The need to involve contractors for a client is caused by special knowledge, skills, methods, and means possessed by contractors and required by the client in order to achieve certain results. Contractors, however, do not always support the client’s policies and attitudes to the occupational safety values; whereas the safety culture of contractors is, to a certain extent, conditioned by a subjective judgment and personal definition of safety criteria by the contractors’ management. Therefore, the client is exposed to additional professional risks associated with the admission of contractors to work on the client’s territory. One of the main sources of professional risks is the human factor, i.e., hazardous and mistaken actions of the contractors’ personnel. The cost of such actions in the conditions of highly hazardous work on the territories of active productions is specifically high. International and Russian studies have indicated the dependence between employee competence and the number of mistakes causing injuries. The level of competencies of both workers and managers is crucial. The impact of the human factor of contractors on the professional risk level of clients has been considered; and the relevant risk management methods have been proposed. One of the methods is the evaluation of employees’ cognitive abilities before admission to highly hazardous work as human cognitive abilities such as the perception of information, memory, and attention affect their actions when performing the jobs. The next step is the improvement of the competencies of contractors’ employees based on the evaluation of knowledge and skills and further theoretical and practical training based on the results obtained. In addition, a model of contractor HR management structure with specifications of the manageability norm has been proposed.