Derailment and fire in Quebec

[Oldddudders]

So, if I'm not mistaken, brakes are not 'fail safe' if they rely on an air reservoir to maintain the braking effect. Safety has gone backwards!

 

JE

It's just like a car. We have a footbrake to bring the vehicle to a stand - then we apply a quite different handbrake to keep it still. Trains are no different.

[Parthia27]

This site http://www.sdrm.org/faqs/brakes.html may help clarify the operation of air brakes. Pan Am's rule book on brakes is at http://www.guilfordrail.com/Bulls/Bulls2/Timetable%20and%20Rule%20Book%20Docs/PAR%20ABTH%20Rules%20121104.pdf Section 403 on page 100 details the procedure for securing trains to be left unattended.

 

An apparently reliable local source states that there were 4 propane tankers in the yard in Lac Megantic http://www.pressherald.com/news/propane-suspected-in-explosions_2013-07-09.html

 

MM&A has a less than stellar accident record, significantly worse than the industry average: "Federal Railroad Administration statistics show that in 2011, MM&A had a train accident rate of 10 accidents per million train miles throughout the company’s network, compared with a rate of 3.7 at Pan Am and a national average of 2.8 accidents per million train miles." (Bangor Daily News article, http://bangordailynews.com/2013/07/09/business/ten-years-of-highs-and-lows-for-montreal-maine-and-atlantic-railway/) Some of the accidents in recent years are not really the railroad's fault (a car that was being set out for repair ran away because of a fault with the brake rigging resulting in the brakes not being applied despite the actions of the conductor), others most certainly are, either various derailments resulting from poor track or a runaway trio of locomotives left with no handbrakes applied, air bled off, locomotives ran nearly a mile before colliding with a stationary train. The FRA reports make interesting reading.

 

This is going to be an interesting accident report and I hope it will be as exhaustive in scope as the analysis of the 1989 air crash at Dryden http://en.wikipedia.org/wiki/Air_Ontario_Flight_1363.The immediate cause of the accident appears fairly clear (air brakes were either inadvertently released during the firefighting operation or bled off as a result of shutting the unit down, insufficient handbrakes were applied to restrain the train once the air brakes were released, possible that previously applied handbrakes were released for some reason) but I think a lot of other questions about indirect factors need to be examined such as crew change procedures (is it wise to leave trains unattended for relatively long periods of time?); the relationship between poor track conditions, slow transit times and the impact on re-crewing; coordination with local fire departments (the fire chief, responding to the railroad's statement about the brakes being released by a third party, inadvertently revealed a flawed understanding of air brake systems) and the ability of a single engineer to cope with all the demands of this kind of operation, especially laying the train up at the end of his shift.

 

Beyond the accident investigation, the stakes are quite high for a number of railroads. For instance, Pan Am is running similar traffic in Maine, bound for the same refinery, over very marginal track. They have made some progress in upgrading their infrastructure, but such a long period of deferred maintenance can't be fixed overnight. Trains creep along at 10mph due to track conditions (and faster than 10mph and you run a serious risk of derailments due to harmonic rock and roll on stick rail with lousy cross-levels on staggered joints). They had a minor derailment in Veazie last week, the fact that the tank cars involved were either carrying CO2 or fumes will likely get lost in the debate that I am sure is going to start once the tragic mess in Lac Megantic is cleaned up.

 

Roads like MM&A and Pan Am can get away with lousy infrastructure and dodgy motive power when they are carrying newsprint, the stakes go up considerably when it's big oil trains. It will be interesting to see the politics of this play out.

 

You have hit the nail on the head, in most tragedies such as this, the causal or initiating factor(s) are usually failures in training, procedure or in organisational culture at a human level which, when combined inadequate infrastructure and poor equipment, create a disaster. My heart goes out to all affected by this terrible accident, I only hope that the response of government and all railroad businesses in North America (and the rest of the world) is a measured one, and makes it mandatory to invest in adequate training, procedures, infrastructure and equipment, wherever hazardous substances are produced, conveyed or stored. It is so easy to let vested interests, economics and politics get in the way of doing 'the right thing'. BTW is it fate that this incident comes so close to the 30th anniversary of the Piper Alpha Disaster in 1988 (http://en.wikipedia.org/wiki/Piper_Alpha)?

 

Food for thought...

 

Chris

Edited July 13, 2013 by Parthia27

[dave1905]

So, if I'm not mistaken, brakes are not 'fail safe' if they rely on an air reservoir to maintain the braking effect. Safety has gone backwards!

