Opinion ID: 2830346
Heading Depth: 2
Heading Rank: 1

Heading: The Rock-Crushing Plant

Text: In 1980 Terex’s predecessor manufactured and sold the portable rock-crushing plant at issue. As the name suggests, a rock-crushing plant is a large machine that crushes larger rocks into smaller ones. This particular plant was about the size of a large semitrailer and consisted of several components: a set of wheels, a chassis, a feeder system to carry material into the crusher, the crusher itself, a diesel engine to drive the crusher, and a conveyor to carry crushed material from the crusher. 2 Because a central issue in this case is whether the rock-crushing plant had a defective part—a “toggle plate”—that caused Kirkbride’s injury, we describe how the plant works. The process begins with material being loaded into a long, narrow feeder (about 20 feet long by 3.5 feet wide) that leads into the opening at the top of the crushing chamber. To prevent oversize rocks from clogging the chamber’s opening, the crushing plant when sold had a large metal bar called a crossmember before the opening to the crusher. Material that passes under the crossmember continues forward until it falls into the crushing chamber. Reproduced below from the plant’s operation and maintenance (O&M) manual is a diagram of the crusher: 3 Aplt. App., Vol. 11 at 2389. When material enters the crushing chamber, it is crushed by two jaws, one stationary (labeled “7” in the diagram) and one movable (8). The top of the movable jaw, powered by the pitman (1), follows a circular path with a diameter of 1¼ inches, closer to and then farther from the stationary jaw. The cyclical compression 4 progressively breaks the material, allowing it to slip farther down the “V” between the jaws until it is small enough to fall through the gap at the chamber’s bottom. The bottom of the movable jaw is connected to a rectangular metal plate called a toggle plate (10) and two tension rods (15), which pull the movable jaw toward the toggle plate and away from the stationary jaw. Besides keeping the bottom of the movable jaw in place, the toggle plate also functions as a protective device for workers and the jaw crusher itself. When uncrushable material (such as a large piece of metal) falls between the jaws, the jaws can jam and store energy as they exert pressure in an effort to crush the uncrushable material. As the pressure builds, the toggle plate acts as the “weakest link” and breaks before other, more expensive components (like the pitman) are damaged. Id., Vol. 7 at 1621. When it breaks, there is nothing to hold the bottom of the movable jaw in place, so it swings open and the uncrushable material falls out. The danger to workers is that if the toggle plate does not break and a worker tries to dislodge the uncrushed material, the stored energy can cause the material to eject violently from the crushing chamber when it is released. Terex’s manuals explain the purpose of the toggle plate and the dangers of stored energy caused by jaw-crusher jams. The O&M manual contains two statements. The first is: “The toggle plate is the oscillating link between the bottom of the pitman and the base toggle seat. It serves as a safety device in the crusher and will break when uncrushable material is encountered.” Id., Vol. 11 at 2417. The second is: “The replaceable cast iron toggle plate also serves as a fuse or safety device in the crusher, as it 5 will break when uncrushable material such as a shovel tooth passes between the jaws.” Id. at 2391. And the safety manual contains the following warning for those occasions when material nevertheless gets stuck: “Use extreme caution when removing tramp iron from the crusher. Stored energy in jaw could cause serious bodily injury.” Id. at 2495. The written warning is accompanied by an illustration of a worker reaching down into the crushing chamber and being struck in the face by an ejected foreign object. That is what happened to Kirkbride.