In the preliminary stages of chemical plant design, selecting the chemical process route is one of the main design decisions. Previously, the most important factor in selecting the best chemical process route was economics. Now safety, environmental and occupational health issues have become important considerations. Health risks to workers could be reduced by better selection of the chemical process route during the initial stages of process design. The chemical process route may be defined as the raw material(s) and the sequence of reactions that converts them to the desired product(s). In order to choose the 'healthiest' one from a number of alternative routes, the potential health hazards must be quantified. Ranking of alternative chemical process routes based on the severity of potential health effects to the workers exposed could provide an assessment method for avoiding potential harm to humans. The Process Route Healthiness Index (PRHI) has been developed to quantify the health hazards that might arise from chemical processes; the higher the index, the higher the hazards. The PRHI is influenced by the health impacts due to potential chemical releases and the concentration of airborne chemicals inhaled by workers. The index has been applied to six alternative routes to methyl methacrylate (MMA). The resulting ranking is compared to those obtained from an Inherent Safety Index, an Environmental Hazard Index and production cost estimates for the same chemical process routes.