Canada train blast Lac-Megantic

[whole diary]

[ellendune]

All this talk of runaway trains seemed to me like something from the long past (Armagh 1915 1889 came to mind) and I though continuous fail safe automatic brakes were the result.  I have three questions:

1) Are continuous automatic fail-safe brakes a requirement on all trains in the UK^▸ (United Kingdom)?

2) Is this the case elsewhere?

3) Do these still apply when the train is parked and the engine turned off?

[grahame]

Here are some UK^▸ (United Kingdom) ones from a long time ago .... err NOT always!

Armargh, 1889: http://en.wikipedia.org/wiki/Armagh_rail_disaster
Tebay, 2004: http://www.bbc.co.uk/news/uk-england-cumbria-11043428
London, 2010: http://www.bbc.co.uk/news/uk-england-10964766

From Canada, arial images including a before and after (at end of page):
http://www.bbc.co.uk/news/world-us-canada-22953194

[Chris from Nailsea]

We discussed the 'runaway train' incident on the London Underground in 2010 at http://www.firstgreatwestern.info/coffeeshop/index.php?topic=7379.0

The Rail Accident Investigation Branch report on that particular incident makes interesting reading - and see page 49 for details of similar such incidents.

[eightf48544]

All this talk of runaway trains seemed to me like something from the long past (Armagh 1915 1889 came to mind) and I though continuous fail safe automatic brakes were the result.  I have three questions:

1) Are continuous automatic fail-safe brakes a requirement on all trains in the UK^▸ (United Kingdom)?

Yes now air brakes (are there any charters still vacuum?) for passenger and freight previously up to 60/70s mostly vacuum for passenger and unfitted for freight. Although some pre grouping companies used Westinghouse air brakes for passenger. eg LBSC

2) Is this the case elsewhere?

Pretty well universal although it is reported Wikipedia in some poorer countries Myanmar (Burma) for instance freight trains run unfitted due to lack of vacuum hoses to couple wagons.

3) Do these still apply when the train is parked and the engine turned off?

No, that's why all wagons have hand brakes, without the engine providing high pressure air the brakes will will gradually leak off. Hence the runaway happenning some time after the train is parked if sufficient hand brakes have not been operated.

[broadgage]

My understanding of UK^▸ (United Kingdom) train brakes is that they are fail safe, throughout the train but only in the short term in some cases.

Compressed air is used, stored in a reservoir on each vehicle. Any division of the train WILL without fail apply the brakes, as will the drivers air brake control, or the pulling of the communication cord.

Any failure of the compressor that supplies the air, will NOT in the short term result in any lack of stopping power, the air stored in the main reservoirs of each coach will still apply the brake.

However in the longer term, if the compressor is not working, or if air braked coaches are not coupled to an engine, then the air will gradually leak away and the brakes become ineffective.
Under such circumstances the hand brake must be applied, or scotches be placed under the wheels.
Some more modern stock has a spring operated parking brake that is applied automatically in case of loss of air pressure.

[Red Squirrel]

I've obviously been labouring under a misconception then - I though that whether brakes are worked by positive or negative pressure (i.e. air or vacuum) they fail 'on'. Is that really not the case?

[eightf48544]

I've obviously been labouring under a misconception then - I though that whether brakes are worked by positive or negative pressure (i.e. air or vacuum) they fail 'on'. Is that really not the case?

Only if you have a completely leak proof system where either the air pressure or vacuum is fully maintained indenfinitely. With the number of joints along a train this is obviously not possible so as Broadgauge says the brakes leak off over time.

This is what hapeened a Lac Magantic the locos were uncoupled and insufficient hand brakes applied. With no loco maintaining the pressure the brakes slowly leaked off and with too few handbrakes to hold the train it ran away.

[Red Squirrel]

Well perhaps I'm not being clear but my understanding is that in an 'open pipe' situation, both air and vacuum brakes fail 'on' - the loco's role is to either pull or push the brakes 'off'. If a brake pipe is punctured, or a train becomes divided, the brakes come on - resulting, for example, in a trainload of poor b*gg*rs getting stuck in the middle of a field near Pewsey for 6 hours, frustrated but safe (provided they don't die of hunger or dehydration).

Any other system would be what we engineers call 'fail-dangerous'. Are train brakes really fail-dangerous?

That's why I don't understand how this accident happened.

[broadgage]

If the train becomes divided or the brake pipe is broken for any other reason, the brakes will without fail be applied.
The force to apply the brakes is from the compressed air stored in the reservoir of each vehicle.
In time this will leak away and the brakes gradually release, hence the need for parking brakes, handbrakes, or wheel scotches.

If a train is left unattended with the brakes applied and the engine running to supply air, then the brake should work indefinatly.
If however the engine stops, whether by mechanical failure, human intervention, or for want of fuel, then in time the brakes will gradually "leak off" and if the train is on a gradient it will run away.

In case of the accident above it seems that the train was left unattended, complete reliance being placed on the engine providing air for the brakes.

This is most unwise, especialy for many hours, on a significant gradient, and with a highly flammable load.

