This paper describes a series of projects in four organizations, each of whom wished to deepen their understanding of the human factors that influence accidents and incidents at work. A set of human factors analysis tools were developed which encompassed violations, errors and aspects of safety culture. Following a trial period and a peer review, the methods have been implemented, and used by investigators who were typically from an engineering background, and did not possess human factors expertise. The process and outcomes of these projects is described, with examples of how a human factors approach can add value to existing analytical methods. Some of the difficulties encountered are described, together with areas for future development.