Abstract The HAZard and OPerability technique has been used for many years as a formal means for the review of chemical process designs, specifically from the standpoint of safety and operability. In addition to application of the technique to hardware systems, such as chemical process systems, the technique has been developed to address the same issues in systems which combine software and hardware, such as the drilling of oil and gas wells. The Drillers HAZOP technique has been used to review the drilling process where multidisciplinary teams of men work with high specification equipment to get or enhance the production of oil and gas from subterranean reservoirs while working to procedures. This paper describes the further development of the technique, to incorporate more recent ideas for the identification of hazards and human factors to better assess the contribution made by the operator to the hazard as well as his potential for hazard mitigation. Development of the technique has been based upon the use of theoretical concepts which have been validated through use on commercial projects. The potential applications of the technique to procedural activities are enumerated to allow the reader to assess the relevance of the technique to his own environment. Further, development of the technique by integration with planning and improvement of the means of hazard identification are discussed.