Forgive me, this is going to be long, but this is a situation where the truth matters.
Lac-Megantic, site of a particularly catastrophic rail disaster. The heart of the town was destroyed when an uncrewed freight train -- consisting of 73 tank cars loaded with crude oil, a "buffer car" and five engines -- hit a road crossing and curve posted for 10 mph doing 63 mph. The locomotives and buffer car negotiated the curve; roughly half of the tank cars did not. (I have seen a report indicating that the locomotives rolled to a stop ~800m beyond the crash scene.)
The resultant derailment, oil spill, fire, and explosions (probably BLEVEs
) razed Lac-Megantic's central business district and killed approximately 50 people. This happened just past 01:00 on Saturday July 6th, 2013.
Why? The train was parked 7 miles away -- uphill -- in the town of Nantes at around 23:00 hours so that the sole crewman could take his mandated rest period. The Maine Montreal & Atlantic (MMA) railroad executives are now saying that the engineer failed to set all of the 16 handbrakes he claimed to have set, and probably skipped the legally required "securement test" to insure that the brakes could hold the train. Even 16 handbrakes is skimpy and inviting trouble. Railroaders have given differing opinions as to the right number, but Canadian National's guidelines say 40% of the brakes should be set for a train parked on a 1 - 1.5% grade. The track at Nantes has a 1.2% grade down to Lac-Magantic. The general number cited is around 30 hand brakes (ranging from 20 to 40+).
There has been much talk about the role of the Nantes Fire Department, who responded to the parked train after passers-by saw flames (not sparks - I have seen video, it's flames
) coming from the lead engine and called 911. Nantes FD arrived, and per the protocol they were trained in by the railroad, shut down the engine and put out the fire. Railroad track workers gave the NFD the all clear, and everyone left. Not long after, the train began to roll down hill on its own...
Here's where the media is just endlessly repeating wrong information initially released by the MMA: The NFD shut down the burning engine, the only one of the five that had been left running "to supply air pressure for the brakes." With the engine stopped, air pressure slowly bled out of the brake system and the air brakes lost their hold on the cars. Air brakes off, not enough hand brakes set = disaster.
This is both right and WRONG. The right part: a train left standing with the air brakes applied will slowly bleed pressure out into the atmosphere, and the brakes will eventually release. The WRONG part: this will happen whether there is a running engine attached, a stopped engine attached, or no engine attached to the train.
Train air brakes are not like truck air brakes. On a truck with no pressure in the air system, springs hold the brake pads to the brake drums (or discs) at each wheel. To release the "spring brakes" air is pumped into the side of the brake cylinders opposite the springs, pushing the pads back from the brake drums. Pressing the brake pedal puts pressurized air into the brake cylinders on the same
side as the springs, causing the brake shoes press against the brake drums and stop the truck. To set the parking brake (the "spring brakes"), all air is vented from the brakes and the springs push the brake pads into the brake drums. This is why you hear the PSSSSH of escaping air when a big truck or bus parks.
This system doesn't work on a quarter-mile long train (about what trains were in the 1862 when George Westinghouse
invented the modern railroad air brake. The length attenuates pressure and draws out the time it takes to apply the brakes from the front of the train to the back. Westinghouse created a differential pressure system which overcame these problems. Here's how it works.
On a train with no pressure anywhere in the air system, the brakes are released. This is a Good Thing when you are switching cars around in a yard or sorting them with a gravity hump
. To get a train ready to roll you must first pressurize the system (70-90 psi on most US railroads). Westinghouse's genius was the "triple valve" - a differential pressure valve that responds to the relative air pressures in the train's main brake pipe vs. the air reservoir on each car. When pressure is higher in the brake pipe than the reservoir, the triple valve lets air into the reservoir and vents the car's brake cylinders to the air. When pressure is equal, the valve goes to a middle position where the brake cylinder vents are closed. When pressure is greater in the reservoir than the main brake pipe (e.g. when the Engineer applies the brakes), the valve goes to its 3rd position - allowing air from the car's reservoir to pressurize the brake cylinders and thus apply the brakes.
Activating the emergency brake on a train vents all air from the brake pipe ensuring a high differential between pipe and reservoir and ensuring a strong, full brake application.
Now this gets us back to the right and WRONG. A train left standing with the air brakes set will slowly leak air out of the brake cylinders. These are rough-and-tumble industrial devices, not space shuttle components: they leak. Eventually there will be too little air pressure left in the car reservoirs and brake cylinders to effectively hold the brakes.
As explained above ("To get a train ready to roll..."), the only way to (re)charge the air reservoirs on the train cars is for the Engineer to release the brakes
by putting more pressure into the main brake pipe than there is in the reservoirs. FYI, in railroading, making multiple quick brake applications without allowing time for the system to recharge is a newbie mistake called pissing away your air
Having an engine running ensures only one thing: that the locomotives' air supply reservoirs will be fully charged, enabling the crew to charge the train brake line faster and get going faster than if there was no pressure anywhere in the system. It does nothing to recharge the pressure in the car reservoirs
So, shutting down the burning engine had NOTHING AT ALL to do with the inevitable leakage of air from the brake cylinders and the resulting runaway train. Handbrakes are the only guaranteed way to hold a train still for any length of time. When a (possibly fatigued) engineer (took a possible short cut to get to bed quicker and) fails to set enough brakes to hold 31,000,000 lbs of crude oil and its train parked on a slope, disaster happens.
Can someone please get an Engineer (either type - train driver or degreed professional) on the air to call BULLSHIT on MMA's excutives? Please?