United States
Environmental Protection
Agency
Office of Noise
Abatement & Control
Washington, D.C. 20460
November 1978
EPA 550/9-79-100
Protective Noise Levels
Condensed Version
of EPA  Levels Document

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PURPOSE

This publication is intended to complement the EPA's "Levels Document,"* the 1974 report examining
levels of environmental noise necessary to protect public health and welfare.  It interprets the contents of
the Levels Document in less technical terms for people who wish to better understand the concepts
presented there, and how the protective levels were identified. In that sense, this publication may serve as
an introduction, or a supplement, to the Levels Document.


* "Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an
 Adequate Margin of Safety," EPA/ON AC 550/9-74-004, March, 1974.

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                                TABLE OF CONTENTS


                                                                               PAGE

PURPOSE	ii

TABLE OF CONTENTS	iii

INTRODUCTION	1

ABOUT SOUND	3
    Amplitude	 3
    Frequency	3
    Time Pattern	3

MEASUREMENT OF ENVIRONMENTAL NOISE: SOUND DESCRIPTORS	3
    A-Weighted Sound Level	 4
    Sound Exposure Level	 4
    Equivalent Sound Level	  .4
    Day-Night Sound Level	9

LEVELS OF ENVIRONMENTAL NOISE IN THE UNITED STATES	9
    Outdoor  Levels	9
    Relationship Between Indoor and Outdoor Levels	11

INDIVIDUAL NOISE EXPOSURE PATTERNS	11

HEARING DAMAGE FROM ENVIRONMENTAL NOISE	15
    Basic Assumptions Involved in Determining Protective Levels	15
    Calculation of the Maximum Allowable Noise Exposure	17
    Discussion of Assumptions	17

SPEECH  COMMUNICATION	18
    Speech Interference Indoors	18
    Speech Interference Outdoors	18
    Discussion	20

ACTIVITY INTERFERENCE AND ANNOYANCE	  20
    Activity Interference	20
    Community Reactions to Noise	21
    Social Surveys	21
    Discussion	21

SUMMARY	24

MISUSES, MISUNDERSTANDINGS, AND QUESTIONS	24

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INTRODUCTION

  During the last 20 years there has been increasing concern with the quality of the environment. Along
with airiand water contaminants, noise has been recognized as a serious pollutant. As noise levels have
risen, the effects of noise have become pervasive and more apparent.
  Noise is defined as "unwanted sound." In the context of protecting the public health and welfare, noise
implies adverse effects on people and the environment.  Noise causes hearing loss, interferes with human
activities at home and work, and is in various ways injurious to people's health and well-being. Although
hearing loss is the most clearly measurable health hazard, noise is also linked to other physiological and
psychological problems.
  Noise annoys, awakens, angers and frustrates people. It disrupts communication and individual
thoughts, and affects performance capability. Noise is one of the biological stressors associated with
everyday life. Thus, the numerous effects of noise combine to detract from the quality of people's lives
and the environment.
  Noise emanates from many different sources. Transportation noise, industrial noise,  construction noise,
household noise, and people and animal noise are all large-scale offenders. It is important, then, to ex-
amine the total range and combination of noise sources and not to focus unduly on any one source.
  Through the Noise Control Act of 1972, Congress directed the Environmental Protection Agency (EPA)
to publish scientific information about the kind and extent of all identifiable effects of different auaiities
and quantities of noise. EPA was also directed to define acceptable levels under various conditions which
would protect public health and welfare with an adequate margin of safety. The EPA collaborated with
other Federal agencies  and the scientific community to publish a "Levels Document,"* which would fulfill
these requirements in the Noise Control Act.
  Initial public reaction was quite favorable, but it was discovered that the document was too complex,
too technical, and too long for some audiences. This summary presents the contents of the Levels Docu-
ment in less technical terms. It defines the basic measurement of noise, analyzes noise exposure, and
presents the best understood effects of noise —  hearing damage, speech interference, and  annoyance  —
using information contained in the Levels Document. The identified protective levels are then summarized,
followed by a number of often-asked questions and answers about the  Levels Document.
  No attempt has been made here to incorporate recent research findings pertaining to effects of noise on
people.  Considerable new information has developed since initial  publication of the Levels Document, in-
cluding new findings on community response to noise, sleep disruption, and speech interference. Sum-
maries and analyses of some recent  information on noise effects are available through EPA  and other
agencies.
* "Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an
 Adequate Margin of Safety", EPA 550/9-74-004, March, 1974, U.S. Environmental  Protection  Agency,
 Washington, D.C. 20460.

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ABOUT SOUND

  The sound we hear is the result of a sound source inducing vibration in the air. The vibration produces
alternating band of relatively dense and sparse particles of air, spreading outward from the source in the
same way as ripples do on water after a stone is thrown into it. The result of the movement of the par-
ticles is a fluctuation in the normal atmospheric pressure, or sound waves. These waves radiate in all direc-
tions from the source and may be reflected and scattered or, like other wave actions,  may turn corners.
When the source stops vibrating, the sound waves disappear almost instantaneously, and the sound
ceases. The ear is extremely sensitive to sound pressure fluctuations, which are converted into auditory
sensations.
  Sound may be described in terms of three variables:
  1. Amplitude (perceived as  loudness)
  2. Frequency (perceived as pitch)
  3. Time pattern


