Equal Outcome

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Slide 4 of 14


How can we determine whether the outcome of a hearing loss prevention program is providing equal protection to what would be expected if engineering controls had reduced a worker’s risk of sound exposure to 90 dB(A) TWA or lower? One simple to implement method is already available. All workers at risk of sound exposures of 85 dB(A) TWA and greater must be included in a medical surveillance program consisting of an annual audiogram and a comparison of this current audiogram to a baseline audiogram is performed to compute the OSHA Standard Threshold Shift (STS).

Much debate has occurred as to what is an acceptable level of STS (often expressed in percent number of workers at risk with STS divided by total number of workers at risk per year) in order to deem a program to be effective. Using this commonly available index and recognizing that cost-effectiveness requires that the outcome of a hearing loss prevention process must be equal to that achieveable if engineering noise controls had been implemented; it is my premise that the annual age-corrected STS rate for noise induced hearing loss - work related - has to be 0.5% or lower.

Now I am aware that many of us here at AIHA over the past few years have said this target should be 2.5% or less, and others have said even 5% is okay. But, it is my opinion that these rates are just reflective of what is happening in the better run hearing conservation programs. Just because these programs average 2.5% STS per year does not mean that the programs are effective. Remember that I said earlier the criteria of success cannot be based on arguments of cost-benefit. The question is not: ” What is the appropriate amount of money to spend for what we seem to be getting in terms of benefit?” The question is: “What is the amount of money we have to spend to have an equal outcome to engineering controls where the cost would have been $500 - $3,000 per worker?”

And on that basis, we come to 0.5% by assuming that if a worker works 40 years under a hearing conservation program, that in order to have 20% of the workers show noise induced hearing loss related to the work environment, the annual STS rate has to be 0.5%. And if we were to consider 85 dB(A) TWA as being our “equally protective goal” the risk of hearing impairment for a group of at-risk-workers is more in the neighborhood of 5 to 10% over a work career. For this case, 0.25% is the annual STS rate for equal protection. I doubt if anyone will disagree that 0.25% is getting pretty close to talking about zero tolerance.