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Audiometric testing is the cornerstone of any OSHA hearing conservation program. Understanding the procedure matters: it explains why the 14-hour pre-test quiet period is non-negotiable, what the test is actually measuring, why certain results trigger required employer actions, and what can go wrong if the procedure is not followed correctly. This guide walks through the complete occupational pure tone audiometry procedure from start to finish.
Soundtrace audiometric testing takes 5–7 minutes per worker using a microprocessor audiometer — no audiometric booth required, conducted on-site at any time with automated STS calculation and result storage.
Pure tone audiometry measures the softest sound a person can hear at specific frequencies — the hearing threshold expressed in decibels HL. In an occupational context its purpose is surveillance: comparing individual thresholds over time to determine whether hearing is stable or deteriorating and whether changes trigger the OSHA Standard Threshold Shift action threshold.
OSHA 1910.95 requires workers to be free from workplace noise for at least 14 continuous hours before audiometric testing. Temporary Threshold Shift (TTS) — a reversible elevation caused by recent noise exposure — produces falsely elevated thresholds that look like permanent NIHL. Workers who must work a noisy shift beforehand should wear adequate HPDs from the start of their shift.
OSHA allows workers who cannot avoid noise exposure in the 14 hours before testing to wear hearing protection adequate to reduce effective exposure to safe levels. The 14-hour quiet period produces more reliable results and is preferred.
OSHA requires audiometric testing in a space meeting ANSI S3.1 maximum permissible ambient noise limits (incorporated by reference in OSHA Appendix D). Background noise exceeding these limits can mask test tones and produce falsely elevated thresholds. Modern microprocessor audiometers include real-time ambient noise monitoring that verifies test conditions meet these limits before and during each test.
OSHA requires audiometers meeting ANSI S3.6 with two required calibration types: a biological check (daily, before each testing day) and an exhaustive calibration (annual, by qualified technician). Calibration records are part of the required program documentation and may be challenged in workers’ compensation proceedings if missing.
OSHA requires testing at 500, 1000, 2000, 3000, 4000, and 6000 Hz per ear. The STS calculation uses the average of 2000, 3000, and 4000 Hz. The 4000 Hz threshold is the most sensitive early indicator of NIHL — the frequency damaged first by occupational noise. The 4 kHz notch pattern (threshold dip at 3000–4000 Hz with preserved lower-frequency thresholds) is the classic audiometric signature of NIHL.
Threshold is established using the ascending method (OSHA Appendix C): start at a clearly audible level, descend in 10 dB steps until the worker stops responding, then ascend in 5 dB steps and record the level at which the worker responds on at least 2 of 3 presentations. Microprocessor audiometers automate this process, completing the full bilateral six-frequency test in 5–7 minutes with higher repeatability than manual testing.
Normal hearing is ≤25 dB HL across speech frequencies. Key patterns: the 4 kHz notch (NIHL signature); flat audiogram (age-related or conductive loss); asymmetric results (warrants medical investigation, since NIHL is typically bilateral). The most important comparison is always annual vs. baseline — a worker with 30 dB HL at baseline who shows 40 dB HL annually has a potential STS even though 40 dB HL may appear “moderate” in isolation.
Invalid test conditions include: quiet period not observed; ambient noise exceeded ANSI limits; audiometer not calibrated; inconsistent worker responses; cerumen blockage not addressed; or incorrect headphone placement. OSHA permits retesting within 30 days when an apparent STS is found. An STS that disappears on retest was likely a testing artifact. Only confirmed STSs require recordkeeping and follow-up actions.
Average thresholds at 2000, 3000, and 4000 Hz on the current annual test; subtract the average at those frequencies on the baseline; if ≥10 dB in either ear, an STS exists. Optionally apply age correction per OSHA Appendix F. An STS triggers required employer actions: HPD refit and retrain, noise control review, medical referral if indicated, and OSHA 300 log recordability evaluation.
Soundtrace conducts OSHA-compliant pure tone audiometry on-site with real-time ANSI S3.1 ambient noise verification — no booth, no van, no scheduling delays. Automated threshold determination, STS calculation, and 30-year record retention.
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