At the preliminary stages of chemical plant development and design the choice of the chemical process route is the key design decision. In the past, economics were the most important criterion in choosing the chemical process route. Safety and environmental issues have now become important considerations. Methods are lacking for assessing chemical process routes for environmental friendliness. The Environmental Hazard Index (EHI) ranks routes by the estimated environmental impact of a total release of chemical inventory. The EHI is a function of the environmental effects of the chemicals and the estimated inventory thereof in a plant that, if designed and built, would implement the route. The lower the EHI the more environmentally friendly is the route. The EHI has been tested on six potential and established routes to Methyl Methacrylate (MMA). These results have been compared with those for the Inherent Safety Index for the same chemical process routes. An expression has been derived which relates the EHI to an estimated fish kill.