Safe operation of thermally sensitive chemical reactors remains a crucial engineering issue. Thermal runaway occurs mainly due to loss of temperature control, and many chemical accidents initiated by thermal runaway can be foreseen by an appropriate analysis of thermal process data. Thermal runaway criteria can be applied to determine the onset of runaway phenomena and safety boundary diagrams can be constructed. However, several runaway criteria exist, which define the runaway-and safe zones differently. In this work nine commonly applied thermal runaway criteria were analyzed and compared based on their critical curves. As a result of this analysis, two new criteria were developed. Reliability of the derived criteria were investigated, where the occurrence of real runaway was determined based on the number of indications applying different criteria. The two new criteria were tested in three general reaction systems and in case a complex problem, where feeding trajectory of fed-batch reactor was optimized applying new criteria as non-linear constraint. One of the new criteria shows the highest reliability in indication of runaway development from all investigated runaway criteria. (C) 2018 Elsevier Ltd. All rights reserved.