Risk assessment on a construction site is based on the probability and consequences of the accident. But due to the complexity of the construction processes, this new methodology for the evaluation of occupational risks, called Level of Preventive Action, develops a new parameter for evaluating preventive action based on documentary environment that reflects the complexity of the work units, location and interdependence, construction environment referred to construction and protection systems, and social environment relative to the perception of the environment and the workers’ emotional states. The evaluation criteria of the new method are established by developing the William T. Fine methodology and incorporating concepts such as risk tolerance, the importance of work and personal satisfaction, which justify the degree of correction of preventive actions. This methodology determines the amount of preventive action control that is required during the construction process. This research proposes a risk assessment protocol adapted to construction sites based on specialized technical observation with a psychosocial survey on site. Some results of the implementation of the method in real work are shown. In conclusion, the determining parameter towards optimal control of preventive action is the direct and active participation of workers in safety matters.