Understanding audiogram patterns is essential for EHS managers who review occupational audiometric surveillance results. This guide covers flat hearing loss: what it looks like on an audiogram, what it means clinically, what OSHA 1910.95 obligations it triggers, and the required employer response. Note that audiogram interpretation in the context of OSHA compliance always requires involvement of a licensed Professional Supervisor — a licensed audiologist, otolaryngologist, or other physician. The EHS manager's role is to understand the pattern well enough to act appropriately and ensure timely PS review.
Soundtrace provides audiometric testing supervised by a licensed audiologist who reviews all audiograms, identifies STSs, and makes clinical determinations — ensuring employer compliance with every 1910.95 audiometric obligation.
What Is Flat Hearing Loss?
A flat audiogram shows roughly equal threshold elevation across the entire tested frequency range (500–6000 Hz), with no pronounced notch or slope. This is distinct from the classic NIHL pattern (4 kHz notch) and from age-related hearing loss (high-frequency slope). On an audiogram, all threshold markers appear at approximately the same height rather than worsening progressively toward higher frequencies.
Clinical Significance
Flat hearing loss affects communication across the full speech frequency range and typically produces more significant speech understanding difficulties than a high-frequency notch of comparable severity. Workers with flat hearing loss may have difficulty understanding speech at any volume level, not just in noise. The differential diagnosis of flat hearing loss is broader than for the NIHL 4 kHz notch: causes include conductive hearing loss overlaid on sensorineural loss, Meniere's disease, autoimmune inner ear disease, sudden hearing loss, and some medication effects, in addition to noise exposure at non-typical frequencies.
All clinical interpretations of occupational audiograms — including determinations of audiogram pattern, work-relatedness, and STS confirmation — must be made by the Professional Supervisor (licensed audiologist, otolaryngologist, or other physician) under OSHA 1910.95(g)(3). EHS managers should understand these patterns to recognize when PS review is needed and to act on PS findings promptly, not to replace the PS role.
OSHA 1910.95 Implications
A flat hearing loss pattern changes the STS analysis. The 10 dB STS threshold is calculated at 2000, 3000, and 4000 Hz regardless of the shape of the audiogram. A flat loss that elevates thresholds equally at all frequencies will show STS at the 2–4 kHz range if the elevation from baseline meets the threshold. However, flat audiograms warrant Professional Supervisor review to assess whether the pattern is consistent with occupational noise exposure or suggests a non-occupational etiology requiring medical referral.
Required Employer Response
Flat hearing loss requires review by the supervising audiologist or physician to determine whether the pattern is consistent with occupational NIHL or suggests a non-occupational cause requiring medical evaluation. An EHS manager should not attempt to interpret flat audiograms independently.
The PS review should consider: medication effects (loop diuretics, aminoglycoside antibiotics, cisplatin), sudden hearing loss events, Meniere's disease indicators, and conductive overlay from middle ear pathology. Medical referral may be appropriate.
If the average change at 2000, 3000, and 4000 Hz compared to baseline equals or exceeds 10 dB, an STS is confirmed regardless of audiogram shape, triggering notification, HPD refitting, and OSHA 300 log evaluation.
Audiologist-supervised audiometric testing with automatic STS detection
Soundtrace audiometric testing is supervised by a licensed audiologist who reviews every audiogram, identifies all STSs, and makes clinical determinations — ensuring your program meets every 1910.95 requirement.
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A flat audiogram shows roughly equal threshold elevation across the entire tested frequency range (500–6000 Hz), with no pronounced notch or slope. This is distinct from the classic NIHL pattern (4 kHz notch) and from age-related hearing loss (high-frequency slope). On an audiogram, all threshold markers appear at approximately the same heigh
A flat hearing loss pattern changes the STS analysis. The 10 dB STS threshold is calculated at 2000, 3000, and 4000 Hz regardless of the shape of the audiogram. A flat loss that elevates thresholds equally at all frequencies will show STS at the 2–4 kHz range if the elevation from baseline mee. The Professional Supervisor must review all audiograms with significant findings to determine STS status and work-relatedness.
The Professional Supervisor — a licensed audiologist, otolaryngologist, or other physician — must review any audiogram with clinically significant findings. OSHA 1910.95(g)(3) requires PS involvement in all STS determinations and medical referral decisions. EHS managers should not attempt to interpret audiogram patterns independently.