550/9-74-004
INFORMATION ON LEVELS OF
ENVIRONMENTAL NOISE
REQUISITE TO PROTECT
PUBLIC HEALTH AND WELFARE
WITH AN ADEQUATE MARGIN
OF SAFETY
MARCH 1974
PREPARED BY
THE U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF NOISE ABATEMENT AND CONTROL
This document has been approved for general
availability. It does not constitute a standard,
specification, or regulation.
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TABLE CF CONTENTS
FOREWORD i
I. INTRODUCTION 1
A. Sunomary 1
B. Legislative History 6
II. ENVIRONMENTAL NOISE EXPOSURE 14
III. RATIONALE FOR IDENTIFICATION OF LEVELS OF ENVIRONMENTAL 21
NOISE REQUISITE TO PROTECT PUBLIC HEALTH AND WELFARE
A. Basis for Identifying Levels 21
B. Identification of Maximum Exposure Levels to Avoid
Significant (Measurable) Adverse Effects 25
1. Hearing 25
a. Basic Considerations 25
b. Explanation of Identified Level
for Hearing Loss 26
c. Adequate Margin of Safety 27
2. Activity Interference/Annoyance 2J3
a. Basic Considerations 29
b. Identified Levels of r
Interference 30
c. Adequate Margin of Safety 33
C. Maximum Exposure to Special Noises 34
1. Inaudible Sounds 34
a. Infrasound 34
b. Ultrasound 34
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Page
2. Impulse Noise 35
a. Hearing 35
b. Non-Audible Effects of Inroulsive
Sound 36
c. Sonic Booms 36
IV. IDENTIFIED LEVELS OF ENVIRONMENTAL NOISE IN DEFINED AREAS ... 38
A. Individual Levels 38
B. Use of Identified Environmental Noise Levels 43
V. REFERENCES 45
VI. APPENDICES
GLOSSARY
A. EQUIVALENT SOUND LEVEL AND ITS RELATIONSHIP TO OTHER
NOISE MEASURES
B. LEVELS OF ENVIRONMENTAL NOISE IN THE U.S. AND TYPICAL
EXPOSURE PATTERNS OF INDIVIDUALS
C. NOISE-INDUCED HEARING LOSS
D. NOISE INTERFERENCE WITH HUMAN ACTIVITIES AND RESULTING
OVERALL ANNOYANCE/HEALTH EFFECTS
B. GENERAL EFFECTS OF NOISE NOT DIRECTLY USED IN IDENTIFYING
LEVELS OF NOISE REQUISITE TO PROTECT PUBLIC HEALTH AND
WELFARE
F. EPA's RESPONSIBILITY TO IDENTIFY SAFE LEVELS FOR
OCCUPATIONAL NOISE EXPOSURE
G. IMPULSE NOISE AND OTHER SPECIAL NOISES
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FOREWORD
The Congress included among the requirements of the Noise Control
Act of 1972 a directive that the Administrator of the Environmental
Protection Agency "... develop and publish criteria with respect to
noise ..." and then "publish information on the levels of environ-
mental noise the attainment and maintenance of which in defined areas
under various conditions are requisite to protect the public health
and welfare with an adequate margin of safety."
Not all of the scientific work that is required for basing such levels
of environmental noise on precise objective factors has been completed.
Some investigations are currently underway, and the need for others has
been identified. These involve both special studies on various aspects of
effects of noise on humans and the accunulation of additional epidemiologi-
cal data. In some cases, a considerable period of time must elapse before
the results will be meaningful, due to the long-term nature of the investiga-
tions involved. Nonetheless, there is information available from which
extrapolations are possible and about which reasoned judgments can be made.
Given the foregoing, EPA has sought to provide information on the
levels of noise requisite to protect public health and welfare with
an adequate margin of safety. The information presented is based on
analyses, extrapolations and evaluations of the present state of
scientific knowledge. This approach is not unusual or different from
that used for other environmental stressors and pollutants. As
pointed out in "Air Quality Criteria" - Staff Report, Subcommittee on
Air and Water Pollution, Committee on Public Works, U.S. Senate,
July, 1968, .
The protection of public health is required action based upon best
evidence of causation available. This philosophy was appropriately
expressed by Sir E. B. Hill, 1962, when he wrote: All scientific
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work is incomplete - whether it be observational or experimental.
All scientific work is liable to be upset or modified by advancing
knowledge. That does not confer upon us freedom to lower the knowl-
edge we already have, or to postpone the action that it appears to
demand at a given time. The lessons of the past in general health
and safety practices are easy to read. They are characterized by
empirical decisions, by eternally persistent reappraisal of public
health standards against available knowledge of causation, by con-
sistently giving the public the benefit of the doubt, and by ever
striving for improved environmental quality with the accompanying
reduction in disease morbidity and mortality. The day of precise
quantitative measurement of health and welfare effects has not yet
arrived. Until such measurement is possible, action must be based
upon limited knowledge, guided by the principal of the enhancement
of the quality of human life. Such action is based on a philosophy
of preventive medicine.
The foregoing represents the approach taken by EPA in the preparation
of this present document on noise. As the fund of knowledge is expanded,
improved and refined, revisions of this docunent will occur.
The incorporation of a margin of safety in the identification
of non-hazardous levels is not new. In most cases, a statistical
determination is made of the lowest level at which harmful effects
could occur, and then an additional correction is applied as a.
margin of safety. In the case of noise, the margin of safety has
been developed through the application of a conservative approach
at each stage of the data analysis. The cumulation of these results
thus provides for the adequate margin of safety.
In should be born in mind that this Docunent is published to
present information required by the Noise Control Act, Section 5 (a) (2),
and that its contents do not constitute Agency regulations or
standards. Its statistical generalizations should not be applied
to a particular individual. Moreover, States and localities will
approach this information according to their individual needs and
situations.
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I. INTRODUCTION
The Noise Control Act of 1972 established by statutory mandate a national
policy "to promote an environment for all Americans free from noise that
jeopardizes their public health and welfare". The Act provides for a division
of powers between the Federal and state and local governments, in which the
primary Federal responsibility is for noise source emission control, with
the states and other political subdivisions retaining rights and authorities
for primary responsibility to control the use of noise sources and the levels
of noise to be permitted in their environment,
In order to provide adequately for the Federal emission control require-
ment and to insure Federal assistance and guidance to the state and localities,
the Congress has established two separate but related requirements with regard
to scientific information about health and welfare effects of noise. First,
the Environmental Protection Agency was called upon to publish descriptive
data on the effect of noise which might be expected fron various levels and
exposure situations. Such "criteria" statements are typical of other environ-
mental regulatory schemes. Secondly, the Agency is required to publish
"information" as to the levels of noise "requisite to protect the public
health and welfare with an adequate margin of safety".
A. Summary
The first requirement was completed in July, 1973, when the document
"Public Health and Welfare Criteria for Noise" was published. The present
document represents the second step. Much of the scientific material on
which this document is based was drawn from the earlier "Criteria Document",
while additional material was gathered from scientific publications and other
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sources, both fron the U.S. and abroad. In addition, two review meetings were
held which were attended by representatives of the Federal agencies as well
as distinguished neribers of the professional ccranunity and representatives
fron industrial and environmental associations. The reviewers' suggestions,
both oral and wHUen, »*t» m,,.^ WM^Uul atteuUun, and their connents
incorporated to the extent feasible and appropriate.
After a great deal of analysis and deliberation, levels were
identified to protect public health and welfare for a large number of
situations. These levels are subject to the definitions and qualifica-
tions contained in the Foreword. They are summarized in Table 1
according to the public health and welfare effect to be protected
against, the requisite sound level, and the areas which are appropriate
for such protection.
in order to identify these levels, a number of considerations and
hypotheses were necessary, which are listed below with reference to the
appropriate appendices where they are discussed in detail.
1. In order to describe the effects of environmental noise
in a simple, uniform and appropriate way, the best descriptors
are the long-term equivalent A-weighted sound level (Leq) and
a variation with a nighttime weighting, the day-night sound
level (I
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c. One cannot be damaged by sounds considered normally
audible, which one cannot hear.
d. Protecting the population up to a critical percentile
(ranked according to decreasing ability to hear) will
also protect those above that percentile, (in view of
consideration 4c above) thereby protecting virtually
the entire population.
3. To correct for intermittency and duration in identifying the
appropriate level to protect against hearing loss (also, see
Appendix C):
a. The Equal Energy Hypothesis
b. The TTS Hypothesis
4. To identify levels requisite to protect against activity
interference (see AppendixD):
a. Annoyance due to noise, as measured by conitunity surveys,
is the consequence of activity interference.
b. Of the various kinds of activity interference, speech inter-
ference is the one that is most readily quantifiable.
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T.ble 1
OF NOISE LEVELS IDENTIFIFD AS REQUISITE TO PBOTECT PUBLIC
HEALTH AND WELFARE WITH A\T ADEQUATE MARGIN OF SAFETY
(see T-5b4.e 4 for detailed description)
Effect
Level
Area
Hearing Loss
Leq(24) 6 70 dB
All areas
Outdoor activity
interference and
annoyance
55 dB
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.
Leq(24)-55dB
Outdoor areas where people
spend limited amounts of tine,
such as school yards, play-
grounds, etc.
Indoor activity
interference and
annoyance
Ldn -45 dB
Indoor residential areas
Leq(24) - 45 dB
Other indoor areas with human
activities such as schools, etc.
Explanation of Table 1 :
1. Detailed discussions of the terms L^, Lgq(8) an(^ Leq(24) aPPear
later in the document. Briefly, Leq(8) represents the sound energy
averaged over an 8-hour period while Leq(24) energy averages over
a 24-hour period. Lcjn represents the Lgq with a 10 dB nighttime
weighting.
2. The hearing loss level identified here represents annual averages
of the daily level over a period of forty years. (These are
energy averages, not to b - confused rf_ch arithmetic averages.)
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3. Relationship of an L /r>4x of 70 dB to higher exposure levels.
EPA has determined that for purposes of hearing conservation alone, a
level which is protective of that segment of the population at or below the
96th percentile will protect virtually the entire population. This level
has been calculated to be an LQQ of 70 dB over a 24-hour day.
Given this quantity, it is possible to calculate levels which, when
averaged over given durations shorter than 24 hours, result in equivalent
amounts of energy. For example, the energy contained in an 8-hour exposure
to 75 dB is equivalent to the energy contained in a 24-hour exposure to 70
dB. For practical purposes, the former exposure is only equivalent to the
latter when the average level of the remaining 16 hours per day is negligible
(i.e., no more than about 60 dB* for this case).
An Leq(g) of 75 is considered an appropriate level for this particular
duration because 8 hours is the typical daily work period. In addition, the
24-hour exposure level was derived from data on 8-hour daily exposures over
a 40-year working life. In planning comnunity noise abatement activities,
local governments should bear in mind the special needs of those residents
who experience levels higher than I«q(8) at 70 on their jobs.
These levels are not to be construed as standards as they do not take
into account cost or feasibility. Nor should they be thought of as discrete
numbers, since they are described in terras of energy equivalents. As speci-
fied in this document, it is EPA's judgment that the maintenance of levels
* This is not to imply that 80 dB is a negligible exposure level in terms
of health and welfare considerations, but rather that levels of 60 dB
make a negligible contribution to the energy average of Lgq = 70 dB when
an 8-hour exposure of 75 dB is included.
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of environmental noise at or below those specified above, are requisite to
protect the public from adverse health and welfare effects. Thus, as an
individual moves from a relatively quiet hone, through the transportation
cycle, to a somewhat noisier occupational situation, and then back home
again, his hearing will not be impaired if the daily equivalent of sound
energy in his environment is no more than 70 decibels. Likewise, undue
interference with activity and annoyance will not occur if outdoor levels
are maintained at an energy equivalent of 55 dB and indoor levels at 45
dB. However, it is always assumed throughout that environmental levels
will fluctuate even though the identified energy equivalent is not
exceeded. Likewise, human exposure to noise will vary during the day,
even though the daily "dose" may correspond well to the identified
levels.
Before progressing further, it would be helpful to differentiate between
the terms "levels", "exposure" and "dose". As used in this document, the
word "level" refers to the magnitude of sound in its physical dimension,
whether or not there are humans present to hear it. "Exposure" is used to
mean those sound levels which are transmitted to the human ear, and "dose"
is the sunmed exposure over a period of time.
B. Legislative History
Pursuant to Section 5(a)(l), EPA developed and published on
July 27, 1973, criteria reflecting:
. . . the scientific knowledge most useful in indicating
the kind and extent of all identifiable effects on the public
health or welfare which may be expected from differing
quantities and qualities of noise.
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Under Section 5(a)(l), EPA was required to provide scientific data
that, in its judgment, was most appropriate to characterize noise effects.
The present "levels information" document is required by Section
5(a)(2), which calls for EPA to publish,
. . . information on the levels of environmental noise the
attainment and maintenance of which in defined areas under
various conditions are requisite to protect the public health
and welfare with an adequate margin of safety.