Amplitude

  Sound pressure is the amplitude or measure of the difference between atmospheric  pressure (with no
sound present) and the total pressure (with sound present). Although there are other measures of sound
amplitude, sound pressure is the fundamental measure and is the basic ingredient of the various measure
ment descriptors in the next section, "Measurement of  Environmental Noise."
  The unit of sound pressure is the decibel  (dB); thus it is said that a sound pressure  level is a certain
number of decibels. The decibel scale is a logarithmic scale, not a linear one such as the scale of length. /
logarithmic scale is used because the range of sound intensities is so great that it is convenient to com-
press the scale to encompass all the sounds that need to be measured. The human ear has an extremely
wide range of response to sound amplitude. Sharply painful sound is 10 million times greater in sound
pressure than the least audible sound. In decibels, this 10 million  to 1 ratio is simplified logarithmically to
140 dB.
  Another unusual property of the decibel scale is that the sound pressure levels of two separate sounds
are not directly (that is, arithmetically) additive. For example, if a sound of 70 dB is added to another
sound of 70 dB, the total is only a 3-decibel increase (to 73 dB), not a doubling to 140 dB.  Furthermore, if
two sounds are of different levels, the lower level adds less to the higher as this difference increases. If the
difference is as much as 10 dB, the lower level adds almost nothing to the higher level. In other words,
adding a 60 decibel sound to a 70 decibel sound only increases the total sound pressure level  less than
one-half decibel.


Frequency

  The rate at which a sound source  vibrates, or makes the air vibrate, determines frequency.  The unit  of
time is usually one second and the term "Hertz" (after an early investigator of the physics of sound) is
used to designate the  number of cycles per second.
  The human ear and that of most animals  has a wide range of response. Humans can identify sounds
with frequencies from about 16 Hz (Hertz) to 20,000 Hz. Because pure tones are relatively rare in real-life
situations, most sounds consist instead of a complex mixture of many frequencies.


Time Pattern

  The temporal nature of sound may be described  in terms of its pattern of time and level:  continuity,  fluc-
tuation, impulsiveness, intermittency. Continuous sounds are those produced for relatively long periods at
a constant level, such as the noise of a waterfall. Intermittent sounds are those which are produced for
short periods, such as the ringing of a telephone or aircraft take-offs and landings. Impulse noises are
sounds which are produced in an extremely short span of time, such as a pistol shot or a hand clap. Fluc-
tuating sounds vary in level over time, such as the  loudness of traffic sounds at a busy intersection.


MEASUREMENT OF ENVIRONMENTAL NOISE: SOUND DESCRIPTORS

  EPA has adopted a system of four "sound descriptors" to summarize how people hear sound and to
determine the impact of environmental noise on public health and welfare. These four descriptors are: the
A-weighted Sound Level, A-weighted Sound Exposure Level, Equivalent Sound Level, and Day-Night

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Sound Level. They are related but each is most useful for a particular type of measurement. The descrip-
tors and some examples of their uses are described below.


A-weighted Sound Level

  One's ability to hear a sound depends greatly on the frequency composition of the sound. People hear
sounds most readily when the predominant sound energy occurs at frequencies between 1000 and 6000
Hertz (cycles per second). Sounds at frequencies above 10,000 Hertz (such as high-pitched hissing) are
much more difficult to hear, as are sounds at frequencies below about 100 Hz (such as a low rumble).  To
measure sound on a scale that approximates the way it is heard by people, more weight must be given to
the frequencies that people hear more easily.
  A method for weighting the frequency spectrum to mimic the human ear has been sought for years.
Many different scales of sound measurement,  including A-weighted sound level (and also B, C,  D, and
E-weighted sound levels) have evolved in this search. A-weighting was recommended by EPA to describe
environmental noise because it is convenient to use, accurate for most purposes, and is used extensively
throughout the world. Figure 1 shows the A-weighted levels of some environmental noises. Note that
these ranges of measured values are the maximum sound levels.
  The A-weighting of frequency also is used in the three descriptors discussed below. When used by
itself, an A-weighted  decibel value denotes either a sound level at a given,instant, a maximum level, or a
steady-state level. The following three descriptors are used to summarize those levels which vary over
time.


Sound Exposure Level

  Since the levels of  many sounds change from moment to moment, this variation must also be accounted
for when measuring environmental noise. One method  for measuring the changing magnitude of sound
levels is to trace a line on a sheet of moving paper, so  that the movement of the pen is proportional to the
sound level in decibels. Figure 2 illustrates such a recording, about which  several features are noteworthy.
First,  the sound level  varies with time  over a range of about 30 dB. Second, the sound appears to be
characterized by a fairly steady-state lower level, upon  which are superimposed sound levels associated
with  individual events. This fairly constant lower level is often called the background  ambient sound level.
  Each single event in Figure 2 may be partially characterized by its maximum level. It may also  be partially
characterized by its time pattern.  In the example, the sound level of the aircraft is above that of the back-
ground ambient level  for about a minute, whereas the sound levels from cars are above the background
level  for much less time.
  The duration of sounds with levels that vary from moment to moment is more difficult to characterize.
One way is to combine the maximum sound level with  the length of time during which the sound level is
greater than a certain number of decibels below the maximum level — for example, the number of seconds
that the sound rises from 10 dB below maximum, as in Figure 3.
  Using this procedure one can measure the total energy of the sound by summing the intensity during
the exposure duration. This  procedure produces the second measurement descriptor, sound exposure level
(Ls),  referred to in the Levels Document as the single event noise exposure level (SENEL).

