The CSB estimated that the flammable release occurred when the reactor reached a pressure of 23 pounds per square inch gauge (psig), which was well below the reactor's maximum working pressure of 75 psig. Further, Synthron had a longstanding practice of improperly securing the reactor hatch, using only four of the 18 metal clamps recommended by the manufacturer. Once the condenser cooling capacity was exceeded during the runaway reaction, the failure to fully clamp down the hatchway compromised the performance of the hatchway gasket, which allowed flammable solvent vapors to be released into the building.