Given that most railroads operate on a brake pipe pressure of 90 PSI, these numbers would likely be inaccurate.
90 psi is at the engine, the 70 psi assumes “normal” trainline leakage.
With conventional power the gradient is a straight slope front to back, with DPU it slopes from either end and is lowest at the furthest point from the engines (depending on where they are in the train). Times and pressures higher than 70 psi will yield better results.
If the head end is charged to 90 and the rear end only reads 70 - the Conductor is going to expend shoe leather looking for the leaks.
Let’s throw something else into the mix. A DPU can initiate service and emergency braking from the rear of the train. The EOT device can initiate emergency braking from the rear of the train. Could not an EOT be equipped to also initiate a service brake application from the rear?
Seems that might negate the need for a lot of expensive equipment on each car and would reduce the stopping distance. It would require radio communication from the locomotive but surely would be less costly than ECP.
Just a thought.
http://www.cbsnews.com/news/north-dakota-town-evacuated-after-oil-train-derailment/
No comment necessary.
Buslist,
Regarding the statement that a 5,526-ft. long train with conventional air brakes takes 16 seconds for the brakes to fully apply in an emergency:
The 16 seconds includes 6 seconds of brake pipe signal propagation time and 10 seconds (maximum) for air to flow from the reservoirs to the cylinders. I understand your point that the 10 seconds is maximum, so it could be less, but it will be some time interval in addition to the propagation time.
I will call the time for brake pipe signal propagation, propagation time; and the time for the air to flow from the reservoirs to the cylinders, transfer time.
Therefore: propagation time + transf
ECP does not have “zero” propagation time, and engineers and government people alike will laugh at your state of knowledge if you say that. There is a finite time for the valve to open and establish flow once it is energized, and then a lag before pressure becomes sufficient at the brake cylinders to take the slack out of the linkage and bring the shoes into contact with the wheels. This is unavoidable delay in any foundation-braked system that is not equipped with, say, some whackjob version of pyrotechnic devlces like seat-belt tensioners that eliminate all slack and lost motion quickly – and even in that case there wouldn’t be “zero” reaction or activation time.
Your ‘transfer time’ is something that’s already been partially answered: the rate of transfer can be, and almost always is, quicker (it can be MUCH quicker) on a proper ECP system than for pneumatic control.
One very important reason why this can be done is the existence of graduated release on a proper ECP system. If the rate of brake application is too high, the ECP valves can be modulated to control the ‘transfer’ rate, and even if the brake application force has ‘overshot’ in the interval, the situation can be corrected (and proper braking profile restored) in no more than seconds. With the triple system, the only way to relieve the situation is to spill the brakes and wait for the line to recharge sufficiently to reapply – not something likely to happen effectively, in a number of regards, during an ‘emergency’ application.
Buslist: surely there are terms in current ECP practice that distinguish the setup time from the actual brake-application time. Can we determine what thos are, and then use them instead of Euclid’s made-up terms in the technical discussion going forward?
Some, but not much. Air brake valves have some amount of damping and throttling built in to keep the valve response stable. Much less is need if you are going to just pop open a magnet (solenoid) valve. There is still a bit of time to get the brake rigging to settle out and get the full force against the wheels.
Residents have returned to homes. Noteworthy is the fact that the oil in the shipment had been treated by Hess to reduce volatility, yet the six derailed cars still exploded, although probably less in scale compared to those at Lac Magentic. Wheel problems (as at Galena) seem to be the focus of the investigation.
http://www.sunherald.com/2015/05/07/6214911/evacuated-residents-allowed-home.html
I want to bump this thought up, considering I am becoming aware of a growing number of voices that say oil trains CAN’T be effectively made ‘safe enough’ strictly through technical ‘improvements’ like a few 16ths added shell thickness, ‘rollover protection’, or ECP-that-doesn’t-help-in-many-situations.
The most logical conclusion, I think, is to extend the kind of provisions airlines (and FedEx et al.) already enjoy: they don’t take explosives, oxidizers, and a wide range of other hazardous cargoes, and are not required by the Government to do so. The justification is that unavoidable hazard (to aircraft in flight) is posed by these. That is no different from the evolving consensus on oil fireballs following accidents such as derailments. It really is no different from toxic release or damage following breached PIH-carying cars following accidents such as derailments.
I can easily see a political consensus building around giving railroads the authority to refuse ‘automatic’ carriage of HHFT or PIH traffic, and demand either a surcharge or additional ‘named insured’ coverage on specific policies to handle any such traffic. If there is additional cost, expense, or inconvenience on railroads for the special train arrangements the Government now proposes for oil trains, it should be borne entirely by shippers, should be borne up front or in advance, and should include some factor for the ‘consequential damage’ to other traffic, specifically including Amtrak, that is delayed or inconvenienced by at least that proportion of oil-train handling troubles t
Yes it will explode. If a car was filled with water and immersed in a fire, the car of water would explode. That’s why the new standards call for thermal jackets on the cars. That extends the time to heat the contents (raising the internal pressure) from dozens of minutes to dozens of hours.
Still if you look at the derailment, the major risks are from fire, (most of that is the areas downhill of the site, the fire spreads not by “explosion” but by liquid commodity flowing downhill) and from pollution (air and water).
