Estimations of heights of past tsunamis are a key to forecast oncoming earthquakes and tsunamis. Generally, the heights of the historical tsunamis have been measured based on historical documents which describe actual marks of the tsunami inundation, such as “the tsunami came up to the fifth steps from the bottom in the temple”, and based on measurements of their heights by field surveys. However, some of the historical documents recorded only number of houses damaged due to the tsunamis. The records obviously indicate that the large tsunamis actually inundated. They are difficult to estimate the tsunami heights because they include no marks which the tsunami rose up to. Tsunami fragility can be useful to estimate the tsunami heights from the damage data, but no existing tsunami fragility targets historical tsunamis. Because strength of houses in historical era may be different from that in nowadays, formulation of tsunami fragility for historical tsunamis is necessary.

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The divergent experts' views on the risk of low level exposure to radionuclides in foods as a result of the Fukushima Daiichi Nuclear Power Plant accident were one of the sources of public distrust and confusion in the aftermath of the disaster. How should the decision-makers develop risk management measures in face of such complex risk and uncertainty? Joint Fact-Finding (JFF) is a collaborative approach or process that provides a forum for (a) co-framing what problem needs to be addressed and (b) co-producing “jointly found fact” including the areas of agreement and disagreement. The aim of this paper is to analyze the findings from the experimental case of JFF. Through JFF, the following findings were identified; different views among experts stemming from their disciplines, various approaches towards scientific uncertainty, the interface issue between risk assessment and management, and the different management paradigms between food risk control and radiological protection.

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This paper will review current radiological protection (RP). Risk concept has been proposed in the light of precautionary principle since 1950's, although RP philosophy has been historically built partly based on scientific evidence. RP uses the risk estimate of cancer obtained by epidemiological studies. Linear-Non-Threshold (LNT) models assume there is some probability no matter how low dose is received, since convinced evidence has not been established on radiation risk at low-dose and low-dose rate. How to apply the risk concept is a key issue in radiological protection. RP introduces three fundamental principles such as justification, optimization and dose limitation. Furthermore, RP uses a situation-based approach where planned, emergency and existing exposure situations are defined. In an existing exposure situation after the Fukushima accident, reference levels can be applied to drive risk reduction using protective actions such as evacuation and foodstuff restriction. The risk concept can explain why the dose limits used in a planned exposure situation should not be applied in terms of risk-tradeoff.

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This paper discusses safety goals in the field of chemical risk management. Safety goals have been quantitatively described as a magnitude of risk and applied on genotoxic carcinogens. In the US or European society, 10⁻⁵ or 10⁻⁴ of lifetime risk as “acceptable risk” and 10⁻⁶ of lifetime risk as “de minimis risk” have been applied commonly. 10⁻⁴ or 10⁻³ of lifetime risk is used as a reference value when we characterize risk in the field of occupational health. The historical background of selecting the safety goal values in the US was reviewed. It is challenging and important to identify the safety goals which are suitable for Japanese societal context, and a framework of decision making and review of the social safety goals will be required.

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