The present document, and its approach to identifying noise levels
based on cumulative noise exposure is in response to the expressed intent of
the Congress that the Agency develop such a methodology. The EPA Report to
the President and Congress, under Title IV, PL 91-60, contained considerable
material on the various schemes for measuring and evaluating coranunity noise
response, and it contained a recommendation that the Federal government should
make an assessment of the large number of varying systems, with a goal of
"standardization, simplification, and interchangeability of data".
The need for such action was the subject of considerable Congressional
interest in the hearings on the various noise control bills, which finally
resulted in enactment of the Noise Control Act of 1972. The concept under-
lying this present document can be better appreciated from the following
pertinent elements of the legislative history of the Act.
In the course of the hearings before the Subcommttee on Public
Health and Environment of the Committee on Interstate and Foreign Commerce,
House of Representatives ("Noise Control" HR Serial 92-30), the subject of the
relation of physical noise measurements to human response was given considerable
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attention. The Ccranittee, in reporting the bill (House of Representatives
Report No. 92-842, Noise Control Act of 1972), stated the following on this
matter:
The Conmittee notes that most of the information relating to
noise exposures was concerned with specific sources, rather than
typical cumulative exposures to which urban and suburban dwellers
are commonly exposed. There is a need for much greater effort
to determine the magnitude and extent of such exposures and the
Conmittee expects the EPA to promote studies on this subject and
consider development of methods of uniform measurement of the
impact of noise on communities.
The Committee went on in the Report to assign responsibility to the
Administrator to coordinate all Federal noise programs, with a specific
expression of concern over the "different systems of noise measurement" in
use by the various Agencies. The following is especially important with respect
to the purposes of this document:
The Committee gave some consideration to the establishment of a
Federal ambient noise standard, but rejected the concept. Establish-
ment of a Federal ambient standard would in effect put the Federal
government in the position of establishing land use zoning require-
ments on the basis of noise. . . .It is the Committee's view that
this function is one more properly of the states and their political
subdivisions, and that the Federal Government should provide guidance
and leadership in undertaking that effort.
The need for EPA action on this subject under the legislative authority
of the Act was presented in Agency testimony before the Subcommittee on Air and
Water Pollution, Conmittee on Public Works, U.S. Senate. The following portion
is important (Noise Pollution Serial 92-H35 U.S. Senate):
A variety of specialized schemes have been evolved over the past
years to quantify the relationship between these various conditions
and their effects on humans. . . .Suffice it to say that no
simplistic single number system can adequately provide for a
uniform acceptable national ambient noise level value. This,
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however, does not preclude the undertaking of a noise abatement
strategy involving the proper use of the available scientific
data on the part of the Federal Government in conjunction with
the state and local governments. . . .The complex nature of the
considerations we have outlined above in our judgment require
that the Federal Government undertake to provide the necessary
information upon which to base judgments. . . .
Taking both the specific language of the Act, cited above, and the
legislative history discussed in the foregoing, EPA interprets Section 5(a)(2)
as directing the Agency to identify levels based only on health and welfare
effects and not on technical feasibility or economic costs.
Throughout this report, the words "identified level" are used to
express the result of the inquiry mandated by Section 5(a)(2). The words "goals",
"standards", or "reccranended levels" are not used since they are not appropriate.
Neither Congress nor the Environmental Protection Agency has reached the con-
clusion that these identified levels should be adopted by states and localities.
This is a decision which the Noise Control Act clearly leaves to the states and
localities themselves.
Certain of the statutory phrases in Section 5(a)(2) need further
definition and discussion in order to make clear the purpose of this docunent.
Congress required that EPA "publish information on environmental noise" levels.
This mandate is basically one of "description". Such description is to be
made in the specific context of "defined areas" and "under various conditions".
The phrase "in defined areas under various conditions" is used in both a
geographical and an activity sense, for example, indoors in a school classroom
or outdoors adjacent to an urban freeway. It also requires consideration not
only of the human activity involved, but also of the nature of the noise impact.
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The next and last statutory phrase in Section 5(a)(2) is most important.
It is that the noise levels are to be discussed on the basis of what is requisite
to protect "the public health and welfare wi£h an adequate margin of safety".
The use of the words "public health" requires a statistical approach to determine
the order of magnitude of the population affected by a given level of noise. The
concept of a margin of safety implies that every sector of the population which
would reasonably be exposed to adverse noise levels should be included by the
specifically described levels.
The phrase "health and welfare" as used herein is defined as "complete
physical, mental and social well-being and not merely the absence of disease
and infirmity". This definition would take into account sub-clinical and sub-
jective responses (e.g., annoyance or other adverse psychological reactions)
of the individual and the public. As will be discussed below, the available
data demonstrate that the most serious clinical health and welfare effect
caused by noise is interference with the ability to hear. Thus, as used in
this document, the phrase "health and welfare" will necessarily apply to those
levels of noise that have been shown to interfere with the ability to hear.
The phrase" health and welfare" also includes personal comfort and well-
being and the absence of mental anguish and annoyance. In fact, a considerable
portion of the data available on the" health and welfare" effects of noise is
expressed in terms of annoyance. However, "annoyance" is a description of the
human reaction to what is described as noise "interference"; and though
annoyance appears to be statistically quantifiable, it is a subjective reaction
to interference with some desired human activity. From a legal standpoint,
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annoyance per se is not a legal concept. Annoyance expresses the human
response or results, not its cause. For this reason, the common law has
never recognized annoyance as being a compensable injury, absent a showing
of an interference with a personal or property right. Of the many
community surveys on noise which have been conducted, speech interference
emerges as the most tangible component of annoyance, whereas sleep and
other kinds of activity interference are important, but less well-defined
contributors. Thus, although it is important to understand the importance
of annoyance as a concept, it is the actual interference with activity
on which the levels identified in this document are based.
There was a great deal of concern during the preparation of this
document that the levels identified would be mistakenly interpreted as
Federal noise standards. The information contained in this document
should not be so interpreted. The general purpose of this document is
rather to discuss environmental noise levels requisite for the protection
of public health and welfare without consideration of those elements
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necessary to an actual rule-making. Those elements not considered, in
this document Include economic and technological feasibility and
attitudes about the desirability of undertaking an activity which
produces interference effects. Instead, the levels identified here
will provide State and local governments as well as the Federal
Government and the private sector with an informational point of
departure for the purpose of decision-making.
An even more important, but related, point must be kept in mind
when this document is read. The data on which the informational levels
in this document are based are not "short run" or single event noises.
Rather, they represent energy equivalent noise levels over a long period.
For example, the exposure period which results in no more than 5 dB
hearing loss at the identified level is a period of forty years.
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The definition of "environmental noise" is provided in Section 3(11)
of the Noise Control Act of 1972. "The terra 'environmental noise' means the
intensity, duration, and the character of sounds from all sources." As dis-
cussed earlier, it is the intent of Congress that a simple, uniform measure
of noise be developed. Not all information contained in the noise environment
can be easily considered and analyzed. Instead, for practical purposes, it
needs to be condensed to result in one indicator of the environmental quantity
and quality of noise which correlates with the overall long-term effects of
noise on public health and welfare.
2 3
Many rating and evaluation procedures are available in the literature'
in voluntary national and international standards, and conroonly used engineering
practices, (see Appendix A). These methods and practices are well established,
and it is not the purpose of this document to list them, elaborate on them or
imply a restriction of their use. Instead, the purpose is to discuss levels of
environmental noise using a measure which correlates with other measures and
can be applied to most situations. Based on the concept of the cumulative
human exposure to environmental noise associated with the various life styles
of the population, maximum long-term exposures for individuals and the corre-
sponding environmental noise levels at various places can be identified. It
is iirportant to keep in mind that the selected indicator of environmental
noise does not correlate uniquely with any specific effect on human health or
performance. Admittedly, there are uncertainties with respect to effects in
individual cases and situations. Such effects cannot be completely accounted
for, thus, the necessity to employ a statistical approach.
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Section II of the report addresses the details of characterizing and
measuring human exposure to environmental noise. The equivalent sound level
(Lgq) and a variation weighted for nighttime exposure (I
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It is obvious that the practical application of the levels to the
various purposes outlined earlier requires considerations of factors not
discussed here. Although some guidance in this respect is included in
Section IV, not all problems can be anticipated and some of these questions
can only be resolved as the information contained in this report is considered
and applied. Such practical experiences combined with results of further
research will guide EPA in revising and updating the levels identified. In
this regard, it should be recognized that certain of the levels herein might
well be subject to revision when additional data are developed ,>
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II. ENVIRONMENTAL NOISE EXPOSURE
A complete physical description of a sound must describe its magnitude,
its frequency spectrum»and the variations of both of these parameters in time.
However, one must choose between the ultimate refinement in measurement
techniques and a practical approach that is no more complicated than necessary
to predict the impact of noise on people. The Environmental Protection Agency's
choice for the measurement of environmental noise is based on the following
considerations:
1. The measure should be applicable to the evaluation of pervasive long-
term noise in various defined areas and under various conditions over long
periods of time.
2. The measure should correlate well with known effects of the noise
environment on the individual and the public .
3. The measure should be simple, practical and accurate. In principle, it
should be useful for planning as well as for enforcement or monitoring purposes.
4. The required measurement equipment, with standardized characteristics,
should be comnercially available.
5, The measure should be closely related to existing methods currently
in use.
6. The single measure of noise at a given location should be predictable,
within an acceptable tolerance, from knowledge of the physical events producing
the noise.
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7. The measure should lend itself to small, simple monitors which can
be left unattended in public areas for long periods of time.
These considerations, when coupled with the physical attributes of
sound that influence human response, lead EPA to the conclusion that the
magnitude of sound is of most importance insofar as cumulative noise effects
are concerned. Long-term average sound level, henceforth referred to as
equivalent sound level (Leq), is considered the best measure for the magnitude
of environmental noise to fulfill the above seven requirements. Several ver-
sions of equivalent sound level will be used for identifvina levels
of sound in specific places requisite to protect public health and welfare.
These versions differ from each other primarily in the time intervals over
which the sound levels are of interest, and the correction factor employed.
Equivalent A-weighted sound level is the constant sound level that, in
a given situation and time period, conveys the same sound energy as the actual
time-varying A-weighted sound.* The basic unit of equivalent sound levels is the
decibel (see Appendix A), and the symbol for equivalent sound level is L .
Two sounds, one of which contains twice as much energy but lasts only half as
long as the other, would be characterized by the same equivalent sound level;
so would a sound with four times the energy lasting one fourth as long. The
relation is often called the equal-energy rule. A more complete discussion
of the computation of equivalent sound level, its evolution and application
to environmental noise problems, and its relationship to other measures used
to characterize environmental noise is provided in Appendix A.
* See Glossary for a detailed definition of terms. Note that when the term
"sound level" is used throughout this document, it always implies the use
of the A-weighting for frequency.
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The following caution is called to the attention of those who may
prescribe levels: It should be noted that the use of equivalent sound level
in measuring environmental noise will not directly exclude the existence of
very high noise levels of short duration. For example, an equivalent sound
level of 60 dB over a twenty-four hour day would permit sound levels of 110 dB
but would limit them to less than one second duration in the twenty-four hour
period. Comparable relationships between maximum sound levels and their per-
missible durations can easily be obtained for any combination, relative to any
equivalent sound level (see the charts provided in Appendix A).
Three basic situations are used in this document for the purpose of
identifying levels of environmental noise:
1. Defined areas and conditions in which people are exposed to environ-
mental noise for periods of time which are usually less than twenty-four hours,
such as school classrooms, or occupational settings.
2. Defined areas and conditions in which people are exposed to environ-
mental noise for extended periods of time, such as dwellings.
3. Total noise exposure of an individual, irrespective of area or
condition.
Three versions of equivalent sound level are used in this document in
order to accommodate the various modes of noise exposure that occur in these
situations. They are distinguished by the periods of time over which they are
averaged and the way in which the averaging is done.
1. L for 8-hour work day (Lgq/gO: This is the equivalent A-weighted
sound level (in decibels relative to 20 micropascals) computed over any
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continuous time period of eight hours identified with the typical occupational
exposure. As will be shown in later sections of this document, L ^g\ serves
as a basis for identifying environmental noise which causes damage to hearing.
2. L for 24-hour weighted for nighttime exposure (Lcfa): This formula
of equivalent level is used here to relate noise in residential environments
to chronic annoyance by speech interference and in some part by sleep and
activity interference. For these situations, where people are affected by
environmental noise for extended periods of time, the natural choice of dura-
tion is the 24-hour day. Most noise environments are characterized by
repetitive behavior from day to day, with some variation imposed by differences
between weekday and weekend activity, as well as some seasonal variation.
lb account for these variations, it has been found useful to measure environ-
mental noise in terms of the long-term yearly average of the daily levels.
In determining the daily measure of environmental noise, it is impor-
tant to account for the difference in response of people in residential areas
to noises that occur during sleeping hours as compared to waking hours. During
nighttime, exterior background noises generally drop in level from daytime
values. Further, the activity of most households decreases at night, lowering
the internally generated noise levels. Thus, noise events become more intru-
sive at night, since the increase in noise levels of the event over background
noise is greater than it is during the daytime.
