California Sea Grant College Program

The source of a majority (more than 80%) of high-consequence marine accidents can be attributed to compounded human and organizational errors (HOE). Recent examples include the Exxon Valdez tanker grounding (258,000 barrels of oil spilled), and the Occidental Piper Alpha platform explosions and fires (167 men killed). Currently, there is no structured quantitative approach to assist engineers, operators, and regulators of marine systems to either design HOE tolerant systems or to include considerations of HOE as an integral part of the design, construction, and operation of marine systems. The human element has generally been ignored.

The objective of this dissertation is to introduce a quantitative modeling methodology to assess the impacts of HOE in operation of tankers and offshore platforms. This methodology includes a systematic approach to structuring critical elements that lead to accident scenarios and a quantitative modeling procedure to assess the impacts of operational risks under various operating conditions that can lead to these scenarios.

The modeling methodology incorporates structuring accident scenarios into underlying, direct, and compounding factors. Diagrammatic representations of the unique factors leading to accident scenarios using influence diagrams are proposed. The diagrams are used to develop simplified general "templates" for that particular class of accident. The function of the templates are to form a basis that preserve the central causative mechanisms for a similar operation, yet do not preserve the unique aspects of the disaster being modeled.

Insufficient and unreliable data linking complex effects of human errors to marine casualties has led to limitations in quantitative human error modeling. A quantitative measuring technique, the Human Error Safety Index Method (HESIM), has been proposed that measures organizational, task and system complexities, and environmental factors that affect operators abilities to perform decisions and actions to mitigate or aggravate accident events. These measurement techniques rely upon judgments and experiences of those familiar with the operations being modeled and objective data to formulate a "safety index". A methodology for coiiection of the objective data, the Human and Organizational Error Data Quantification System (HOEDQS), is also proposed. The HOEDQS allows updating of human errors such that there becomes a greater reliance upon objective data and less upon the judgmental indexing procedure.

Two marine casualties were identified as case study examples for confirmation of the modeling procedures: the Exxon Valdez and Piper Alpha disasters. These casualties were selected because of the quality, completeness, accessibility, and availability of information related to the accident events. The unique aspects of each disaster are modeled and templates are developed. Quantitative analyses were performed on each operation to confirm that high risk levels were measured conditional upon the operating factors for each disaster. The results from this dissertation will be of interest to engineers, operators, managers, and regulators concerned with preventing and mitigating the effects of HOE to increase safety of marine systems.