 May 19th, 2018, the Carare America Chemical Plant in Pasadena, Texas. The plant manufactures eval, a copolymer made from ethylene and vinyl alcohol. Eval is used in food packaging and storage containers. Carare shut down the Pasadena plant on April 6th for a maintenance turnaround and to install various equipment upgrades. By May 18th, Carare operations personnel were taking steps to bring one of four reactors back online. The reactor, known as eval reactor 2, looked similar to the others but had a lower maximum design pressure of 740 psi. The design pressure of the other three reactors was 1150 psi. The reactor already had liquid methanol and ethylene vapor inside as operators began incrementally raising the reactor system pressure. They did so by adding additional ethylene vapor. Pressure was raised in order to reach the target pressure necessary for the reactor to start up while also checking for leaks. In the meantime, chilled liquid from the plant's newly installed refrigeration system was circulating through the reactor's heat exchanger. After 11.20 p.m., the reactor pressure, together with the low temperature from the chilled liquid created conditions that allowed the ethylene gas in the reactor to condense to liquid. This caused the temperature in the reactor to decrease. Around 7 a.m. on May 19th, a supervisor noticed the low temperature in the reactor and instructed operators to stop circulating the chilled liquid through the heat exchanger. The reactor was surrounded by a heat transfer jacket which uses water to control the temperature inside the reactor. To further help warm the reactor, Karare personnel periodically added steam to the jacket, increasing the temperature of the water. As the temperature of the reactor increased with each injection of steam to the heat transfer jacket, some liquid ethylene inside the reactor vaporized. This raised the pressure inside the reactor. By about 8.45 a.m., the reactor reached the target operating pressure of nearly 600 psi, but pressure continued to increase. Around 9 a.m., the pressure reached 640 psi and the high pressure alarm went off. A board operator responded by periodically opening a pressure control valve to send some of the vapor inside the reactor to a flare. The board operator was concerned about exceeding environmental emissions limits for the flare. As a result, he did not fully open the pressure control valve. He was also focused on other startup activities and did not realize the valve was not open as much as it needed to be to bring the pressure under control. Pressure inside the reactor continued to climb. Shortly after 10 a.m., operators initiated the next step in the startup. At that time, a new board operator took over and noticed the pressure in the reactor was over 700 psi. But the operator did not recall that this reactor had a maximum design pressure of 740 psi. He thought it could withstand higher pressure, like the others. Like the first board operator, the new operator only partially opened the pressure control valve, not realizing how dangerously close the pressure was to the reactor's limit. The partially open control valve was not enough to relieve the pressure in the reactor. Shortly before 10.30 a.m., the emergency pressure relief system activated. High pressure ethylene vapor discharged from the reactor into the atmosphere. It was released horizontally toward an area where many people were working, rather than vertically to a safe location. Soon after, a nearby welding machine likely ignited the vapor, the large fire erupted. 23 people were injured, many as they urgently tried to evacuate. The ethylene-fueled fire stopped after approximately three minutes when the emergency relief valve closed as pressure in the reactor normalized. In total, over 2,000 pounds of ethylene