East Palestine, Ohio: An Abnormal Accident

 

When a wheel bearing overheated on a train carrying five tank cars of vinyl chloride through East Palestine, Ohio on Feb. 3, a sequence of events began that turned into a major accident with nationwide political implications. 

 

Overheated bearings (so-called "hot boxes") are not new to railroading.  With the thousands of wheel bearings in use every day, it's almost inevitable that some of them will fail by running hot and basically grinding themselves to pieces.  What is new in the last few decades are a number of safety devices that the railroads have installed to deal with overheated bearings. 

 

The Ohio train's bearing was sensed by three track-side hot-bearing detectors.  The National Transportation Safety Board (NTSB) has determined that one sensor noted the suspect bearing was warm (38 F above ambient, which was a cold 10 F) about twenty minutes before the derailing occurred.  Ten miles and 12 minutes or so later, it had heated up to 103 F above ambient.  The detector system's threshold was set so that these readings did not set off an audible alarm in the cab.  But the third sensor's reading of 253 F did.

 

By that time, it was too late.  Trains up to a mile or more long can't be stopped on a dime.  Three crew members were on the train, all in the lead engine.  By the time the engineer stopped the train, they could see fire and smoke behind them.  The train dispatcher authorized the crew to set hand brakes on the lead cars and move the front engines a mile or so down the track to safety. 

 

A total of 38 railcars had left the tracks, and the ensuing fire damaged 11 more.  Firefighters determined during the following two days that some intact tanks of vinyl chloride were heating up.  This chemical, which is used to make the ubiquitous plastic PVC (polyvinyl chloride), can undergo a spontaneous polymerization reaction that can cause an explosion.  To avoid that dire consequence, firefighters released the vinyl chloride into ditches they had dug nearby and burned it. 

 

Subsequent news coverage has dealt with the environmental consequences of the release of vinyl chloride and other toxic chemicals into the air, water, and soil around East Palestine.  One news report says monitors have estimated about 43,000 animals have perished, but 38,000 or so of that number were non-endangered minnows.  Residents have complained of odd tastes in the drinking water and air, and extreme measures have been and will be taken to clean up the extraordinary mess that several tank cars of toxic chemicals can make.

 

In an interview, NTSB chair Jennifer Homendy said that the accident was "100% preventable."  On the face of it, that makes railroad operator Norfolk Southern look pretty bad.  But exactly how could this accident have been prevented?

 

Certain safety requirements such as advanced braking systems for "high-hazard" trains that the Biden White House said the Trump administration removed would not have made a difference in this case, according to Homendy.  So attempts to turn the accident into a political football seem to amount to more smoke than fire, so to speak.

 

Norfolk Southern may rethink their thresholds for hot-box detectors.  This particular bearing seems to have gone from barely sensibly warm to disintegrated in less than 30 minutes.  The spacing and sensitivity of such detectors is a matter of engineering judgment, and accidents have a remarkable way of leading designers to reconsider safety precautions and adjust them so that the previous accident, at any rate, will not happen again. 

 

Too low a threshold on the detectors would mean that the trains are stopping needlessly, as a bearing may run warm for some unknown time before it fails.  Only the railroads have the statistics on these kinds of problems, but now that we know what can go wrong if the detection system doesn't stop the train in time, there may be a lot of readjusting going on in the future.

 

Some statistics from the Federal Railroad Administration cited by National Review say that train accidents caused by axle and bearing-related failures have fallen 59 percent from 1990 to 2019, largely due to the use of hotbox detectors.  So far from doing nothing about the problem, the railroads have been steadily improving their performance in this regard.

 

Sociologist Charles Perrow devised the term "normal accident" to express the type of mishap that very complex systems such as nuclear reactors can produce when multiple interacting parts do something that is very hard to predict, let alone forestall.  The East Palestine derailment was not that complicated.  But the system that should have prevented it failed in this case, and because of the particular cargo being carried, the consequences were awful. 

 

Despite an apocalyptic-looking crash scene, no one was killed or even injured in the derailment or fire.  This accident was far less consequential in that sense than the one, also involving derailed tank cars, that devastated the town of Lac-Mégantic, Quebec, on July 6, 2013 and killed 47 people.  So as bad as the East Palestine situation is, it could have been much worse.

