Process engineers and operators should understand reactor runaway phenomenon to avoid hazard situations and accidents. Reactor runaway occurs when an exothermic reaction takes place in a reactor with insufficient heat transfer area. The reaction rate increases due to the temperature rise, causing a further increase in reaction rate and temperature. Without any safety action, only the reactant consumption limits the maximum temperature. One of the safety actions can be the application of runaway criteria to characterize the safe operating regimes where the optimal operating conditions can be found. This paper presents runaway criteria and the application of these in case of the feeding trajectory optimization of a fed-batch reactor model. The most important runaway criteria and the relations between them are presented, and critical curves of criteria are calculated using a simple dimensionless tubular reactor. The optimal feeding trajectory is determined in case a pilot plant fed-batch reactor using different runaway criteria as a non-linear constraint based on particle swarm optimization and sequential quadratic programming. Designers need to know how they can choose the right criterion, and the results can help with it. Selectivity and profit can be decreased if runaway occurs in a fed-batch reactor, therefore it is important to deal with this problem. (C) 2016 Elsevier Ltd. All rights reserved.