Equivalent Sound Level

  Yet another method of quantifying the noise environment is to determine the value of a steady-state
sound which has the  same A-weighted sound  energy as that contained in the time-varying sound. This is
the third measurement descriptor, termed the Equivalent Sound Level (Leq). The Equivalent Sound Level is
a single value of sound level for any desired duration, which includes all of the time-varying sound energy
in the measurement period.  In Figure 2,  for example, the Leq equals about 58 dB, indicating that the
amount of sound energy in all the peaks and valleys  in  the figure is equivalent to the energy in a con-
tinuous sound of 58 dB.
  The major virtue of the Equivalent Sound Level is that it correlates reasonably well with the effects ef
noise on people, even for wide variations in environmental sound levels and time patterns. It is used when
only  the durations and levels of sound, and not their times of occurrence  (day or night), are relevant.  It is
easily measurable by available equipment. It also is the basis of a fourth and final measurement descriptor
of the total outdoor noise environment, the Day-Night  Sound Level (Ldn)-

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                                           Maximum Sound Level
                                                  Area in Which Energy
                                                  is Summed to Obtain
                                                  Sound Exposure Level
Duration at 10dB
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                               Time L
                 FIGURE 3. DESCRIPTION OF THE SOUND
                            OF A SINGLE EVENT

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      in dB                Outdoor Location
                     Apartment Next to Freeway

                     3/4 Mile From Touchdown at Major Airport
   —80—
           	       Downtown With Some Construction Activity
                     Urban High Density Apartment
                     Urban Row Housing on Major Avenue
                     Old Urban Residential Area
                     Wooded Residential



                     Agricultural Crop Land


                     Rural Residential


                     Wilderness Ambient
FIGURE 4. EXAMPLES OF OUTDOOR DAY-NIGHT AVERAGE
          SOUND LEVELS IN dB MEASURED AT VARIOUS
          LOCATIONS

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   Day-Night Sound Level

     The Day-Night Sound Level is the A-weighted equivalent sound level for a 24-hour period with an addi-
   tional 10 dB weighting imposed on the equivalent sound levels occurring during nighttime hours (10 pm to
   7 am), Hence, an environment that has a measured daytime equivalent sound level of 60 dB and a
   measured  nighttime equivalent sound level of 50 dB, can be said to have a weighted nighttime sound  level
   of 60 dB (50 + 10) and an Ldn of 60 dB.  Examples of measured Ldn values are shown in Figure 4. Table I
   summarizes the use of the four sound descriptors used by EPA.


                                       Table I. Descriptors of Sound*


TYPICAL USE                         NAME OF DESCRIPTOR   NATURE OF DESCRIPTOR

To describe steady airconditioning sound   A-weighted Sound Level     The momentary magnitude of sound
in a room or measure maximum sound                               weighted to approximate the ear's fre-
level during a vehicle passby with a                                   quency sensitivity.
simple sound  level meter.

To describe noise from a moving source   A-weighted Sound Exposure  A summation of the energy of the momen-
such as an  airplane, train, or truck.        Level                      tary magnitudes of sound  associated with
                                                                  a single event to measure  the total  sound
                                                                  energy of the event.

To measure average environmental noise   Equivalent Sound  Level      The A-weighted sound level that is "equi-
levels to which people are exposed.                                   valent" to an actual time varying sound
                                                                  level, in the sense that it has the same
                                                                  total energy for the duration of the sound.

To characterize average sound levels in    Day-Night Sound  Level      The A-weighted equivalent sound level for
residential areas throughout the day and                              a 24-hour period with  10 decibels added to
night.                                                             nighttime sounds (10 pm - 7 am).
*The unit for all descriptors is the decibel.


   LEVELS OF ENVIRONMENTAL NOISE IN THE UNITED STATES

     In residential areas of the United States, major contributions to outdoor noise come from transportation,
   industrial,  construction, human and animal sources. Inside homes, appliances, radio and television, as well
   as people  and animals, are predominant noise sources. On the job, workplace equipment can create
   moderate to extremely high levels of noise. The daily noise exposure of people depends on how much time
   they spend in different outdoor and indoor locations and on the noise environments in these places.
   Typical daily exposure patterns are discussed in this section, following short descriptions of outdoor and
   indoor levels of environmental noise throughout the United States.


   Outdoor Levels

     The noise environment outside residences in the United  States can be highly  variable.  As seen in Figure
   4, outdoor Day-Night Sound Levels in different areas vary over a range of 50 dB.  Levels occur as low as
   Ldn = 30 to 40 dB in wilderness areas and as high as Ldn  =  85 to 90 dB in urban areas.
     Most Americans live in areas with a much smaller ranger of outdoor noise levels. Figure 5 shows that for
   urban dwellers (roughly 135 million people, more than half the U.S. population), 87% live in areas of Ldn
   = 48 and  higher from traffic noise alone. Most of the other 13% of the urban population experience lower
   noise levels than  those of Figure 5. Figure 5 also shows that nearly half of the urban population  live in
   areas exposed to traffic sounds that range over only 5 dB (Ldn  = 55 to 60 dB).  Rural populations enjoy
   average  outdoor sound levels generally lower than Ldn  = 50 dB.

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  FIGURE 5. ESTIMATED PERCENTAGE OF URBAN

           POPULATION EXPOSED TO OUTDOOR

           DAY-NIGHT SOUND LEVELS DUE TO

           TRAFFIC
                       10

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  It is useful to know the number of people living in areas characterized by different levels of environmen-
tal noise. Figure 6 presents estimates for urban traffic, freeway traffic, and aircraft noise. The figure shows
that urban traffic noise is much more widespread than either aircraft or freeway noise, but the figures are
not strictly additive, because many of the people counted in one category are also exposed to another
category of noise. Fifty-nine million people live in areas with urban traffic noise of l_dn  = 60 dB or higher,
in contrast to only 16 million and 3.1 million people who live in areas with outdoor levels of l_dn = 60 dB
or higher for aircraft and freeway noise, respectively. On  the other hand, more people are exposed to
higher levels of noise from freeway and aircraft operations than from urban traffic: about 300,000 people
live in areas exposed to levels of l_dn = 80 dB or higher from freeway traffic; 200,000 from aircraft opera-
tions; and 100,000 from urban traffic. Bear in mind, however, that there may be differences  between in-
dividual at-ear exposure levels and outdoor levels, because people move from place to place for varying
amounts of time.


