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Since the publication of A Practical Guide to Effective Hearing Conservation Programs in the Workplace in 1990, many things have changed, while some have not. Things remaining the same include the Hearing Conservation Amendment to the OSHA Noise Standard. The NIOSH hierarchy of controls endures and can be summarized as: 1) first, prevent or contain the escape of the hazardous workplace agent at its source (engineering control); 2) control exposure by relocating the worker to a safe area (administrative controls); and 3) control the exposure with barriers between the worker and the hazard (personal protective equipment). This hierarchy underscores the principle that the best of all prevention strategies is to have no exposure to agents that can cause or contribute to hearing loss. Corporations that have embarked upon buy-quiet programs are moving towards the creation of a workplace where there will be no harmful noise. Many companies are automating equipment or setting up procedures that can be operated by workers from a quiet control room free from harmful noise, chemical agents, and heat. When it is not possible to remove the harmful agent or relocate the worker to a safe area, the worker must be protected. In the arena of hearing loss prevention, protection is a many-faceted process that includes exposure assessment, provision of protective equipment, assessment of hearing with appropriate management and follow-up actions, worker education and training, and continuous evaluation of program effectiveness.

Some things which should have changed have not. There are no requirements for recording threshold shifts due to noise exposure, nor is there a national occupational audiometry register. Without these data, it is not possible to effectively track and evaluate the successes and failures of occupational hearing loss prevention programs.

Use of the term occupational hearing loss reflects a change since 1990. No longer is noise considered to be the only source of hearing loss associated with work. Exposures to chemicals, such as aromatic solvents and metals such as lead, arsenic, and mercury can result in hearing loss. Combined exposures to noise and chemicals can cause more hearing loss than exposure to either agent alone. Vibration and extreme heat are also potentially harmful to hearing when combined with noise. To better respond to the potential hearing hazards and hearing loss risk many of today's workers face, an additional ingredient (Hearing Loss Prevention Program Audit) has been added to the recommended approach for preventing hearing loss.

The emphasis on prevention rather than conservation also reflects a change. The shift from conservation to prevention is not minor. Conserving hearing means to sustain the hearing that is present, regardless of whether it is impaired or not. Prevention means to avoid creating hearing loss. Conservation can start when one is first exposed to an occupational agent that is potentially harmful to hearing. Prevention starts long before the first exposure. Conservation comes from a program that is created and imposed. An emphasis on prevention evolves from beliefs that it is not necessary to suffer an impairment, illness, or injury to hold a job and that it is within one's own purview to employ techniques, use behaviors, and rely upon personal protective equipment to prevent impairment, illness, or injury.

Finally, there have been substantial changes since 1990 related to the recommended definition of hazardous noise (85 vs 90 dBA), the use of the equal-energy principle in integrating noise exposures, and the definition of standard threshold shift (STS). The combined result of such changes as these has been to stir the core tenets of hearing loss prevention. To keep step with the new directions in hearing loss prevention, it became apparent that the time had come to recast the "Practical Guide."

No guide such as this could be assembled solely by a group of scientists in an agency. So, just as with A Practical Guide to Effective Hearing Conservation Programs in the Workplace, this updated document was prepared by consulting experts in preventing occupational hearing loss. They reviewed the prepared materials, and made suggestions for changes, deletions, and additions. It is our hope that the ideas contained in this guide will provide the inspiration to others to promote actions needed to protect a vital human function -- hearing.

Linda Rosenstock, M.D., M.P.H.

Director, National Institute for Occupational

Safety and Health

Centers for Disease Control and Prevention

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