Methods for accounting for these differences between daytime and
nighttime exposures have been developed in a number of different noise assess-
ment methods employed around the world, (see Appendix A). In general, the
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method vised is to characterize nighttime noise as more severe than corre-
sponding daytime events; that is, to apply a weighting factor to noise that
increases the numbers commensurate with their severity. Two approaches to
identifying time periods have been employed: one divides the 24-hour day
into two periods, the waking and sleeping hours, while the other divides the
24 hours into three periods — day, evening, and night. The weighting applied
to the non-daytime periods differs slightly among the different countries,
but most of them weight nighttime activities by about 10 dB. The evening
weighting, if used, is 5 dB.
An examination of the numerical values obtained by using two periods
versus three periods per day shows that for any reasonable distribution of
environmental noise levels, the two-period day and the three-period day are
essentially identical; i.e., the 24-hour equivalent sound levels are equal
within a few tenths of a decibel. Therefore, the simpler two-period day is
used in this document, with daytime extending from 7 a.m. to 10 p.m. and
nighttime extending from 10 p.m. to 7 a.m. The symbol for the 15-hour daytime
equivalent sound level is l^, the symbol for the 9-hour nighttime equivalent
sound level is 1^, and the day-night weighted measure is symbolized as L^.
The L^ is defined as the A-weighted average sound level in decibels
(re 20 micropascals) during a 24-hour period with a 10 dB weighting applied
to nighttime sound levels. Examples of the outdoor present day (1973) day-
night noise level at typical locations are given in Figure 1.
3. L-,, for the 24-hour average sound level to which an individual is
t*4
exposed (Leq(24))' This situation is related to the cumulative noise exposure
19
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QUALITATIVE
DESCRIPTIONS
DAY-NIGHT
SOUND LEVEL
DECIBELS
_90_ OUTDOOR LOCATIONS
LOS ANGELES— 3rd FLOOR APARTMENT NEXT TO
FREEWAY
CITY NOISE
(DOWNTOWN MAJOR 4C
METROPOLIS)
VERY NOISY _70-
NOISY URBAN
LL TOWN 8 _.,.
OUIET -50s-
SUBURBAN I!
LOS ANGELES- 3/4MILE FROM TOUCH DOWN AT
MAJOR AIRPORT
LOS ANGELES- DOWNTOWN WITH SOME CON-
STRUCTION ACTIVITY
- - \ HARLEM- 2nd FLOOR APARTMENT
BOSTON- ROW HOUSING ON MAJOR AVENUE
WATTS-8 MILES FROM TOUCH DOWN
AT MAJOR AIRPORT
NEWPORT- 3.5 MILES FROM TAKEOFF AT
SMALL AIRPORT
LOS ANGELES— OLD RESIDENTIAL AREA
FtLLMORE-SMALL TOWN CUL- de-SAC
SAN DIEGO- WOODED RESIDENTIAL
CALIFORNIA-TOMATO FIELD ON FARM
— 40—
Fieri ITS. 1
Outdoor Dav-Nlqht Sound Level in dB (re 20 micro-
pascals) at Various Locations4
20
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experienced by an individual irrespective of where, or under what situation,
this exposure is received. The long-term health and welfare effects of noise
on an individual are related to the cumulative noise exposure he receives over
a lifetime.
Relatively little is known concerning the total effect of such life-
time exposures, but dose-effect relations have been studied for two selected
situations:
a. The average long-term exposure to noise primarily in residential
areas leading to annoyance reactions and complaints.
b. The long-term effects of occupational noise on hearing, with the
daily exposure dose based on an eight-hour work day.
An ideal approach to identifying environmental noise levels in terms
of their effect on public health and welfare would be to start by identifying
the maximum noise not to be exceeded by individuals. However, the noise dose
that an individual receives is a function of lifestyle. For example, exposure
patterns of office workers, factory workers, housewives, and school children
are quite different. Within each group the exposures will vary widely as a
function of the working, recreational, and sleeping patterns of the individual.
Thus, two individuals working in the same office will probably accumulate
different total noise doses if they use different modes of transportation,
live in different areas, and have different TV habits. Examples of these
variations in noise dose for several typical life styles are provided in
Appendix B. However, detailed statistical information on the distribution
of actual noise doses and the relationship of these doses to long-term
21
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health and welfare effects is still missing. Therefore, a realistic approach
to this problem is to identify appropriate noise levels for places occupied
by people as a function of the activity in which they are engaged, including
a gross estimate of typical average exposure times.
From a practical viewpoint, it is necessary to utilize the wealth
of data relating to occupational noise exposure, some of it,albeit,subject
to interpretation, in order to arrive at extrapolations upon which the identi-
fication of safe levels for daily (24-hour) exposures can be based.
In the following sections of this report, the various modes of
exposure to noise and the human responses elicited will be discussed, leading
to the identification of appropriate noise exposure levels. In order to assist
the reader in associating these levels with numerical values of noise for
familiar situations, typical noise levels encountered at various locations
are listed in Table 2- For further assistance, Figure 2 provides an
estimate of outdoor noise levels for different residential areas.
III. RATIONALE FOR IDENTIFICATION OF LEVELS OF ENVIRONMENTAL NOISE
REQUISITE TO PBDTECT PUBLIC HEALTH AND WELFARE
A. Basis for Identifying Levels
For the identification of levels to protect against the direct,
disease-producing effects of noise, protection against hearing loss is the
guiding consideration. At this time, there is insufficient scientific evidence
that non-auditory diseases are caused by noise levels lower than those that
cause noise-induced hearing loss. In the event that future research renders
this conclusion invalid, this document will be revised accordingly (See
Appendix E).
22
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TABLE 2
EQUIVALENT SOUND LEVELS IN DECIBELS
NORMALLY OCCURRING INSIDE VARIOUS PLACES6
Space * Lcq(+)
Small Store (1-5 clerks) 60
Large Store (more than 5 clerks) . 65
Small Office (1-2 desks) 58
Medium Office (3-10 desks) 63
Large Office (more than 10 desks) 67
Miscellaneous Business 63
Residences
Typical movement of people - no TV or radio W " ^5
Speech at 10 feet, normal voice 55
TV listening at 10 feet, no other activity 55-60
Stereo music 50-70
(+) These measurements were taken over durations typical of the operation
of these facilities.
23
-------
300
100
10
I
•Estimated
Rural Areas
Aircraft
Incremen*
o
o
I
a.
3
u
Urban Noise
Freeway Increment
0.1
0.01
20
30
40
50
60
70
80
dB
Figure 2
Residential Noise Environment of the National Population As A
Function of Exterior Day-Night Average Sound Level (Ref B_5)
90
24
-------
In addition to direct disease-producing health effects, inter-
ference by noise with various human activities, such as speech-perception,
sleep, and thought can lead to annoyance and indirect effects on well-being.
All of these direct and indirect effects are considered here as effects on
public health and welfare. It is important to note, however, the distinction
between voluntary and involuntary exposures. Exposures to high levels of
environmental noise are often produced or sought by the individual. For
example, voluntary exposures to loud music are common. Consequently, the
concept of total individual noise dose with regard to annoyance, must be
applied only to involuntary exposure, although, of course, this argument
does not apply to the effects of noise on hearing.
A further consideration is the physical setting in which the exposure
takes place. Although there are no data to justify the assumption, it is
judged here that, whereas a small amount of speech interference in most out-
door places is not detrimental to public health and welfare, the same is not
true for most indoor environments. Based on this reasoning, adequate protec-
tion of the public against involuntary exposure to environmental noise requires
special consideration of physical setting and the communication needs associated
with each.
In the following Subsection B, the above rationale is applied to
identify the maximum noise level consistent with an adequate margin of safety
for the general classes of sound found most often in the environment. Certain
special classes of sound, such as infrasound, ultrasound, and impulsive sounds
are discussed in Subsection C.
25
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B. Identification of Maximum Exposure Levels to Avoid Significant
Adverse Effects
1. Hearing
a. Basic Considerations
The following considerations have been applied in identifying
the environmental noise levels requisite to protect the hearing of the general
population. For detailed derivation, justification and references, (see
Appendix C).
(1) The human ear, when damaged by noise, is typically
affected at the 4000 Hz frequency first, and, therefore, this frequency can
be considered the most noise-sensitive frequency. The averaged frequencies
of 500 Hz, 1000 Hz and 2000 Hz have traditionally been employed in hearing
conservation criteria because of their importance to the hearing of speech
sounds. Since there is considerable evidence that frequencies above 2000 Hz
are critical to the understanding of speech in lifelike situations, and since
4000 Hz is considered the most sensitive frequency, 4000 Hz has been selected
as the most important frequency to be protected in this document.
(2) Changes in hearing level of less than 5 dB are generally
not considered noticeable or significant.
(3) As individuals approach the high end of the distribution
and their hearing levels are decreased, they become less affected by noise
exposure. In other words, there comes a point where one cannot be damaged by
sounds which one cannot hear.
26
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(4) The noise level chosen protects against hearing loss up
to and including the 96th percentile of the population, ranked according to
decreasing ability to hear at 4000 Hz. By doing so, the percentiles above that
point are also protected (see previous point), thereby protecting virtually the
entire population against incurring more than a 5 dB noise-induced permanent
threshold shift.
b. Explanation of Identified Level for Hearing Loss
Taking into account the assumptions and considerations men-
tioned above, the 8-hour exposure level which protects virtually the entire
5 dB NIPTS is
population from greater that/73 dB, (see Figure 3). Before this value of 73
dB for 8-hour exposures can be applied to the environmental situation, however,
certain correction or conversion factors must be considered. These correction
factors are:
(1) Interim.ttency: allows the exposure level to be 5 dB
higher. This correction factor is required because most environmental noise
is inteimittent (not at a steady level, but below 65 dBA more than 10% of any
one-hour period) and intermittent noise has been shown less damaging than
continuous noise of the same LQQ. This correction should normally be applied
except in situations that do not meet this criterion for intermittency.
(2) Correction to yearly dose (250 to 365 days): requires
reduction of the exposure level by 1.6 dB. All data used as the basis of
Figure 3 come from occupational exposures which are only 250 days per year,
whereas, this document must consider all 365 days in a year.
(3) Correction to twenty-four hour day: the identified
level of 73 dB is based on 8-hour daily exposures. Conversion to a 24-hour
27
-------
period using the equal-energy rule requires reduction of this level by 5 dB.
This means that continuous sounds of a 24-hour duration must be 5 dB less
intense than higher level sounds of only 8 hours duration, with the remaining
16 hours considered quiet.
Using the above corrections and conversions implies that
the average 8-hr .daily dose (based on a yearly average and assuming intermittent
noise) should be no greater than I^_(g\ = 73 + 5 - 1.6 = 76.4 dB. Extending
the duration to 24 hours would yield a value of 71.4 dB. Ibr continuous noise,
this value would be 66.4 dB. However, since environmental noise is inter-
mittent, this level is below that which is considered necessary to protect
public health and welfare. In view of possible statistical errors in the basic
data, it is considered reasonable, especially with respect to a margin of safety,
to round down from 71.4 dB to 70 dB. Therefore, the level of intermittent
noise identified here for purposes of protection against hearing loss is:
Leq(24) = 70 <*
(For explanation of the relationship between exposures of Lgq^g) = 75 d
and L £24) = 70 dB, please see page 5.)
c. Adequate Margin of Safety
Section 5(a)(2), as stated previously, requires an adequate
margin of safety. The level identified to protect against hearing loss, is
based on three margin of safety considerations:
(1) The level protects at the frequency where the ear is
most sensitive (4,000 Hz).
28
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20
40 60
PERCENTAGE OF POPULATION
80
100
FIGURE 3 - Percentage of Exposed Population That Will
Incur No More Than 5 dB NIPTS Shown as a Function of
Exposure Level. Population Ranked by Decreasing Ability
to Hear at 4000 Hz. (See Appendix C for Rationale).
29
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(2) It protects virtually the whole population from
exceeding 5 dB NIPTS.
(3) It rounds off in the direction of hearing conserva-
tion, (downward) to provide in part for uncertainties in analyzing the data.
2. Activity Interference/Annoyance
a. Basic Considerations
The levels of environmental noise which interfere with human
activity (see Appendix D for detailed discussion) depend upon the activity and
its contextual frame of reference; i.e., they depend upon "defined areas under
various conditions". The effect of activity interference is often described
in terms of annoyance. However, various non-level related factors, such as
attitude towards the noise source and local conditions, may influence an
individual's reaction to activity interferences.
The levels which interfere with listening to a desired sound,
such as speech or music, can be defined in terms of the level of interfering
sound required to mask the desired sound. Such levels have been quantified for
speech conraunication by directly measuring the interference with speech
intelligibility as a function of the level of the intruding sound, relative
to the level of the speech sounds.
