In conceptual design, process routes can be compared and ranked by using inherent safety indices. In this paper, some inherent safety index methods presented in literature are compared and their properties and limitations discussed. As a case study, an inherent safety evaluation of methyl methacrylate process routes is presented. Three index based inherent safety evaluation methods are compared with expert evaluations on methyl methacrylate process routes and their subprocesses. Also the index based inherent safety ranking of process routes is compared with an expert ranking. (c) 2005 Elsevier Ltd. All rights reserved.