Monday, July 15, 2013

Update on Oil Train Fire

The accident investigation into the derailment, fire and explosions of the crude oil train in Lac-Megantic, Quebec a little over a week ago still has a long way to go in determining the details of the fire and explosion. News reports (see here, here and here for example) over the last week have begun to fill in some of the questions about the proximate cause of the derailment and it seems abundantly clear that this was not terrorism, but a much more complex transportation accident.

Brake Failure

The initial starting point of the accident occurred when the air brakes that had been set on the parked train failed. The train crew had parked the train so that they could take a service break to get some sleep in a local motel in a town just up the tracks from Lac-Megantic, a routine action by all accounts (trains only carry a very limited crew and have hours of operation restrictions like most transportation professionals).

In this case, while the crew was getting their rest a fire broke out in the engine compartment of the one locomotive that was left running to supply power to the compressor that maintained air to the air brakes. The local fire department responded, put out the blaze and turned off the engine as a safety measure (the fire was apparently associated with a fuel leak in that engine). With no compressor running, the air pressure bled off the system over time and the air-brakes released. With the train parked on an incline it started to roll and ended up hitting the curve in Lac-Megantic at too high a speed and derailed.

There are still lots of questions to be asked and details to fill in about the above scenario and investigators are hard at work filling in those blanks. One of the particular details that may be important is how many of the manual brakes had actually been set and how many would have been needed to be set to stop the train from rolling away when the air brakes failed. It is not clear that a sufficient number could have been set.

DOT-111 Tank Cars

As with most serious accidents there is more than one system failure that lead to the devastating fire and explosions in this case. In this case there was a loss of containment of the crude oil that allowed the initial fires to start. Again, details have to be determined, but it seems clear that as the cars left the track and skidded into one another on their side, one or more of the DOT-111 train cars was punctured and the crude oil was released.

At least one news report is blaming flaws in the design of the DOT-111 tank car as being a factor in the initial fire in the incident. An NTSB slide presentation from 2012 would certainly seem to justify that claim. That report shows a number of possible failure point where the initial release may have come from including:

• Tank puncture from contact with other train cars or immovable objects along track;
• Housings for the protection of top fittings are “inadequate to withstand the forces of a derailment”; and
• Bottom outlet valves may open and release the product.

In October of 2011, the American Railroad Association began taking steps to replace the current fleet of DOT-111 railcars with newer model that would withstand impacts with a lower chance of release. It is not clear that those improvements would have prevented all of the leaks that may have happened in this accident.

Even if they would, it will take a long time to phase out all of the current cars in service (DOT-111 cars are the most common tank cars in general service) because of the high-cost and long service lives of the cars. This is even more of an issue due to the increasing use of railcars for the transportation of both crude oil and ethanol (over 40,000 DOT-111 railcars are currently in ethanol service according to the NTSB slides).

Point of Ignition

A crude oil spill is a nasty mess in its own right, but this disaster was due to fire and explosions. There had to be a point of ignition somewhere I this story. As I mentioned in my earlier post just the action of sliding across the pavement and ground, not to mention the collisions between cars would have produced lots of sparks. Whether or not these could have been the ignition source would depend in large measure on the flash point of the crude oil in question.

There is another potential ignition source that is alluded to in one of the news reports. A resident saw what was reported as flames on the train as it passed into Lac-Megantic. The observation was made as the train sped past and it was dark. I suspect that what was actually seen was a glowing white-hot wheel bogey from one or more of the wheels where the handbrake had been set. The friction between the brake and the rolling wheel or the fixed wheel sliding on the track would certainly heat that metal to a high enough temperature to ignite any crude oil that came in contact with it in the subsequent derailment.

Unit Trains

Unit trains, collections of a large number of railcars carrying a single commodity, have a long history in the United States. They are an efficient method of hauling large quantities of commodities to a single processing point. While not as efficient as pipeline, they do provide shippers with the flexibility of shipping to multiple receiving points from a single source.