The levels interfering with human activities which do not
involve active listening have not been as well quantified relative to the
level of a desired sound. These relationships are more complicated because
interference caused by an intruding sound depends upon the background level
and the state of the human auditor; e.g., the degree of concentration when
30
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endeavoring to accomplish a mental task, or the depth of sleep, etc. For-
tunately, there is a wealth of survey data on comnunity reaction to environ-
mental noise which, although subject to some shortcomings when taken alone,
can be used to supplement activity interference data to identify noise levels
requisite to protect public health and welfare. Thus, the levels identified
here primarily reflect results of research on comnunity reaction and speech
masking.
b) Identified Levels for Interference
The level identified for the protection of speech
conrounication is an 1^ of 45 dB within the home in order to provide for
100% intelligibility of speech sounds. Allowing for the 15 dB reduction
in sound level between outdoors and indoors (which is an average amount
of sound attenuation that assumes partly-open windows), this level becomes
an outdoor I^g of 60 dB for residential areas. For outdoor voice com-
munication, the outdoor I^q of 60 dB allows normal conversation at
distances up to 2 meters with 95% sentence intelligibility.
Although speech-interference has been identified as the primary
interference of noise with human activities and is one of the primary reasons
for adverse ccranunity reactions to noise and long-term annoyance,
the 10 dB nighttime weighting (and, hence, the term L. ) is applied
to give adequate weight to all of the other adverse effects on activity
interference. For the same reason, a 5 dB margin of safety is applied
to the identified outdoor level. Therefore, the outdoor L, identified
on
for residential areas is 55 dB. (See Appendix E for relationship of
Leq t0 Ldn'>
The asHociaU*i interior day-night wound level within a typical
home which results from outdoors is 15 dB less, or 40 dB due to the attenuation
of the structure. The expected indoor daytime level for a typical neighborhood
which has an outdoor 1^ of 55 dB is approximately 40 dB, whereas the nighttime
31
-------
level is approximately 32 dB (see Figure A-7). This latter value is consistent
with the limited available sleep criteria (°-5). Additionally, these indoor
levels of 40 dB during the day and approximately 32 dB at night are consistent
with the background levels inside the home which have been reconmended by
acoustical consultants as acceptable for many years, (see Table D-10).
The effects associated with an outdoor day-night sound level
of 55 dB are summarized in Table 3. The sunraary shows that satisfactory
outdoor average sentence intelligibility may be expected for normal voice
conversations over distances of up to 3.5 meters; that depending on attitude
and other non-level related factors, the average expected community reaction
is none, although 1% may complain and 17% indicate "highly annoyed" when
responding to social survey questions; and that noise is the least important
factor governing attitude towards the area.
Identification of a level which is 5 dB higher than the 55
dB identified above would significantly increase the severity of the average
coranunity reaction, as well as the expected percentage of complaints and
annoyance. Conversely, identification of a level 5 dB lower than the 55 dB
> identified above would reduce the indoor levels resulting from outdoor noise
well below the typical background indoors, (see Table 3), and probably make
little change in annoyance since at levels below the identified level, individual
attitude and life style, as well as local conditions, seem to be more
important factors in controlling the resulting magnitude of annoyance or
coranunity reaction than is the absolute magnitude of the level of the intruding
noise.
32
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TABLE 3
vPxY OF HUXAN EFFuCTS IN TEPJ1S OF SPEED! CO.',-VJNICATIG:;, COMUNITY
REACT 10", CO>?!.AINTSt ANNOYANCE AND ATTITUDE TOV;,i.-.:3 AREA
ASSOCIATED WITH AH OUTDOOR DAY/IIICHY SOUND LEYU
OF 55 ti3 rs 20 MICBDPASCALS
Type of Effect
Speech - Indoors
- Outdoors
of Effect
Average Coir^unlty Reaction
Cor.pl ai nts
Annoyance
Attitudes Towards Area
0^ sentence intelligibility (average)
v;ith a 5 dB margin of safety
100% sentence intGlligibility (averts)
at 0.35 meters
93% sentence intelligibility (average)
• at 1.0 in
952 sentence intelligibility (average)
at 3.5 utters
None evident; 7dB below level of significant
"coir.pl ei nts and threats of lecjal acticri"
and at least 16 dB l-elav "vigorous action"
(attitudes and other non-level related
factors rnay affect this result)
}% dependent on attitude and other non-
level related factoi-s
17% dependent on attitude and other rion-
level related factors
Noise essentially the least important of
various factors
(REF: Derived from Appendix D)
33
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Accordingly, L^ of 45 dB indoors and of 55 dB outdoors in
residential areas are identified as the maximum levels below which no effects
on public health and welfare occur due to interference with speech or other
activity. These levels would also protect the vast majority of the population
under most conditions against annoyance, in the absence of intrusive noises
with particularly aversive content.
c. Adequate Margin of Safety
The outdoor environmental noise level identified in Table 3
provides a 5 dB margin of safety with respect to protecting speech communica-
tion. This is considered desirable for the indoor situation to provide for
homes with less than average noise reduction or for persons speaking with less
than average voice level. A higher margin of safety would be ineffective
most of the time due to normal indoor activity background levels.
The 5 dB margin of safety is particularly desirable to protect
the population against long-term annoyance with a higher probability than
would be provided by the levels protecting indoor and outdoor speech communica-
tion capability alone. The 5 dB margin clearly shifts coranunity response as
well as subjective annoyance rating into the next lower response category than
would be observed for the maximum level identified with respect to speech
comnunication alone. According to present data, this margin of safety pro-
tects the vast majority of the population against long-term annoyance by
noise. It vould reduce environmental noise to a level where it is
least important among environmental factors that influence
the population's attitude toward the environment. To
34
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define an environment that eliminates any potential annoyance by noise occa-
sionally to some part of the population appears not possible at the present state
of knowledge.
C. Maximum Exposures to Special Noises
1. Inaudible Sounds
The following sounds may occur occasionally but are rarely found
at levels high enough to warrant consideration in most environments which the
public occupies. For a more detailed discussion, see Appendix G.
a. Infrasound
Frequencies below 16 Hz are referred to as infrasonic fre-
quencies and are not audible. Complaints associated with extremely high
levels of infrasound can resemble a mild stress reaction and bizarre auditory
sensations, such as pulsating and fluttering. Exposure to high levels of
infrasound is rare for most individuals. Nevertheless, on the basis of
existing data^»^, the threshold of these effects is approximately 120 dB SPL
(1-16 Hz). Since little information exists with respect to duration of
exposure and its effects, and also since many of the data are derived fron
i-
research in which audible frequencies were present in some amount, these
results should be interpreted with caution.
b. Ultrasound
Ultrasonic frequencies are those above 20,000 Hz and are
also generally inaudible. The effects of exposure to high intensity ultrasound
is reported by some to be a general stress response. Exposure to high levels
of ultrasound does not occur frequently. The threshold of any effects for
o
ultrasound is 105 dB SPL . Again, many of these data may include frequencies
35
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within the audible range, and results are, therefore, to be interpreted
cautiously.
2. Impulse Noise
It is difficult to identify a single-number limit requisite to
protect against adverse effects from impulse noise because it is essential
to take into account the circumstances of exposure, the type of impulse, the
effective duration, and the number of daily exposures, (see Appendix G).
a. Hearing
Review of temporary threshold shift data leads to the con-
clusion that the impulse noise limit requisite to prevent more than a 5 dB
permanent hearing loss at 4000 Hz after years of daily exposure is a peak
sound pressure level (SPL) of 145 dB. This level applies in the case of
isolated events, irrespective of the type, duration,or incidence at the ear.
However, for duration of 25 microseconds or less, a peak level of 167 dB SPL
would produce the same effect, (see Figure 4),
(1) Duration Correction: When the duration of the impulse
is less than 25 microseconds, no correction for duration is necessary. For
durations exceeding 25 microseconds, the level should be reduced in accordance
with the "modified CHABA limit" shown in Figures 4, and G-i of Appendix G.
(2) Correction for Number of Impulses:
Number of impulses 1 10 100 103 104
per day:
Correction factor: 0 -10 -20 -30 -40 dB
(More detailed information is provided in Figure 4.)
36
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Furthermore, if the average interval between repeated
impulses is between 1 and 10 seconds, a third correction factor of -5 dB is
applied. Thus, to prevent hearing loss due to impulse noise, the identified
level is 145 dB SPL, or 167 dB peak SPL for impulses less than 25 microseconds,
for one impulse daily. For longer durations or more frequent exposures, the
equivalent levels are as shown in Figure 4.
b. Non-Auditory Effects of Impulsive Sound
Impulses exceeding the background noise by more than about
10 dB are potentially startling or sleep-disturbing. If repeated, impulsive
noises can be disturbing to some individuals if heard at all (they may be at
levels below the average noise levels). However, no threshold level can be
identified at this time; nor is there any clear evidence or documentation of
any permanent effect on public health and welfare.
c. Sonic Booms
Little or no public annoyance is expected to result from
one sonic boom during the daytime below the level of 0,75" pounds per square
foot (psf) as measured on the ground (see Appendix G). The same low
probability of annoyance is expected to occur for more than one boon per
day if the peak level of each boom is no greater than:
Peak Level = ' /\w psf
Where N is the number of booms. This value is in agreement with the
equal energy concept.
37
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MAX. PERMISSIBLE SPL-
MODIFIED CHABA L!?.V.TS
PARAMETER" 'NU.Y.BER OF
IMPULSES PER DAY.
10
0.025 0.05 O.I 0.2 0.5 I 2 5 10 20
B-DURAT10N (msec)
50 100 200 500 1000
Figure 4 - Set of Modified CHABA Limits for Daily Exposure
to Inpulse Noises Having B-Durations in the
Range 25 Microseconds to 1 Second. (Para-
meter: number (N) of impulses per daily expo-
sure. Criterion: NIPTS not to exceed 5 dB at
4 kHz in more than 10% of people.)
(KEF: Derived from Appendix G)
38
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IV. IDENTIFIED LEVELS OF ENVIRONMENTAL NOISE IN DEFINED AREAS
A. Identified Levels
Table 4 identifies the levels requisite to protect public
health and welfare with an adequate margin of safety for both activity
interference and hearing loss. The table classifies the various areas
according to the primary activities that are most likely to occur in
each. The following is a brief description of each classification
and a discussion of the basis for the identified levels in Table 4
For a more detailed discussion of hearing loss and activity interference,
see Appendices C and D>
1. Residential areas are areas where human beings live, including
apartments, seasonal residences,and mobile homes ,as well as year-round
residences. A quiet environment is necessary in both urban and rural
residential areas in order to prevent activity interference and annoyance,
and to permit the hearing mechanism to recuperate if it is exposed to higher
levels of noise during other periods of the day.
An indoor L, of 45 dB will permit speech ccmnunication in the home,
On
while an outdoor L - not exceeding 55 dB will permit normal speech communication
at approximately three meters. Maintenance of this identified outdoor level will
*
provide an indoor L^ of approximately 40 dB with windows partly open for
ventilation. The nighttime portion of this L^ will be approximately 32 dB, which
should in most cases, protect against sleep interference. An L
39
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TABLE 4
YEARLY AVERAGE EQUIVALENT SOUND LEVELS IDENTIFIED AS REQUISITE TO
PROTECT THE PUBLIC HEALTH AND WELFARE WITH AN ADEQUATE MARGIN OF SAFETY
Indoor
Outdoor
Residential with outside
space and Farm Residences
Residential with no outside
space
Commercial
Inside Transportation
Industrial
Hospitals
Educational
Recreational areas
Farm Land and General Unpopulated
i
S
Ldn
Leq(24)
Ldn
Leq(24)
Leq(24)
Leq(24)
Leq(24)(d)
Ldn
Leq(24)
^(.24)
. Leq(24)(d)
Leq(24)
£
eq(24)
«
o
0)
^1 M
JJ a)
•H M
•H 0)
•P JJ
O C
< H
45
45
(a)
(a)
(a)
45
45
(a)
no i M
CXKU -P (0 4-) 0)
Ct3 .W -P -H M-l
•H-H CO > H
V< 10 -H «J -HO)
nt C id u-i 4J 4J
JS
CO -H JJ 4J -— -
3** o o .c
nj M #Q v_x
D> fl) 4J to
c -a w 4J
•H-H CO
)H W -HO)
>0 C 18 <*-!
-------
6f 70 dB is identified as protecting against damage to hearing.
Although there is a separate category for connercial areas,
commercial living acccmodations such as hotels, motels, cottages, and
inns should be included in the residential category since these are
places where people sleep and sometimes spend extended periods of time.
2. Commercial areas include retail and financial service
facilities, offices, and miscellaneous commercial services. They do not
include warehouses, manufacturing plants,and other industrial facilities,
which are included in the industrial classification. Although a level for
activity interference has not been identified here (see footnote a), suggestions
for such levels will be found in Table MO of Appendix D. On the other
hand, a level of 1^(34) of 70 dB has been identified to protect against
hearing loss.
3. Transportation facilities are included so as to protect
individuals using public and private transportation. Included within
this classification are commercial and private transportation vehicles.
Identification of a level to protect against hearing loss is the only
criterion used at this time, although levels lower than an L of
eq
70 dB are often desirable for effective speech communication. However,
because of the great variety of conditions inside transportation
vehicles, and because of the desirability of speech privacy in certain
situations, a level based on activity interference cannot be identified
for all modes of transportation at this time.