 

JE

 

There seem to be huge misconceptions on how NA air brakes work.  I described how they work in an earlier post.  The reservoir is used to supply air to pressurize the brake cylinder, but once the brakes are set, what maintains pressure in the brake cylinder is the seals on the cylinder and in the brake valve on the car.  Until there is a material difference in pressure between the train line and the reservoir the cylinder and the reservoir are not connected.  They are set to "fail safe".  But in order to "fail safe" something has to fail.  So far though I haven't read of anything where the brake system "failed".  The air brake system is designed to allow the engineer to control a moving train.  The train initially wasn't moving and when it did move there was no engineer on it to control it.  While the train was stopped there was a different system that was designed to hold the train, the handbrakes.  Much like a car has a brake system operated by the big pedal under the steering wheel and a parking brake.  If you car rolls out of your garage in the middle of the night, it wasn't the brakes attached to the big pedal that failed, it was something to do with the parking brake.  Either you didn't put the parking brake on, you didn't put it on hard enough, it failed, or something else happened to cause the car to move. 

 

I don't understand the statement "safety has gone backwards" since this is essentially the same system that has been in place since the 1880's.  Here have been numerous improvements to speed both the application and release of the brakes but the basic methodology of how the Westinghouse air brake works has been the same for over 125 years.  Nothing has gone backwards because nothing has materially changed.  NA has had a consistent, uniform, comprehensive system of couplers, air brakes and safety appliances for over 100 years.  A car from the 1920's would couple into a modern freight train and the air brakes would work.

[PaulRhB]

Air or vac brakes all have the ability to be bled off to allow a vehicle to roll free so they can be moved without a loco if required, such as hump shunting, and to allow that they have a system that will bleed off over time. The handbrakes are there to secure any train left long term. Same in the UK or USA there's been no relaxing of standards

[highpeak]

Maine's governor has ordered a safety review: http://www.pressherald.com/news/is-maine-on-top-of-oil-by-rail-risks_2013-07-12.html

If I was in David Fink's shoes I'd be getting that report and a check up to Augusta pretty quick...

[Budgie]

Is there any flat level track near there where the train could have been parked with no danger of its running away if the brakes leaked off?

[highpeak]

Some background on MM&A operating practices from trainorder.net:
"In common with some other regionals and shortlines, MM&A doesn't assign specific trains to operating crews, but has numbered "jobs" with assigned tasks.

"Job 1" is based out of Farnham QC, (43 miles south east of Montreal) and operates 132 miles east to Megantic QC (Lac Megantic).
"Job 2" is based out of Brownville Jct., Maine and operates 117 west to Megantic. The operating employees at Farnham are Canadian, those in Brownville Jct. are American.

There are 75 MM&A employees, 20 of which are operating employees.

The one person crew concept was introduced in 2012 and has been gradually going into effect since then.

"Job 1" from Farnham and "Job 2" from Brownville Jct. don't always make a close connection. Reports don't mention whether there was a "Job 2" westbound Brownville Jct-Megantic train secured somewhere near Megantic, but they do mention there was a Brownvile Jct. crew person taking rest at Megantic, and that the crude oil train would run when he was rested. The reason the train was parked at Nantes QC was to not block any public highway crossings for a prolonged period. It seems that parking the train at Nantes was a frequent occurrence.

One operating practice which CP requires when a train is secured awaiting a crew is a "train status report" from the incoming crew which includes brake test status,details of roll by inspections, and details of when the train was stopped, and how many handbrakes are applied and other details which would usually be communicated between crews at a "change off location".

I think it likely the MM&A requires a similar form to be completed by the incoming crew. More than the event recorder, such a form would be a key piece of evidence. That would be where the engineer in question would have documented how many handbrakes he applied.

Mention was made by a Brownville Junction MM&A operating employee who had recently left the company that he was making 40% less working for his most recent employer than previous employers operating the railway. Not only were the wages lower, but he was working less frequently. He also mentioned lower track speeds since the shortlines took over which resulted in longer on duty times to accomplish his run.

The Farnham engineer involved in the runaway has been working the route since 1980, hence would have worked for CP, Canadian-American and MM&A. He is in his 50's so he would have been in his 30's when CP had the route shortlined."

http://www.trainorders.com/discussion/read.php?15,3125784

[The Stationmaster]

Does a 'smart' EOTD allow for that function to be done from the cab?

