[SystemSafety] Lac-Megantic disaster

Thu Jul 11 11:48:01 CEST 2013

Train brakes rely on pressure in what's called the brake pipe to keep them 'off'. When brake pipe pressure falls below a set value the brakes engage. This is the Westinghouse system of air brakes basically. 

That gives you a fail safe train brake that will actuate in the event that the train inadvertently parts, in freight operations a not insignificant risk due to excessive inter-train dynamic forces. 

However the brake actuation force is also normally provided by a pneumatic reservoir on each car, these are kept topped up by what's called the main reservoir pipe. Which is pressurized from air reservoirs located on the locomotives in the train, which are in turn pressurized by locomotive air compressors.

Like all pneumatic systems there's a certain amount of leakage, so, if the locomotive doesn't keep the main reservoir topped up with its air compressor the pressure will slowly bleed off and the train brake will disengage. 

Which is kind of why mechanical spring style park brakes are always used to park, and why the comments in the media that the loco was running to keep the brakes on is misleading. 

The actual reason has to do with operational efficiency as it takes time to pump up a trains reservoirs from ambient. Leave one loco on to run its air compressor and you can get away quickly in the morning.

Of course if all the needed park brakes aren't applied and then for some reason the online loco is shutdown...

As a side note, an increasing number of locomotives have what's called an Auto Engine Start Stop function to save fuel. With AESS the locomotives control system will monitor air reservoir pressure and only start the main engine if needed to run the air compressor. Modern freight trains are quite sophisticated and complicated systems. 

So one should be careful of believing what's being said about the 'cause' of the shutdown, just yet.

Hope that helps. :)-- 
Matt Squair
Sent with Sparrow (http://www.sparrowmailapp.com/?sig)

On Thursday, 11 July 2013 at 7:09 PM, Rolf Spiker wrote:

> I always thought that the brakes of a train (also for trucks) have to be energized to makes them free.
> (Vacuum driven energizing)
> With no any power (in this case vacuum), all brakes are fully engaged.  
>  
> Regards
>                 Rolf Spiker
> Rolf Spiker of Exida.com
> Senior Safety Consultant & Partner
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> From: systemsafety-bounces at techfak.uni-bielefeld.de [mailto:systemsafety-bounces at techfak.uni-bielefeld.de] On Behalf Of Peter Bernard Ladkin
> Sent: Thursday, July 11, 2013 7:17 AM
> To: Matthew Squair
> Cc: Bielefield Safety List
> Subject: Re: [SystemSafety] Lac-Megantic disaster 
>  
> There are a lot of questions. The BBC is saying that the locomotive was left running as the train was parked 7 miles up the line, to power braking systems; that fire services powered down the locomotive in the course of extinguishing a small fire; that the train started moving downhill shortly after that:
> 
>  
> 
> [begin BBC quote]
> 
> 
> 
> 
> The train, carrying 72 cars of crude oil, was parked shortly before midnight on Friday in the town of Nantes about seven miles (11km) away.
> 
> 
> Local firefighters were later called to put out a fire on the train.
> 
> 
> While tackling that blaze, they shut down a locomotive that had apparently been left running to keep the brakes engaged.
> 
> 
> Shortly afterwards the train began moving downhill in an 18-minute journey, gathering speed until it derailed in Lac-Megantic and exploded.
> 
> 
> [end BBC quote]
> 
> 
> 
> Questions. 
> 1 (HaroldThimbleby) Powered braking systems on freight are often air-powered. But they are fail-safe - losing power means they engage. So what system here requires power to remain engaged?
> 
> 2. Fire services called to a plant usually have an operator's emergency number to contact about plant details, and the operation of unattended running equipment. Is there no such system for freight trains? Why not?
> 
> 3. That an engine attached to a train with HazMat on board could be left running and unattended. 4. How the railroad company could tell at this stage whether and how many handbrakes were or were not applied.
> 
> BTW, this is another accident situation predicted explicitly by sociologists Perrow and Clarke ( The Next Catastrophe, Princeton U.P., 2007, resp. Worst Cases, U. Chicago Press 2005), as with flooding Mark 1 BWRs. But they were more concerned with Hazmats such as chlorine and hydrogen fluoride than oil.
> 
> It should give engineers pause that sociologists are better at identifying hazards than they are. (Except for computer networks, of course, where I think Bellovin's 1992 paper on possible TCP/IP exploits takes some beating for prediction.)
> 
> PBL
> 
> Prof. Peter Bernard Ladkin, University of Bielefeld and Causalis Limited
> 
> On 11 Jul 2013, at 00:26, Harold Thimbleby ....... wrote:
> 
> <a comment about air brakes>
> 
> > 
> > 
> > .... BBC News iPad App .......
> > 
> > 
> > 
> > Engineer blamed for Canada blast
> > 
> > 
> > 
> > A rail operator's chief executive blames a local engineer for a runaway train that derailed and exploded in a Quebec town, killing at least 15.
> > 
> >   
> > http://www.bbc.co.uk/news/world-us-canada-23264397
> 
> 
> Prof. Peter Bernard Ladkin, University of Bielefeld and Causalis Limited 
> 
> On 11 Jul 2013, at 04:03, Matthew Squair <mattsquair at gmail.com (mailto:mattsquair at gmail.com)> wrote: 
> > Bigger picture is that there's been a modal shift of oil transport to rail due to restrictions on pipeline construction, which drives a greater operational tempo in rail movements in turn.
> > 
> >  
> > On Thu, Jul 11, 2013 at 6:44 AM, Gergely Buday <gbuday at gmail.com (mailto:gbuday at gmail.com)> wrote:
> > http://www.bbc.co.uk/news/world-us-canada-23264397
> > 
> > Rail World boss Ed Burkhardt: "It is very questionable whether the hand brakes were properly applied. In fact I'll say they weren't". [...]
> > 
> > "He said he applied 11 hand brakes. We think that's not true. Initially we believed him but now we don't." [...]
> > 
> > The fire department and the train's owners have appeared in recent days to point the finger at one another over the disaster. 
> > - Gergely
> > 
> > 
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> >  
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