4. Industrial areas include such facilities as manufacturing plants,
warehouses, storage areas, distribution facilities, and mining operations.
Only a level for hearing loss is identified due to the lack of data with
41
-------
respect to annoyance and activity interference. Where the noise exposure
is intermittent, an I^q(24) of 70 dB is identified as the maximum level
for protection of hearing from industrial exposure to intermittent noise.
For 8-hour exposures, an 1^(8) of 75 dB is considered appropriate so long
as the exposure over the remaining 16 hours per day is low enough to result
in a negligible contribution to the 24-hour average.
5. Hospital areas include the imnediate neighborhood of the
hospital as well as its interior. A quiet environment is required in
hospital areas because of the importance of sleep and adequate rest to
the recovery of patients. The maintenance of a noise level not exceeding
an Lfa of 45 dB in the indoor hospital environment is deemed adequate to
prevent activity interference and annoyance. An outdoor L^ of 55 dB should
be adequate to protect patients who spend some time outside, as well as insuring
an adequately protective indoor level. An 1^(24) of 70 dB is identified to
prevent hearing loss.
6. Educational areas include classrooms, auditoriums, schools
in general, and those grounds not used for athletics. The principal considera-
tion in the education environment is the prevention of interference with
activities, particularly speech conmunication. An indoor noise level not
exceeding I^eq(24) of 45 dB is identified as adequate to facilitate thought
and coranunication. Since teaching is occassionally conducted outside the
classroom, an outdoor I^q(24) of 55 dB is identified as the maximum level to
prevent activity interference. To protect against hearing loss an Lgq/24)
of 70 dB is identified for both indoor and outdoor environments. As in the
industrial situation, eight hours is generally the amount of time spent in
educational facilities. Therefore an I^q(8) of 75 dB is considered appropriate
to protect against hearing loss, so long as the exposure over the remaining
42
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16 hours is low enough to result in a negligible contribution to the
24-hour average.
7. Recreational areas include facilities where noise
exposure is voluntary. Included within this classification are nightclubs,
theaters, stadiums, racetracks, beaches, amusement parks, and athletic
fields. Since sound exposure in such areas is usually voluntary, there
is seldom any interference with the desired activity. Consequently, the
chief consideration is the protection of hearing. An L ,24) of 70 dB is
therefore identified for intermittent noise in order to prevent hearing
damage.
8. Farm and general Unpopulated Land primarily includes
agricultural property used for the production of crops or livestock.
For such areas, the primary considerations are the protection of
human hearing and the prevention of adverse effects on domestic and
wild animals. Protection of hearing requires that an individual's
exposure to intermittent noise do&s not exceed Leac24>\ °^ 70 dB.
A separate level for the exposure of animals is not identified due to
the lack of data indicating that hearing damage risk for animals is
substantially different from that of humans. The unpopulated areas include
wilderness areas, parks, game refuges, and other areas that are set aside
to provide enjoyment of the outdoors. Although quiet is not always of
paramount importance in such areas, many individuals enjoy the special
qualities of serenity and tranquility found in natural areas. At this time
it is not possible to identify an appropriate- level to prevent activity
interference and annoyance. However, when it becomes possible to set such
a level, a clear distinction should be made between natural and man-made noise.
43
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B. Use of Identified Environmental Noise Levels
One of the purposes of this document is to provide a basis for
judgment by states and local governments as a basis for setting standards.
In doing so the information contained in this document must be utilized
along with other relevant factors. These factors include the balance
between costs and benefits associated with setting standards at particular
noise levels, the nature of the existing or projected noise problems in any
particular area, the local aspirations and the means available to control
environmental noise.
In order to bring these factors together, states, local governments
and the public will need to evaluate in a systematic manner the following:
1. The magnitude of existing or projected noise environments
in defined areas as compared with the various levels identified in this
document.
2. The community expectations for noise abatement with respect
to existing or projected conditions.
3. The affected elements of the public and the degree of impact
of present or projected environmental noise levels.
4. The noise sources, not controlled by Federal regulations,
that cause local noise problems.
5. Methods available to attack environmental noise problems
(use limitations, source control through noise emission standards, compatible
land use planning, etc.).
6. The costs inherent in reducing noise to certain levels and
benefits achieved by doing so.
44
-------
7. The availability of technology to achieve the desired
noise reduction.
The levels of environmental noise identified in this report
provide the basis for assessing the effectiveness of any noise abate-
ment program. These noise levels are identified irrespective of the
nature of any individual noise source. One of the primary purposes
of identifying environmental noise levels is to provide a basis by
which noise source emission regulations, human exposure standards,
land use planning, zoning, and building codes may be assessed, as to the
degree with which they protect the public health and welfare with respect
to noise. Such regulatory action must consider technical feasibility and
economic reasonableness, the scale of time over which results can be
expected, and the specific problems of enforcement. In the process of balancing
these conflicting elements, the public health and welfare consequence
of any specific decision can be determined by comparing the resultant noise
environment against the environmental noise levels identified in this report.
45
-------
REFERENCES
1. Noise Control Act of 1972, Public Law 92-574, 92 Congress, HR 11021,
October 27, 1972.
2. Public Health and Welfare Criteria for Noise, EPA, July 27, 1973,550/9-73-002.
3. "Report to the President and Congress on Noise," EPA, NRC 500.1,
December 31, 1971.
4. "Impact Characterization of Noise Including Implications of Identifying
and Achieving Levels of Cumulative Noise Exposure," 1973, EPA Report #
NTID 73.4.
5. Proceedings of the Conference on Noise as a Public Health Problem,
EPA Report 550/9-73-008.
6. Seacord, D.F., J. Acoustical Society of America, 12: 183, 1940.
7. Johnson, D., "Various Aspects of Infrasound," presented at the Colloquin on
Infrasound, Centre National de la Recherche Scientifique Paris, Sept 1973.
46
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APPENDICES
-------
GLOSSARY
I. Definitions
AUDIBLE RANGE (OF FREQUENCY) (AUDIO-FREQU.:NCY RANGE). The
frequency range 16 Hz to 20,000 Hz
(20 kHz). Note; Thi ; is conventionally
taken to be the normal frequency rango
of human hearing.
AUDIOMETER. An instrument for measuring the threshold or
sensitivity of hearing.
AUDIOMETRY. The measurement of hearing.
BROAD-BAND NOISE. Noise whose energy is distributed over a
broad range of frequency (generally
speaking, more than one octave).
CONTINUOUS NOISE. On-going noise whose intensity remains at
a measurable level (which may vary) with-
out interruption over an indefinite
period or a specified period of time.
DEAFNESS. 100 percent impairment of hearing associated with
an otological condition. Note: This is
defined for medical and cognate
purposes in terms of the hearing threshold
level for speech or the average hearing
threshold level for pure tones of 500,
1000 and 2000 Hz in excess of 92 dB.
EQUIVALENT SOUND LEVEL. The level of a constant sound which, in a given
situation and time period, has the same sound
energy as does a time-varying sound. Technically,
equivalent sound level is the level of the time-
weighted, mean square, A-weighted sound pressure.
The time interval over which the measurement is
taken should always be specified.
ENVIRONMENTAL NOISE. By Sec 3 (11) of the Noise Control Act of 1972, the
term "environmental noise" means the intensity, dura-
tion, and character of sounds from all sources.
Glossary-l
-------
HEARING LEVEL. The difference in sound pressure level between
the threshold sound for a person ( or the
median value or the average for a group)
and the reference sound pressure level
defining the ASA standard audiometric
threshold (ASA: 1951). Note: The term is
now commonly used to mean hearing threshold
level (qv). Units: decibels.
HEARING LOSS. Impairment of auditory sensitivity: an elevation
of a hearina threshold level.
HEARING THRESHOLD LEVEL. The amount by which the threshold of
hearing for an ear (or the average for a
group) exceeds the standard audiometric
reference zero (ISO, 1964; ANSI, 1969).
Units: decibels.
IMPULSE NOISE (IMPULSIVE NOISE). Noise of short duration
(typically, less than one second) especially
of high intensity, abrupt onset and rapid
decay, and often rapidly changing spectral
composition. Note: Impulse noise is charac-
teristically associated with such sources
as explosions, impacts, the discharge of
firearms, the passage of super-sonic air-
craft (sonic boom) and many industrial
processes.
INFRASONIC. Having a frequency below the audible range tor man
(customarily deemed to cut off at 16 Hz).
INTERMITTENT NOISE. Fluctuating noise whose level falls once or more
times to low or immeasurable values during an
exposure. In this document intermittent noise
will mean noise that is below 65 dBA at least
10% of any 1 hour oeriod.
NOISE EXPOSURE. The cumulative acoustic stimulation reaching
the ear or the person over a specified
period of time (eg, a work shift, a day,
a working life, or a lifetime).
NOISE HAZARD (HAZARDOUS NOISE). Acoustic stimulation of the
ear which is likely to produce noise-
induced permanent threshold shift in
some of a population.
Glossary-2
-------
NOISE-INDUCED PERMANENT THRESHOLD SHIFT (NIPTS). Permanent
threshold shift caused by noise exposure,
corrected for the effect of aging (presby-
acusis).
NOISE-INDUCED TEMPORARY THRESHOLD SHIFT (NITTS). Temporary
threshold shift caused by noise exposure.
NON-VOLUNTARY EXPOSURE TO ENVIRONMENTAL NOISE. The exposure of an
individual to sound which (1) the individual
cannot avoid or (2) the sound serves no useful
purpose (e.g., the exposure to traffic noise or
exposure to noise from a lawn mower).
OCCUPATIONAL EXPOSURE TO ENVIRONMENTAL NOISE. The noise exposure of an
individual defined under P.L. 91-596, Occupational
Safety and Health Act of 1970.
OTOLOGICALLY NORMAL. Enjoying normal health and freedom from
all clinical manifestations and history of
ear disease or injury; and having a patent
(wax-free) external auditory meatus.
PEAK SOUND PRESSURE. The absolute maximum value (magnitude)
of the instantaneous sound pressure
occurring in a specified period of time.
PRESBYACUSIS (PRESBYCUSIS). Hearing loss, chiefly involving
the higher audiometric frequencies above
3000 Hz, ascribed to advancing age.
RISK. That percentage of a population whose hearing level, as
a result of a given influence, exceeds the
specified value, minus that percentage whose
hearing level would have exceeded the speci-
fied value in the absence of that influence,
other factors remaining the same. Note;
The influence may be noise, age, disease.,
or a combination of factors.
Glossary-3
-------
SOUND LEVEL.
The quantity in decibels measured by a sound level meter
satisfying the requirements of American National
Standards Specification for Sound Level Meters
SI.4-1971. Sound level is the frequency-weighted
sound pressure level obtained with the standardized
dynamic characteristic "fast" or "slow" and
weighting A, B, or C; unless indicated otherwise,
the A-weighting is understood. The unit of any
sound level is the decibel, having the unit symbol
dB.
SOUND tXPOSURt LEVEL,
The level of sound accumulated over a given time
interval or event. Technically, the sound exposure
level is the level of the time-integrated mean
square A-weighted sound for a stated time interval
or event, with a reference time of one second.
SOUND PRESSURE LEVEL.
In decibels, 20 times the logarithm to the base
ten of the ratio of a sound pressure to the
reference sound pressure of 20 micropascals (20
micronewtons per square meter). In the absence
of any modifier, the level is understood to be
that of a mean-square pressure.
SPEECH DISCRIMINATION. The ability to distinguish and under-
stand speech signals.
TEMPORARY THRESHOLD SHIFT (TTS). That component of threshold
shift which shows a progressive reduction
with the passage of time after the apparent
cause has been removed.
THRESHOLD OF HEARING (AUDIBILITY). The minimum ettective sound
pressure level of an acoustic signal
capable of exciting the sensation of hearing
in a. specified proportion of trials in
prescribed conditions of listening.
ULTRASONIC.
Having a frequency above the audible range for
man (conventionally deemed to cut off
at 20.000 Hz).
Glossary-4
-------
II. Abbreviations
AAOO American Academy of Ophthalmology and Otolaryngology
APR Air Force Regulation
AI Articulation Index
AMA American Medical Association
ANSI American National Standards Institute (formerly USASI)
ASHA American Speech and Hearing Association
CHABA Committee on Hearing and Bio-Acoustics
dBA A-weighted decibel (decibels). Also written dB(A).
EPA Environmental Protection Agency
IEC International Electrotechnical Commission
ISO International Oraanization for Standardization
NIOSH National Institute for Occupational Safety and Health
NIPTS Noise-Induced Permanent Threshold Shif+
NITTS Noise-Induced Temporary Threshold Shift-
NPL Noise Pollution Level (also National Physical Laboratory
in England,
NR Noise Rating
OSHA Occupational Safety and Health Act
RMS Root Mean square
SIL Soeech Interference Level
SPL Sound Pressure Level
TTS Temporary Threshold Shift
TTS-, TTS determined 2 minutes after cessation of exposure
Glossa.ry-5
-------
III. Symbols
L/t\ Time-varying noise level
LA A-weighted sound level
l_b "Background" or "residual" sound level, A-weighted
LH Daytime equivalent A-weighted sound level between the hours
of 0700 and 2200
Le Sound exposure level - the level of sound accumulated during
a given event.
