Author Topic: Animated Sequence of Events - Lac-Mégantic MMA Train Accident - 6 July 2013  (Read 1225 times)

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Mark W

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Purrs

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Very interesting. As always it is never one thing but a combination of errors that leads to a disaster. So long as everyone learns from this tragic mistake, then the deaths and property damage will not be in vain.

eric220

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Perhaps some of the railroaders in the group can answer this, but I'm confused by the air brake system here. Whenever someone posts a video of a train going into emergency, you hear a rush of pressurized air, and people talk about "dumping the air". I thought that air brakes were redesigned not long after their development so that the air pressure kept the brake pads away from the wheels. That way, any air pressure failure would "fail safe" and result in a brake application. I understand that there must be cutoffs and workarounds for specific applications, but the scenario in this video seems like a perfect example of why you'd want the brakes to apply when the system is de-pressurized. What am I missing here?
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Robbman

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Multiple drawbacks, you'd have to have a system in place to apply constant pressure and each would need to be tailored to each car based on light weight and loaded weight.  Also, the biggest drawback, you wouldnt be able to sort, drop, or pick up cars without a source of air.


wcfn100

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*This is how I understand it - anyone feel free to correct where I go wrong*

The air brake system has two parts.  The air line which controls whether the brake are applied or not, and the air reservoirs, valve, and brakes on each car that do the actual braking.

To apply the brakes, there is a release of air pressure in the line.  The triple valve senses this and will use air from the reservoir to apply the brake.  So in an emergency,  all the air is dumped and the valves on each car apply the brakes with the air in the reservoir.  In this case it was a slow release but still works the same way,  as the line is reduced, air is released from the car's reservoir.  Eventually there's not enough air to keep the brakes set.  Under normal circumstance the hand/electronic brake would have been applied, but as the video states, the electronic brake was turned off.


Jason

Mark W

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Interesting.  I was with Eric in thinking the default state with no air pressure was brakes applied. 

Another thing, one of the comments elsewhere is that the video indicates of the 7 hand brakes that were applied 5 were the locomotives.  Apparently this is also a big no-no, and all hand brakes should be non-locomotives.  Does anyone know whether or not that is true?
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victor miranda

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welcome to reading and deciding what it means....

in my case  (From what I have read from various sources...)
I understand pressurized air applies the brake to the wheels
AND any given car has a hand wheel or crank dingus that can also apply the brakes
the above two are independent of the other cars in the train.
important to note is that the independent air brakes often leak... a little.
so a car sitting alone should have the hand brake applied because eventually
the independent air will release the brakes.

here comes the fun part.
there is ANOTHER air pressure system for the train.
lots of things happen using that other pressure system.
It is used to control the brakes of the individual cars
AND the car's independent air brake gets filled from the train
pressure system.

it is a little strange to me how this works.
I am going to skip over an important detail here.

the above is done because a lot of people want a system
that sets the independent brakes and stops the car(s)
should the train control system lose pressure.

think  "pipe breaks" --> "train stops"

If you can't keep the independent brakes pressurized,
then you have to set hand brakes before you lose
independent pressure and the car(s) start rolling again.

all that to answer a simple question...








peteski

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This http://en.wikipedia.org/wiki/Railway_air_brake should shed some light on the brake operation.
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victor miranda

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This http://en.wikipedia.org/wiki/Railway_air_brake should shed some light on the brake operation.

It seems accurate... but it is not an easy read.
a lot of info that is not needed... yet





peteski

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It seems accurate... but it is not an easy read.
a lot of info that is not needed... yet

I agree that the way train brakes work is really non-intuitive and weird.
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Mark W

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I wouldn't say non-intuitive now that I've read the wiki and understand it better.

Basically there are two pressure systems.  The brake tanks store air pressure to be used for brake application, the brake line uses pressure to keep the tank pressure from releasing.  When the brake line loses pressure, the tanks then release their pressure also, engaging brakes.  Of course in this incident, there was no air-supply to replace/sustain the brake tanks, eventually allowing them to release.


I'm curious, what affects would wheel blocks/portable de-railer on the locomotives have in preventing the initial roll-away on the down grade?  Seems like something that would add further redundancy in securing a train that's left unattended, especially when all locomotives are powered down. 
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cv_acr

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Multiple drawbacks, you'd have to have a system in place to apply constant pressure and each would need to be tailored to each car based on light weight and loaded weight.  Also, the biggest drawback, you wouldnt be able to sort, drop, or pick up cars without a source of air.

And hump yards couldn't exist...

victor miranda

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I wouldn't say non-intuitive now that I've read the wiki and understand it better.

Basically there are two pressure systems.  The brake tanks store air pressure to be used for brake application, the brake line uses pressure to keep the tank pressure from releasing.  When the brake line loses pressure, the tanks then release their pressure also, engaging brakes.  Of course in this incident, there was no air-supply to replace/sustain the brake tanks, eventually allowing them to release.


I'm curious, what affects would wheel blocks/portable de-railer on the locomotives have in preventing the initial roll-away on the down grade?  Seems like something that would add further redundancy in securing a train that's left unattended, especially when all locomotives are powered down.

yeah, I often wonder what seems so clear to me as I write...
often seems to be read as something else.

once I read in the news paper that the engines were shut down,
I knew the brakes released... after everyone left.

May this mistake never happen again.

victor

oh ETA:

chocks or derailers might work.
the problem is that they can fail because the rest of the train can drag a derailed loco.
the loco can jump the derailer and be back on the rails.
and chocks can be very hard to remove.

It may be the best thing to do is consider that a one man crew is not a safe concept.

« Last Edit: August 22, 2014, 09:51:39 PM by victor miranda »

ljudice

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Interesting, but the bottom line is that if there was a second employee there, the two mistake probably wouldn't have been made.


GaryHinshaw

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The Transportation Safety Board of Canada issued their final report on this incident last week.  Among their findings was this fairly benign statement about single-person crews:

Quote
The TSB looked very carefully at single-person train operations, and at whether having just one crew member played a role in the accident. After looking at the circumstances that night, the investigation was not able to conclude that having another crew member would have prevented the accident.
However, there are some clear lessons for the system. If railways in Canada intend to implement single-person train operations, then they need to examine all the risks and make sure measures are in place to mitigate those risks. Transport Canada, for its part, should consider a process to approve and monitor the railways’ plans so as to assure safety.