Relationship  Between Indoor and Outdoor Levels

  The contribution of outdoor noise to indoor noise levels is usually small.  That part of a sound level
within a building caused by an outdoor source obviously  depends on the source's intensity and the sound
level reduction afforded by the building. Although the sound level reduction provided by different buildings
differs greatly, dwellings can be categorized into two broad classes—those built in warm climates and
those built in cold climates. Further, the sound level reduction of a building is largely determined by
whether its windows are open or closed. Table II shows typical sound  level  reductions for these categories
of buildings and window conditions, as well as an approximate national average sound level  reduction.
                                              Table II
                             Typical Sound Level Reductions of Buildings

                                                      Windows                         Windows
                                                       Opened                            Closed

Warm Climate                                           12 dB                             24 dB
Cold Climate                                            17 dB                             27 dB
Approximate National Average                            15 dB                             25 dB


  Sample measurements of outdoor and indoor noise levels during 24-hour periods are depicted in Figure
7. Despite the sound level  reduction of buildings,  indoor levels are often comparable to or higher than
levels measured outside. Thus, indoor levels often are influenced primarily by internal noise sources such
as appliances, radio and television,  heating anc ventilating equipment, and people. However, many out-
door noises may still annoy people  in their homes more than indoor noises do. Indeed, people sometimes
turn on indoor sources to mask the noise coming  from outdoors.
  An example of the range of hourly sound levels measured inside living areas in plotted for each hour of
the day in Figure 8. The figure shows the median levels and the range of levels observed for 80% of the
data. During late night hours the typical  hourly sound level was approximately 36 dB. This level was prob-
ably dominated by outdoor noise. However, during the day, the hourly average levels ranged from about
40 to 70 dB, indicating the wide range of activities in which people engage.


INDIVIDUAL NOISE EXPOSURE PATTERNS

  During a 24-hour period, people are exposed to a wide range of noises,  including noise at home, work,
school, places of recreation, shopping establishments, and while enroute to these or other locations. Clear-
ly, no single exposure pattern can be typical of all people,  or even of those people who follow a common
life style. Figure 9 shows hypothetical exposure patterns for broad classes of people. From these levels and
some assumptions about the hours spent at different daytime activities, 24-hour average sound levels can
be estimated for factory and office  workers, housewives, and preschool and school-age children. Estimates
based on these assumptions are found in Table III.
                                                11

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 FIGURE 6. CUMULATIVE NUMBER OF PEOPLE IN URBAN AREAS EXPOSED
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          FROM DIFFERENT SOURCES
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 FIGURE 7.  COMPARISON OF SAMPLE OUTDOOR AND
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                                      14

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   For most people, nighttime noises do not contribute significantly to the 24-hour average.  For many, the
 24-hour average is determined primarily by the noise exposure of a single activity, frequently occurring for
 a short period of time.


                                              Table III
                        Hypothetical  Examples of Noise Exposures of Individuals

                                                            24-Hour Average Sound Level, dB

                                             Suburban                                 Urban
 Individual                                  Environment                            Environment

 Factory Worker                                  87                                       87
 Office Worker                                    72                                       70
 Housewife                                       64                                       67
 School Child                                     77                                       77
 HEARING DAMAGE FROM ENVIRONMENTAL NOISE

   There is no question that exposure to certain levels of noise can damage hearing. However, determining
 exposure  levels that protect hearing with an adequate margin of safety is a complicated matter.
   This is because hearing is a complex ability that cannot be summarized by a single number in the way an
 individual's height or weight can be described. In fact, sizeable differences exist between individuals' hear-
 ing abilities. Hearing acuity tends to change progressively with age. Also, environmental noise exposure
 may vary  considerably from moment to moment, so that specification of protective levels should include
 dynamic considerations. Further, relationships between  hearing damage and noise exposure must be in-
 ferred, since available scientific information was gathered from groups of people who differed not only in
 noise exposure, but also in other important ways.  Finally,  individual and group noise exposures (especially
 over a working lifetime) are rarely known with precision.
   In reaching conclusions about hearing loss, then, one must rely to a degree on assumptions,
 hypotheses, and extrapolations from existing data. Since complete agreement within the scientific com-
 munity on these matters is lacking, an attempt was made  in the  Levels Document to consider alternative
 assumptions and hypotheses  to ensure that the methods used to derive protective levels were based on
 the most defensible practice.  As new data  become available these levels may change slightly.


