Assembly plants are noisy. Stamping presses, power tools, welders, robots, vibratory feeders, power-and-free conveyors, and the constant clacking of pneumatic actuators can raise quite a cacophony. It’s enough to literally make you deaf.

According to the National Institute of Occupational Safety and Health (NIOSH), more than 22 million U.S. workers are exposed to noise levels that put them at risk for hearing loss. NIOSH estimates that 25 percent of 60-year-old men who experienced an average noise exposure of 90 decibels over a 40-year career will suffer significant hearing loss.

If you believe noise is only a problem for people operating jackhammers or servicing jets on the tarmac, think again. In 2000, researchers at the University of Michigan surveyed more than 1,000 people diagnosed with permanent hearing loss. Some 51 percent were employed in manufacturing. Of the 28,400 cases of occupational hearing loss reported to NIOSH in 2004, 84 percent were from manufacturing.

Once acquired, noise-induced hearing loss is permanent and irreversible. Fortunately, it’s entirely preventable.

A variety of hearing protection devices (HPDs) is available, including expandable foam plugs, premolded reusable plugs, canal caps and earmuffs. The key, of course, is getting workers to take advantage of them. Although one-third of all manufacturing workers report regular exposure to loud noise, 25 percent of workers so exposed do not use HPDs.

One reason for the disconnect may be confusion over what constitutes adequate protection. To that end, the Environmental Protection Agency recently proposed changes to the noise reduction rating system for HPDs. One change involves revising the labeling of HPDs from a single-number estimate to a two-number range showing high and low values of protection. Another change redefines the methods by which HPDs are tested and rated in the laboratory. A third change adds electronic hearing protectors to the list of recommended HPDs, and a fourth requires HPD manufacturers to retest their products every five years.

“The current single-number rating system can mislead purchasers to believe the same earplug will provide everyone the same level of protection,” says Brad Witt, director of hearing conservation at Sperian Hearing Protection LLC. “In real life, protection levels vary widely among individuals, due to their training, fit and usage. Implementing a two-number range gives safety managers a more realistic estimate of how much protection their workers are really capable of achieving.”

Witt makes an excellent point. We urge plant managers to train their employees thoroughly and regularly in hearing conservation practices. Managers who simply put out a box of earplugs and leave employees to fend for themselves are doing their people a disservice. We also advise managers to regularly measure noise levels throughout their plants, and to consider noise levels when designing or purchasing new equipment.