Ldn Day-night average sound level - the 24 hour A-weighted
equivalent sound level, with a 10 decibel penalty applied
to nighttime levels
Leq Equivalent A-weighted sound level over a given time interval
l-eq(8) Equivalent A-weighted sound level over eight hours
Leq(24) Bquivalent A-weighted sound level over 24 hours
Lh Hourly equivalent A-weighted sound level
Ln Nighttime equivalent A-weighted sound level between the hours
of 2200 and 0700
Lmax ^ximum A-weighted sound level for a given time interval or
event
Lx x.percent sound level, the A-weighted sound level equaled or
exceeded x% of time
AL Difference in decibels between two different A-weighted sound
levels
Glossary-6
-------
APPENDIX A
EQUIVALENT SOUND LEVEL AND ITS RELATIONSHIP
TO OTHER NOISE MEASURES
I. Development of Equivalent Sound Level
The accumulated evidence of research on human response to sound
indicates clearly that the magnitude of sound as a function of frequency
and time are basic indicators of human response to sound. These
factors are reviewed here, and it is concluded that it is not necessary
to invent a new concept for the purpose of identifying levels of environ-
mental noise.
A. Magnitude
Sound is a pressure fluctuation in the air; the magnitude of
the sound describes the physical sound in the air; (loudness, on the
other hand, refers to how people judge the sound when they hear it).
Magnitude is stated in terms of the amplitude of the pressure fluctua-
tion. The range of magnitude between the faintest audible sound and
the loudest sound the ear can withstand is so enormous (a ratio of
about 1,OOO,OOO to 1) that it would be very awkward to express sound
pressure fluctuations directly in pressure units. Instead, this
range is "compressed" by expressing the sound pressure on a logarithmic
scale. Thus, sound is described in terms of the sound pressure level
(SPL), which is ten times the common logarithm of the ratio of the
square of the sound pressure in question to the square of a (stated
or understood) reference sound pressure, almost always 20
A-l
-------
micropascals. * or, in mathematical terms, sound pressure level L
expressed in decibels is:
/ 2
L = 10 log p/'\ (Bq. A-l)
where p is the pressure fluctuation and p is the reference pressure.
B. Frequency Characteristics of Noise
The response of human beings to sound depends strongly on
the frequency of sound. In general, people are less sensitive to
sounds of low frequency, such as 1OO hertz (Hz)**, than to sounds at
1000 Hz; also at high frequencies such as 8000 Hz, sensitivity decreases.
Two basic approaches to compensate for this difference in response to
different frequencies are (1) to segment the sound pressure spectrum
into a series of contiguous frequency bands by electrical filters so
as to display the distribution of sound energy over the frequency range;
or (2) to apply a weighting to the overall spectrum in such a way that
the sounds at various frequencies are weighted in much the same way as
the human ear hears them.
In the first approach a sound is segmented into sound
pressure levels in 24 different frequency bands, which may be used to
calculate an estimate of the "loudness" or "noisiness" sensation which
the sound may be expected to cause. This form of analysis into bands
*One pascal = one newton per square meter.
**Hertz is the international standard unit of frequency, until recently
called cycles per second ; it refers to the number of pressure fluctua-
tions per second in the sound wave.
A-2
-------
is usually employed when detailed engineering studies of noise sources
are required. It is much too complicated for monitoring noise
exposure.
To perform such analysis, especially for time-varying sounds,
requires a very complex set of equipment. Fortunately, much of this
complication can be avoided by using approach 2 , i.e., by the use
of a special electrical weighting network in the measurement system.
This network weights the contributions of sounds of different frequency
so that the response of the average human ear is simulated. Each
frequency of the noise then contributes to the total reading an amount
approximately proportional to the subjective response associated with
that frequency. Measurement of the overall noise with a sound level
meter incorporating such a weighting network yields a single number,
such as the A-weighted Sound Level, or simply A-level, in decibels.
For zoning and monitoring purposes,this marks an enormous simplifica-
tion. For this reason,the A-level has been adopted in large-scale
surveys of city noise coming from a variety of sources. It is widely
accepted as an adequate way to deal with the ear's differing sensitivity
to sounds of different frequency, including assessment of noise with
respect to its potential for causing hearing loss. Despite the fact
that more detailed analysis is frequently required for engineering
noise control, the results of such noise control are adequately des-
cribed by the simple measure of sound level.
A-3
-------
One difficulty in the use of a weighted sound level is that
psychoacoustic judgment data indicate that effects of tonal components
are sometimes not adequately accounted for by a simple sound level.
Some current ratings attempt to correct for tonal components; for
example, in the present aircraft noise certification procedures,
"Noise Standards: Aircraft Type Certification," FAR Part 36, the
presence of tones is identified by a complex frequency analysis pro-
cedure. If the tones protrude above the adjacent random noise spectrum,
a penalty is applied beyond the direct calculation of perceived noise
level alone. However, the complexities involved in accounting for
tones exceed practicable limits for monitoring noise in the community
or other defined areas. Consequently, EPA concludes that, where
appropriate, standards for new products will address the problem of
tones in such a way that manufacturers will be encouraged to minimize
them and, thus, ultimately they will not be a significant factor in
environmental noise.
With respect to both simplicity and adequacy for character-
izing human response, a frequency-weighted sound level should be used
for the evaluation of environmental noise. Several frequency weightings
have been prpposed for general use in the assessment of response to
noise, differing primarily in the way sounds at frequencies between
100O and 4000 Hz are evaluated. The A-weighting, standardized in
current sound level meter specifications, has been widely used for
A -1
transportation and community noise description. For many noises
-------
the A-weighted sound level has been found to correlate as well with
human response as more complex measures, such as the calculated per-
ceived noise level or the loudness level derived from spectral
A-2
analysis. However, psychoacoustic research indicates that, at
least for some noise signals, a different frequency weighting which
increases the sensitivity to the 100O-40OO Hz region is more re-
A-3
liable . Various forms of this alternative weighting function have
been proposed; they will be referred to here as the type "D-weightings".
None of these alternative weightings has progressed in acceptance to
the point where a standard has been approved for commercially available
instrumentation.
It is concluded that a frequency-weighted sound pressure
level is the most reasonable choice for describing the magnitude of
environmental noise. In order to use available standardized instru-
mentation for direct measurement, the A frequency weighting is the
only suitable choice at this time.* The indication that a type
D-weighting might ultimately be more suitable than the A-weighting
for evaluating the integrated effects of noise on people suggests that
at such time as a type D^weighting becomes standardized and available
in commercial instrumentation, its value as the weighting for environ-
mental noise should be considered to determine if a change from the
A-weighting is warranted.
*A11 sound levels in this report are A-weighted sound pressure levels
in decibels with reference to 20 micropascals.
A-5
-------
C. Time Characteristics of Noise
The dominant characteristic of environmental noise is
that it is not steady—at any particular location the noise usually
fluctuates considerably, from quiet at one instant to loud the next.
Thus, one cannot simply say that the noise level at a given location
or that experienced by a person at that location -is "so many decibels"
unless a suitable method is used to average the time-varying levels.
To describe the noise completely requires a statistical approach.
Consequently, one should consider the 'noise exposure which is
received by an individual moving through different noisy spaces.
This exposure is related to the whole time-varying pattern of sound
levels. Such a noise exposure can be described by the cumulative
distribution of sound levels, showing exactly what percent of the
whole observation period each level was exceeded.
A complete description of the noise exposure would distin-f
guish between daytime, evening and nighttime, and between weekday and
weekend noise level distributions. It would also give distributions
to show the difference between winter and summer, fair weather and
foul.
The practical difficulty with the statistical methodology
is that it yields a large number of statistical parameters for each
measuring location; and even if these were averaged over more or less
homogeneous neighborhoods, it still would require a large set of
numbers to characterize the noise exposure in that neighborhood. It
-------
is literally impossible for any such array of numbers to be effectively
used either in an enforcement context or to map existing noise
exposure baselines.
It is essential, therefore, to look further for a suitable
single-number measure of noise exposure. Note that the ultimate goal
is to characterize with reasonable accuracy the noise exposure of
whole neighborhoods (within which there may actually exist a fairly
wide range of noise levels), so as to prevent extremes of noise
exposure at any given time, and to detect unfavorable trends in the
future noise climate. For these purposes, pinpoint accuracy and
masses of data for each location are not required, and may even be a
hindrance, since one could fail to see the forest for the trees.
A number of methodologies for combining the noise from
both individual events and quasi-steady state sources into measures
of cumulative noise exposure have been developed in this country and
in other developed nations, e.g., Noise Exposure Forecast, Composite
Noise Rating, Community Noise Equivalent Level, Noise and Number
Index, and Noise Pollution Level. Many of these, methodologies, while
differing in technical detail (primarily in the unit of measure for
individual noise events), are conceptually similar and correlate
fairly well with each other. Further, using any one of these method-
ologies, the relationships between cumulative noise exposure and
A-4 A-5
community annoyance ' also correlate fairly well. It is there-
fore unnecessary to invent a new concept for the purpose of identi-
fying levels of environmental noise. Rather, it is possible to select
A-7
-------
a consistent measure that is based on existing scientific and practical
experience and methodology and which meets the criteria presented in
Section II of the body of this document. Accordingly, the Environ-
mental Protection Agency has selected the Equivalent sound Level
(L ) for the purpose of identifying levels of environmental noise.
Equivalent Sound Level is formulated in terms of the
equivalent steady noise level which in a. stated period of time would
contain the same noise energy as the time-varying noise during the
same time period.
The mathematical definition of L for an interval defined
eq
as occupying the period between two points in time t and t is:
Leq '
10 log
^/,
(Eq. A-2)
where p(t) is the time varying sound pressure and p is a reference
pressure taken as 2O micropascals.
The concept of Equivalent Sound Level was developed in
both the United States and Germany over a period of years. Equivalent
level was used in the 1957 original Air Force Planning Guide for
noise from aircraft operations, " as well as in the 1955 report
on criteria for short-time exposure of personnel to high intensity
jet aircraft noise, which was the forerunner of the 1956 Air Force
A-8
-------
A-8
Regulation on "Hazardous Noise Exposure". A more recent applica-
tion is the development of CNEL (Community Noise Equivalent Level)
measure for describing the noise environment of airports. This
measure, contained in the Noise Standards, Title 4, Subchapter 6,
of the California Administrative Code (1970) is based upon a summation
of L over a 24-hour period with weightings for exposure during
eq
evening and night periods.
The Equivalent Noise Level was introduced in 1965 in
Germany as a rating specifically to evaluate the impact of aircraft
A-9
noise upon the neighbors of airports • it was almost immediately
recognized in Austria as appropriate for evaluating the impact of
A-10 A-ll
street traffic noise in dwellings , and in schoolrooms • It
A-12
has been embodied in the National Test Standards of both East Germany"
A-13
and West Germany for rating the subjective effects of fluctuating
noises of all kinds, such as from street and road traffic, rail traffic,
canal and river ship traffic, aircraft, industrial operations (includ-
ing the noise from individual machines), sports stadiums, playgrounds,
A-14
etc. It is the rating used in both the East German and West
A-15
German standard guidelines for city planning. It was the rating
that proved to correlate best with subjective response in the large
Swedish traffic noise survey of 1966-67. it has come into such
general use in Sweden for rating noise exposure that commercial
instrumentation is currently available for measuring L directly;
the lightweight unit is small enough to be held in one hand and can
A-16
be operated either from batteries or an electrical outlet.
A-9
-------
The concept of representing a fluctuating noise level in
terms of a steady noise having the same energy content is widespread
in recent research, as shown in the EPA report on Public Health and
Welfare Criteria for Noise (1973). There is evidence that it
accurately describes the onset and progress of permanent noise-induced
A-17
hearing loss > and substantial evidence to show that it applies to
A-18
annoyance in various circumstances • The concept is borne out by
A-19
Pearsons' experiments on the trade-off of level and duration of
a noisy event and by numerous investigations of the trade-off between
A-20
number of events and noise level in aircraft flyovers • Indeed,
A-21
the Composite Noise Rating is a formulation of L , modified by
corrections for day vs. night operations. The concept is embodied
in several recommendations of the International Standards Organization,
A—22
for assessing the noise from aircraft", industrial noise as it
** + •* A-23 . ,. . . - . . A-24
affects residences , and hearing conservation in factories •
II. Computation of Equivalent Sound Level
In many applications >it is useful to have analytic expressions
for the equivalent sound level L in terms of simple parameters of
the time-varying noise signal so that the integral does not have
to be computed. it is often sufficiently accurate to approximate
a complicated time-varying noise level with simple time patterns.
For example, industrial noise can often be considered in terms of
a specified noise level that is either on or off as a function of
time. Similarly, individual aircraft or motor vehicle noise events
can be considered to exhibit triangular time patterns that occur
A-10
-------
intermittently during a period of observation. (Assuming an aircraft
flyover time pattern "to be triangular in shape instead of shaped like
a "normal distribution function" introduces an error of, at worst,
0.8 dB). Other noise histories can often be approximated with
trapezoidal time pattern shapes.
