The accident occurred when plant managers attempted to fulfill an order for acrylic polymer that exceeded the normal batch size for this product. Instead of making two smaller batches to fill the order, managers decided to make a single, larger batch. Managers decided to add all the extra acrylic monomer during the first stage of the reaction process, which was a critical mistake. Subsequent laboratory testing by the CSB showed that increasing the batch size in this manner raised the maximum heat output from the reaction by a factor of at least 2.3. The heat output exceeded the cooling capacity of the condenser, and the reaction accelerated out of control or "ran away.