Page 27 - Spring 2009

Standards
HOW MANY PEOPLE WILL BE AWAKENED BY NOISE TONIGHT?
26 Acoustics Today, April 2009
Nicholas P. Miller
Harris Miller Miller & Hanson Inc. Burlington, Massachusetts 01803
and
Paul D. Schomer
Schomer and Associates, Inc. Champaign, Illinois 61821
Introduction
Noise can disturb sleep and is
especially a problem around air-
ports with many night flights.
There have been eight major studies
worldwide on the effects of noise on
sleep that included the study of behav-
ioral awakenings.1-8 “Behavioral awak-
enings” means that the individual is
awake enough to press a button, and
behavioral awakening is the sole meas-
ure of effect in American National
Standards on this topic. In contrast, the
European Union (EU) has concentrated on motility (body movements while asleep) as their major measure of effect. The use of motility as a measure of effect has been rejected in the USA. Imagine telling a judge or planning body, “These increases in noise will cause twenty percent of the
“Imagine telling a judge or planning body, ‘These increases in noise will cause twenty percent of the population to move ten percent more in their sleep’.”
population to move ten percent more in their sleep.” What concrete meaning does it convey? Compare it to the state- ment, “These increases in noise will double the number of people awak- ened—from 20 percent to 40 percent of the population.”
All of the eight studies referenced above provide data that relate the prob- ability of being awakened to the Sound Exposure Level (SEL) of the individual noise events. It was on these kinds of data that both the original and the new
9 standard ANSI/ASA S12.9/Part 6–2008 are based. Figure 1
(Annex B of the new standard) indicates the prediction of the likelihood of behavioral awakenings in response to unique, single events, but it does not provide a means to predict the effect of an ensemble of events distributed in some fashion throughout the night.
The EU has advanced a method to possibly overcome these shortcomings. This method and regulatory guidance specifies the cumulative metric—annu- al-average equivalent sound level between 11:00 p.m. and 7:00 a.m.
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But it is dif- ficult, if not impossible, to relate specif- ic aircraft-noise effects to such cumula- tive metrics, e.g., “What percent of the population will be awakened?”. Again, it is difficult to communicate to deci- sion-makers and to the public the meaning of changes in such cumulative metrics—especially in easily under- stood terms such as the expected change in percent of the population
awakened.
Fig. 1. Probability of awakening versus indoor Sound Exposure Level (SEL) from ANSI/ASA S12.9/Part 6-2008. The dashed curve is for subjects newly experiencing the noise of nighttime discrete noise events (Eq. 1); the solid curve is for acclimated subjects (Eq. 2).
(Lnight)—to assess sleep disturbance. For sleep disturbance produced by air- craft noise, this regulatory guidance addresses (1) the expected maximum number of noise-induced motilities and (2) the increase in mean motility—
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both as a function of Lnight.
ANSI/ASA S12.9/Part 6–2008