Air Brakes are supposed to be "fail-safe". So what caused the Lac-Megantic disaster?

On Saturday, a train carrying crude oil was left parked uphill of the Quebec town of Lac-Megantic; It then rolled down the hill, into town and derailed. (see Runaway oil train explodes in Canadian town, 5 dead, 40 missing). A lot of articles talked about "brake failures", and that seemed odd; Air brakes are supposed to be "fail-safe".

Or are they? How do air brakes work and what would cause them to fail? Here's a quick explainer.

Westinghouse brakes, 1909/Public Domain

In the early days of trains, brakes were applied manually by brakemen. After seeing a wreck in about 1867, a 22 year old George Westinghouse patented a "fail-safe" air brake system. If the pressure in the air line drops, either because the engineer applies the brakes or the line is broken for some reason, then the brakes are applied by air pressure from a reservoir in each car. The brakes can only stay open if the compressor is pressurizing the line. As Wikipedia explains,

Under the Westinghouse system, therefore, brakes are applied by reducing train line pressure and released by increasing train line pressure. The Westinghouse system is thus fail safe—any failure in the train line, including a separation ("break-in-two") of the train, will cause a loss of train line pressure, causing the brakes to be applied and bringing the train to a stop, thus preventing a runaway train.

But it's not like the brakes are held in place by giant springs; they are pressed by air pressure from the reservoir tanks. What happens when that runs down? Evidently, the brakes eventually let go.

In the Lac-Megantic disaster, the engineer whose shift was over left one engine running to keep the pressure up in the brake system, and went off to his hotel. Somehow this engine caught fire, and it was turned off by the Nantes fire department before they put the fire out. The Chairman of the Montreal, Maine & Atlantic Railway, Ed Burkhardt told the Toronto Star:

If the operating locomotive is shut down, there's nothing left to keep the brakes charged up, and the brake pressure will drop finally to the point where they can't be held in place any longer.

According to Reuters, the MN&A were informed by the fire department about what they did.

[Fire chief] Lambert said once the blaze was out, the Nantes fire service contacted Montreal, Maine & Atlantic Railway. "We told them what we did and how we did it," he said.

Asked whether there had been any discussion about the brakes, he replied: "There was no discussion of the brakes at that time. We were there for the train fire. As for the inspection of the train after the fact, that was up to them."

So what happened?

I am not an engineer, but have been interested in trains since childhood (my father was involved in transportation and I spent a lot of time around freight trains). Based on the news reports, this is my conjecture:

  1. The engineer completing his shift leaves an engine running to keep the pressure up. There is no parking brake, backup, no setting of the manual brakes that are built into each car.
  2. The engine catches fire; the Nantes fire department turns off the engine and puts out the fire.
  3. Without the engine supplying air to the reservoirs, The pressure eventually runs down and the brakes let go, and the train, parked on a slope with no manual brakes set, starts rolling.

This is very different from the way it used to be. Not that long ago, before cutbacks and efficiencies, there were brakemen who would manually lock each car down and then tell the engineer he could shut down his engine. (see comment at bottom of post).

In this case, the railway was shipping 73 tanker cars full of oil, parked it by the side of the road with the engine running and didn't even put on the parking brakes. This isn't a couple of wagons full of wheat, it is explosive stuff that is taking over the railroads.

This wasn't brake failure; The air brakes did exactly what air brakes do when you turn off the air supply and leave. This was human failure in neglecting to set the hand brakes. It was a systemic failure in designing a system without backups. It was a management failure, with cutbacks so severe that trains are run by one person, they leave running engines unattended and don't have the brakemen to do what is obviously a critical job, setting the handbrakes.

Don't blame the brakes, it's people that failed.

Update: Great comment in Globe and Mail:

In my day, a well-run railway always ensured that each train had a staff-complement comprising at least four employees: locomotive-driver, conductor, head-end brakeman, and tail-end brakeman. On parking a train for the night, the two brakemen (and the conductor, if he wished to earn the brakies' loyalty) would "set" the handbrakes on the locomotive(s) and on a number of cars commensurate with the "grade" (ie, the slope of the tracks) and the total weight of the oil tankers. Under no circumstances would an old-style conductor and/or locomotive driver have relied solely on the "service" brakes (ie, the air brakes) to hold a 78-unit "drag (ie, the reported five locomotives and 73 oil tankers) in place overnight. In the morning, only after the driver started the locomotive and ensured that the air brakes' compressors were working, would the brakies have felt free to release the handbrakes. Yes, the whole process requires more personnel and more time (evening and morning). However, it sure does beat the hell out of the eternity into which this incident has consigned Lac Megantic's deceased.

UPDATE II Chris writes: CBC reports statements from Edward Burkhardt, the chairman of the board of Rail World Inc., that confirms Lloyd Alter's theory that the fire earlier in the night is when the engine-powered air brakes were shut down. This has not stopped Burkhardt from denying that his railway company is negligent in this disaster.


Edward Burkhardt, the chairman of the board of Rail World Inc., said that by shutting off the locomotive in order to deal with the fire, the firefighters could have unknowingly shut off the train's air brakes.

"As the air pressure depletes, [the brakes] will become ineffective," he said.

However, firefighters in Nantes said when they left the train it was in the care of a track maintenance employee.

Burkhardt said the track maintenance employee might not have known how to re-secure the train's brakes, but he said local firefighters should have done more, suggesting they could have called the engineer who was asleep just across the street.

Nantes fire chief, Patrick Lambert, said his colleagues did their job.

"Nothing the firefighters did could have put the train in jeopardy," Lambert said. "They had two people come meet us … They said everything was out, the fire was out and everything was stabilized and that we could leave."

Ultimately, Burkhardt downplayed his company's responsibility.

"Is any of this huge negligence? No you can't point to that," he said.

Tags: Trains | Transportation