 Basic Premises Involved in Determining Protective Levels

   1. Changes in ability to hear in the region of 4000 Hz are the most important signs of irreversible  hearing
 loss, indicating actual physiological destruction within the hearing mechanism.  This frequency  is usually
 the first frequency affected when the ear is damaged  by exposure to noise. Furthermore, the protection of
 hearing acuity at this frequency is critical for understanding of speech and appreciation of music and other
 sounds.
  2. Changes in individual hearing  level, like changes  in height or weight, are only significant if they are
 sizeable. Changes smaller than 5 dB are considered insignificant.
  3. At all ages, it is assumed that hearing acuity  cannot be damaged by sounds that cannot be heard.
 This may be important in that aging and other causes may produce appreciable shifts in hearing.
  4. Because hearing ability varies from person to person, recommendations must be made in terms of a
 critical percentage of the  population, ranked with superior hearing over the remainder. EPA's recommenda-
tions were based on the 96th percentile—that is, on providing protection for 96% of the people. It is
assumed that people with poorer hearing than the  96th  percentile are not affected by noise of typical levels
 (see 3 above), so that the recommendations protect virtually the  entire population.
  5. An individual's total  noise exposure is evaluated  by an "equal energy" rule: two noise exposures are
expected to produce equal hearing  loss if the product  of exposure intensity and exposure time are equal.
This rule allows a 3-dB decrease in sound pressure level (expressed in dB) for each doubling of the dura-
tion. Thus an exposure of 76 dB for one hour is  equivalent to 73 dB for two hours, or 70 dB for four
hours. This procedure is probably accurate for exposures of 30 minutes or more. It is also more protective
for very short exposures and for noise  that fluctuates greatly in level.
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  6. Intermittent noise produces less hearing damage than the "equal energy" rule would predict. To be
considered intermittent for this purpose, a noise must fall below 65 dB for 10% of each hour and have
peaks that exceed the background level by 5 to 15 dB. Intermittent noise is assumed to produce 5 dB less
effect than does continuous noise of the same average level.


Calculation of the Maximum Allowable  Noise Exposure

  Three major scientific studies have attempted to assess hearing damage for various noise exposures. All
are based on a comparison  of groups of noise-exposed people and comparable non-exposed groups. All
three studies attempted to predict hearing loss as a function of noise exposure of a certain percentage of
people. Because these studies were  of exposure to high-level  noise, extrapolations of the data were
necessary to estimate the protective exposure level that would produce minimal hearing loss: less than 5
dB  at 4000 Hz for 96% of the people.
  Forty years of exposure (250 working days per year) to a noise level of 73 dB for 8  hours per day  was
calculated to produce a hearing loss smaller than 5 dB for 96% of the people. This is the basic datum used
to calculate hearing-protective levels of noise exposure. To use it in specific situations, certain corrections
must be applied. One correction is to determine  the yearly (rather than working day) level (250 to 365
days).  This consideration amounts to a reduction 1.6 dB. Another correction,  based on exposure on a
24-hour rather than 8-hour basis, produces an additional reduction of 5 dB.
  Table IV contains at-ear noise exposure levels that produce negligible hearing losses for both 8-hour and
24-hour exposure on a yearly and working day basis. The 8-hour calculation assumes the remaining  16
hours of the day are spent in relative quiet.
  Since an individual often  experiences intense noise exposure outside of working hours (for example,
while using noisy appliances or  pursuing noisy recreation), protection on a 24-hour basis 365 days per year
requires exposure of an intermittent  variety at an equivalent level of less than 71.4 dB. This value is
rounded to 70 dB to provide a slight margin of safety. Exposure to greater levels would produce more than
5 dB hearing loss in at least some of the population.


                                             Table IV
                         (At-Ear) Exposure Levels that Produce No More Than
                      5 dB Noise-Induced Hearing Damage  Over a 40-Year Period

                                                  Steady                                 With
                                               (Continuous)          Intermittent      Margin of
                                                   Noise                 Noise          Safety

Leq, 8 hour           250 day/year                  73                     78
                     365 day/year                  71.4                   76.4              75

Leq, 24 hour          250 day/year                  68                     73
                     365 day/year                  66.4                   71.4               70


Discussion of Assumptions

  Several assumptions have been made in calculating  the 24-hour yearly hearing-protective level of 70 dB.
It is reasonable to ask how alternative assumptions would affect this level, and what the range of error
might be.
     Q.  How would the recommended level be  affected by a change in the percentage of the population
         protected?
     A.  Reducing the 96th percentile value to the 50th percentile (i.e., protecting half the population)
        would increase the protective level value from 70 dB to 77 dB.
     Q. Since agreement on the value of the intermittency correction is imperfect, what other values
        might be used?
     A. The estimated intermittency correction  used in the Levels Document is 5 dB. The true intermit-
        tency correction is probably within the range 0 to 15 dB.
     Q. How accurate is the equal energy assumption?
     A. The equal energy assumption when applied to the long times (8 hours to 24, or 250 to 365 days) is
        fairly accurate. It may be subject to error when applied to short exposures of extreme level.
                                                17

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     Q. How meaningful are the basic studies of hearing damage risk?
     A. The probable errors of estimates in the three basic studies cannot be stated with absolute ac-
        curacy. There are a number of problems in extrapolating percentages of the population damaged
        from relatively high exposure levels to the protective level. Also, there is the problem of determin-
        ing the amount of hearing damage when  the control (non-exposed) population is subject to high
        levels of non-occupational noise. Thus, the 70 dB protective level  is simply the best present
        estimate, subject to change if better data become available.


SPEECH COMMUNICATION

  Communication is an essential element of human society, and speech is its most convenient form of ex-
pression. Interference with speech can degrade living directly, by disturbing normal social and work-related
activities, and indirectly, by causing annoyance and stress. Sometimes the communications disturbed by
noise are of vital importance, such  as warning  signals or cries for assistance.  Prolonged speech in-
terference and resulting annoyance are clearly not consistent with public health and welfare.
  Speech interference from environmental noise can occur at home, at work, during recreation, inside
vehicles, and in many other settings. Of  chief concern for current purposes are the effects of noise on
face-to-face conversations (indoors and outdoors), telephone conversations, and radio or television use.
  The degree to which noise disturbs speech depends not only on physical factors (such  as noise levels,
vocal effort, distances between talkers and listeners, and room acoustics), but also on non-physical fac-
tors. The latter  include the speaker's enunciation, the familiarity of the listener with the speaker's
vocabulary and  accent, the topic of conversation,  the listener's motivation, and the hearing acuity of the
listener. Years of research on speech intelligibility have produced considerable information about how these
factors interact. Accurate predictions of  speech intelligibility can be based on average noise levels and
distances between speakers and listeners.


