Definitions of Noise Terms in OSHA

The United States Occupational Safety & Health Administration (OSHA) regulates the amount of noise a worker can be exposed to in the workplace. This includes both maximum bursts of noise and a baseline of noise throughout the day. The regulations include "mitigations" employers may put in place for workplaces that feature high noise levels. States, counties, cities, and employers may choose to enact stricter noise codes, but the OSHA standards represent a minimum for the entire country.

Hearing Conservation Program

• If a workplace exceeds the OSHA standards for background noise or occasional bursts of noise, it must by law enact a hearing conservation program. This program can include noise monitors, hearing-test programs for employees, hearing protectors, training on noise avoidance, and insulation of noise sources. OSHA requires that all companies keep detailed records of their hearing conservation program, which can be inspected upon request.

Baseline Audiogram

• A baseline audiogram is the result of a hearing test given to an employee as the start of a hearing conservation program. The test must take place during the employee's first six months of exposure to high noise levels, and must take place after 14 consecutive hours without exposure to the workplace. This test represents the hearing measure against which subsequent annual tests will be measured.

Standard Threshold Shift

• This is the term for a significant change in an employee's hearing capabilities for reasons other than workplace exposure. An employee is considered to have a standard threshold shift if his or her hearing has decreased by 10 decibels or more in comparison to the baseline audiogram. An audiologist or physician may make the determination that this shift is due to aging or other natural degeneration as opposed to workplace noise exposure. If this determination is made, the shift becomes the employee's new baseline audiogram level.

Noise Dosage

• The level of noise used to determine whether a hearing conservation program is necessary is called the noise dosage. The dose is determined by the formula D = C/T, where C is the actual noise exposure during a given measurement period, and T is the allowable noise exposure during a given measurement period (see the table of T values in References). Several measurements are taken and added together to achieve D. If D is less than or equal to 1, the level of noise is considered to be acceptable. A result greater than 1 results in a hearing conservation program.