,
these people (the Plaintiffs) took their case to the court.

Both the Hiroshima District Court(tribunal of first instance) and the Hiroshima High Court (second instance) accepted the demandof the Plaintiffs doing justice to all of them.
The gist of Hiroshima High Court ruling is as follows:l“Those who were placed in situations where the occurrence of any health damage by Abomb radiation cannot be denied” shall be considered as category (3) hibakusha.

lWhile it belongs to the Plaintiffs to prove that they were actually caught in the “Black Rain”
and that the possibility of incurring health damage by exposure to radiation cannot beexcluded, they do not need to prove that the radiation exposure in question was so3

“significant” as to cause late effects on their health.
l

Even if a person is not showered with “Black Rain”, in the event that this person aspires
air-born radioactive particles, drinks well water containing radioactive particles that fell on
the soil or eats vegetables with these particles stuck on their surface, he or she is likely tosuffer from health damage due to internal radiation exposure. The Plaintiffs are recognized
as having suffered these types of radiation exposure and therefore they can be categorizedas (3) hibakusha.

l

It is not appropriate to conclude that the “Black Rain” did not fall at all in the areas locatedoutside the “downpour zone”(see the map).

l

Having disease is not a requirement for the recognition as category (3) hibakusha.

3. Significance of Hiroshima High Court RulingIn this part of the report, the significance of the ruling, as well as how the decisions containedin the ruling could be used efficiently for providing relief to the victims of radiation exposure
other than those caused by the atomic bombing are discussed. The opinion of Lawyer
TAKEMORI Masahiro, Plaintiffs’ representative in the A-bomb “Black Rain” lawsuit, is used
as reference in the discussion.
i The ruling took into account the stochastic effects of mutations in DNAs as well as inchromosomes provoked by the A-bomb radiation and acknowledged that being showered with
“Black Rain” might have caused health damage on human body. This way of thinking is at theantipode of that of the Ministry of Health and Labor which ignored the stochastic effects ofradiation exposure, in its attempt to deny health damage insisting on the difference in exposure
dose of each individual hibakusha.
iiThe ruling decided that the scope of category (3) was wider than it had been usuallyunderstood. Therefore a wider interpretation of the category (3) definition should be used forthe hibakusha recognition procedure. The Ministry of Health and Labor claimed that, at thetime of atomic bombing in Nagasaki, no precipitation of the “Black Rain” was seen in the areas
7.5km from the hypocenter or beyond, to assert that people who were in these areas cannot be
considered as falling under category (3). This argument is not appropriate since it is clear that,in Nagasaki, radioactive particles fell over a vast area spreading to the east of the ground zero.

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iii

The ruling judged that it was possible (not deniable) that the intake of radioactive

particles produced by the atomic explosion into the body (internal exposure) caused healthdamage and concluded that the people suffering the damage should be entitled to official
hibakusha aid scheme. Such an idea of aid for radiation victims should be largely taken into
account for designing appropriate aid measures for other type of radiation exposure sufferers
such as those victims of Fukushima nuclear power plant accident.
iv

In dealing with nuclear power plant accidents or pollution with harmful substances, theJapanese government intends to use scientific knowledge as they did with the damage of atomic
bombing, for the purpose of minimizing the extent of damage and reducing the scope ofremedies provided to victims. This ruling, on the contrary, argues that if possibility of healthdamage cannot be totally excluded by the latest scientific knowledge, measures for relief should
be provided to victims. Scientific knowledge should be used in this way.
I wish to examine whether or not the aid for A-bomb victims provided by virtue of the A-Bomb
Survivors Relief Law is appropriate in the light of Article 6-1 of the Treaty on the Prohibitionof Nuclear Weapons, but I will do it in another occasion.
----------------------------------------------------<References>
Tamura Kazuyuki and Takemori Masayasu. Atomic Bomb “Black Rain” Lawsuit.
Honnoizumisha, 2023. (in Japanese)
Koyama Misa. ”Black Rain” Lawsuit. Shueisha, 2022. (in Japanese)56