Unit trains also have some very specific additional hazards. When a 70-car train of crude-oil like the one involved in this accident is involved in a derailment, only a limited number are punctured in the accident. Without a fire the damage would be limited and not immediately life threatening to nearby structures and people.

Once a fire is started and a pool of burning liquid engulfs undamaged tanks, they can produce a BLEVE (boiling liquid expanding vapor explosion) that will cause some of the other undamaged cars to begin leaking in-turn and expanding the problem. It is entirely likely that all of the cars involved in the derailment (and some number still on the tracks) were involved in the subsequent conflagration instead of just those that were damaged on impact.

This BLEVE problem is aggravated by the fact that the pressure relief devices that are intended to help prevent this situation are now horizontal and filled with liquid (and crude is not necessarily a real free flowing liquid) which interferes with its operation. Add in structural weaknesses caused by the impact and it is a wonder that more of the cars did not explode.

This accident is causing even more people to question the use of unit trains for hazardous material. One item that is being missed in this discussion is that government HAZMAT shipping rules almost require unit trains when large numbers of cars are headed in the same direction. Most HAZMAT cars are limited by regulation in the speed at which they can be hauled; an effort to reduce the consequences of a derailment. Placing these cars in multiple trains would slow down commodity deliveries that could otherwise be hauled at higher speeds.

HAZMAT Routing

This accident would have been serious no matter where it happened, but statistically most rail accidents happen in the open countryside with limited loss of life. This accident caused so many deaths because it happened in town and it would have been worse if it had happened between 9:00 am to 5:00 pm on a weekday.

For historical reasons (towns and cities grow up along transportation corridors) rail lines go through cities and towns. Recent efforts have been made to require the routing of particularly hazardous chemicals (crude oil is not anywhere near close to hazardous enough) around major urban areas, but it is a fact of life that trains generally cannot go around towns like Lac-Megantic; that is where the rails go.

Railroads understand the hazards of traversing towns like this and they slow their speed limits even further. At least one article has quoted the Canadian Pacific RR as saying that the speed limit through town was 10 mph (16 Kmph). At that speed, even if the train did derail, there would not have been this kind of accident. Even with DOT-111 railcars there probably would not have been any punctures because there wouldn’t have been any cars laying on their side; no puncture, no fire, no explosions, no devastation.

Accident Investigation Proceeding

As I noted earlier, the accident investigation is still proceeding. We will have about a year to wait (if the Canadian agency is as effective as the NTSB and I suspect they are) before we see a final report on the accident. The pundits (myself included) will not wait for that report to call for changes in processes and procedures to prevent future accidents of this sort. And the environmental advocates are wasting no time in using this as additional justification to call for the abolition of crude oil trains in general.

The open question is if Congress will take up the issue. A wise man (my father) once told me that a smart man learns from his mistakes, but a wise man learns from the mistakes of others. This accident happened in Canada and, while the crude oil was from North Dakota, it seems as if the Canadians didn’t need our help in causing the accident. I expect that Congress will ignore the issue as it wasn’t our problem; it has been a long time since someone accused Congress of being wise.


Anonymous said...

I understand rail air brakes are fail-safe, in that you must have air pressure to release the brakes. No air, the brakes are applied. If this concept is true, you might want to revisit the brake failure cause.

Robert Ridgeway said...

Someone needs to go back to school on this incident. Tank cars loaded with heavy, crude flammable liquids are not capable of producing a BLEVE. Heavy oils of that type simply don't possess the liquid to vapor expansion ratio necessary to for this phenomenom to occur. Whatever caused the reported explosion, it sure wasn't caused by a BLEVE.

Patrick Coyle said...

I'm not sure that I agree with that statement. By definition crude has light ends, but I don't know the light end contents in these cars. Additionally, these cars were damaged so that their structural integrity was compromised, requiring less pressure to cause a container rupture.

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