The following sections provide explicit analytic expressions for
estimating the equivalent sound level in terms of such time patterns,
and graphic design charts are presented for easy application to
practical problems. Most of the design charts are expressed in
terms of the amount (AL) that the level (L) of the new noise source
exceeds an existing background noise level, L, . (£L = L - L, ). This
background noise may be considered as the equivalent sound level that
existed before the introduction of the new noise, provided that its
fluctuation is small relative to the maximum value of the new noise
level.
A-ll
-------
A. Constant Level Noise - Steady or Intermittent
The L for a continuous noise having a constant value of
eq
L is
max
L = L , which is derived from
eq max
max
L = lOlog 1 r1 . ... .
^ Tj 10X 'U /dtSLjiax(dB) (Bq. A.3)
i ^
When L is intermittently on during the time period T for a fraction
max .
x of the total time, with a background noise level L, present for the
time fraction (1-x), L is given by:
Leq = Lb + lOlog L (1-x) * x V° / J (dB) (Bq'
where AL = L^^. - L^. This pattern is illustrated and the expression is
plotted in Figure A-1 for various values of L and x. For values of
Lmax that are 10 ^ or more higher than L,, L is approximated quite
accurately by:
Leq = Lmax + 10 lo9 x <<«)
-------
•D
O
T3
•O
X
O
H
I
•J
H
*
A-13
-------
duration T for
These results may be described by:
- Lfc greater than 1O is given in Figure A-2.
(Eq. A-6)
for (L
> 10
-max " Lb>
B. Triangular Time Patterns
The equivalent sound level for a single triangular time
pattern having a maximum value of L and rising from a background
level of L, is given by:
Leq - Lb
101°9
10
oir o°
10
(dB) (Bq. A-7)
where again AL = Lmax - Lfa. When AL Is greater than 10 dB, the
following approximation for LCQ is quite accurate:
Leq • Lmax ' 101°9
2.3AL
10
(dB) (Eq. A_8)
Except in extreme cases as noted on the graph. The value of L for
a series of n identical triangular time patterns having maximum levels
of L is given by:
Leq = Lb + 101°9
nr
2.3
To
(dB)
A-14
-------
90r-
80
70
ASSUMED
PULSE
MAX
••-DURATION
COMBINED
PULSE DURATION IN(nr)
SECONDS PER HOUR 10.0
.0
PULSE MAXIMUM SOUND LEVEL(LMAX)INdB
Figure A-2 Hourly Equivalent Sound Level as a Function of Pulse
Duration and Maximum Sound Level for One Pulse per
Hour or a Succession of nShorter Pulses Having A Total
of the Indicated Duration During One Hour. (Back-
ground sound level less than 30 dB)
(Derived from equation A-5)
A-15
-------
Where th* durTtion between (Lmax - 10 dB) points* isT seconds, the
background level is Lb5 and the total tirae period is T. (See Fig. A-3)
A design chart for determining Leq for different values of AL as a
function of m per hour is provided in Figure A-3.
An approximation to equation (A-9) for cases where L is
greater than 10 dB is given by:
Le = Lma
nT
(dB) (Eq. A-iO)
This equation yields fairly good results except in extreme cases as can be
seen in the graph.
C. Trapezoidal Time Patterns
The equivalent sound level, L , for a trapezoidal time pattern
having maximum level of
(Lmax - 10 dB) points of f and duration at
background level L^, duration between
of £ is given by
Leq = lOlog
b
w:
10
w
..o / \
max
10
(J^JMO -V +10
c • 0 ,
(dB) (Eq. A- 11)
The approximation to L when AL is greater than 10 dB,
for £. small compared to T, is:
Leq = Lmax
10 log
(dB) (Eg. A-12
This equation yields adequate results except in extreme cases as noted
on the graph. Noting the similarity between equations (A-5) (A-8) , and
(A-12), one can approximate Lecf for
* The duration for which the noise level is within 10 dB of L ; also called
the "10 dB down" duration.
A-16
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A-17
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a series of trapezoidal pulses by suitably combining design data
from Figure A-l and A-3. That is, the approximate L for a series
eq
of n trapezoidal pulses is obtained by the L value for trianqular
eq
pulses plus an additional term equal to 10 log n, e.g.,
Leq = Lmax * 101°9 FW+ 101°9 ^ (^ .(*!• A-13)
D. Time Patterns of Noise Having a Normal Statistical Distribution
Many cases of noise exposures in communities have a noise
level distribution that may be closely approximated by a normal
statistical distribution. The equivalent sound level for the distribution
can be described simply in terms of its mean value, which for a normal
distribution is I™, and the standard deviation (s) of the noise level
distribution:
= L50 + OJ15 s2 (dB>
A design chart showing the difference between Leq and L^Q as a function
of the standard deviation is provided in Figure A-4.
It is often of interest to know which percentile level of a
normal distribution is equal in magnitude to the L value for the
distribution. A chart providing this relationship as a function of
the standard deviation of the distribution is provided in Figure A-S.
Various noise criteria in use for highway noise are
expressed in terms of the L-JQ value. For a normal distribution, the
A-18
-------
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Figure A-4. Difference Between L and L-n for a Normal Distribution
C(J <)U
Hax'ing Standard Deviation of s.
(REF: Task Group #3 Report and equation A-14 .
A-19
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L value is specified in terms of the median and standard deviation
by the expression L = L5Q + 1.28 s. The difference between LIQ and
2
L is qiven by L, „ - L = 1.28 s - 0.115 s . This expression is
eq 10 eq
plotted as a function of s in Figure A-6,.
It should be noted that traffic noise does not always yield
a normal distribution of noise levels, so caution should be used in
determining exact differences between L and L .
III. Relationships Between Daytime and Nighttime Equivalent Sound Levels
The day-night sound level (L , ) was defined as the equivalent
A-weighted sound level during a 24-hour time period with a 10 decibel
weighting applied to the equivalent sound level during the nighttime
hours of 10 pm to 7 am. This may be expressed by the equation:
L +10
n
Ld/10 10
Ld = 10 log-L [ 15(10 d ) + 9 (10 )]
(dB) (Bq. A-15)
24
where Lrf = L forThe daytime (0700-2200 hours")
and Ln = L for the nighttime (2200-0700 hours)
The effect of the weighting may perhaps be more clearly visualized
if it is thoughtof as a method that makes all levels measured at night
10 dB higher than they actually are. Thus, as an example, if the noise
level is a constant 70 dB all day and a constant g0 dB all night, Ldn
would be 70 dB.
Methods for accounting for the differences in interference or
A-22
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annoyance between daytime/nighttime exposures have been employed in
A-5
a number of different noise assessment methods around the world .
The weightings applied to the nondaytime periods differ slightly
among the different countries but most of them weight night activities
A-24
on the order of 10 dB; the evening weighting if used is 5 dB.
The choice of 10 dB for the nighttime weighting made in Section II
was predicated on its extensive prior usage, together with an examina-
tion of the diurnal variation in environmental noise. This variation
is best illustrated by comparing the difference between L, and L as
a function of L, over the range of environmental noise situations.
dn
Data from 63 sets of measurements were available in sufficient
detail that such a comparison could be made. These data are plotted
in Figure A-7. The data span noise environments ranging from the
quiet of a wilderness area to the noisiest of airport and highway
environments. It can be seen that, at the lowest levels (L, around
x dn
40-55 dB), L, is the controlling element in determining L, , because
the nighttime noise level is so much lower than that in the daytime.
At higher L. levels (65-9O dB), the values of L are not much lower
than those for L,; thus, because of the 1O dB nighttime weighting, L
will control the value of L, .
dn
The choice of the 1O dB nighttime weighting in the computation of
Ld has the following effect : In low noise level environments below
L, of approximately 55 dB, the natural drop in L values is approxi-
^M* ±1
mately 10 dB, so that L, and L contribute about equally to L, . How-
u n dn
ever, in high noise environments, the night noise levels drop relatively
A-24
-------
little from their daytime values. In these environments, the night-
time weighting applies pressure towards a round-the-clock reduction
in noise levels if the noise criteria are to be met.
The effect of a nighttime weighting can also be studied indirectly
by examining the correlation between noise measure and observed
community response in the 55 community reaction cases presented in the
A—1
EPA report to Congress of 1971 . The data have a standard deviation
of 3.3 dB when a 10 dB nighttime penalty is applied, but the correlation
worsens (std. dev. = 4.0 dB) when no nighttime penalty is applied.
However, little difference was observed among values of the weighting
ranging between 8 and 12 dB. Consequently, the community reaction
data support a weighting of the order of 10 dB but they cannot be
utilized for determining a finer gradation. Neither do the data support
"three-period" in preference to "two-period" days in assigning non-
daytime noise penalties.
IV. Comparison of Day-Night Sound Level With Other Measures of Noise
Used by Federal Agencies
The following subsections compare the day-night sound level with
three measures utilized for airport noise, CNR, NEF, and CNEL , the
HUD Guideline Interim Standards and the Federal Highway Administration
Standards.:
A. Comparison of L, With Composite Noise Rating (CNR), Noise
Exposure Forecast (NEF), and Community Noise Equivalent Level(CNEL)
CNR, NEF, and CNEL are all currently used expressions for
weighted, accumulated noise exposure. Each is intended to sum a series
of noise While weighting the sound pressure level for frequency and then
A-25
-------
appropriate
adding'nighttime weightings. The older ratings, CNR and NEF, are
expressed in terms of maximum Perceived Noise Level and Effective
Perceived Noise Level, respectively; each considers a day-night
period identical to L, .
dn
The measure CNEL itself is essentially the same as L^ except
dn
for the method of treating nighttime noises, in CNEL,the 24-hour period
is broken into three periods: day (O70O-19OO), evening (190O-220O), and
night (2200-070O). Weightings of 5 dB are applied to the evening
period and 10 dB to the night period. For most time distributions of
aircraft noise around airports, the numerical difference between a
two-period and three-period day are not significant, being of the order
of several tenths of a decibel at most.
One additional difference between these four similar
measures is the method of applying the nighttime weighting and the
magnitude of the weighting.The original CNR concept, carried forward
in the NEF, weighted the nighttime exposure by 10 dB. Because of the
difference in total duration of the day and night periods, 15 and 9 hours
respectively, a specific noise level at night receives a weighting of
10 + 10 log (JJL)j0r approximately 12 dB in a reckoning of total exposure. *
Given the choice of weighting either exposure or level, it is simpler
to weight level directly, particularly when actual noise monitoring is
eventually considered.
The following paragraphs describe the method utilized to
calculate CNR, NEF, and CNEL, as applied principally to aircraft
sounds, together with the analogous method for calculating L^n -.
A-26
-------
1. Composite Noise Rating Method (CNR)
The original method for evaluating land use around
civil airports is the composite noise rating (CNR). It is still in
wide use by the Federal Aviation Administration and the Department of
Defense for evaluating land use around airfields (Civil Engineering
Planning and programming, "Land Use Planning with Respect to Aircraft
Noise," AFM 86-5, TM 5-365, NAVDOCKS P-98, October 1, 1964). This
noise exposure scale may be expressed as follows:
The single eventnoise level is expressed (without a duration
or tone correction) as simply the maximum perceived noise level
(pNLmax> 1n PNdB-
The noise exposure in a community is specified in terms of
the composite noise rating (CNR), which can be expressed approximately
as follows:
CNR = PNT + 10 log N,. - 12 (Eq.A-16)
max * f
where
PRT = approximate energy mean maximum perceived noise level
roax (PNL) at a given point
N|? = (N. + 16.7 Nn), wnere N and Nf the numbers of daytime
and nighttime events, respectively.
The constant (-12) is an arbitrary constant, and the
factor 16.7 is used to weight the nighttime exposure in the 9~hour
night period on a 10 to 1 basis with the daytime exposure in the 15
-hour daytime period.
A-27
-------
2. Noise Exposure Forecast (NEF)
This method, currently in wide use, for making noise
exposure forecasts utilizes a perceived noise level scale with additional
corrections for the presence of pure tones. Two time periods are used
to weight the number of flights ^Galloway, W.J. and Bishop, D.E.,
"Noise Exposure Forecasts: Evolution, Evaluation, Extensions and Land
Use Interpretations," FAA-NO-70-9, August 1970).
The single event noise level is defined in terms of
effective perceived noise level (EPNL) which can be specified approximately
by:
At
EPNL = PNL + log _Ji + F, (EPNdB) (*q. A-17)
max 20
where
PNL = maximum perceived noise level during flyover, in PNdB,
At-jQ ="10 dB down"duration of the perceived noise level time
history, in seconds,
and F = pure tone correction. Typically, F = o to + 3dB
Community noise exposure is then specified by the Noise Exposure
Forecast (NEF). For a given runway and one or two dominant aircraft
types, the total NEF for both daytime and nighttime operations can be
expressed approximately as:
NEF = ETNT+ 10 log Nf - 88.0 (Eq. A-18.)
where
fpjjr = energy mean value of EPNL for each single event at
the point in question
Nf = same as defined for CNR
A-28
-------
3. Community Noise Equivalent Level (CNEL)
The following simplified expressions are derived from
the exact definitions in the report, "Supporting Information for the
Adopted Noise Regulations for California Airports." They can be used
to estimate values of CNEL where one type of aircraft and one flight
path dominate the noise exposure level.
