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Acoustic trauma is a sudden, single-event hearing injury caused by exposure to an extremely loud impulse sound — an explosion, gunshot, pneumatic tool discharge, or industrial blast. Unlike the gradual threshold shift that develops over years of noise overexposure, acoustic trauma can produce immediate, permanent, and profound hearing loss in a fraction of a second. It is both an OSHA recordable event and a workers’ compensation incident that requires prompt medical response, precise documentation, and a specific compliance response that differs in several important ways from the routine STS workflow.
Soundtrace’s audiometric baseline records are critical evidence in acoustic trauma cases — establishing the hearing status that existed before the event to accurately characterize the injury.
Acoustic trauma is a specific injury pattern caused by a single, extremely intense sound event. The defining characteristics are its suddenness (milliseconds to seconds rather than years), its typical severity (often profound unilateral or bilateral loss), and its frequent association with middle ear damage (tympanic membrane perforation, ossicular disruption) in addition to cochlear injury. Common workplace causes include explosive decompression, industrial blasts, powder-actuated tool discharges, gunshots, and catastrophic equipment failures producing extreme pressure events.
Acoustic trauma is distinct from noise-induced hearing loss in the legal and clinical record. NIHL develops gradually and is typically symmetric. Acoustic trauma is immediate, may be asymmetric (depending on the blast direction relative to the worker), and involves a specific, identifiable precipitating event that can be precisely documented. That documentation distinction matters significantly in both workers’ compensation and OSHA proceedings.
The outer hair cells in the basal turn of the cochlea — the region responsible for processing 4000–6000 Hz frequencies — are the most vulnerable to acoustic overstimulation. An extremely intense impulse causes mechanical disruption of the stereocilia on these cells, rupture of the reticular lamina, and secondary metabolic injury from reactive oxygen species generated by the acoustic overload. The damage is typically maximal at 4000 Hz, the same notch pattern seen in gradual NIHL, but the degree and abruptness distinguish acoustic trauma from chronic overexposure.
When the blast is sufficiently intense, middle ear structures are also damaged. Tympanic membrane perforation is common in close-range blast exposure and produces a conductive hearing loss component on top of the cochlear sensorineural loss. This combination of conductive and sensorineural loss on the post-trauma audiogram is a clinical signature of acoustic trauma that distinguishes it from purely cochlear NIHL.
Under OSHA 1910.95(b)(2), no worker may be exposed to impulsive or impact noise exceeding 140 dB peak sound pressure level. This is an absolute ceiling — not a time-weighted average, not adjustable by HPD use, not subject to engineering control defenses. Any exposure above 140 dBC peak is a prima facie regulatory violation. In a workplace blast scenario, peak levels frequently exceed 140 dBC, and the incident is both a potential OSHA violation and an OSHA 300 Log recordable event.
The recordability determination follows the standard 1904.10 two-part test: is the hearing loss work-related (almost always yes in a blast scenario), and does the resulting hearing threshold level meet the 25 dB above audiometric zero criterion? The baseline audiogram is essential here — it establishes what the worker’s thresholds were before the event, against which post-trauma thresholds are compared.
OSHA’s 7-day 300 Log recording deadline runs from the date the employer determines the case is recordable — not from the date a follow-up audiogram is completed. In an acute acoustic trauma case, the work-relatedness determination is immediate. Begin the compliance response documentation on the day of the incident, even if a clinical audiogram cannot be scheduled until later.
Within hours of the event: ensure the affected worker receives immediate medical evaluation; ENT evaluation is appropriate for suspected tympanic membrane perforation or profound hearing loss; preserve and copy the worker’s baseline audiogram from the HCP record. Within the first day: notify workers’ compensation carrier; pull noise exposure records for the area where the event occurred; document all witnesses and physical evidence of the blast event. Within 7 days: complete the OSHA 300 Log assessment; arrange follow-up audiometry; notify the affected worker in writing if the assessment indicates a recordable hearing loss case.
In a workers’ compensation acoustic trauma claim, the employer’s pre-event baseline audiogram is the single most important document. It establishes with precision what hearing the worker had before the blast — making the difference between the pre-event baseline and the post-event audiogram the documentable, attributable injury. An employer whose baseline audiogram was taken on the worker’s first day of employment has a clean, credible pre-event record. An employer without a baseline audiogram has no way to contest the worker’s claim that all of their current hearing loss was caused by the blast event at this employer.
Soundtrace establishes baseline audiograms before first noise exposure — creating the pre-event hearing record that is essential evidence in any acoustic trauma workers’ compensation or OSHA proceeding.
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