Speech Interference Indoors

  The solid line in Figure 10 shows the effects of steady masking noise on sentence intelligibility for per-
sons with  normal hearing in a typical living room. At distances  greater than about one meter from the
speaker, the level of speech  is fairly constant throughout the room.
  The highest noise level that permits relaxed conversation with 100% sentence  intelligibility throughout
the room is 45 dB. People tend to raise their voices when the background noise  exceeds 45-50 dB.


Speech Interference Outdoors

  The sound level of speech outdoors decreases with increasing distance between speaker and listener.
Table V shows  distances between speaker and listener for satisfactory outdoor speech  intelligibility at two
levels of vocal effort in steady background noise levels.
  The levels for normal and raised-voice "satisfactory conversation" shown in Table V  permit sentence in-
telligibility of 95% at each distance. Ninety-five percent sentence intelligibility usually permits reliable com-
munication because of  the redundancy in normal conversation.
  If the noise levels in Table V are  exceeded, the speaker and listener must either move closer together or
expect reduced intelligibility. For example, consider a conversation at normal vocal effort at a distance of
three meters in  a steady background noise of 56 dB. If the background level increases to 66 dB, the
speakers either  will  have to move closer  (to one meter apart) to maintain the same intelligibility, or alter-
natively, raise their voices appreciably. If they remain three meters apart without raising their voices,
speech intelligibility  would drop considerably.


                                              Table V
                   Steady A-weighted  Sound Levels That Allow Communication with
                       95 Percent Sentence  Intelligibility Over Various Distances
                                  Outdoors for Different Voice Levels

VOICE LEVEL                       COMMUNICATION DISTANCE (meters)

                             0.5           1            2345

Normal Voice (dB)            72           66          60           56          54           52
Raised Voice (dB)            78           72          66           62          60           58


                                                 18

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    100

0)
u


0)
c
0)
u


I
     40
     20 —
     0
      45
50
55
60
65
70
75
                    Steady A-Weighted Sound Level in dB
          FIGURE 10.  INDOOR SENTENCE INTELLIGIBILITY
                              19

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Discussion

  In summary, an l_dn of 45 dB permits virtually 100% intelligibility inside buildings. Assuming that a
typical home reduces outdoor noise by 15 dB, the outdoor noise level should be no greater than l_dn = 60
dB to permit 100% intelligible speech indoors. Allowing a 5 dB margin of safety, the outdoor level should
be Ldn = 55 dB. This outdoor level would also guarantee sentence intelligibility of 95% outdoors with nor-
mal voice levels at a  distance of three meters.
     Q.  What do percentages of sentence intelligibility signify?
     A.  A given percentage of sentence intelligibility, such as 95% or 99%, indicates the proportion of
         key words (in a group of sentences) which are correctly  heard by normal-hearing listeners.
     Q.  How are the speech criteria affected by the fact that people tend to raise their voices in noise?
     A.  The speech criteria are based on the principle that an adequate communication environment does
         not necessitate raised voices.
     Q.  How do the identified continuous  equivalent levels relate to the fact that, in everyday life, noise
         fluctuates and is intermittent in nature?'
     A.  The Levels  Document tabulated speech interferences for different combinations of levels and
         durations to test the limits of certain Leq values under intermittent conditions. It is  acknowledged
         that, given  equal Leq values, fluctuating noise may reduce less total speech interference than
         continuous noise on average. On the other hand, during those times when the higher level noises
         occur, the speech interference will be greater than its average value.


ACTIVITY INTERFERENCE AND ANNOYANCE

  Noise interferes with human activities to varying degrees. Intruding noises can interfere with human ac-
tivities by distracting attention and by making activities more difficult to perform, especially when concen-
tration is needed. Interference from noise can even make some activities (such as  communication or sleep)
virtually impossible.  Except in the case of speech interference, however,  the degree of interference is hard
to specify and difficult to relate to the level of noise exposure.
  Because  people's reactions to time-varying noise differ from moment to moment, and because people's
reactions differ in general, protective levels  for annoyance and activity interference are determined from
data collected from groups of people, rather than from individuals. Fortunately, considerable data from
social surveys of community reactions to  noise exposure are available for this purpose. Although there are
some shortcomings in practically all such  data, sufficient agreement exists to allow confident predictions of
the noise levels that lead to certain degrees of activity interference and annoyance.


Activity Interference

  Social surveys most often have been used to assess community reaction to noise exposure  around air-
ports. Table VI shows the percentage of people who reported noise interference with activities among a
larger group which was extremely disturbed by aircraft noise.
  It  is hardly surprising that four of the nine activities in Table VI involve listening. Aircraft noise may also
be found annoying because it may startle people, cause houses to shake, or elicit fear of a crash.
  Another widely studied source of community noise exposure is vehicular traffic. Activity interference
produced by traffic noise closely resembles that of aircraft noise, since interference with conversation,
radio, television, and telephone use are all high on the list of activities disturbed.