As I understand it the answer is 'yes'.  When I tried to get GM to get hold of one and bring it over for our 'supertrain' trial with the Yeoman Class 59s I was assured that it would give a brake pipe pressure reading and a flow rate so effectively it can be used to check that the brake pipe has fully vented to the appropriate pressure on a brake application and to establish that the pressure is rebuilding at a sufficient rate to release the brakes.  So we knew exactly what one would do - but GM still decided not to play ball to the extent of getting hold of one for us fr the trial served 'em right that a Class 59 got broken as a result of not having information an EOTD would have given!

 

However in this case we're talking about a different sort of test where the auto brake is used to stop and hold thh trains stationary, handbrakes are applied, and the the auto brake is released to check that sufficient handbrakes have been applied.

[Guest Belgian]

It's just like a car. We have a footbrake to bring the vehicle to a stand - then we apply a quite different handbrake to keep it still. Trains are no different.

Thank you Ian, I (as an interested observer rather than a railway worker) had always believed that the train brakes were set to 'on' unless released by air or vacuum action and were thus 100% fail-safe, a leak causing them to go 'on'. I 'presumed' (always a dangerous thing) that the air or vacuum reservoir was needed to release them for shunting purposes and that the handbrake was merely a back-up in case of equipment failure. I had not appreciated that a brake could fail if there was a leak.

 

JE

[dave1905]

Is there any flat level track near there where the train could have been parked with no danger of its running away if the brakes leaked off?

Y'all just don't seem to be grasping the concept here.

 

The air brakes aren't supposed to hold the train there.

 

They aren't designed to hold the train there.

 

They aren't intended to hold the train there.

 

Whether the air leaked off or not should have no bearing holding the train.

 

If the air leaked off, if the instructions had been correct and if the instructions were followed and there was no other unusual event, the air could have bled off and the train would have stayed put.  It wouldn't have rolled away.  If the air brakes were being used to hold the train then that is a failure in itself.

 

What is supposed to hold the train are hand brakes.  They do not bleed off.

[Guest Belgian]

It's OK, I get it now.

 

JE

[highpeak]

And the procedure for testing the effectiveness of the handbrakes at holding the train is on page 51 of the Canadian Rail Operating Rules (CROR) available at http://www.railcan.ca/assets/images/regulations/rules/2008_03_19_CROR_TCO_093_en.pdf Rule is 112, three parts to it.

MM&A may have added some other stuff such as guidelines for number of brakes to apply and so on, but the CROR is the underlying rule.

 

[BG John]

What is supposed to hold the train are hand brakes.  They do not bleed off.

But even so, it doesn't exactly seem wise to hold an unattended train on a gradient, especially when it's carrying a dangerous cargo and there's a town at the bottom of the hill, without some way of preventing a runaway reaching the town. Even with more than enough handbrakes on, something could go wrong, including sabotage as there's no one around to stop it.

[dibber25]

I am glad to hear that TSB will go beyond proximate causes for the accident, but frankly I would prefer to see a judicial inquiry of the kind that was done after the Dryden plane crash (which is why I referred to that in my first post). A typical inquiry into that crash would have blamed the pilot for attempting to take off with contaminated flight surfaces, harrumphed about the chain of command and communications and noted the lack of a ground power unit at Dryden. Judge Moshansky found a lot of other things to question including accepted industry practices and regulatory failures. Sound at all familiar?

TSB published a report into a collision in Alberta in January 2012 (reference in post 184) that included the following risk findings:

1. When clear instructions are not provided detailing the manner in which the hand brake effectiveness test must be conducted, there is a risk that insufficient hand brake force will be applied and uncontrolled movements will occur.
2. When sidings are frequently used to set out cars and special derails are not installed, there is an increased risk of uncontrolled movements entering the main track, especially where sidings are located on steep grades.
3. Applying only the minimum number of hand brakes, as set out in Section 7.12 of Canadian National's General Operating Instructions, to cars held on tracks with significant grades may not provide adequate securement.

Canadian National did subsequently install a special derail (meaning it is normally locked clear of the track rather than locked in place on the rail) on the siding. Did MMA read that report? How widely read are these reports within the industry? Were any steps taken to change rules and procedures? Or are we happy to note that in North America we don't put derails on sidings and leave it at that?

 

Chris Leigh and Mike Stationmaster have asked some pertinent questions and countervailing points have been made. One of these issues involved the age and reliability of the motive power. It is certainly true that brand new equipment of any kind can be defective, out of the box. It is also true that old equipment can be as reliable as the newest. But come on, is anybody really going to suggest that some of the roads are meticulously maintaining these engines? They are wrecks on wheels, patched up and sent out for another run. Was the equipment a direct cause of the accident? Was it an indirect cause of the accident?

