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"It's rare they're looking to harm anyone or anything,"

We must assume they want to do harm.

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[This is the story in the Houston Chronicle]

SAN ANTONIO -- The rear 50 cars of a freight train detached and rolled backward for two miles near San Antonio, smashing into another train, a Union Pacific spokesman said.

The Burlington Northern Sante Fe and Union Pacific trains collided about 11 p.m. Friday, derailing about 25 cars from both trains and spilling magnesium chloride from one car. There were no reported injuries and no one was evacuated from their homes.

Union Pacific spokesman John Bromley said unlawful riders on the eastbound Burlington Northern Sante Fe train may have pulled a brake lever, detaching the cars that hit the Union Pacific train.

Magnesium chloride is neither flammable nor toxic, said Randy Jenkins, district chief of the San Antonio Fire Department.

"We're not looking at a major environmental concern, and we're not looking at any health hazards," he told the San Antonio Express-News for today's online edition.

Trespassers are common on trains, Bromley said, and regular riders know how to stop a train.

"It's rare they're looking to harm anyone or anything," Bromley said. "I think they just wanted to get off."

It's the city's third train derailment this year. This is the second time this year Union Pacific and Burlington Northern Santa Fe trains have collided in the area. Previously, a Union Pacific train derailed near the location of Friday night's derailment.

http://www.chron.com/cs/CDA/ssistory.mpl/front/2814655

Carrying both acid and lye? Does having both on the same train make things more or less dangerous (mixing the two together will produce a very powerful exothermic reaction, but the by-products of that reaction will be sodium sulfate and water--not nearly as nasty as either NaOH or H2SO4).

I'm puzzled, though--wouldn't uncoupling cars on a moving train cause all the brakes along the entire train to get automatically thrown pretty quickly? Or did whoever uncoupled the cars cap the brake lines to prevent that from happening?

I wonder how the boxcars could run downhill for two miles. It is my understanding that the air brakes on train cars are designed to apply the brakes if air pressure is lost, such as would be the case when a series of cars are decoupled. Here is a quote from a webpage on train braking systems:

Brake Pipe
The pipe running the length of the train, which transmits the variations in pressure required to control the brake on each vehicle. It is connected between vehicles by flexible hoses, which can be uncoupled to allow vehicles to be separated. The use of the air system makes the brake "fail safe", i.e. loss of air in the brake pipe will cause the brake to apply. Brake pipe pressure loss can be through a number of causes as follows:

* A controlled reduction of pressure by the driver

* A rapid reduction by the driver using the emergency position on his brake valve

* A rapid reduction by the conductor (guard) who has an emergency valve at his position

* A rapid reduction by passengers (on some railways) using an emergency system to open a valve

* A rapid reduction through a burst pipe or hose

* A rapid reduction when the hoses part as a result of the train becoming parted or derailed.

The Railroad Consortium in the USA does not properly maintain it's rolling stock and their tracks, nor do they admit any culpability when these incidents occur.

They will calmly bribe, obfuscate, deny, and also murder when it suits them...they are not held accountable for their shameful disregard for safety and the prevention of such incidents

This incident is one more of many that will be blamed on mythical causes...as posted above several times, a rolling disconnect should cause immediate braking of the loose rolling stock...so in conclusion, place the blame where it truly belongs...on the railroad - the rolling stock - the sleeping driver. ! .

A few items to throw into the pile that I have access to..

The BNSF train originated in Eagle Pass, TX.
The "new" boxcars were new construction from a plant in Mexico.
Angle cocks (hand valves) control the flow of air throught the brake pipe.
At the point of the uncoupling, the angle cocks were closed on both cars, on the one left coupled to the train and the one that was part of the roll-away. The air was "bottled" in the rear 50 cars and the brakes were inoperative.
The uncoupling lever was lifted which opens the knuckle and separates the couplers.
There is a .34% to .92% westward descending grade from the point of the uncoupling.
Evidence was found on the east car of the cut that rolled indicating the presence of a "UDA" on the railcar. Empty water bottles - clothing - papers - excrement.
Tracker dogs were used, first on the rail car which they got a good hit on. Tracked the scent along the railroad, through a wooded area and onto the sidewalk of Commerce St. in San Antonio. Along the sidewalks for a few hundred yards and then to the curb where the scent dissappeared as if the person/persons got into a vehicle..

Hundreds of "UDA" are pulled off of and from under trains across the southwest daily..