To anyone who has seen what water does to a burning match, the idea of using fire to cut steel underwater might seem incomprehensible.
But the cutting torches used by the divers working on the new Tacoma Narrows bridge burn with such a hot, concentrated flame, the water is nearly inconsequential.
"The metal in the rod burns at 10,000 degrees," said Gary Maines, vice president of Broco Inc., manufacturer of the brand of rod used at the Narrows. "That's hot enough to burn or melt anything known to man."
The cutting torch resembles a power drill, with a collet for holding the rods and a trigger for controlling the flow of oxygen from the surface.
The rods are bundles of seven different metal alloy wires - their exact composition is proprietary information - that react with each other to burn at ferociously hot temperatures.
The individual wires are arranged in a bundle about 3/8-inch in diameter with a hole through the middle, like an oversize drinking straw. A powerful jet of oxygen is forced through the center of the rod, keeping the flame going and blowing molten metal out of the cut.
The divers ignite the rods with a spark from an electrical current. When in position and ready to cut, the diver radios a tender to "Make it hot." The tender flips the switch on a welder at the surface, sending a hot current along a wire connected to the steel surface. A ground wire is connected to the cutting torch.
When the diver touches the tip of the rod to the steel, the electrical circuit closes, making a spark that ignites the rod. The divers aren't shocked because they're insulated by their rubber diving suits.
The rods are hot, but they burn out quickly. Each 18-inch rod lasts about 40 seconds - enough to cut 8 to 10 inches of half-inch steel in the most accessible places.