 

Here's a thought process: how seriously would anybody take a business proposal spelling out exactly what MMA did to take on this business?

 

I realise I am being a bit abrasive and persistent with this, but 50 people have died and a town levelled in an event that in many ways can't be called an accident and is the latest in a depressing sequence of similar events, different because of location but not so much because of causes. For the rail industry's own good, it can't be business as usual.

 

I think you're right and I like your style. I am getting the sense that some rail accidents are viewed almost as inevitable in Canada. Three significant freight derailments in four weeks (all through different causes, its true, but the public just sees 'unsafe railways'). Look back at the TSB reports and you'll find two derailments of unit coal trains (2011 IIRC) six weeks apart because of broken wheels - wheels that were in an appalling state and yet one set was within acceptable standards). The concept of putting voice recorders and cameras in locomotives, following the Burlington accident report, is based entirely on the assumption that there will be more such accidents and the only way to find out what happened is to know what the crew said and did. But that will be different each time and each accident. It's the system that needs to be looked at. In that case the signals should tell the engineer WHERE he's going, NOT how fast to go.  The Lac Megantic accident seems to have been a result of numerous incidents, all comparatively minor, combining together to create a catastrophe. That's not unusual. I've read dozens of accident reports (British, US and Canadian) in 50 years of railway journalism and that is a common factor in many of them. But if you can reduce the risk of those minor incidents, you take links out of the chain of events and a major disaster is not so easily created. Locomotives running round in patched up 30year old paint (on a railway that likes its red and gold) suggest to me that they aren't necessarily well maintained. In any event five old locomotives instead of one or two new(er) ones must increase your chances of trouble. More to the point though, little or nothing seems to have been done to make this railway better able to cope with this significant extra tonnage, which is likely a revenue windfall. Where were the track upgrades? Sure, trap points have been phased out on passenger lines in the UK but this is a freight line in Canada where they could do their job just fine. Furthermore, you can forget to set and lock a derail. You can't reset for the main line without setting the trap point. Yes, Canada has trouble with kids getting onto property and spraying graffiti, so you NEED to have secure places where hazardous goods trains can be stabled up in relative safety - yes, decent fences, gates, lighting, and security guards if necessary - it's only going to be one or two carefully planned places on the route. We live in dangerous times and Canada has two alleged railway terrorists in custody. Is it reasonable to expect one man to drive a complete shift at mind-numbingly low speed, hour after hour, to tie up his train at dead of night, to walk 1,000yds climbing up and down on 76 cars to screw down handbrakes and then 1,000yds back again (sometimes in VERY inclement weather) - a job which will take another hour or more? There's a lot in here that has far more to do with wringing the last ounces of profit out of a tired old railway, than with the safe efficient 21st century movement of dangerous goods. Finally, there's the PR aspect of not having an incident plan that says who talks to the press and what they say. So you add a PR disaster by having your Chief Exec first blame the Fire Brigade, then a 'non-railway person' and finally rounding on his own engineer and hanging him out to dry before he's even been charged with anything, never mind tried. It just might be that something good can come out of this tragedy if it is seen as a wake-up call.

 

This makes interesting reading:

http://www.pressherald.com/news/is-maine-on-top-of-oil-by-rail-risks_2013-07-12.html?fb_action_ids=4625639932717&fb_action_types=og.recommends&fb_source=aggregation&fb_aggregation_id=288381481237582

Edited July 13, 2013 by dibber25

[Oldddudders]

But even so, it doesn't exactly seem wise to hold an unattended train on a gradient, especially when it's carrying a dangerous cargo and there's a town at the bottom of the hill, without some way of preventing a runaway reaching the town. Even with more than enough handbrakes on, something could go wrong, including sabotage as there's no one around to stop it.

To those of us used to UK railway operations, it certainly doesn't seem sensible. But US and Canadian railway operations and priorities, and the expectations of the communities through which they run, are very different from ours. After all, we wouldn't dream of using a signalling system that involved the working timetable as a key component, yet in North America millions of trains have been run safely that way in the last century+. And this train had run multiple times previously, as evidenced by the taxi-driver's comments about taking the engineer to his hotel, and the graphs already linked showing MMA's volume of oil carried. We need to stand a little further back from the method of operation, perhaps.

