It has been demonstrated that incidents, accidents and disasters tend to result from complex socio-technical failures, rather than just human error on the one hand, or simple technical failures on the other. For the reduction of accidents, therefore, it is necessary to deal with systems factors, in which both technical and human-factors elements play an equal and complementary role. However, many of the existing techniques in ergonomics and risk management concentrate on plant/technical issues and downplay human factors and subjectivity.