The identification of hazards and risk assessment are key factors in the safety of the industries, including power plants. This paper contains an original risk analysis method that increases the level of safety in commissioning and start-up operations. With the proposed method, which has been tested in real industrial facilities, it has been possible to increase the safety of the system and reduce the likelihood of incidents and accidents in one of the most dangerous stages of project construction activities. This paper also gives an overview of the processes and procedures used in the construction of power plants compared to other industry sectors, proposing some areas for potential improvement. It has been verified that temporary systems used during commissioning apply risk evaluation techniques that do not consider some aspects related to process hazards, something that can be important for the prevention of accidents that historically happen at this stage. Analysis of the data has determined that, in these stages, there have been incidents and accidents, some of them severe. Thus, in this paper, a methodology is proposed. The method allows addressing the particularities of the execution of temporary systems in a safe way by putting into practice an agile and flexible method that can be applied to these particular systems, so that the risk levels can be reduced. The method was applied to one real application representative of this kind of system and yielded excellent results. The proposed methodology is highly recommended as an improvement for the power industry.