 

Norfolk Southern is going to be paying for the consequences of this accident for a long time.  Already, millions of gallons of contaminated firefighting water have been shipped to Deer Park, Texas, where a specialist firm will inject it deep underground.  While some would question the propriety of this type of disposal method, Deer Park is in the middle of the most concentrated cluster of oil refineries and petrochemical plants in the U. S., and a little vinyl-chloride-contaminated water way beneath their feet will trouble Deer Park residents not at all. 

 

Someone will have to pay for all the contaminated dirt to be dug up and shipped somewhere else, and so East Palestine is getting more national attention and commerce, although of an undesirable kind, than the mayor and city council ever dreamed of.  While I hope that life returns to whatever passes for normal in eastern Ohio, East Palestine will never be the same again.

 

Sources:  I referred to the following articles:  the NTSB preliminary report on the accident at https://www.ntsb.gov/investigations/Pages/RRD23MR005.aspx, a CNN piece on the report at

https://www.cnn.com/2023/02/24/us/ohio-train-derailment-east-palestine-friday/index.html, a USA Today report at https://www.usatoday.com/story/news/nation/2023/02/24/east-palestine-train-derailment-fish-animal-deaths/11337404002/, a National Review article at https://www.nationalreview.com/2023/02/whats-going-on-with-the-ohio-train-crash/, and the Wikipedia article on "Normal Accidents." 

The Quebec Rail Disaster: Nine Notorious Necessities

In the science of logic, a necessary condition for a thing to occur is a circumstance that will stop the thing from occurring if the circumstance is not present.  Having fuel in my car is a necessary condition for getting it to run.  No fuel, no go. 

In the study of industrial disasters, you often find that instead of a single cause, there are multiple interlocked causes, each one of which was a necessary condition for the accident to take place.  The longer the chain of necessary conditions, the less likely it is that all of them will happen in a way that leads to a problem.  This is one reason why such situations are hard to anticipate.  The disaster that struck the town of Lac-Mégantic, Quebec on the night of July 5 and 6 is just such a tragedy.  While the full details have yet to be investigated, by going only a little beyond what is known I can assemble a chain of nine separate conditions, each of which had to prevail in order for the accident to happen. 

Lac-Mégantic is a community of about 5,000 on the tip of a lake of the same name, near the Canada-Maine border.  It was founded during the construction of the Canadian transcontinental railway in 1884, and a heavily-used rail line still runs directly through the center of town and extends westward up a rather steep grade to the next town of Nantes.  About 11 P. M. on the night of July 5, a five-locomotive eastbound train consisting of 73 tank cars filled with crude oil, besides other cargo, pulled into Nantes and stopped.  The engineer, Tom Harding, was done with his day’s run and planned to spend the night in a hotel in nearby Lac-Mégantic.  Before he left for the night, he followed what was apparently standard procedure in securing the train:  setting the handbrakes on all five locomotives and ten freight cars, and leaving one engine running to maintain pressure on the air brakes.

Railroad air brakes were an invention of George Westinghouse, who had the clever idea that a loss of brake pressure, such as would occur if part of a train broke away and lost its air connection to the engine’s compressor, should apply the brakes.  The same basic system is used today.  Each car has an air storage tank that provides the actual pressurized air that is applied to the brake cylinders on each “truck” or set of wheels.  The air from the tank is valved to the brakes when the main-line pressure falls, either gradually for controlled braking or suddenly, as when a train comes apart. 

But each tank holds only so much air, and so the other function of the air in the line is to maintain pressure in the tanks on each car. 

By setting the handbrakes, Harding was taking extra precautions.  In principle, as long as the engine was running to maintain air pressure, the air tanks would stay pressurized and the brakes would hold.  Satisfied that he had done his job, he made his way to Lac-Mégantic and to bed.

At 11:30 P. M., a concerned citizen reported to the Nantes fire department that the one running engine was on fire.  Local firemen reported to the scene and rousted out the nearest available rail employee, who turned out to be a track worker unfamiliar with the operation of locomotives.  The firemen and the railway employee managed to turn off the engine and put out the fire, but no one re-started the engine after the fire, and everyone left the scene by midnight.

For reasons that remain to be determined, about an hour later the train’s brakes ceased to hold, probably because the pressure in the air tanks dropped after the engine and its compressor were shut off.  The steep (1.2%) grade combined with the heavy load to send the train accelerating down the line six miles (10 km) along a straight track that executes a sharp bend in the center of Lac-Mégantic, near a strip of bars where late-night patrons were enjoying themselves.  Several people noticed the train rushing past at up to 66 MPH (100 km/hr).  When the leading locomotives hit the curve, they left the track and landed a few blocks away.  But the easily-punctured single-walled tank cars ruptured and caught fire, turning Lac-Mégantic into an inferno.  At the time of this writing (July 14), thirty-three bodies have been recovered, and seventeen more persons are missing and presumed dead. 

