The intent of this blog article is not an in-depth comparison of the two noise standards.  There are numerous differences between the two which are minor and of little real consequence.  Rather, this blog will focus on three of the more significant differences.

Dual Hearing Protection
Both the OSHA and MSHA Noise Standards utilize a two-number system:  a 90 dBA TWA Permissible Exposure Level (PEL) and an 85 dBA TWA Action Level.  Exposures in excess of the PEL require engineering and/or administrative noise control as well as hearing protection.  Exposures at and above 85 dBA TWA require inclusion in an effective hearing conservation program (HCP) and providing workers the option to wear hearing protection.

One area in which the MSHA standard is more protective than the OSHA standard is specifying a noise exposure level above which both earplugs and earmuffs (dual protection) are required.  MSHA specifies that an exposure above 105 dBA TWA requires dual protection.  There is no similar requirement in the OSHA standard.  However, the OSHA Field Operations Manual (2014) specifies that OSHA will consider issuing a citation for lack of engineering and/or administrative noise controls above 100 dBA TWA.  OSHA considers this a noise exposure level above which persons may not be adequately protected even with dual protection.

Engineering Noise Control
Compared to OSHA, the MSHA Noise Standard places more emphasis on engineering and administrative noise control.  The OSHA standard simply states that the employer will implement engineering and administrative noise controls above the PEL – a requirement rarely enforced in practice.  The MSHA standard has the same requirement but goes beyond in two important respects.  First, when a miner has an STS, the MSHA standard requires the mine operator to review the effectiveness of engineering and administrative noise controls, and to correct any deficiencies.  It is difficult to say if this additional requirement makes any real difference, but it is at least a requirement which MSHA can enforce if it so chooses to emphasize the importance of engineering and administrative noise control. Second, MSHA’s annually required hearing conservation training incorporates miner training in the maintenance of noise controls – no such employee noise control training is required by OSHA.

Reportable Hearing Loss

The level of hearing change reported on the OSHA 300 Log and the MSHA Form 7000-1 is perhaps the most significant difference between the two standards.  OSHA requires a hearing loss be reported on the OSHA 300 Log when the following three conditions are met:

  • Standard Threshold Shift (STS) is found, and
  • The average hearing loss on the current test exceeds 25 dB HL, and
  • The hearing change is determined to be at least partially work-related

By way of review, an STS is an average change of at least 10 dB HL at 2000, 3000 and 4000 Hz in either ear compared to the baseline.  For OSHA purposes, the baseline may be the original baseline, a baseline revised for improved hearing, or a baseline revised for persistently worse hearing.  Each ear can have a different baseline.  Age correction is allowed in order to not penalize the employer for hearing loss associated with aging.  The second criterion is simply the average of the 2000, 3000 and 4000 Hz thresholds on the current test, calculated for the ear showing the STS.  If that average exceeds 25 dB HL, then the second criterion is met and the STS must be considered potentially reportable.  The idea underlying this is that hearing loss is not considered handicapping until it exceeds 25 dB HL and so the employer should not be penalized for it.  Whereas the first two criteria are just math that any software package can calculate, the third criterion involves the judgment of a licensed health care provider, typically an Audiologist or Physician, as to whether working conditions contributed to the STS.

Common sense dictates that reasonable efforts made to prevent hearing loss will likely pay off in the long term.

What MSHA considers a reportable hearing loss is quite different.  The STS is calculated exactly the same for MSHA as it is for OSHA, but MSHA does not consider the STS a reportable hearing loss.  Unless determined by an Audiologist or Physician to be neither work-related nor aggravated by occupational noise exposure, MSHA considers reportable a 25 dB HL average change at 2000, 3000 and 4000 Hz.  Age correction is allowed in the calculation.  This is exactly the same calculation as the STS, but with a criterion of 25 dB HL instead of 10 dB HL.  Importantly, the current test is always compared to the original baseline unless that baseline has been revised for improvement (this does not often happen).  What this means is that a miner can have one set of baselines for STS calculation and a different set of baselines for 25 dB Average Change calculation, and they can be different for each ear.  It is also important to note…and this is found in the Final Rule correction issued 17 Oct 2000…that what is reportable is first a 25 dB average change, then a 50 dB average change, then a 75 dB average change compared to the original baseline and allowing for age adjustment.  Notice, too, that the OSHA criterion requires the average hearing loss to exceed 25 dB whereas the MSHA criterion is 25 dB, a minor but important difference.  All of this makes MSHA hearing loss reportability more complex compared to OSHA.  But there is also less reportable MSHA hearing loss compared to OSHA due the criterion being a 25 dB average change instead of a 10 dB average change.

At this point, it is difficult to determine if these differences have resulted in less hearing loss in the mining industry.  Work-related hearing loss is a long-term, chronic issue and assessing the efficacy of hearing conservation efforts is notoriously difficult.  However, common sense dictates that reasonable efforts made to prevent hearing loss will likely pay off in the long term.