                                              Table VI
                             Percentage of Those People Who Were Highly
                           Disturbed by Aircraft Noise, by Activity Disturbed

                 ACTIVITY                                     PERCENT

                 TV-Radio Reception                                   20.6
                 Conversation                                         14.5
                 Telephone                                           13.8
                  Relaxing Outside                                      12.5
                  Relaxing Inside                                       10.7
                  Listening to Records/Tapes                             9.1
                  Sleep                                                 7.7
                  Reading                                               6.3
                  Eating                                                3.5


                                                 20

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Community Reactions to Noise

  Two major indices of the cumulative effects of environmental noise on people are (A) specific actions
taken by individuals or groups (such as complaints), and (B) responses to social survey questionnaires.
Over the last 25 years, numerous studies have been conducted to increase understanding of the relation-
ship between noise exposure and  its effects on people in communities.
  Several factors beyond the magnitude of exposure have been found to influence community  reaction.
These factors include:
     1.   Duration of intruding noises and frequency of occurrence
     2.   Time df year (windows open or closed)
     3.   Time of day of noise exposure
     4.   Outdoor noise level in  community when intruding noises are not present
     5.   History of prior exposure to the noise source
     6.   Attitude toward the noise source
     7.   Presence of pure tones or impulses.
  Since each of these factors may affect community reactions to noise exposure, adjustments for each
have been developed to improve the predictability of community reactions beyond that available from a
simple measure of exposure level.  Figure 11 shows the results of several different case studies,  relating Ldn
(in dB) to community response with various correction factors added. The addition of the correction fac-
tors makes it possible to predict community reaction to within + 5 dB. As is common with annoyance and
interference caused by noise, the effects of context and situation may be almost as important as the
magnitude or intensity of the source. Caution is also needed in applying these relationships to communities
that are significantly quieter than average urban areas.

Social Surveys

  Extensive social surveys have been conducted around Heathrow Airport near London and at eight major
airports  in the United States. The  relationship found in these surveys between noise exposure levels and
the percentage of respondents who were considered annoyed by noise is summarized in  Figure 12.


Discussion

     Q.  Is annoyance simply a  "welfare" effect?
     A.  Annoyance is a reflection of adverse effects which cannot  be  ascribed solely  to "health" or
         "welfare." "Public health and welfare" in the context of the Noise Control Act  is an indivisible
         term; there are no separate "health" effects or "welfare" effects. "Public health and welfare" in-
         cludes personal comfort  and well-being, and the absence of mental anguish,  disturbances  and
         annoyance as well as the absence of clinical symptoms such as hearing loss or  demonstrable
         physiological injury.
     Q.   What is  annoyance due to noise?
     A.   Noise annoyance may  be viewed as any negative subjective reaction to noise on the part of an
         individual or group. It is not an indication of weakness or inability to cope with  stress  on the part
         of the annoyed. More  likely it signifies transient (or possibly lasting) stress beyond the control of
         the conscious individual. This is often expressed on  social surveys as the percentage of people
         who express differing degrees of disturbance or dissatisfaction due to the noisiness  of their en-
         vironments. For the purpose of identifying protective noise levels, annoyance is quantified  by us-
         ing the percentage of people who are  annoyed by noise. This is felt to be the best estimate of
         the average general adverse response  of people, and in turn, is viewed as reflecting activity in-
         terference and the overall desire for quiet.
     0   Are people annoyed at levels below an Ldn of 45 or 55 dB?
    A.   Individuals,  or even groups, may be annoyed by noise at low levels —the dripping faucet or hum-
         ming flourescent bulb are good examples. Annoyance  depends very much on the situation, and
         on individual differences  and noise durations.
    Q.   What do complaints represent?
    A.   Complaints are used  by officials as an indication that a noise problem exists (although a noise
         problem  may well exist in the absence of specific complaints). However, they do not necessarily
         represent the magnitude  of a noise problem. The number of people who file complaints is  only a
         very small percentage of  those who are annoyed.
                                                 21

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o
03
CC.
E

I
Vigorous Action

Widespread Threats
of Legal Action, Strong
Appeals to Local
Officials to Stop Noise

Widespread Complaints,
Individual Threats of
Legal Action

Sporadic Complaints

No Overt Reaction
Although Noise is
Generally Noticeable
                                                 ••H *t   i*
                          40          50         60         70        80         90

                          Adjusted Outdoor Day/Night Sound Level of Intruding Noise in dB
           FIGURE 11.  COMBINED DATA FROM COMMUNITY CASE
            STUDIES ADJUSTED FOR CONDITIONS OF EXPOSURE
                                       22

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0)



u

03
a.
    30
20
10
                 50          60          70


                     Day - Night Sound Level (L-dn) in dB
                                                80
        FIGURE 12. PERCENTAGE OF POPULATION ANNOYED BY

          COMMUNITY NOISE (HEATHROW AIRPORT STUDY)
                             23

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     Q.  How is the margin of safety for annoyance applied?
     A.  The identified indoor level of Ldn = 45 incorporates a margin of safety for 100% protection of
         speech perception which is used as a surrogate for annoyance. The outdoor identified level of 55
         l_dn protects speec, outdoors to a level  of 95% intelligibility at up to 2 meters, while incor-
         porating a 5 dB margin of safety for speech, and giving added weight to the range of  adverse ef-
         fects.
     Q.  Why is the nighttime penalty 10 decibels?
     A.  The 10 dB nighttime weighting had two bases: first, this weighting value has been applied suc-
         cessfully here and in other countries; secondly, in quiet environments,  the natural drop in level
         from day to night is about 10 dB.