[Red Squirrel]

Ah, now I inderstand. Thanks for explaining!

[eightf48544]

In case of the accident above it seems that the train was left unattended, complete reliance being placed on the engine providing air for the brakes.

Re Editted after checking source.

In this case the engines were shut down completely so weren't supplying air.

Locos with their lower centre of gravity made it round the curve but the tankers didn't.

It also appears that the company running the train has effectively been forced out of business by the Canadian and US authorities, It's in Chapter 11.

[stuving]

The Transportation Safety Board of Canada (TSB) has published its final report into the runaway and main-track derailment at Lac-M^gantic, Quebec on 06 July 2013 (Railway Investigation Report R13D0054).

Summary

On 06 July 2013, shortly before 0100 Eastern Daylight Time, eastward Montreal, Maine & Atlantic Railway freight train MMA-002, which was parked unattended for the night at Nantes, Quebec, started to roll. The train travelled approximately 7.2 miles, reaching a speed of 65 mph. At around 0115, when MMA-002 approached the centre of the town of Lac-M^gantic, Quebec, 63 tank cars carrying petroleum crude oil (UN 1267) and 2 box cars derailed. About 6 million litres of petroleum crude oil spilled. There were fires and explosions, which destroyed 40 buildings, 53 vehicles, and the railway tracks at the west end of Megantic Yard. Forty-seven people were fatally injured. There was environmental contamination of the downtown area and of the adjacent river and lake.

The report describes a great many safety actions already undertaken or required, including changes to the way safety is managed and monitored. It is, not surprisingly, a very damning document.

[Rhydgaled]

If the train becomes divided or the brake pipe is broken for any other reason, the brakes will without fail be applied.
The force to apply the brakes is from the compressed air stored in the reservoir of each vehicle.
In time this will leak away and the brakes gradually release, hence the need for parking brakes, handbrakes, or wheel scotches.

If a train is left unattended with the brakes applied and the engine running to supply air, then the brake should work indefinatly.
If however the engine stops, whether by mechanical failure, human intervention, or for want of fuel, then in time the brakes will gradually "leak off" and if the train is on a gradient it will run away.

Oh, I had assumed it was that the brakes were on at normal air pressure, and the engine had to reduce or increase the air presure in order to take the brakes off. Thus a leak would cause the brakes to come on and there would be no risk of them leaking off. There must be a good reason why this is not the case, but I can't think what that is.

[ellendune]

Oh, I had assumed it was that the brakes were on at normal air pressure, and the engine had to reduce or increase the air presure in order to take the brakes off. Thus a leak would cause the brakes to come on and there would be no risk of them leaking off. There must be a good reason why this is not the case, but I can't think what that is.

I seem to recall that the old vacuum brakes were applied by a big spring and the vacuum was required to release them. I assumed this was the case with air brakes too. It appears not.  Someone will be able to tell us how it works in the UK^▸ (United Kingdom).

[broadgage]

Modern air brakes on trains in most developed countries use two pipes, these may be seen on a locomotive, ready for coupling to air braked stock. The couplings are red for one pipe and yellow for the other.

One pipe, known as the main reservoir pipe, is kept continually charged with compressed air by the engine, this air charges reservoirs under each vehicle via a non return valve such that the air can not escape if a pipe fails. For correct normal operation this air pressure must be maintained, many locomotives and multiple units have a sensor that detects the air pressure and prevents it being driven if the air be insufficient.

The other pipe known as the brake pipe is also charged with compressed air, and provided that the pressures in the two pipes are equal then the brakes are held off and the train may be moved.
When the driver needs to brake, he releases the air in the brake pipe by means of the brake control. The air may be partially released for a gentle slowing or stopping, or completely vented for an emergency stop.
An automatic valve under each vehicle detects the difference in air pressure between the brake pipe and the reservoir and uses compressed air from the reservoir to apply the brake.
If the train becomes divided, then both pipes will be broken and open to the air. The breaking of the main reservoir pipe is of no immediate consequence since the non return valve will retain the air in each reservoir. The breaking of the brake pipe will immediately apply the brake on both portions of the divided train due to the substantial difference in air pressure across the automatic valve.
The brake will remain fully applied until the air in the main reservoir leaks away, no air system is leak proof. Once the air has leaked away the train will be un braked and liable to run away if not held by handbrakes, wheel scotches or other means.

Various faults and failures may render the brake ineffective on one vehicle, but it should still work correctly on the rest of the train because each vehicle has its own brake reservoir and control valve, a failure on one vehicle wont affect others. (the equipment is duplicated on single car trains)

The main merit of this rather complex system is that the brake is very quick to apply and release. To apply the brake requires venting air from the brake pipe, this small volume of air is quickly released.
To release the brake requires charging the brake pipe, which again is quickly achieved due to the small volume of air involved.
Note that no large reservoirs or cylinders etc need to be charged or vented, which would cause delay.

If the train has been unused for a while then the main reservoirs will be empty and charging these takes some time, but that is only needed at the start of the days work, not after each stop.