Tuesday, July 16, 2013

Reader Comment – 7-15-13 – Westinghouse Brakes

An alert reader caught me in an apparent mistake in my description of the brake failure involved in the Lac-Megantic train derailment. Anonymous wrote:

“I understand rail air brakes are fail-safe, in that you must have air pressure to release the brakes. No air, the brakes are applied. If this concept is true, you might want to revisit the brake failure cause.”

First off, I am not a train engineer, so I am not completely familiar with the design of air brakes. My description of the problem was based upon reports from the railroad and local fire responders.

But, I have been a train buff at various times in my life and have spent considerable time around freight trains in the Army and the chemical business, observing their loading and local movement up close and personal. In general, Anonymous is correct, each car in a train is typically equipped with a Westinghouse style brake that fails closed (brakes applied) if the air supply from the locomotive is lost during movement. That obviously would not match with the description of the break problem in this case.

So, I went back to the Wikipedia entry on ‘Railway Air Brake’. It seems that while the rolling stock is equipped with Westinghouse brakes the locomotives are still equipped with the old-style straight air brake. I’m guessing that the brake systems on each of the five locomotives on the doomed train were interconnected and being supplied air from the locomotive that was left idling.

The interesting question that comes to mind is why did the engineer choose the locomotive brake system, which has a single fail point that would (and did) lead to catastrophic consequences rather than using the full-train brakes system that would fail in the safe mode (stopping the train) rather than allowing the train to roll into town?

An interesting comment from  Marcy Barnett over at the Emergency Management and Homeland Security Professionals group on LinkedIn. Commenting on my post she said “I thought there was only one engineer on this train”, noting that had a potential impact on train safety controls.

If that is true, that might provide an explanation for the poor brake choice. In the event that one or more of the car brakes locked up during their prolonged engagement (a not uncommon occurrence) that would mean that a lone operator would have to walk the train to unstick those brakes. With a 70 car train that is a lengthy hike carrying to tools of the trade.

I’m betting that the use of the locomotive brakes looked like the easier choice. That is supposition on my part and not intended as a slur on the operator’s reputation. Absent specific instructions to the contrary, most people take the easy way out.

Again, this is just one more point that needs to be clarified in the investigation.

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