Hearing Conservation - Can Compliance Prevent Hearing Loss?
Noise has been with us since the beginning of the Industrial Age, but it wasn't until about World War II that programs were developed to protect workers from its' effects. A combination of research, science, and practical experience led to a series of rules and regulations culminating in the current US Federal Hearing Conservation Amendment (29CFR1910.95). Separate rules are in place for the mining and construction industries which are similar in nature and intent to the general industry rule, but each has subtle nuances that require investigation for professionals dealing in these specialized industries.
Compliant Does Not Mean Effective
Compliance with the Hearing Conservation Amendment (HCA) does not necessarily lead to prevention of hearing loss. Measuring noise and measuring hearing, the key aspects of a compliance-oriented hearing conservation program, may document risk and effect, but do not in themselves prevent hearing loss. If properly implemented, however, the law does contain nearly all of the steps necessary for effective hearing loss prevention.
Full text of the HCA is available from the OSHA noise and hearing website at www.osha-slc.gov/SLTC/noisehearingconservation/index.html; the NIOSH document is available at www.cdc.gov/niosh/98-126.html.
Many professionals have come to the conclusion that the most effective hearing conservation and hearing loss prevention programs are those under the direction of a motivated 'key individual'. While difficult to document and quantify, it is clear that an empowered, motivated individual, with overall responsibility for the program and authority to support it, is in essential in making the program successful.
Assess Risk - Measure Noise
Every hearing conservation program (HCP) or hearing loss prevention program (HLPP) starts with a risk assessment - based on a thorough noise survey. The survey must be designed to identify people at risk of exposure to hazardous noise at or above the action level, defined in the US as a time-weighted average (TWA) of 85 decibels (dB) over an 8-hour workday (TWA8). The survey should also identify predominant sources of noise exposure to drive noise control efforts.
Note that the key is noise exposure, not just noise. It's important to identify not just what makes noise, but how people interact with noise sources in their work environment. The combination of noise, people, and time in noise results in exposure. Instrumentation like noise dosimeters and techniques like task-based assessment modeling, managed by the appropriate experienced professionals, will lead to appropriate decisions for each of the other steps of the program.
Technical criteria for exposure assessment under the HCA include:
- 80 dB threshold. Sound levels lower than 80 dBA are not to be considered in the exposure assessment.
- 5 dB trading or exchange rate. OSHA assumes that the risk of hearing loss due to industrial noise exposure doubles with every 5 dB increase in TWA8.
- Slow response setting on meter.
- Exposure is calculated using dBA, or A-weighted decibels. The A-weighting filter is a way to make the meter respond to noise like the human ear.
- 90 dBA TWA criteria level. This means that OSHA considers 8 hours of exposure to an average of 90 dB to be 100% of the permissible exposure limit (PEL), or 100% dose.
- 85 dBA TWA action level, or 50% dose. This is the level at which the other aspects of the HCP start to take effect.
Once risk of exposure has been determined, an effective HCP takes two tracks - one oriented to people, and one oriented to the noise hazards themselves.
Assess Effect - Measure Hearing
Workers exposed to 85 dBA TWA8 or greater are required to be enrolled in an effective, on-going hearing conservation program. Their hearing ability is assessed as they come into noisy jobs either as a new hire or a transfer, with a baseline audiogram. The baseline audiogram should be preceded by 14 hours of no noise exposure, to allow as true an assessment as possible of the worker's hearing ability, and will not be contaminated with temporary threshold shift (TTS). Pure-tone air conduction audiometry at 500, 1000, 2000, 3000, 4000, and 6000 Hz is required, with testing at 8000 Hz optional.
Audiograms taken yearly while the individual works in noise (annual audiograms) are compared to the baseline to identify changes in hearing that may be due to workplace noise. The sentinel change is called a standard threshold shift (STS), defined as an average 10 dB change at 2000, 3000, and 4000 Hz.
Importantly, please note that industrial audiometric programs are not intended to assess hearing health - absolute thresholds are not a consideration. The purpose is to identify changes in hearing, hopefully with enough lead time to prevent hearing loss from becoming debilitating. Many audiologists address this issue daily in response to patients who say something like 'I had my hearing tested every year at work and they never told me anything was wrong'. Again, the purpose of the industrial program is to look for significant changes in hearing, not hearing loss.
'Correction' for aging, or presbycusis, is allowed when interpreting the hearing test. Many professionals are concerned that using age correction formulas may mask noise induced hearing loss until the opportunity for timely and effective intervention is missed.
If any HCP enrollee exhibits an STS, follow-up actions are required. A retest can be administered within 30 days of the detection of the STS; if the STS is not persistent, no further action is required. If the STS is confirmed on retest, the employee must:
- Be notified of the STS in writing,
- Be refit with hearing protection and retrained in its' use, and
- Use hearing protection when exposed to 85 dBA TWA or greater.
Hearing Protection - Protect the Worker
In addition to those with an STS in areas of 85 dBA, HPD is required for all workers whose exposure exceeds 90 dBA, even if they don't show any hearing change. Many employers choose to require HPD in all areas of 85 or greater to simplify the administrative issue of enforcing a different policy for different people in the same area with similar noise exposures.
Hearing Protection Devices (HPDs) were intended to be a temporary solution to noise exposure problems, with the intent that noise abatement should eventually eliminate the need for HPDs. Unfortunately, real-world administration of the rule has resulted in the opposite - HPDs, intended to be a temporary fix, have become the long-term exposure control of choice by many employers.
