Balancing on STEEL

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The office is steel I-beams with the sky above and danger below. The uniform is a hard hat and sometimes a harness. And the work takes skills, specialized training and the one sense many take for granted: balance.

Ironworkers who build steel structures need a sense of balance and dexterity to put up the frame of a high-rise, says Justin Crandol, senior director of safety and health at the Associated General Contractors of America (AGC), an Arlington-based association that represents more than 33,000 commercial, industrial and highway firms and related companies.

That sense is not as important for other construction workers who work on residential and smaller commercial buildings because they work with guardrails. Nor is it as important for firefighters who do high-angle rescues where training is key.

To do their job, ironworkers have to sit and stand on I-beams from the first floor up and crawl and walk across the beams to bolt them in, Mr. Crandol says.

"These workers are in a strange sensory environment," says John Jeka, professor of kinesiology, biology and neuroscience at the University of Maryland in College Park. "They have to be incredibly sensitive to all that sensory information around them to make sure they don't fall."

Balance is both a function of the muscles and limbs to keep the body upright and of the sensory system, says Mr. Jeka, who has a doctorate in neuroscience.

"An absolutely crucial aspect of balance to stand up bipedally is using sensory information in very sophisticated ways," he says.

The main sensory mechanisms used in balance are vision, the inner ear or vestibular system, and the proprioceptive system, Mr. Jeka says. The proprioceptive system consists of sensors in the muscles, called muscle spindles, that communicate to the nervous system the movement, or stretching and contracting, of the muscles and where the limbs are in space, he says.

"For these construction workers, vision probably plays a larger role than what is typical," Mr. Jeka says.

For example, a tool sitting on an I-beam becomes an obstacle ironworkers need to notice to avoid stumbling over it and falling off the beam, he says. The obstacle, he says, is less of a hazard in a secure setting, such as a roof with guardrails.