Monday, July 08, 2013

First Thoughts on the Lac-Mégantic Disaster

By now I'm sure you have read the news reports about the Lac-Mégantic train accident.. but if not, here's the recap: a Montreal, Maine and Atlantic (MMA) freight train was parked a few miles outside of the town of Lac-Mégantic, Quebec. The engineer booked off and left, and sometime in the early morning the unmanned train rolled into Lac-Mégantic, derailed and a number of explosions occurred, followed by intense fires. At this point it appears that thirteen (13) people were killed but it is likely that this number will rise, as up to 40 are reported missing. The explosion and fires happened in the downtown core and the town is devastated, physically and emotionally. About 2,000 of the 6,000 people living in the town were evacuated and at least 30 buildings downtown have been destroyed.

From this press release from MMA and CBC and National Post reports, the timeline appears to be:
  • July 5, 23:15: Train stopped and tied down by engineer at Nantes. The train had 5 locomotives and 72 car loads of crude oil, destined for Irving Oil in Saint John, NB.
  • July 5, 23:30: Nearby resident calls 911 and reports a fire in the parked train. Firefighters respond and put the fire out. A track maintenance employee of MMA was present.
  • July 6, ?????: Train starts rolling downhill to Lac-Mégantic.
  • July 6, 01:15: Train derailed at Rue Frontenac crossing in downtown Lac-Mégantic
  • July 6 (later): Firefighters battle the intense blaze through the day. 13 intact carloads pulled from rear of train by MMA.
From the second press release by MMA, it appears the engine(s) were shut down after the engineer left, presumably during or after the firefighters arrived to put the fire out. What is disturbing to me is that the MMA statement says that the shutdown "may have resulted in the release of air brakes on the locomotive that was holding the train in place". I am no railroader but section 112 of the Canadian Rail Operating Rules is quite clear on this.

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. If equipment is left on a siding, it must be coupled to other equipment if any on such track unless it is necessary to provide separation at a public crossing at grade or elsewhere.

(emphasis mine)  The implication is that air brakes cannot be relied upon to hold a train in place. Again, I am strictly an amateur but this did catch my eye.

The National Transportation Safety Board is investigating and they have 14 people on the scene. I understand the locomotive event recorder has been recovered. That will help fill in the timeline as to when the train started moving, and most crucially, when the air brakes were released.

In addition to the tragic loss of life, the destruction of the town, there are concerns about water quality due to the quantity of spilled crude oil.

There are some railfan reports that the runaway train may have struck a set of propane cars that were in the town and those are what caused the initial explosions.

My heart is broken at the thoughts of the people killed and injured as a result of this terrible accident.

EDIT: More information here that confirms that the firefighters shut the engine down before battling the blaze.


GP9Rm4108 said...

It depends on the GOI, Steve. On CN, as long as the controlling (for air) locomotive is running NO handbrakes are required on the train if it is left unattended.

The FRA in the U.S. does not allow the handbrake exemption on an unattended train like TC does.

I am sure the MMA must have this in their GOI as well.

The lead engine would have been shut down after the fire and that left the air in the entire train bottled. I can explain how the air can release itself through Facebook message if you like.

Steve Boyko said...

Really? I have the CN CROR (May 28th 2008) and they echo the general CROR. I looked in the special instructions and there is nothing there. I don't have CN GOI, though. The CP GOI from 2001 allow a train to be left running with air brakes on, but the hand brakes must be set.

I believe I know what happens when you bottle the air. The air pressure in the train line slowly decreases, and once it decreases enough, the brakes on each car think they have been commanded to release, and once enough of them release, off you go.

GP9Rm4108 said...

The handbrake exemption for trains is in section 7 of CN's GOI,

You're backwards on your release on the brakes. A drop in brake pipe pressure applies the brakes.

You need a rise in brake pipe pressure to release them.

Two things can happen when you bottle the air:

1. It slowly leaks out of the brake pipe causing a service application of the brakes.

2a. The brake pipe hasn't finished venting off yet so when you close the angle cock it causes a damming effect and sends the rushing air wave back towards the tail end of the train. This ave of air travelling back is sensed as a release (as long as it's 1.5-2 psi) by the system.

2b. Everything is hunky dory. You have the brakes applied on the cars and the angle cocks closed.

The service reservoir on a car is leaking and it dumps a few more pounds of air into atmosphere/the control valve/cylinder. The brake pipe is now a higher pressure than the car's system. This is sensed as the car needs to release the brakes. So it does.

That's all fine and dandy as just that car releases. BUT, if the car is equipped with an accelerated release feature like most today are, the car has the emergency reservoir assist by dumping a few pounds into the brake pipe.

When this happens that car releases and with the rise in local pressure at that car, the rise travels through the entire train releasing every car. If other cars have that accelerated release feature, it's that much faster.

Little Muddy said...

It's been a long time since I worked on CN in the running trades. I was a yard crew conductor, a hump foreman, and some time later a hostler, for which I needed the engineer ticket. From what I remember if you dumped the air whether from the engine or opening the angle cock the whole system shut down. If you were switching cars on a string you'd closed the air on the car you were separating from and the the car you were leaving. The car you were leaving would leak after some time so you could do switching with the yard engine. Opening the angle cock wasn't neccesary after the air leaked off.