[dibber25]

According to my rough calculations and lousy maths:

Gross weight of 76cars = 9,669tons

Weight of 11 cars (allegedly the engineer pinned down 11 cars) = 1,399 tons

Not clear whether loco handbrakes were on. Some reports say they were but the fact they rolled a km out of town after the train derailed, suggests that they weren't. If they were on then 400-500tons extra braked weight?

Would 1,400 tons be likely to hold back 8,270 tons on a gradient?

CHRIS LEIGH

[pH]

The way you explained this is putting the engine in reverse of the direction its moving.  That means either the wheels turn in reverse (sliding the wheels and grinding them down) or turns them (and the motor) against the way they are being powered creating tremendous heat in the traction motors.  The choice between damaging the motors or damaging the wheels is not a really good choice.

 

Why not just put it in dynamic braking?

 

As far as holding a train by putting it in reverse, that means that the force on the wheels has to balance the weight of the train.  So that means putting enough power into the motors to balance the weight of the train.  Pushing that much power through a motor that isn't turning will cook it off ASAP.

 

Dave, I wasn't describing 'plug mode' as a means of stopping a moving train though, apparently, certain railroads will allow this to be done in emergency situations. The results are as you describe, hence the 'emergency only' use. I was asking if the use of 'plug mode', which is used to restrain trains at low speeds during loading operations, could be used, against brakes, to hold a parked train on a gradient.

 

True 'plug mode', it appears, can be used only on DC locomotives. EMD actually rewrote some software on SD75s to allow them to operate in this way - the original version couldn't cope. Some AC locomotives have the function, but whether it's true 'plug mode' or just mimics it, I don't know. Dynamic braking doesn't work on DC locomotives at the speeds 'plug mode' is used.

 

So, it appears 'plug mode', used at very low speeds on a moving train, does not immediately fry traction motors or generators. I was asking if it was possible to use it on a stopped train, and for extended periods, without causing damage.

[pH]

Not clear whether loco handbrakes were on. Some reports say they were but the fact they rolled a km out of town after the train derailed, suggests that they weren't.

 

On the contrary, rolling only a kilometer from a point where they were doing 63MPH (according to the TSB), along what looks like fairly level track would suggest to me the engine handbrakes were on.  

[pH]

Dibber, re your post today at 10:55. It's been said a few times on this topic - railroads in North America are not public services, they are intended to be profit-making organisations. Anything that they can do to increase income or reduce expenditure will be done, short of illegality. Railroads will not do anything else, unless they are compelled to do so by outside forces (which probably means governments or customers). If this outside pressure means that the railroad will have to spend or forgo enough money that the operation involved will no longer make a profit, it is odds on that the operation will be abandoned. 

 

All your suggestions are laudable, and would be valuable. They are not going to happen or, if they were to be enforced in Canada, large parts of the railway network would simply be abandoned.

 

My opinions - other opinions are available. 

[Glorious NSE]

Chris, one danger I think is that if folk insist on regarding this as an abberation by one fly-by-night operator then that allows the rest of the industry, (and any regulators,) to ignore some of the bigger issues as not applying to them, as they would not regard themselves as such.

 

But - so far as I can tell.

 

The loco's used by the MMA are all 'industry standard' types used by assorted railroads, big and small, throughout North America

Their mandated loco maintainence standards and frequencies  are all 'industry standard' and used by assorted railroads, big and small, throughout North America

Their track layouts are typical of 'industry standard' and used by assorted railroads, big and small, throughout North America

Their track maintainence is 'industry standard' and used by assorted railroads, big and small, throughout North America

Their signalling methodology is 'industry standard' and used by assorted railroads, big and small, throughout North America

Their rulebook will be largely (save for single manning related bits) 'industry standard' and used by assorted railroads, big and small, throughout North America

 

About the only thing about MMA that is not 'Industry standard' is the single person crew...

 

Based on that, the error that prompted this disaster could have occurred anywhere in North America, and maybe has done so before for all I know. 

Edited July 13, 2013 by Glorious NSE

[Edwin_m]

According to my rough calculations and lousy maths:

Gross weight of 76cars = 9,669tons

Weight of 11 cars (allegedly the engineer pinned down 11 cars) = 1,399 tons

Not clear whether loco handbrakes were on. Some reports say they were but the fact they rolled a km out of town after the train derailed, suggests that they weren't. If they were on then 400-500tons extra braked weight?

Would 1,400 tons be likely to hold back 8,270 tons on a gradient?

CHRIS LEIGH

Going by these figures the total weight of the train is 9669+500, 10100 tons to make the maths a bit easier. 