For this tragedy to occur as it did, you had to have

1.  A long heavy train full of

2.  Crude oil or other flammable material in

3.  Easily-ruptured tank cars attached to an

4.  Engine that caught fire and was turned off by

5.  A track worker who didn’t know how to start it again, and

6.  A steep grade under the train, and

7.  The engineer asleep in a hotel where nobody could find him, who

8.  Set enough handbrakes to keep the train from moving under normal circumstances, but not enough under the peculiar conditions that prevailed, and

9.  A town built around the closest turn in the tracks downhill from where the train started to roll.

If any of those nine conditions had been otherwise, the accident would not have happened, at least not to the extent that it did.  A shorter, lighter train might not have overcome the fading brakes.  Tanks of a non-flammable substance would have caused physical damage, but would not have burned.  Special double-walled tanks that are recommended for use in crude-oil service but not required, might not have ruptured as easily.  If the engine hadn’t caught fire, it would have kept the brakes going.  If the railroad employee had known how to start another engine, the brakes would have worked.  If the track had been flat instead of on a grade, the train might not have rolled away.  If the engineer had left a note saying where to call him in case of emergency, he might have restarted the engine.  If he had set more handbrakes, it might have prevented the runaway.  And if the bend in the tracks had been in a cornfield instead of in the center of town, no one might have died.

These “ifs” are cold comfort to those who have lost family and friends in the tragedy.  But they show what a long chain of unusual circumstances had to come about for the accident to happen.  Investigations may show that using more rupture-resistant tank cars would have reduced the chances of fire.  And there will certainly be questions raised about the advisability of crude-by-rail, or CBR, as a means of transporting large quantities of crude oil, instead of politically controversial pipelines, for example.  Let’s hope that what engineers, regulators, and the public learn from this accident will help in preventing the next one.

Sources:  I referred to articles on the accident in The Globe and Mail at http://www.theglobeandmail.com/news/national/mapping-the-tragedy-a-timeline-of-the-lac-megantic-train-disaster/article13105115/ and The Guardian at http://www.guardian.co.uk/world/2013/jul/12/quebec-oil-train-crash-disaster-24-bodies, a blog by Lloyd Alter at http://www.treehugger.com/energy-disasters/what-caused-train-disaster-not-brake-failure.html,

and a blog in Railway Age by Tony Kruglinski at http://www.railwayage.com/index.php/blogs/tony-kruglinski/so-now-we-know-they-can-blow-up.html, as well as the Wikipedia articles on Lac-Mégantic (the town) and the Lac-Mégantic derailment. 

  

Note added July 18:  Several comments indicate I did not adequately explain the operation of locomotive air brakes.  They are indeed essentially fail-safe in the short term, but not in the long term. 

An analogy can be made to the type of emergency lighting in stores and restaurants that is powered by storage batteries.  Under normal circumstances, the utility power charges the batteries and signals the emergency lights to remain off.  But when the utility power fails, the loss of voltage signals the emergency lights to turn on and operate from their storage batteries.  However, the storage batteries will eventually lose their charge if the power is not restored within a certain time.  When the storage batteries are depleted, the emergency lights will fail as well.

Here is the analogy.  The utility’s electric power is like the locomotive’s air compressor.  The emergency-light storage batteries are like the compressed-air tanks in each rail car.  The emergency lights coming on are like the brakes on each car becoming actuated by the air pressure from the tanks when the pressure from the locomotive fails (either deliberately or accidentally).  The tanks can supply only so much air (which escapes due to leaks, imperfect seals, etc.) and eventually the pressure falls to the point that the brakes no longer hold, just as the emergency lights will eventually go out. 

One reason the brakes are not actuated by a non-pneumatic method (e. g. springs) is that there are situations in which railway workers need cars to roll freely without being connected to a source of air pressure, as when the cars are sorted by being rolled one at a time over a “hump” and down a controlled grade through a sequence of switches.  If the brakes were always applied in the absence of air pressure, this kind of thing would not be possible. 

I hope this clarifies the question of how air brakes on trains work.