Question 6 of 7: Hearing Loss, Noise/Vibration Controls, and Measurement Instruments
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Exams — May 2015 — 11-CS-2 Engineering in Society: Health and Safety. Closed book; approved calculator permitted. Any five of the seven questions constitute a complete paper; all questions are of equal value. Answers are written in point form but fully, as instructed. Complete answers to all seven questions follow.
Conductive — in the outer/middle ear (wax blockage, damaged eardrum or ossicles); sound is not conducted efficiently to the inner ear; often treatable/reversible.
Sensorineural — in the inner ear (cochlea/hair cells) or auditory nerve; includes noise-induced hearing loss; usually permanent.
Mixed — both conductive and sensorineural components.
Noise exposure first causes a temporary threshold shift (recoverable) that, with repeated exposure, becomes a permanent threshold shift (a sensorineural loss, classically a notch near 4000 Hz).
(ii) Engineering Controls for Noise and Vibration
At the source — quieter/low-vibration equipment and processes, maintenance (lubrication, balancing, replacing worn parts), reduce impact/speed.
Enclosure and barriers — acoustic enclosures, sound-absorbing materials, mufflers/silencers on exhausts.
Isolation and damping — vibration-isolation mounts, resilient couplings, damping treatments to reduce structure-borne noise.
Along the path — distance, absorptive room treatment, isolating the noisy operation.
(iii) Measurement Instruments
(a) Sound level meter — measures instantaneous sound-pressure level in dB (with A-weighting for occupational noise); used for area/noise surveys to identify problem areas.
(b) Impulse (impact) meter — a sound level meter with an impulse/peak setting that captures very short-duration impulsive noise peaks (e.g., stamping, gunfire); used where peak levels matter.
(c) Frequency (octave-band) analyzer — separates noise into frequency bands; identifies the dominant frequencies, guiding the choice of engineering controls and hearing protectors.
(d) Dosimeter — a personal, worker-worn device that integrates noise level over the whole shift to give the individual's noise dose and equivalent TWA; used for personal exposure assessment.
