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" ANCOLD GUIDELINES ON RISK ASSESSMENT . POSITION PAPER ON REVISED CRITERIA FOR ACCEPT ABLE RISK TO LIFE by ANCOLD Working Group on Risk Assessment INTRODUCTION In 1994 A.NCOLD (Australian National Cominittee on Large Dams) published Guidelines on Risk Assessment for the first time. That document sought to identify the fundamental concepts that underpin risk assessment and to provide a philosophic foundation that would enable practitioners to start applying risk assessment principles in the evaluation of dam safety. In the 1994 Guidelines, ANCOLD took the controversial step of setting quantitative criteria for acceptable risk to life after considering actual and proposed criteria in land use planning and in the chemical and nuclear industries. By the early 1990's, there was almost universal acceptance that the earlier trend to value human life in dollar terms (see for example, ASCE, 1973) was not appropriate to contemporary societal values. In other industries, the concept of placing limits on the probability of life loss was emerging as the preferred way of dealing with risks to human populations. Nevertheless very few jurisdictions had actually established quantitative criteria for acceptable risk to life. ANCOLD took the view that it was better to provide clear guidance by way of quantitative criteria, albeit conservative criteria initially, than to make vague statements about the importance of limiting risks to life. The need to stand ready to review those criteria as knowledge and experience were gained, was recognised at the time. The 1994 Guidelines have been very successful in promoting widespread integration of risk assessment into the process of dam safety evaluation in Australia. Understandably, as the Guidelines were put into practice, a need soon emerged for clarifications. Also as better understanding was achieved through experience in applying the Guidelines, improvements were suggested. As a means of dealing with such issues in this rapidly developing field, ANCOLD appointed a working group charged with preparing a Commentary on the 1994 Guidelines. The group has been active since late 1995 and now has ten members. Developments, both in Australia and in other countries, have been so rapid that it is now apparent that updated Guidelines, rather than a Commentary, are needed to keep ANCOLD members abreast of current practice. The Al"lCOLD Executive has approved of the production of new Guidelines and drafting of the document is well in hand. In the interim, the working group has substantially finalised its position on criteria for acceptable risk to life. The primary purpose of this statement is to apprise practitioners of the updated criteria so that they can be taken into consideration in dam safety reviews, pending publication of the new Guidelines. A secondary purpose is to provide an opportunity for debate on the criteria and to identify any aspects requiring clarification, prior to publication of the updated Guidelines. Risk to life criteria are a critically important facet of risk-based decision making. It remains the case that ANCOLD is the only national body to have sel quantitative criteria for acceptable risk to life in the evaluation of dam safety. For these reasons it is desirable that the criteria are publicised as widely as possible and lhat controversial aspects are vigorously