The thermal stability of initiators used in free radical polymerizations has been well documented. Initiators are often used in solutions, with relatively long feed periods to help control the beat of polymerization. In some cases, the stability of the initiator solutions is limited, especially at higher concentrations, and runaway reactions can potentially be severe. This article reviews the chemical reactivity of concentrated initiator solutions and considers PHA studies and feed tank design to help ensure safe handling and manufacture. (C) 2006 American Institute of Chemical Engineers.