Accident and incident analysis is essential to the study of human error and the development of error prevention measures. Human Error research deals essentially with the classification of error and the identification of the causal relation between the error detected and the level of human performance at which it occurred. As a result the literature proposes many error categorization methods and taxonomies. These are not, in themselves, sufficient, however, to analyze (and understand) the circumstances surrounding the error occurrence. For a more complete understanding of human error, it is necessary to associate each error with the sequence of steps taken by the human operator during the task that led to it. This paper proposes an extension of the existing error categorization found in the literature and applies it to the analysis of human error reports originating in the electricity industry.