Safety Tidbit #3 - Noise by the Numbers

Noise-induced hearing loss predates the industrial revolution with cases cited from cannon fire on battlefields and blacksmithing. Furthermore, the OSHA Noise Standard, 1910.95 has its roots in the Walsh-Healy Act, the precursor to the Occupational Safety and Health Act.  Although knowledge and technology continue to march forward (sometimes running and not just marching) occupational hearing loss due to exposure to noise still pervades the workplace. Below are a few numbers I wish to share with you pertinent to noise exposure and hearing loss.

1 – year, At least annually after obtaining the baseline audiogram, the employer shall obtain a new audiogram for each employee exposed at or above an 8-hour time-weighted average of 85 decibels.

2 – years, Minimum time employers must keep noise exposure records.

3 – dB, Equal-Energy exchange rate

5 – dB, OSHA Exchange rate

6 – months, Within six months of an employee's first exposure at or above the action level, the employer shall establish a valid baseline audiogram to compare subsequent audiograms.

10 – dB, a standard threshold shift (STS) is a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear

14 – hours, Testing to establish a baseline audiogram shall be preceded by at least 14 hours without exposure to workplace noise. Hearing protectors may be used as a substitute for the requirement that baseline audiograms be preceded by 14 hours without exposure to workplace noise.

21 – days, the employee shall be informed of a standard threshold shift, in writing, within 21 days of the determination.

25 – decibels, An employee has suffered a hearing injury when an employee's  total hearing level is 25 decibels (dB) (averaged at 2000, 3000, and 4000 Hz) in the same ear(s) as the STS. The employer must record the case on the OSHA 300 Log.

30 - If the annual audiogram shows that an employee has suffered a standard threshold shift, the employer may obtain a retest within 30 days and consider the results of the retest as the annual audiogram.

85 – dBA, OSHA 8-hour Time Weighted Average (TWA) Medical surveillance action level – NIOSH/ACGIH Exposure Limit

90 – dBA, OSHA 8-hour TWA Permissible Exposure limit

100 – dBA, TWA at which OSHA typically enforces engineering controls

105 – dBA, TWA at which double hearing protection is recommended to ensure reduction of exposures below 90 dBA (ideally below 85 dBA).

I hope this overview of noise was helpful. Let me know if you have any questions.  Thanks for reading!

Bryan