 

The force needed to hold a train on a gradient is given by the weight of the train multiplied by the gradient as a fraction, or divided by the gradient as a "1 in".  For an 10600 ton train on a 1% gradient this is 101 tons. 

 

If the coefficient of friction between wheel and rail is 10% this force could be provided by 1010 tons of the train being braked, assuming the brakes are applied hard enough for the coefficient of friction to be the limiting factor (ie wheels slide along the rails rather than turning against the brake blocks). 

 

This back-of-an-envelope calculation suggests that 11 wagon handbrakes on their own would be sufficient but probably not allow enough margin for safety.  Applying the loco handbrakes as well would give nearly a factor of two safety margin. 

 

Anyone please say so if you think I am missing something in this calculation! 

[highpeak]

A CN guide as to what constitutes sufficient handbrakes from their general operating instructions suggests that on a 1.2% grade you would need handbrakes applied on 40% of the cars. The chart does not attempt to consider the weight of the cars other than to say if the weight is below 2,000 tons then an additional two brakes should be set.

 

The chart is referenced in an accident report I have previously cited at http://www.bst-tsb.gc.ca/eng/rapports-reports/rail/2012/r12e0004/r12e0004.asp. The accident involved a cut of 13 loaded coal cars that had been left in a siding with one handbrake set. The conductor believed the 1% grade started beyond the point where the cars were left. The air bled off over the course of the next 31 hours and the cars eventually ran away, colliding with a freight train. CN subsequently installed a special derail on the siding.

[highpeak]

This is a pretty heavy thread, as a brief "commercial break" I offer these two examples of the way it was on the old BAR. Both are F3s, built in 1947, bought new by the B&A, veterans of over thirty years of hard work when the pictures were taken at Northern Maine Jct near Bangor.

[Gerald Henriksen]

According to my rough calculations and lousy maths:

Gross weight of 76cars = 9,669tons

Weight of 11 cars (allegedly the engineer pinned down 11 cars) = 1,399 tons

Not clear whether loco handbrakes were on. Some reports say they were but the fact they rolled a km out of town after the train derailed, suggests that they weren't. If they were on then 400-500tons extra braked weight?

Would 1,400 tons be likely to hold back 8,270 tons on a gradient?

CHRIS LEIGH

 

I think your numbers are off.

 

The train was 72 tank cars.

 

From pictures of the tank cars recovered from the rear of the train (and returned to Nantes) we get  an empty weight of 68,000 lbs and a load limit of 195,000 lbs, assuming fully loaded that takes us to 263,000 lbs per car.

 

Multiply by 72 and convert and we get 9,468 tons for the oil cars.

Multiply by 11 , etc, 1,447 tons for 11 cars.

 

As for the locos, how much brake would be left after being forced downhill?  There has been some talk that people claimed the train was on fire before reaching Lac-Megantic, which could have been the brakes glowing red and giving off sparks (which, also now that I think of it, could be what ignited the oil was a tanker(s) was punctured).

 

Even more fun, consider that these weren't strictly speaking oil tankers but rather generic tank cars.  Looking at the other info that is painted on the cars in addition to the load limit of 195,000 lbs we get a capacity of 30,070 US gallons.  Random website claims light crude oil weighs 7lbs per gallon.  Using this number we get a theoretical load weight possibility of 210,490 lbs, or 15490 lbs over the maximum weight.  So if that weight for light crude is correct, it is possible these tank cars were overweight.

[Edwin_m]

Those are useful updates Gerald but I think Chris is somewhere in the right ball park.  If the wagons were overloaded this would increase the train weight but also by the same proportion the restraining force exerted by any wagon handbrakes that were applied, but it would slightly increase the likelihood of the train rolling away because the loco handbrakes (if applied) would still be the same. 

 

The question of damage to the loco (or indeed wagon) brakes on the journey downhill is not relevant to whether the brakes were sufficient to hold the train where it was stabled, although it would have some effect afterwards and influence where the locos ended up.  This depends on the answer to my question of whether the wheels slid or rotated against the brakes, since one would result in wheelflats and false flanges, and the other in brake blocks wearing and becoming less effective.  The first would be obvious to investigators, the second perhaps less so.  On reflection I think the wheels would still rotate, in which case the effective coefficient of friction might be less than 10%. 

 

It is possible the fire damaged the handbrake on the loco concerned, but we don't know anything about this.  Indeed I don't think the use or otherwise of loco handbrakes in this incident has been mentioned in any of the linked articles.