"Containing Risk," Feature Article, June 2007

FEATURE FOCUS: TRANSPORTATION

containing risk

When it comes to handling highly toxic materials, building stronger tank cars is one solution, but shipping a safer substitute is even better.

by Harry Hutchinson, Executive Editor

Someone working on a railroad crew in Graniteville, S.C., on a night in January 2005 left a switch in the wrong position. The mistake directed a freight train off the main line and onto a siding, where it struck a stationary train. Almost 20 cars derailed. One of them, a tank car carrying chlorine, ruptured.

In all, nine people died in the accident. Most of the dead were found near the scene, but had not been directly involved in the wreck. A passerby, who drove his car through the cloud of escaping gas, died two months later of chlorine inhalation. Some 250 other people were treated for chlorine exposure, and more than 5,000 residents were evacuated from their homes until hazardous-materials crews brought the situation under control.

It was an iconic event, underscoring the danger of failing to follow procedures, and also demonstrating why carriers would prefer not to handle toxic inhalation materials at all. According to a spokesman for the Association of American Railroads, toxic inhalation hazardous materials, which include chlorine, account for 0.3 percent of railroad shipments—but for more than half the liability costs of rail companies.

The shipper, the tank car maker, and the rail operator have joined forces for stronger cars, and now they have government support, too.

The association has published a new set of standards for tank cars that carry anhydrous ammonia and chlorine. The two chemicals account for 82,000 carloads a year, more than 80 percent of the toxic inhalation hazardous materials carried by rail.

The standards will apply to new cars built after Jan. 1, 2008, and will begin an 11-year period in which the rail industry must bring the entire fleet of tank cars carrying those chemicals into compliance. Among their provisions, the new standards require tank car steel to be a full inch thick. The previous standard called for a thickness of three-quarters of an inch.

BNSF Railway Co. has issued a statement saying that it will do its part to encourage shippers to use cars that meet the new standards. The company will restructure its rates after the first of the year and will charge more for handling tank cars that do not measure up to the new standards. Or as the statement put it: "BNSF will publish tariffs (public prices), effective Jan. 1, 2008, to restructure rates based on car risk factors in an effort to encourage shippers to use the most enhanced and upgraded available cars."

The company said that materials of these types—toxic inhalation and poison inhalation hazardous materials—make up "significantly less than one percent of BNSF's total annual volume."

Meanwhile, a longer-range initiative under way is called the Next Generation Tank Car Project. A cooperative R&D effort by Dow Chemical Co., Union Pacific Railroad, and Union Tank Car Co., the goal of the program is to find ways to increase the crashworthiness of railroad cars designed to carry hazardous chemicals.

The interest in the project of the three private stakeholders is clear. Union Tank Car builds and leases the cars. Union Pacific operates them, and the cars carry Dow's merchandise. Earlier this year, the Federal Railroad Administration and a Canadian federal agency, Transport Canada, signed agreements that throw their weight and expertise behind the program.

The project leader for the Next Generation Tank Car Project is a Dow executive, Henry Ward, the chemical company's director of transportation safety and security.

Dow makes 2.5 million product shipments worldwide every year. Two-thirds of its shipments travel by land, and the highest volume over land goes by rail. About 80 percent of the material shipped is not classified as hazardous, and 1 percent is considered highly hazardous, because it is toxic to inhale, as chlorine is, or flammable, like propane.

As the AAR spokesman pointed out, many materials classified as hazardous are not directly toxic to human beings, but represent risks to the environment. Hazardous materials include whiskey, contaminated soil, and motor oil.

Thinner Here, Tougher There

As with any form of transportation, weight is a primary concern, so a design for a stronger tank car has a practical limit in mass. There is a maximum weight that can be placed on rails and bridges. The heavier the car, the less it can contain, and so more cars will be needed to make the same volume of shipments.

Current tank cars include a thermal protection layer, insulation shielding contents from high heat. That layer, usually of fiberglass, is 4 to 8 inches thick in most tank cars today, Ward said.

The project's researchers have found new insulating materials that will take up less room and still give the same thermal protection, or perhaps better. The project is investigating materials from companies that include Microtherm and Aspen Aerogels. "We have identified a material developed for the aerospace industry that is less than 1 inch thick," Ward said.

Reducing the thickness of insulation material leaves space for new materials to add strength to the car.

Ward pointed out that the automotive industry has the same goals as the tank car project—light weight, volume, crashworthiness, and cost. The project has found promising materials in Dow Chemical's own automotive division.

According to Ward, one material under consideration is a dense foam that weighs about 29 pounds per cubic foot. Placed between the outer shell of the car and the insulation layer, it promises to bring significant improvement in crashworthiness.

A car could be built one day using the thinner insulation and the dense foam. The innermost layer would be the actual commodity tank, surrounded by the thermal protection layer. A new crush zone would wrap around that and would be covered by the outer jacket of the tank car.

Composites and Steels

Engineers are also evaluating more complex designs, Ward said. For example, fiber-reinforced plastics around a commodity tank would add even more strength. They might one day permit the construction of a lighter tank using less steel overall without sacrificing strength.

Researchers are also looking at high-performance steels, HPS-70 and HPS-100, for the outside of the car to resist piercing, Ward said. A commonly used steel for tank cars is TC-128, he said.

Besides the strength of the overall structure, the various features are coming in for a share of the attention as well.

The instrument of puncture in tank car crashes is often the coupler. "It looks like a can opener," Ward said. One consideration to make the coupler less hazardous is to give it rounder edges, to blunt its cutting ability. Another is to design the coupler to be pushed back on impact and so reduce the force with which it strikes a car.

The new AAR standards also address the issue of puncture by the coupler. They call for the head shields—the steel facings on the ends of tank cars—to be full height. The previous standard permitted half-height shields. Their purpose is to reinforce the car to deflect couplers in the event of a crash.

