COHC common mistakes
COHC · Understand the traps and how to avoid them.
When asked what triggers a hearing conservation program, the candidate answers '90 dBA' and builds the whole program around the permissible exposure limit, treating the 85 dBA action level as merely advisory.
The 90 dBA PEL is the number candidates see most often in training slides and safety posters, so it gets retrieved first under time pressure, and the two thresholds blur into one.
What to do instead
Memorize a two-column decision table: at 85 dBA TWA (action level) the program, annual audiogram, training, and available HPDs begin; at 90 dBA TWA HPDs become mandatory and feasible engineering controls are required. Recite it aloud until the 85/90 split is automatic.
The candidate schedules the baseline audiogram 'sometime in the first year' and lets annual tests drift past 12 months, or fails to state that a mobile test van needs the 14-hour quiet period documented.
Candidates remember 'annual' as a general idea and never anchor it to a starting point, so the 6-month baseline clock and the 12-month anniversary both disappear.
What to do instead
Draw the timeline: baseline within 6 months of first exposure (or within 1 year if a mobile van is used and the employee wears HPDs and is counseled), then each annual audiogram within 12 months of the previous one. Attach the 14-hour noise-free requirement to the baseline date.
Given a dosimeter result of 150% dose, the candidate converts it using a 3 dB exchange rate, or simply declares the exposure 'over the limit' without computing an 8-hour TWA.
The 3 dB/4 dB exchange rate is standard in much of the acoustics literature, and dose percentages feel self-explanatory, so the OSHA 5 dB rule and the dose-to-TWA formula never get applied.
What to do instead
Drill the OSHA rule set: 5 dB exchange rate, 90 dBA criterion, 8-hour reference. Practice the conversion TWA = 16.61 log(dose/100) + 90, and confirm 50% dose = 85 dBA, 100% = 90 dBA, 200% = 95 dBA until the pattern is obvious.
Shown an audiogram with a 4 kHz notch and normal bone conduction, the candidate calls the loss conductive, or locates the damage in the middle ear or on the eardrum.
The air-bone gap concept is learned early and then over-applied, and candidates conflate 'the ear' with the visible outer and middle structures they can picture.
What to do instead
Anchor the rule: noise-induced loss is sensorineural, air and bone thresholds match, and the lesion is outer hair cell damage in the cochlea near the 4 kHz region of the basilar membrane. A conductive loss shows an air-bone gap and points to outer or middle ear pathology.
The candidate states an employee can be tested immediately after leaving a noisy work area, or treats the pre-test quiet period as a suggestion rather than a documented requirement.
The audiogram is mentally filed as a 'hearing test' rather than an exposure measurement, so the idea that recent noise temporarily shifts thresholds does not occur to the candidate.
What to do instead
Frame it as a temporary threshold shift problem: at least 14 hours without workplace noise before a baseline, and annual tests should follow the same practice. Build the quiet period into the scheduling script as a checkbox item, not an afterthought.
The candidate describes the test sequence as 500, 1000, 2000, 4000, 8000, omits 3000 and 6000 Hz, never retests 1000 Hz, and presents tones in descending order.
A familiar five-frequency sweep from school hearing screenings overwrites the OSHA protocol, and the reason for the untrained order (familiarization) is never taught as a reason.
What to do instead
Practice the exact order until it is muscle memory: right ear 1000, 2000, 3000, 4000, 6000, 8000, retest 1000, then 500; repeat for left. Explain that the first 1000 Hz tone familiarizes the listener and the final 1000 Hz tone checks response consistency.
The candidate says the audiometer needs a full acoustic calibration before each test day, or that the daily biological check substitutes for annual calibration.
'Calibration' is treated as one undifferentiated task, so the daily functional check and the annual exhaustive calibration collapse into a single remembered activity.
What to do instead
Separate the two by frequency and owner: a daily biological check (listening check on a known-stable person, plus a check that the earphones and cords are intact) before testing; an exhaustive calibration annually and after any repair or relocation. Label them 'daily functional' and 'annual exhaustive' on a wall chart.
Asked to identify a standard threshold shift, the candidate requires 15 dB at a single frequency, or averages across 500 through 8000 Hz, or applies the rule to only one designated ear.
Candidates blur the STS definition with the impairment formula used for calculating hearing loss percentage, and both involve 'averaging' and 'the frequencies'.
What to do instead
Lock in the OSHA definition: a change of 10 dB or more averaged at 2000, 3000, and 4000 Hz in either ear, compared with the baseline, with age correction optional. Contrast it explicitly with the impairment formula, which uses a different frequency set and purpose.
Given a 100 dBA exposure and an HPD labeled NRR 25, the candidate subtracts the full 25 and declares the protected level 75 dBA, skipping any derating and any A-versus-C weighting discussion.
The NRR label invites simple subtraction, and the derating factors feel like arbitrary trivia rather than a correction for laboratory versus real-world fit.
What to do instead
Use the OSHA field method: subtract the derated NRR from the A-weighted TWA. Apply the derating (typically 50% for earmuffs, 70% for formable plugs, and use the manufacturer's derating if given), and remember double protection is credited as only about 5 dB beyond the better device.
The candidate states audiometric records are kept two years and noise exposure measurements for the length of employment, reversing the two retention periods, or says both are kept indefinitely.
Both numbers appear in the same regulation and are easy to swap, and candidates rarely rehearse them as a matched pair.
What to do instead
Pair them verbally: audiograms for the duration of employment, noise exposure measurements for two years. Store that pair as a single memorized sentence, and tie each number to its record type rather than to the regulation section number.