The most common method to explore the harmfulness of man-machine systems and to find out the role of "human factor" seems to be the investigation of accidents already happened. If safety officers and other safety experts want to improve the human factor in safety which is seen today the important aspect of safety and accident prevention than they must be enabled to describe demands on safe behaviour in detail and in a systematic way. To provide safety experts with an appropriate instrument to achieve this goal we have begun to develop a questionnaire which is suited to common job analysis procedures. This instrument is geared to preventive application and is entitled the 'Safety Diagnosis Questionnaire' (SDQ). The SDQ represents an attempt to make psychological theories of safe behaviour applicable to practice in organization of work. Available knowledge about factors which determine behaviour in hazardous situations this knowledge is obviously limited has been collected, systematized and made usable for safety officers.