Ohio’s toxic train derailed as crewmen were trying to brake. Shortly before, an alarm signal had sounded warning of overheating of the wheels of one of the wagons, according to the preliminary report published this Thursday by the railway authorities. The investigators have used the records of the train’s black box, other recordings and interviews to prepare their report.
The train derailed when it had just crossed East Palestine, a town in Ohio on the eastern border of the state, right on the border with Pennsylvania. Train 32N consisted of two head locomotives, 149 cars and a distributed power locomotive located between cars 109 and 110. According to the investigation, it was running at about 47 miles per hour (about 76 kilometers per hour) before the derailment, for below the maximum authorized speed of 50 miles per hour (about 80 kilometers per hour).
The investigation has shown that the train was traveling with its brakes activated when it passed a defect detector near East Palestine, at kilometer 49.81. “The track defect detector, or hot bearing detector (HBD), transmitted a critical audible alarm message directing the crew to reduce speed and stop the train to inspect for a hot axle. The engineer increased the dynamic brake activation to further slow and stop the train. During this deceleration, an automatic activation of the emergency brake was initiated and the train came to a stop.”
The report points, therefore, to the overheating of a wheel bearing in one of the wagons, in line with what was advanced by the authorities. When the train was already trying to stop, the emergency brake was activated, perhaps precisely as a result of the derailment. According to the report, the emergency brake can be activated when a train experiences a separation that disconnects the air brake hoses between cars.
The function of Hot Bearing Detectors (HBD) is to detect overheated bearings and provide real-time audible warnings to train crews. The train passed through three HBD systems on its way before going off the track. At the 79.9 mile point, the suspect bearing of car 23, the one that apparently started the derailment, had a recorded temperature of 38°F above ambient temperature.
When the train passed the next HBD, at point 69.01, the recorded bearing temperature was 103°F above ambient (103 degrees Fahrenheit is 39 degrees Celsius). The third HBD, at point 49.81, recorded the suspect bearing temperature as 253°F above ambient (253 degrees Fahrenheit is 123 degrees Celsius). Overheating of more than 200 degrees Fahrenheit is considered critical, which is why the alarm sounded and the train began to slow down.
After the train came to a stop, the crew observed fire and smoke and reported a possible derailment. The crew then applied the parking brakes to the two leading cars of the train, uncoupled the leading locomotives, and moved them about a mile away.
On February 5, response teams put out the fire, but five tank cars carrying 115,580 gallons (about 437,000 liters) of highly toxic vinyl chloride remained a concern for authorities. The rise in temperature inside a tank car suggested that the vinyl chloride was undergoing a polymerization reaction, which could pose an explosion hazard. When it burns, it decomposes into hydrogen chloride and phosgene. Phosgene is highly toxic, causing vomiting and respiratory problems, and was widely used during World War I as a suffocating agent, while hydrogen chloride is an irritant and corrosive.
Response teams scheduled a controlled venting of the five vinyl chloride tank cars to release and burn the vinyl chloride, expanded the evacuation zone to a two-mile area, and dug trenches to contain the vinyl chloride liquid released while it vaporized and burned. Controlled ventilation began at about 4:40 p.m. on February 6 and continued for several hours.
In their investigation, teams from the National Transportation Safety Board (NTSB) have examined rail equipment and track conditions; data from the signal system, track defect detectors, local surveillance cameras and the main locomotive event recorder and forward and inward facing image recorders. Investigators identified and examined the first car to derail, number 23.
The investigation is still open. The NTSB experts will focus on the wheelset and bearings; the design of the tank car and the damage from the derailment. They will also review the response to the accident, including venting and burning vinyl chloride. That burning probably allowed the track to be cleared as quickly as possible and train traffic resumed, to the benefit of the transport company, Norfolk Southern, but questions have been raised as to whether it was the most appropriate action from an environmental and safety point of view.