Audiometric Testing Procedures and Test Environment
Performing a valid test
A pure-tone audiogram plots the lowest level heard at least half the time at each frequency, in dB HL. The ascending method (Hughson–Westlake) is standard: begin at a clearly audible level, descend in 10 dB steps until no response, then ascend in 5 dB steps; a threshold is confirmed by responses at the same level on two of three or three of four ascents. OSHA requires 500, 1000, 2000, 3000, 4000, and 6000 Hz; many programs add 8000 Hz. Instruct the employee carefully and watch for false positives driven by the wish to hear.
Test conditions matter as much as technique. The employee should have at least 14 hours without workplace noise before the baseline. The room must meet OSHA Table D-1 octave-band limits (500 Hz 40 dB; 1000 Hz 40 dB; 2000 Hz 47 dB; 4000 Hz 57 dB; 8000 Hz 62 dB) when earphones are used. Insert earphones reduce room requirements substantially but still need a quiet space.
Traps
Bone conduction is not required by OSHA's standard. 3000 Hz is required and is the frequency most often omitted; it is also where early noise damage frequently appears.
Rule of thumb: if the booth is too loud at a frequency, the measured threshold reads falsely high (worse) at that frequency - an error in the conservative direction, but still invalid data.