[Note that this article is a transcript of the video embedded above.]

On the evening of Friday, February 3, 2023, 38 of 149 cars of a Norfolk Southern Railway freight train derailed in East Palestine, Ohio. Five of the derailed cars were carrying vinyl chloride, a hazardous material that built up pressure in the resulting fires, eventually leading Norfolk Southern to vent and burn it in a bid to prevent an explosion. The ensuing fireball and cloud brought the normally unseen process of hazardous cargo transportation into a single chilling view, and the event became a lightning rod of controversy over rail industry regulations, federal involvement in chemical spills, and much more. I don’t know about you, but in the flurry of political headlines and finger pointing, I kind of lost the story of what actually happened. Freight trains, like the one that derailed in East Palestine, are fascinating feats of engineering, and the National Transportation Safety Board (or NTSB) and others have released preliminary reports that contain some really interesting details. I’m not the train kind of engineer, but I think I can help give some context and clarity to the story, now that some of the dust has settled. I’m Grady, and this is Practical Engineering. In today’s episode, we’re talking about the East Palestine Train Derailment.

Modern freight trains are integral to daily life for pretty much everybody. Look around you, and chances are nearly every human-made object you see has, either as bulk raw materials or even as finished goods, spent time on the high iron. One of the reasons trains are so integral to our lives is because there’s nothing else that comes even close to their efficiency in moving cargo over land at such a scale. Steel wheels on steel rails waste little energy to friction (especially compared to rubber tires on asphalt). Locomotives may look huge, but their engines are almost trivial compared to the enormous weight they move. If a car were so efficient, its engine could practically fit in your pocket. And yet, the trains those locomotives pull are not so much a just a vehicle as they are a moving location, larger and heavier than most buildings.

With this scale in mind, you can see why the crew in a locomotive can’t monitor the condition of all the cars behind them without some help. A rear-view mirror doesn’t do you much good when part of your vehicle is a half hour’s walk behind you. There was a time not too long ago when every freight train had a caboose. Part of their purpose was to have a crew at the end of the train who could help keep a lookout for problems with the equipment. Now modern railways have replaced that crew with wayside defect detectors. These are computerized systems that can monitor passing trains and transmit an automated message to the crew over the radio letting them know the condition of their train in real time. Defect detectors look for lots of issues that can lead to derailment or damage, including dragging equipment, over height or over width cars (a hazard if the train will be passing through tunnels or under bridges), and, important in this case, overheating axles and bearings. Depending on the railway operator and line, these detectors are often spaced every 10 or 20 miles (or 15 to 30 kilometers).

The freight train that derailed in East Palestine, designated 32N, passed several defect detectors along its way, and NTSB collected the data from each one. The suspected wheel bearing responsible for the crash was located on the 23rd car of the train. At mile post 79.9, it registered a temperature of 38 degrees Fahrenheit above the ambient temperature. Ten miles later, the bearing’s recorded temperature was 103 degrees above ambient. That might seem kind of high, but it is still well below the threshold set by Norfolk Southern that would trigger the train to stop and inspect the bearing. Twenty miles later, the train passed another defect detector that recorded the bearing’s temperature at 253 degrees above ambient (greater than the 200-degree threshold), triggering an alarm instructing the crew to stop the train. But, it was too late.

Freight trains are equipped with a fail-safe braking system powered by compressed air. There are two main connections between cars on a train: one is the coupler that mechanically joins each car, and the other is the air line that transmits braking control pressure. As long as this line is pressurized, the brakes are released, and the cars are free to move. But if one of these air lines is severed, like it would be during a derailment, the loss of pressure triggers the brakes to engage on every single car of the train. That’s what happened shortly after that defect detector recorded the over-temperature bearing. When the defect detector notified the crew of an issue, they immediately applied the brakes to slow the train. But before they could reach a controlled stop, the train’s emergency braking system activated. A security camera nearby caught this footage showing significant sparks from what is presumably the failing car moments before the derailment. Understanding the severity of the situation, the crew immediately notified their dispatcher of the possible derailment. They applied handbrakes to the two railcars at the head of the train, uncoupled, and moved the two locomotives at the head end (and themselves) about a mile down the line away from the fire and damage, not knowing the events that would quickly follow.

