The Lac-Megantic Incident, It’s All About The BrakesJuly 9th, 2013 by ant6n
The Lac-Megantic incident was caused by an apparently unmanned train of the Montreal, Maine and Atlantic Railway (MMA) loaded with crude blasting into a small town at high speed. The train consisted of 72 “DOT-111″ tanker cars, which have been criticized in the past to “have a high incidence of tank failures during accidents” (NTSB report report, page 75).
There’s a sharp curve in downtown, and that’s where an explosion and subsequent fire destroyed a large number of buildings, and killed at least 13 people. This happened during Friday night, bad timing because there were some festivities in a bar that was engulfed in the fire (video).
The investigation is still ongoing, so explaining causes is basically just speculation. But we have some information, let’s look at a timeline leading up to the explosion:
- 23:25 The engineer parked the train with 72 crude-carrying tanker cars at a siding near Nantes, QC. This is about 10~11km away from downtown Lac-Megantic. The engineer shut down four of the five engines and left the lead engine (#5017) running to supply the air brakes.
- 23:30 A resident called 911 to report a locomotive engine on fire at the Nantes siding.
- 23:42 Firefighters arrive on the scene. As part of their operations, They shut down the lead engine. The Nantes Fire Chief Patrick Lambert told Reuters that the crew had switched off the locomotive a “good-sized” blaze in the motor, possibly caused by a fuel or oil leak in the engine. “We shut down the engine before fighting the fire.” “Our protocol calls for us to shut down an engine because it is the only way to stop the fuel from circulating into the fire.”
- 0:12 The fire is extinguished
- 0:13-12:15 Two emplyes of the (MMA) show up at the scene
- 1:30 The train derails at high speed at Lac-Megantics Rue Frontenac crossing.
According to MMA’s chairman Ed Burkhardt, the brakes will not work if a train is switched off: “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”.
How many brakes in a train?
A train relies on air brakes to keep the cars from moving. There’s a high pressure air line running through the whole train, supplying power to the brakes and activating the brakes. The brakes are fail-safe, that is they release at high pressure, lower pressure means ‘stop’. If the air pressure fails, it will go into emergency brake mode and stop. The energy for that braking action is supplied by an air pressure reservoir on each car. However, these reservoirs can deplete after a while and will release the brakes. That’s why the lead engine of the runaway train was kept on, so that the onboard air-compressor could maintain the air brake pressure.
Since the air brakes can stop working, every car also has hand brakes, operated by a large steering wheel. The Canadian Rail Operating Rules (CROR) specifies the following:
112. SECURING EQUIPMENT
(a) When equipment is left at any point a sufficient number of hand brakes must be applied to prevent it from moving. Special instructions will indicate the minimum hand brake requirements for all locations where equipment is left. (…)
Equipment here is defined as “One or more engines and/or cars which can be handled on their own wheels in a movement.” The rules also specify that sufficient application of handbrakes has to be tested:
(b) Before relying on the retarding force of the hand brake(s), whether leaving equipment or riding equipment to rest, the effectiveness of the hand brake(s) must be tested by fully applying the hand brake(s) and moving the cut of cars slightly to ensure sufficient retarding force is present to prevent the equipment from moving. When leaving a cut of cars secured, and after completion of this test, the cut should be observed while pulling away to ensure slack action has settled and that the cars remain in place.
So the air brakes may have been made ineffective related to the fire on the lead engine and the fire department operations. But the hand-brakes should have still prevented the trains from moving, if properly applied according to the operating rules. There may not have been enough hand brake force. The MMA claimed that hand brakes were engaged on all five engines, but it is unclear on how many cars, and whether the brake test was performed.
Even if the magnitude of the incident at Lac-Megantic is unusual, air brakes failing and insufficient hand brake force resulting in run-away equipment and a subsequent collision is not. This is exactly what happened in a January 2012 collision near Hanlon, Alberta.
One detail that is unusual is that there was only a single engineer. Usually, freight trains are staffed by an engineer (as the ‘driver’) and a conductor, who among other things has the responsibility to operate the hand brakes. One could speculate that without the conductor, it is too much work to walk along the train and operate a set of hand brakes, then get back into the engine to perform the brake tests. It turns out that in 2012 Transport Canada actually allowed the MMA to operate with reduced staffing levels.
A Runaway Train Rolling Down the Hill
In the title image one can see the path from the Nantes siding to the point where the train derailed, a distance of a bit more than 10km. From the geoprofile one can see that path is basically all on a downward slope, for a total elevation difference of about a 100m. That elevation difference in 10km is a gradient of only about 1%. But steel rail on steel track has extremely low rolling resistance, and air resistance will only come into play at higher speeds.
It doesn’t matter very much whether whether there’s a 1% grade, a 10% grade or a roller-coaster falling down 100m, most of the potential energy will be transferred into the kinetic energy of the train moving forward. A simple calculation (E = mgh = mv²/2 => v = √2gh) shows that this energy can speed the train up to 160km/h, assuming no rolling and air resistance. Even half that is enough to derail the train at the downtown Lac-Megantic curve, and cause the disaster.
The train was travelling from from New Town, North Dakota, over 3000km to it’s destination at the Irving Oil Refinery in Saint John, New Brunswick; it also passed through Toronto.
The investigation will most likely center around all the brake failures. But I hope we will re-visit the safety of leaving trains full of dangerous substances unattended, on inclined sidings with grades targeting populated areas, or the purpose in general of moving crude oil over thousands of miles, whether it be by train or by pipeline.