F-22 Plus-Up Environmental Assessment - Joint Base Elmendorf ...

F-22 Plus-Up Environmental Assessment
Appendix D Aircraft Noise Analysis and Airspace Operations
Table D-3. Average NIPTS and 10th Percentile NIPTS as a Function of L dn *
L dn Average NIPTS (dB)** 10 th Percentile NIPTS (dB)**
80-81 3.0 7.0
81-82 3.5 8.0
82-83 4.0 9.0
83-84 4.5 10.0
84-85 5.5 11.0
85-86 6.0 12.0
86-87 7.0 13.5
87-88 7.5 15.0
88-89 8.5 16.5
89-90 9.5 18.0
dB = decibels; L dn = Day-night Average Sound Level; NIPTS = Noise-induced Permanent
Threshold Shift
*Relationships between L dn and NIPTS were derived from CHABA 1977.
**NIPTS values rounded to the nearest 0.5 dB.
Thus, for a noise exposure within the 80-81 Ldn contour band, the expected lifetime average
value of NIPTS (hearing loss) is 3.0 dB. The Average NIPTS is estimated as an average over all
people included in the at risk population. The actual value of NIPTS for any given person will
depend on their physical sensitivity to noise − some will experience more loss of hearing than
others. The USEPA Guidelines provide information on this variation in sensitivity in the form of
the NIPTS exceeded by 10 percent of the population, which is included in Table D-3 in the “10th
Percentile NIPTS” column. As in the example above, for individuals within the 80-81 Ldn
contour band, the most sensitive of the population, would be expected to show no more
degradation to their hearing than experiencing a 7.0 dB Average NIPTS hearing loss. And
while the DoD policy requires that hearing loss risk be estimated for the population exposed to
80 dB Ldn or greater, this does not preclude populations outside the 80 Ldn contour, i.e. at
lower exposure levels, from being at some degree of risk of hearing loss.
The actual noise exposure for any person living in the at-risk area is determined by the time that
person is outdoors and directly exposed to the noise. Many of the people living within the
applicable L dn contour will not be present during the daytime hours − they may be at work, at
school, or involved in other activities outside the at-risk area. Many will be inside their homes
and thereby exposed to lower noise levels, benefitting from the noise attenuation provided by
the house structure. The actual activity profile is usually impossible to generalize. For the
purposes of this analysis, it was assumed that residents are fully exposed to the L dn level of
noise appropriate for their residence location and the Average NIPTS taken from Table D-3. 3.
The quantity to be reported is the number of people living within each 1 dB contour band inside
the 80 dB L dn contour who are at risk for hearing loss given by the Average NIPTS for that band.
The average nature of Average NIPTS means that it underestimates the magnitude of the
potential hearing loss for the population most sensitive to noise. Therefore, in the interest of
disclosure, the information to be reported includes both the Average NIPTS and the 10th
percentile NIPTS Table D-3. 3) for each 1 dB contour band inside the 80 L dn contour.
According to the USEPA documents titled Information on Levels of Environmental Noise
Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety, and Public
Health and Welfare Criteria for Noise, changes in hearing levels of less than 5 dB are generally
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