A train’s “consist” defines the collection of cars that make it up. 32N’s consist included 2 locomotives at the head, a locomotive near the center of the train called distributed power, and 149 railcars. 38 of those 151 cars had come off the tracks, forming a burning pile of steel and cargo. Of those 38 cars that derailed, 11 were carrying hazardous materials including isobutylene, benzene, and vinyl chloride. Local fire crews and emergency responders worked to put out the fires and address the immediate threats resulting from the derailed cars. But despite the firefighting efforts, five of the derailed cars transporting vinyl chloride continued to worry authorities due to rising temperatures. Norfolk Southern suspected that the chemical was undergoing a reaction that would continue to increase in temperature and pressure within the tanks, eventually leading to an uncontrolled explosion and making an already bad situation much worse.

The cars carrying vinyl chloride were DOT-105 tank cars. These are not just steel cylinders on wheels. The US Department of Transportation actually has very specific requirements for tank cars that carry hazardous materials. DOT105 cars have puncture-resistant systems at either end to keep adjacent cars from punching a hole through the tank. They have a thermal protection system with insulation and an outer steel jacket to protect against fires. They are tested to pressures much higher than they would normally see, and they include pressure relief devices, or PRDs, that automatically open to keep the tank from reaching its bursting pressure. The PRDs on some of the vinyl chloride cars did operate to limit the pressure inside the tanks, but the temperature continued to increase.

As fires continued to burn, state and federal officials noted the temperature in one of the vinyl chloride cars was reaching a critical level. Rather than trust the PRDs to keep the tanks safe from bursting, they decided to perform a controlled release of the chemical to prevent an explosion. While they were still making the decision, the Ohio National Guard and the Federal Emergency Management Agency were running atmospheric models to estimate the extent of the resulting plume. Local emergency managers used these models to evacuate the area most likely to be affected by the release. On February 6, crews dug a large trench in the ground, vented the five vinyl chloride tanks into the trench and set the chemical on fire to burn it off. Despite being done on purpose to reduce the danger of the situation, the resulting fireball and pillar of smoke have become symbolic of the disaster itself.

You might be wondering, like I did, why the controlled burn was necessary if the tank cars were fitted with PRDs. While the NTSB’s full report hasn’t been released yet, they have released some details about their inspections of the vinyl chloride cars. Three of the cars were manufactured in the 1990s with aluminum hatches that cover the valves (as opposed to the more updated standard steel hatches). During the initial fires and “energetic pressure reliefs”, it seems that the aluminum may have melted and obstructed the relief valves, impacting their ability to reduce the building pressure.

You might also be wondering why a train passing through a populated area would be carrying so much vinyl chloride in the first place. Vinyl chloride might sound familiar to some of you as it is the ‘VC’ in PVC. This channel makes a lot of use of PVC demonstrations. It’s a material used in a lot of applications, so we produce it in vast quantities, and railways are usually how we move vast quantities of bulk materials and chemicals. But, vinyl chloride is a toxic, volatile, and flammable liquid, not something you want a big pool of near your city, so officials decided to burn it off. Flaring or burning chemicals is a pretty common practice for dealing with dangerous gases or liquids that can’t easily be stored. It’s essentially a lesser evil, a way to quickly convert a hazardous material to something less hazardous or at the very least, easier to dilute.

While the byproducts of burning vinyl chloride are far from ideal, combusting it into the atmosphere was intended to be a way to quickly address the concern of it harming people on the ground or polluting a larger area. In fact, the US Environmental Protection Agency flew a specially-equipped airplane after the burnoff to measure chemical constituents of the resulting plume. They found low detections of any chemicals of concern and concluded in their report that the controlled burn of the railcars was a success.