For all the comments about “explosions”, the damage in this (and every other oil train derailment) only extends a hundred yards or so from the derailment, except in the areas downhill from the site where the burning liquid oil flows. If you contrast that with West, TX, a true explosion, there was structural damage to buildings a quarter mile away. At West, about 400 tons of product went up. In this derailment about 600 tons and at Lac Megantic 4000 tons. In all the oil train derailments the damage was confined to an area a hundred yards or so from the derailment, except where the burning product flowed away from the site.
Wizlish,
I don’t know why they should laugh at my state of knowledge. I never said what you imply that I said. Despite the considerable effort that I made to define my two terms, you have still managed to fail to understand them. You have combined the two terms, and then say that my definition of one of the terms does not fit the combination of both of them. Of course it doesn’t. That is why I defined them separately. And also the third part you have added about taking slack out of the linkage is not part of either of my two terms.
Wizlish: I want to bump this thought up, considering I am becoming aware of a growing number of voices that say oil trains CAN’T be effectively made ‘safe enough’ strictly through technical ‘improvements’ like a few 16ths added shell thickness, ‘rollover protection’, or ECP-that-doesn’t-help-in-many-situations. The most logical conclusion, I think, is to extend the kind of provisions airlines (and FedEx et al.) already enjoy: they don’t take explosives, oxidizers, and a wide range of other hazardous cargoes, and are not required by the Government to do so. The justification is that unavoidable hazard (to aircraft in flight) is posed by these. That is no different from the evolving consensus on oil fireballs following accidents such as derailments. It really is no different from toxic release or damage following breached PIH-carying cars following accidents such as derailments. I can easily see a political consensus building around giving railroads the authority to refuse ‘automatic’ carriage of HHFT or PIH traffic, and demand either a surcharge or additional ‘named insured’ coverage on specific policies to handle any such traffic.
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BNSF may be using a new strategy or may be only posturing. I wonder how many railroads would refuse to carry hazardous shipments if they actually had the authority to do so? Making money is an attractive lure.
Wizlish,
You have used the terms, reaction time, activation time, setup time and actual brake-actuation time. I have no idea what you mean by “reaction, activation, setup, and actuation.”
And yet you imply that their meanings are somehow what my terms mean; and you imply that my terms, propagation time and transfer time, with their crystal clear definitions, are not clear enough, and therefore should be replaced with approved industry terms. I will bet you cannot find standard industry terms that match the definition of the terms that I have made-up.
One thing I am curious about is have the derailed cars had breeches to their walls or have the appliances (valves, and covers) been the source of the oil spilled in the derailment? I know the 117 cars are supposed to have skids or something to protect the underside valve. Obviously when a car derails, there are excess forces on any and everything. So are the cars splitting at a weld, being punctured or how have they failed? Are they rupturing do to heat created by the fire after the derailment and the fire is from oil that has come out of what opening. This is not clear to me.
No question you have me there!
If that is your purpose, you are either failing dramatically or have a definition of ‘clarity’ that matches ex-President Clinton’s take on ‘truth’.
I was trying to establish that there are several different actions that characterize a brake application. You seem to be going back to your terminology that does not account for what real brakes do in realtime, and then start to get ugly or snide when that terminology is questioned.
By all means, keep using your terms, and keep obfuscating. That will give real engineers time to study and develop effective models of what ECP braking actually does or doesn’t do, relative to conventional brakes, and then refine whatever systems presently exist to see how they can be optimized.
Wizlish,
The main reason for the ECP mandate is that ECP is claimed to stop quicker than Westinghouse. All I want is a clear answer that confirms or denies that claim. I agree that there are several actions that take place in the application of the brakes. The fact that the AAR and the USDOT are at loggerheads over the claim of stopping distance is an indication of how complex the effects of those actions or inputs to the answer must be.
So the only way that I can see to get to the truth is to break apart those inputs and deal with them one at a time. So I describe each input in terms of its limits, and then I give it a name just as a reference handle for clear discussion.
But let’s back up and let me ask the question this way, pertaining only to an emergency application of brakes of a 5,526-ft. long train, using Westinghouse brakes compared to ECP brakes:
As I recall from the Canadian TSB report on the northern Ontario CBR fires this past winter, they said that some of the wrecked cars leaked oil, and subsequent pool fires cooked other tank cars until they ruptured and exploded. They had pictures of large tears where the tank walls had bulged.
If I might suggest: we need to use a train composed of a certain number of cars, each of a certain weight, and only circumstantially (for Westinghouse) determine the brake-pipe length from the car data… I was thinking we should use ‘common oil-train parameters’ here, rather than the reference example. I am preparing a ‘call for graphics’ that will, I hope, clarify a great many things about this.
We know no such thing! That would be the case if NO brake on the Westinghouse train started to apply until the signal had propagated to the end of the trainline. You can readily see how silly an assumption that would be. The Westinghouse will be ‘lagging’ a bit more in actuation at each successive car, so the deceleration force exerted by the train will begin to lag progressively behind the ECP response, but the time of valve actuation at the first few cars is virtually identical. (I won’t yet consider if the respective valves open at different speeds or to different openings) You can approximate the braking response curve by plotting where the brake valves are located along the virtual length of the trainline, determining when the idealized pressure pulse reaches each, and then summing the responses appropriately.
Now, I consider the differential ‘transfer time’ (to use your term here in the sense I think you mean it) to be a much more significant contributor to rapid ECP braking than propagatio