Hearing Loss and Deafness 177ascending- descending method, dropping the decibel level by 10 dB, and doing this repeatedly
until the employee no longer hears the tone. Next, you raise the level by 5 dB until the employee’s
hearing threshold at a par tic u lar frequency— the decibel level at which at least three out of the six
pre sen ta tions of the tone can be heard—is determined. After 1,000 Hz is tested, you determine
the hearing threshold for 2,000, 4,000, and 6,000 Hz and then drop to the lowest frequencies:
125 and 250 Hz. After completing the test in the right ear, you use the same procedure in the left
one. For every threshold obtained, you note the results on an audiogram: red Os for the right ear
and blue Xs for the left one.
The next group of employees is from the turbine-generating section— engineers, technicians,
and mechanics who work behind a protective barrier, monitoring the turbine and cooling facili-
ties. A constant high- pitched hum penetrates the protective walls of the section, requiring them
to speak loudly or shout. When they enter the generating zone, they wear special ear protection.
Many employees have worked in this noisy environment for several years.
Eventually, you test all three shifts of employees from the turbine- generating section and, with
few exceptions, find bilateral hearing loss in the higher frequencies. Some thresholds are more
depressed than others, but a clear pattern of noise- induced hearing loss has emerged. Of course,
there are many variables to consider before attributing the hearing loss to noise exposure in the
workplace, including age, gender, and medical histories. You check each subject’s employment
file and find evidence that the longer an employee has worked in the generating section, the more
depressed are his or her thresholds at 1,000, 2,000, 4,000, and 8,000 Hz. The hearing loss gradually
increases in the higher frequencies.
Your audiological consulting com pany reviews the test results and investigates the sound levels
and the length of time the employees of the turbine- generating section are exposed to the noise.
Sound level meters are used to mea sure the intensity of the noise emanating from the generators.
The effectiveness of the employees’ ear protection is investigated, as is the time each employee
is exposed to extreme noise with and without ear protection. Several months later, the Inkom
Nuclear Generating Plant enacts new regulations about noise and employees’ duration of exposure
and purchases new, more effective, and more comfortable hearing protection. Supervisors also
monitor employees’ compliance with the new regulations.
Case Study 9-2: Meningitis and Deafness in a 5- Year- Old Girl
Faculty and students eagerly anticipate the spring softball tournament. The faculty and their
spouses proudly wear T- shirts labeled “Ossicles,” and those of the students and their guests are
marked “Speechies.” The Audiology and Speech Sciences Department has sponsored this tourna-
ment and picnic for years. The events are held at the fairgrounds picnic area, usually in early May.
This year it is unusually cold, with some rain, but the game and picnic proceed as scheduled. Of
course children are welcome, but one of them, 5- year- old Ilene, seems under the weather.
The softball game begins at 4:00 p.m. By 6:30 p.m., when it ends and the picnic begins, Ilene
stands under a tree obviously cold, with watery eyes, sniff les, and complaining of an earache.
Several persons offer her jackets and blankets. Her mother is concerned, and they leave early.