But “success” is a strong word for an event like this, and I might have chosen a different word. While there were no immediate fatalities resulting from the crash, the impacts are far-reaching. Chemical pollutants were not only released into the air, but also washed into local waterways during the firefighting efforts. Hazardous substances reached all the way to the Ohio River, and the Ohio Department of Natural Resources estimated that roughly 40,000 small fish and other aquatic life were killed in the local creek that flows away from East Palestine. Between the contamination of water and soil, it’s impossible to say what the long term impact on the local ecology will be.

As for the residents, both the state and federal EPAs have been heavily involved in all aspects of the cleanup, monitoring air quality and water samples from wells and the city’s fresh water supply. So far, they haven’t detected any air quality levels of health concern after the derailment. As for the area’s groundwater, out of 126 wells tested, none have shown evidence of significant contamination. But as you’ve seen in some of my previous videos, it can take a while for contamination to move through groundwater.

The EPA has ordered Norfolk Southern to conduct all cleanup actions associated with the East Palestine train derailment. The company itself has pledged to “meet or exceed” regulatory requirements in regards to the cleanup. Cleaning up after such a disaster is no easy feat, from air, water, and soil testing, to disposal of huge volumes of contaminated water and soil, the whole thing is a mess, literally. The cleanup is still underway as I’m releasing this video, but so far they’ve removed over 5,000 tons of contaminated soil and collected about 7 million gallons or 26 million liters of contaminated water from rain falling on the site and washing off trucks working on the cleanup. The response has been robust, but we know how these cleanups can go. The EPA’s list of almost 1,800 hazardous waste sites of highest priority only has 450 examples of sites cleaned up enough to be taken off of the list!

The whole situation has also sparked policy discussions among several agencies. The NTSB is opening a special investigation into the safety culture and practices of Norfolk Southern. From congressional testimonials, to public statements from the Department of Transportation, to political posturing from a huge variety of public officials, one thing seems clear to me: this disaster will have an impact on the way railroading is conducted in America for years to come.

The residents of East Palestine have a long road ahead of them. While all the preliminary testing so far paints a relatively safe and healthy picture of the town after the event, many have reported symptoms and effects. Even if there really are no residual compounds present at dangerous levels, the anxiety and unease of living near a high profile chemical spill is hard to escape. The economic impact of just the perception of contamination is also very real, and things like home values and local agricultural businesses have already taken a direct hit. I live really close to a freight line myself, something that is a unique joy for my two-year-old. But now, when I see those tanker cars roll by, I can’t stop myself from just wondering what’s inside them and what might happen if they came off the rail in my neighborhood.

But I also recognize that much of the lifestyle I enjoy depends on those trains rolling by my house, and despite the tragedy of events like East Palestine, the DOT recognizes rail transportation to be the safest overland method of moving hazardous materials. Even with the bulk of hazardous materials being transported over rails, highway hazmat accidents result in more than 8 times as many fatalities! So, freight rail isn’t going away anytime soon. It’s the only feasible way to move the mountains of materials required for all of the industries in the US, and really, the world. And the fact that we rarely have to consider the incredible engineering details of tanker cars, defect detectors, and hazardous material cleanup operations is a testament to the hard work that goes into regulating and operating these lines.

But freight rail in the US is unlike any other industry. There are only seven companies that operate Class I railroads that make up the vast majority of rail transportation in the country. The US rail market essentially consists of two duopolies: CSX and Norfolk Southern in the east and Union Pacific and BNSF in the west. That gives these companies enormous political power, as we’ve seen in recent news. So, we have to ask ourselves, are accidents like East Palestine, however rare they may be, just a part of doing business, or is there more that can be done? And I think the answer in this case is clear. I expect we’ll see some changes to safety regulations in the future to make sure something like this never happens again. And hopefully the next Practical Engineering video on railway engineering will have a more positive light.