SUMMARY

  On the basis of its interpretation of available scientific information,  EPA has identified a range of yearly
Day-Night Sound Levels sufficient to protect public health and welfare from the effects of environmental
noise. It is very important that these noise levels, summarized in Table VIII, not be misconstrued. Since the
protective levels were derived without concern for technical or economic feasibility, and contain a margin
of safety to insure their protective value, they must not be viewed as standards, criteria, regulations,  or
goals. Rather, they should  be viewed as levels below which there is no reason to suspect that the general
population will be at risk from any of the identified  effects of noise.
                                             Table VIII
                             Yearly l_dn Values That Protect Public Health
                                 and Welfare with a Margin of Safety
EFFECT

Hearing

Outdoor activity inter-
ference and annoyance
LEVEL

Leq(24) ^ 70 dB

Ldn < 55 dB
Indoor activity inter-
ference and annoyance
Leq(24) < 55 dB



Ldn < 45 dB

Leq(24) < 45 dB
AREA

All areas (at the ear)

Outdoors in residential areas and farms
and other outdoor areas where people
spend widely varying amounts of time
and other places in which quiet is a basis
for use.

Outdoor areas where people spend
limited amounts of time, such as school
yards, playgrounds, etc.

Indoor residential areas

Other indoor areas with human activities
such as schools, etc.
  Outdoor yearly levels on the Ldn scale are sufficient to protect public health and welfare if they do not
exceed 55 dB in sensitive areas (residences, schools, and hospitals). Inside buildings, yearly levels on the
Ldn scale are sufficient to protect public health and welfare if they do not exceed 45 dB. Maintaining 55
Ldn outdoors should ensure adequate protection for indoor living. To protect against hearing damage,
one's 24-hour noise exposure at the ear should not exceed 70 dB.


MISUSES, MISUNDERSTANDINGS, AND QUESTIONS

  Perhaps the most fundamental  misuse of the Levels Document is treatment of the identified levels as
regulatory goals. They are not regulatory goals; they are levels defined by a negotiated scientific consen-
sus. These levels were developed without concern for economic and technological feasibility, are inten-
tionally conservative to protect the most sensitive portion of the American population, and include an addi-
tional margin of safety. In short, the levels  in Table VIII are neither more nor less than what Congress re-
                                                 24

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quired them to be: levels of environmental noise requisite to protect the public health and welfare with an
adequate margin of safety.
     Q.  Why doesn't the Levels Document explicity say how much noise is too much noise?
     A.  Decisions about how much noise is too much noise for whom, for how long, and under what
         conditions demand consideration of economic, political, and technological matters far beyond the
         intent of the Levels Document. Such decisions are properly embodied in formal regulations, not
         informational publications such as the Levels Document.
     Q.  How do I use this information for local purposes?
     A.  This question reflects the need to reconcile local economic and political realities with  scientific in-
         formation. People who formulate local noise abatement programs cannot escape the  responsibili-
         ty of making such economic and political compromises for their constituencies. The Levels Docu-
         ment does not impose arbitrary Federal decisions about the appropriateness of noise  en-
         vironments upon any level of government, nor is it a source of prescriptions for solving local
         noise problems. It is best viewed as a technical aid to local decision makers who seek to balance
         scientific information about effects of noise  on people with other considerations, such as cost
         and technical feasibility.
     Q.  If the identified noise levels are indeed sufficient to protect public health and welfare, shouldn't
         they be  considered to be long-range regulatory goals?
     A.  Attainment of the identified levels of environmental noise can only be considered idealized goals.
         Pragmatically,  it is unlikely that local, state,  or Federal regulatory strategies will seek to attain
         such levels for all situations in the near future.
     Q.  Why isn't the Levels  Document more definite  about specific effects associated with various  noise
         exposure conditions?
     A.  Available knowledge about the effects of noise would not support more precise statements. In-
         creasingly specific statements will be incorporated in future informational publications as they are
         justified  by increasing knowledge of  human  response to noise exposure.
                                                25

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
  EPA 550/9-79-100
                                                            3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE

  Protective  Noise Levels


  Condensed Version of EPA Levels  Document
             5. REPORT DATE
                November  1978
             6. PERFORMING ORGANIZATION CODE
                ONAC
 . AUTHOR(S)

  EPA Office  of Scientific Assistant to DAA/Noise
                                                            8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
                                                            10. PROGRAM ELEMENT NO.
  EPA/ONAC
                                                            11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
                                                            13. TYPE OF REPORT AND PERIOD COVERED
  Environmental  Protection Agency
  Office of  Noise Abatement S Control  (ANR-471)
  401 M Street,  S.W.
  Washington,  D.C. 20460
             14. SPONSORING AGENCY CODE
                EPA/ONAC
15. SUPPLEMENTARY NOTES
16. ABSTRACT

  This publication is intended to  promote understanding  of EPA's findings about
  levels of environmental noise that  protect public health and welfare.  It  seeks
  to clarify  the  proper use of the 1974 "Levels Document"  by interpreting its
  contents in  less technical terms.   The manual deals with measurement descriptors
  of environmental noise.  Also addressed are the best understood effects of noise
  on people (hearing damage, speech interference and annoyance).  Protective levels
  are summarized.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                             COS AT I Field/Group
  Environmental noise  levels, indoor and
  outdoor levels, measurement descriptors,
  noise exposure patterns,  hearing damage,
  speech interference,  annoyance, pro-
  tective noise exposures
18. DISTRIBUTION STATEMENT
  Limited supply available at EPA/ONAC or
  NTIS,  Springfield, VA  22151
19. SECURITY CLASS (This Report)

   Unclassified
                                                                          21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
-25.
                           22. PRICE
EPA Form 2220-1 (9-73)

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