Another feature that may undergo change in the next generation is the valve for loading and unloading a car. A lower profile, for instance, would expose less material to break off if a car rolls, Ward said. Internal closures would keep a car sealed even if the valve were lost.

Along similar lines, the AAR standards will require improved top fittings on new tank cars after January 1. They will have to be made of inch-thick steel, as opposed to the current standard of three-quarter-inch steel. The standards also call for stronger gussets and covers to reduce the risk of rupture.

The FRA, meanwhile, has been conducting its own research program into tank car design. The agency has created finite element analysis models involving forces acting on tank cars in accidents. It has also sponsored tests conducted by the Southwest Research Institute in San Antonio, of various steels used in tank cars.

Jo Strang, associate administrator for safety at the FRA, said the agency not only plans to help with the project's test program, but will also be able to contribute FEA models and other products of its tank car research.

Risk Control

A third part of the FRA's tank car work is a risk assessment of tank cars to identify those most vulnerable to catastrophic failure. The agency said it expects completion of that research this August.

According to Ward, Dow Chemical's risk-control program works on a number of fronts. The Next Generation Tank Car Project is one of them. Looking at the supply chain is another.

When Dow is moving highly hazardous materials, the company looks at distance and routes. It avoids dense population areas, for instance. It is also involved in programs that train first responders—police, fire, and rescue workers—in communities along the way. They learn what the chemicals are and how to deal with them.

Dow also looks at alternative ways of doing business to reduce the need to ship hazardous materials. Ward said one solution, along these lines, brought about a safer way to handle one customer's shipments of acrolein.

Acrolein, which is present in minute amounts in automobile exhaust and cigarette smoke, is used industrially in the manufacture of various organic compounds. The U.S. Environmental Protection Agency considers acrolein extremely toxic to humans and warns that it can kill someone who inhales concentrations as low as 10 parts per million. The substance was used as a chemical weapon during World War I.

According to Ward, industrial acrolein is produced by Dow in a facility on the Gulf Coast. The company used to ship it to a customer some distance away. Dow learned, though, that the customer was using acrolein to make an intermediate product, which was safer to handle. The intermediate was later used in a final product.

The risk of handling was sharply reduced when the customer agreed to move its intermediate production into Dow's site. Now, instead of crossing states, acrolein crosses a plant, and a much safer product moves by rail.

The AAR spokesman pointed out a trend that has reduced shipments of chlorine. Various cities have begun to use chlorinated bleach as a substitute for chlorine to treat water. Although bleach in large quantities may not be without risk, it is certainly safer in all ways than chlorine.

The rail industry would probably be pleased to see all chlorine shipments end. The risk of handling it far outweighs any reward or benefit to the carrier. But handle it they must, and they will do it in what promises to be stronger tank cars.

But even if they could build those cars to be unbreakable, it would still be a simpler world if none of the tanks had to hold chlorine.

ASME Standard for Passenger Rail Cars

A Codes & Standards committee expects to publish a draft this summer of ASME's first standard addressing the crashworthiness of passenger rail cars. The draft , which will cover heavy rail cars, will be published by the ASME Rail Transit Vehicle Standards Committee.

The committee's chair, Martin P. Schroeder, who is senior program manager for rail programs at the American Public Transportation Association, said the heavy rail standards are applicable to cars used in high-speed, self-contained transit systems, like the New York City subway or the Chicago El. Schroeder said that proposals for these cars include designing vehicle cab-end structures to absorb energy during a crash.

The committee plans eventually to issue an additional draft standard for light rail vehicles. Schroeder said the group has been using finite-element models to simulate crash dynamics of light rail vehicles. The aim is to apply principles of crash energy management to optimize the safety of passengers when light rail vehicles are involved in collisions.

Schroeder explained that crash energy management is "controlled absorption of energy," the conversion of kinetic energy principally into structural plastic deformation. "Through controlled and progressive absorption of energy, vehicle deceleration rate is reduced when compared to completely rigid vehicles, thus protecting passengers from impact into interior vehicle structures caused by a sudden stop," he said. "Crash energy management also provides the added benefit of producing vehicle designs with behavior that is more predictable in a collision. Crush deformation is limited by design to specified areas of the cab-end structure, further protecting occupant space for passengers and train operators that might otherwise collapse."

The committee's staff secretary, Geraldine Burdeshaw of ASME, pointed out that the philosophy of crash energy managment is similar to that which has provided crumple zones to protect passengers in automobiles during crashes.

The controlled energy management studies for light rail are nearing completion, Schroeder said. They have been supported by funding from the Transit Cooperative Research Program of the Transportation Research Board.

The committee's researchers have simulated collisions between various light rail vehicles. Complicating the issue, however, is that light rail systems operate in street traffic, and so most frequent collisions of light rail vehicles in the U.S. are with automobiles. According to Schroeder, one of the areas being studied is ways to use controlled energy management to reduce injury to passengers in automobiles, as well as to those inside the rail cars. Besides energy absorption designs, the committee's research is also considering shape design of the rail cars. Sharp edges on carriage cab ends, nonenclosed cab ends, and couplers can damage street vehicles during collisions.

Houston, Minneapolis, and Denver are among U.S. cities that operate light rail systems.

According to Schroeder, the committee was formed several years ago, when the American Public Transportation Association was considering the need for published standards covering transit cars. APTA approached ASME to make use of the Society's established mechanical expertise. Schroeder said he was not with APTA at that time, but was working with the Transportation Technology Center Inc. in Pueblo, Colo.

The light and heavy rail vehicles that the committee is studying are those used in municipal transit systems, and are not subject to U.S. Federal Railroad Administration rules. The FRA's jurisdiction extends to traffic using the common rail system.