Noise Reduction Ratings (NRRs)
The noise reduction rating (NRR) on the HPD package is developed in a laboratory setting under optimal test conditions. Research indicates that the lab values don't match up very well with the real world experience. OSHA assumes that HPDs will provide half of the published NRR in real world application (50% de-rating). There are a multitude of factors that affect the actual protection achieved by real users in a real work environment. For further reading see Berger,.
HPD must protect the worker to an effective exposure of 90 dBA, or 85 dBA for those with STS.
Recordkeeping and Recordability
Records maintenance is a compliance key.
- Hearing tests should be retained in accordance with other medical records, typically for the duration of employment plus 30 years.
- Noise exposure (sound survey) records must be maintained for two years. However, the HCA requires that 'the most recent exposure assessment' be stored with the employee's audiogram, inferring that the exposure records should be maintained in line with audiometric records.
- Training records, including content and evidence of which employees received training, should be maintained.
Occupational hearing loss is defined by OSHA as an illness which, if it meets certain criteria, must be recorded on OSHA Form 200 (soon to be replaced with Form 300). The OSHA rule covering recordkeeping issues (CFR 1904) is currently undergoing revision, with significant and specific changes expected in hearing loss aspects.
Training
The intent of the training requirements under CFR 1910.95 is to engage the worker in understanding the risk entailed by noise, and to provide them the tools and knowledge to protect themselves from its' effect. Employees included in the program must be trained annually. The training requirements are specific, and include:
- The effect of noise on hearing
- The procedure and purpose of the hearing test
- Types of hearing protectors, and the advantages and disadvantages of each.
Many HCPs follow the letter of the law by providing training in the form of a video tape or handout booklet. While this may meet the technical requirements of the law, evidence indicates that training should be varied year-to-year and should be tailored to individuals and their situations to be truly effective.
Engineering - Reduce or Eliminate the Hazard
The most desirable approach to noise exposure management is to eliminate the hazard. Noise control engineering should be considered the first line of attack for noise issues - if the hazard can be eliminated, the balance of the program requirements can go away in their entirety!
The hierarchy of health and safety controls should be predominant when considering noise controls. Can the noise hazard be eliminated by substituting a quieter process? Can the noise be 'fixed' through engineering controls? Only when all of the possibilities for elimination, substitution, and control have been exhausted should hearing protection, warnings, and training be considered as viable alternatives.
Select controls for early consideration if there may be double paybacks. If controlling part free-fall, for example, can improve quality, the noise control can be easier to 'sell' to management. A similar phenomenon exists for control of compressed air. Reduced utility costs achieved through reducing demand for compressed air though air leak repair programs or demand-cycled compressed air applications, for example, will have the significant side benefit of reducing noise levels.
Feasibility considerations play a large part in selecting noise control issues for abatement. Feasibility is defined as having three aspects.
- Technical feasibility. Does the control exist, and can it be applied to the noise problem at hand with a reasonable expectation of the outcome?
- Economic feasibility. Do the costs of controls balance with the costs involved with administering an on-going, effective hearing conservation program? Many industries use a benchmark of about $200-$250 per employee per year as a general hearing conservation program cost figure. Typically these costs include cost for the hearing test, time off the job for the worker to get the test, and replacement labor to cover the worker's job while they are getting the test; noise exposure assessment; provision of hearing protectors; recordkeeping and program management time; and similar costs. On-going costs of the control should be considered as well, factoring in issues like downtime for maintenance, life-cycle, and production compromises involved with noise abatement measures.
- Significant benefit. The control must provide a benefit to the employee. OSHA considers any reduction of 5 dBA TWA8 or more; reduction to less than 100 dBA TWA8; and reduction to less than 90 dBA TWA8 as having significant benefit. Add the preferred design goal of 85 dBA TWA8, which will eliminate the need for the hearing conservation program altogether.
Program Audit/Evaluation
While the HCA has always required an 'effective, on-going hearing conservation program', no criteria are provided in the law describing effectiveness measures. Various approaches to evaluating HCP effectiveness have been developed.
One approach has been to use STS rates as a measure of program effectiveness. OSHA, for example, may consider HCPs with confirmed STS rates of 5% or less as 'effective'. One difficulty with this approach is that it tends to assess program effectiveness late in the process - after hearing has been lost.
Others use various exposure measures as an aid to assess program effectiveness. If, for example, the number or percentage of workers exposed at action level or greater decreases over time, it can be assumed that the controls portion of the HCP if functioning well. This metric, however, does not take into account the effect of noise - what is going on with the hearing of those who remain noise-exposed?
It is likely that the best program evaluation protocol will include:
- Evidence of the existence, and a measure of the effectiveness, of each program component.
- Measures of and trends in hearing ability, possibly more sensitive to change than age-corrected OSHA STS.
- Mechanisms to assess the effectiveness of noise controls, such as regular sound surveys tracking changes in the number of workers exposed to hazardous levels.
Some authors have suggested that program effectiveness can be determined through audiometric database analysis (ADBA). While ADBA can be a valuable tool for assessing important metrics like audiometric variability, it requires that program selection and inclusion criteria be intact and immaculate before it can be applied to maximum benefit.
Effective hearing conservation program management boils down to managing workers and how they interact with noise sources. Compliance can be a good start, but attention to the details can make the difference between a compliant program and an effective one.
