The concern for occupational health and safety in construction work is reflected in the many preventive measures taken. However, examples of the systematic assessment of project alternatives aimed at minimizing occupational hazards are rare. This paper proposes a measure of occupational safety, the occupational risk index (ORI), that is based solely on the project design and resulting construction process, and is a function of the activities carried out and their specific occupational risks (probability of occurrence and most probable consequence). The proposal is illustrated with an example in which two alternatives, one precast and the other constructed in situ, are prioritized in terms of occupational safety, and certain aspects related to redesign are briefly addressed. The research is based on an analysis of the applicable legislation and interviews with experts on risk prevention. With the ORI, occupational safety goes from having a passive influence (applications to projects that have already been designed) to an active one on the design concept itself. The ORI can thus be used as an indicator to feed multicriteria decision-analysis tools.