Reactive chemicals pose a significant hazard to the process industries arising from their inherent nature. This paper examines four reactive chemical accidents caused by self-heating that led to thermal runaway reactions. Although none of these case studies resulted in serious injuries, the runaway reactions caused fires, explosions, or toxic gas releases that resulted in extensive damages and loss of production. This paper considers the causal factors of these accidents, identifies the thermal stability data available before the accidents, and presents simple hazard calculations indicating the predictability of the accidents. The paper concludes with a discussion of lessons learned from these accidents. © 2005 American Institute of Chemical Engineers Saf Prog, 2006