Slide 4 of 14
Notes:
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 costeffectiveness 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 agecorrected 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 costbenefit. 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 atriskworkers 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.
