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In paragraph 6.2.2.2 Probability of a Specific Failure Mode of EEUMA Publication No. 159 is the following text, "The cornerstone of RBI is the assessment of an item's risk classification, since the RBI methodology is risk-based. Generally, risk is defined as the probability of occurrence (likelihood) of harm (failure) and the consequences of that harm... Generally, the RBI method takes into account those degradation mechanisms affecting the tank during normal operations (corrosion, fatigue, etc.). However, failures as a result of excursions outside the defined operating window should also be considered. Many degradation mechanisms are time -dependent (e.g., general corrosion, settlement)... In reality, the degradation rate may vary over time. This aspect should be considered, and `worst case' assumptions made to provide acceptable safety margins. Through inspection, the average rates of degradation may become better defined. Some degradation mechanisms are independent of time, and occur when there are specific conditions present. These conditions may not have been predicted in the original assessment. For this reason, RBI should be applied on a single or individual basis, where tank history and specific experiences with the particular tank are taken into account within the whole RBI process." In paragraph 6.2.2.4 Risk Rating of EEUMA Publication No. 159 is the following text, "Quantification of the risk is generally assessed in a semi -quantitative way by estimating the probability of a (specific) failure mode and a consequence rating for that failure mode which, combined in a risk matrix, leads to a risk class or rating... The main purpose of risk rating is to focus attention on the high risk items..." Risk-based inspections and the SP001 Standard EEUMA Publication No. 159, as well as API Recommended Practice 580, Risk -Based Inspection, and API Publication 581, Risk -Based Inspection, provide the steps necessary to establish a risk-based preventive maintenance program. Likewise, these publications include steps needed to assigning numerical values to both likelihoods and consequences (as described in paragraph 6.2.2.4 of EEUMA Publication No. 159). Lastly, it is recommended that users of these publications consult individuals knowledgeable in tank design and RBI methodology in establishing inspection programs based on the RBI principles. 4