Single event noise is specified by the single event noise
exposure level (SENEL) in dB and can be closely approximated by:
SENEL =NLmax + 10 log10tf/2 (dB) (Eq. A-19)
where
ML = maximum noise level as observed on the A scale of a
standard sound level meter
and
^ = duration measured between the points of (L -10) in seconds
The effective duration is equal to the "energy" of the integrated noise
level (NL), divided by the maximum noise level, NLmax, when both are
expressed in terms of antilogs. It is approximately 1/2 of the 10 dB
down duration.
A measure of the average integrated noise level over one
hour is also utilized in the proposed standard. This is the hourly
A-29
-------
noise level (in dB), defined as:
HNL = SENEL + 10 log n - 35.6 (dB) (Bq. A-20)
where
SENEL = energy mean value of SENEL for each single event,
and
n = number of f 1 ights .per hour
The total noise exposure for a day is specified by the community noise
equivalent level (CNEL) in dB, and may be expressed as:
CNEL = SENET + 10 log NC - 49.4 (dB) (Bq. A-21)
where
Nc - (Nd + 3Ne + 10Nn)
or
= (12rf. + 9n_ + 90F )
Q e n
Nj , rrj = total number and average number per hour, respectively, of
flights during the period 0700 to 1900
Ne , n" = total number and average number per hour, respectively, of
flights during the period 1900 to 2200
and
Nn , rf = total number and average number per hour, respectively, of
n n flights during the period 2200 to 0700
4. Day-Night Sound Level (L^ )
on
The following simplified expressions are useful for
estimating the value of Ldn for a series of single event noises which
are of sufficient magnitude relative to the background noise that
A-30
-------
they control Ldn :
Single event noise is specified by the sound exposure
level (L ) measured during a single event. It can be closely
C A
approximated by:
Lex = Lroax + 10
where
L = maximum sound level as observed on the A scale of a
max standard sound level meter on the slow time characteristic
and t- duration measured between the points of (L^^IO) in
seconds
The day-night sound level may be estimated by:
Ldn = Lex + 10 log N - 49.4 (dB) (Bq. A-23)
where
L^ = the energy mean value of the single event Lex values
N = (Nd + 10Nn)
or
N^ = total number of events during the period 0700 to 2200
and
Nn = total number of events during the period 2200 to 0700
A-31
-------
There is no fixed relationship between L. or CNEL and
CNR or NEF because of the differences between the A-level and PNL
frequency weightings and the allowance for duration, as well as the
minor differences in approach to day-night considerations. Nevertheless',
one may translate from one measure to another by the following
approximate relationship:
Ldn = CNEL = NEF + 35 = CNR - 35 (Eq. A-24)
For most circumstances involving aircraft flyover noise, these relation-
ships are valid within about a ±3 dB tolerance.
B. Comparison of L with HUD Guideline Interim Standards
(1390.2 Chg. 1)
The interim HUD standards for outdoor noise are specified for
all noise sources, other than aircraft, in terms of A-weighted sound
level not to be exceeded more than a certain fraction of the day. Air-
craft noise criteria are stated in terms of NEF or CNR.
The HUD exposure criteria for residences near airports
are "normally acceptable" if NEF 30 or CNR 100 is not exceeded. A
"discretionary acceptable" category permits exposures up to NEF 40 or
CNR 115.
For all other noise sources,the HUD criteria specify a
series of acceptable, discretionary^and unacceptable exposures. Since
these specifications are similar to points on a cumulative statistical
description of noise levels, it is of interest to compare the HUD
A-32
-------
criteria with L for different situations. For discussion purposes,
consider the boundary between the categories "discretionary-normally
acceptable" and "unacceptable."
The first criterion defining this boundary allows A-weighted
noise levels to exceed 65 dB up to 8 hours per 24 hours, while the
second criterion states that noise levels exceeding 80 dB should not
exceed 60 minutes per 24 hours. These two values may be used to
specify two limit points on a cumulative distribution function,
LOO i - 65 dB and L. „ = 80 dB. The relationship between L and the
3o.J 4.2 eq
HUD criteria may then be examined for different types of distribution
functions, restricting the shape of the distribution only so that it
does not exceed these two limit points.
First consider two cases of a normal distribution of noise
levels, comparable to vehicle traffic noise. For the first case,
assume a distribution with quite narrow variance so placed on the graph
that the 65 dB point is not exceeded (see Fig. A-SJ. For this curve,
to the nearest decibel, UQ = 64 dB, and the corresponding standard
deviation (arbitrarily chosen small) is 2.3 dB. The resulting L is
equal to 64.6 dB.
Now consider a normal distribution with the widest
permissible variance (the curve marked Maximum Variance in Figure A-S);
1f the variance were any greater, the distribution would violate HUD's
requirement that the level not exceed 80 dB for more than 60 minutes
per 24 hours. This distribution, to the nearest decibel, has
A-33
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-------
LJQ = 60 dB, LJQ = 74 dB and a standard deviation of approximately
11 dB. The resultant Leq = 74 dB, is almost 10 dB higher than for the
previous case. Both curves meet HUD's interim standards.
Next, consider a series of intermittent high level noises,
superposed on a typical urban/suburban background noise level, such
that 80 dB is not exceeded more than 60 minutes per 24 hours, say 4%.
Choosing a series of repeated triangular-shaped time signals of 90 dB
maximum sound level will produce an L value of 72.4 dB without
exceeding an L^ value of 80 dB.
However, one can allow the maximum level to increase
indefinitely provided L^ remains at 80 dB or less. The limiting
case is that of a square-shaped time pattern, switched on and off.
In this instance, if the total "on-time" is 4% or less, the value of
Leq is equal to Lmax - 14 dB, and both Lmax and I can increase with-
out limit and still remain acceptable within the HUD interim standards.
Maximum A-levels for an aircraft can be as high as 110 dB, which would
permit Leq values of 96 to be obtained without exceeding the L^ limit
of 80 dB.
It is clear that no unique relationship can be specified
between the HUD non-airport standards and L . Values of L ranging up
to 95 dB can be found in compliance with the HUD outdoor noise standard
depending on the time distribution of noise levels considered. Even
if the nighttime penalty were applied to Leq to yield L^ there would
still be no unique relation with the HUD standards.
A-35
-------
C. Comparison of L With Federal Highway Administration Noise
Standards, PPM 90-2, February 8, 1973.
The primary criteria of PPM 90-2 are that L,Q for noise
levels inside people-occupied spaces shall not exceed 55 dB, or for
sensitive outdoor spaces"—in which serenity and quiet are of extra-
ordinary significance—," 60 dB.
Highway noise xrften -has a -random distribution of noise
level, the distribution function being approximately normal in many
instances. In this case, the relationship between L and L,Q is given
by the expression:
Leq = L10 - 1-28 s + °-115 s* (dB)
where s is the standard deviation of the noise level distribution. The
difference between Lin and L for normal distribution of sound level is
10 eq
plotted in Figure A-6. It can be noted that Leq = L,Q -2 dB within ±2
dB, for s ranging from 0 to 11 dB. Highway noise rarely has a
standard deviation of 11 dB; 2 to 5 dB is more typical.
Thus, setting L-JQ at 60 dB for highway noise impacting a
sensitive outdoor space, we find that an Leq value of 60 -2 = 58 +_2 dB
would meet the most sensitive FHWA criterion.
A-36
-------
REFERENCES FOR APPENDIX A
A-l. "Report to the President and Congress on Noise," Environmental
Protection Agency, NRC 500.1, December 31, 1971.
A-2. Bishop, D. E.,"Judgements of the Relative and Absolute
Acceptability of Aircraft Noise," J. Acoust. Soc. Am. 40_:103,
December 1966.
A-3. Kryter, K. D.,"The Effects of Noise on Man," Academic Press,
New York", 1970.
A-4. "House Noise - Reduction Measurements for Use in Studies of
Aircraft Flyover Noise," Society of Automotive Engineers, Inc.
AIR 1081, October 1971.
A-5. Bishop, D. E.,and Horonjeff, R.O. ."Procedures for Developing
Noise Exposure Forecast Areas for Aircraft Flight Operations,"
FAA Report DS-67-10, August 1967.
A-6. Stevens, K. N.,and Pietrasanta, A. C., and the Staff of Bolt
Beranek and Newman,Inc., "Procedures for Estimating Noise
Exposure and Resulting Community Reactions from Air Base
Operations," WADC Technical Note 57-10, Wright-Patterson Mr
Force Base, Ohio, Wright Air Development Center, 1957.
A-7. Eldred, K. M., Gannon, W. J., and von Gierke, H.E.,
"Criteria for Short Time Exposure of Personnel to High Intensity
Job Aircraft Noise," WADC Technical Note 55-355, Wright-Patterson
Air Force Base, Ohio, 1955.
A-8. Air Force Regulation 160-3, "Hazardous Noise Exposure," USAF,
October 29, 1956.
A-9. Burck, W.,3rutzmacher, M., Meister, F. J., Muller, E. A., and
Matschat, K., "Fluglarm, Gutachten erstattet im Auftrag des
Bundesministers fur Gesundheitswesen,"(Aircraft Noise: Expert
Recommendations Submitted under Commission from the German
Federal Ministry for Public Health), Gottingen, 1965.
A-37
-------
A-10. Bruckmayer, F. and Lang, J., "Storung der Bevolkerung durch
Verkehrslarm" (Disturbance of the Population by Traffic Noise),
Oesterreiche Ingenieur-Zeitschrift, Jg. 1967, H.8, 302-306;
H. 9, 338-344; and H. 10, 376-385.
A-ll. Bruckmayer, F., and Lang, J., "Storung durch Verkehrslarm in
Uhterrichtstraume" (Disturbance Due to Traffic Noise in School-
roans), Oesterreichische Ingenieur-Zeitschrift, 11^ (3): 73-77,
1968.
A-12. "Schallschutz: Begriffe" (Noise Control: Definitions), TGL
10 687, Blatt 1 (Draft), Deutsche Bauinformation, East Berlin,
Nbverrtoer 1970.
A-13. "Mittelung zeitlich schwankender Schallpegel (Aquivalenter
Dauerschallpegal)" (Evaluation of Fluctuating Sound Levels (The
Equivalent Continuous Sound Level)), DIN 54 641, (Draft),
Deutsche Normen, Beuth-Vertrieb GmbH, Berlin 30, April 1971.
A-14. "Schallschutz: Territoriale und Stadtebauliche Planung" (Noise
Control: Land Use and City Planning), TGL 10 687, Blatt 6,
(Draft), Deutsche Bauinfontation, East Berlin, November 1970.
A-15. "Schallschutz in Stadtebau" (Noise Control in City Planning),
DIN 18 005, (Draft), Deutsche Normen, Beuth-Vertrieb GrrfoH,
Berlin 30, August 1968.
A-16. Benjegard, Sven-Olaf, "Bullerdosimetern" (The Noise Dose Meter),
Report 51/69, Statens institut fur byggnadsforskning, Stockholm,
1969.
A-17. Robinson, D. W. and Cook, J. P., NPL Aero Report No. Ac 31,
National Physical Laboratory, England, June 1968.
A-18. Meister, F. J., "Der Einfluss der Einwirkdauer bei der Beschallung
des Ohres" (The Influence of the Effective Duration in Acoustic
Excitation of the Ear), Larmbekampfung 10_ (3/4), June/August 1966.
A-19. Pearsons, K. S., "The Effects of Duration and Background Noise
Level on Perceived Noisiness," FAA ADS-78, April 1966.
A-38
-------
A-20. Galloway, W. J., and Bishop, D. E., "Noise Exposure Forecasts:
Evolution, Evaluation, Extensions and Land Use Interpretations,"
Bolt Beranek and Newman, Inc., Report No. 1862, August 1970;
also FM-No-70-9.
A-21. "Procedure for Describing Noise Around an Airport," R-507,
International Standards Organization, Geneva, 1970.
A-22. "Noise Assessment with Respect to Community Noise," R-1996,
International Standards Organization, Geneva, 1970.
A-23. "Assessment of Noise-Exposure During Work for Hearing Conserva-
tion," R-1999, International Standards Organization, Geneva,
1970.
A-24. Galloway, W. J., "Review of Land Use Planning Procedures,"
Interim Technical Report, Aerospace Medical Research Laboratory,
WPAFB, Ohio, March 1972.
A-25. "Impact Characterization of Noise Including Implications of
Identifying and Achieving Levels of Cumulative Noise Exposure,"
Environmental Protection Agency, NTID 73.4, 1973.
A-39
-------
APPENDIX B
LEVELS OF ENVIRONMENTAL NOISE IN THE U.S. AND TYPICAL
EXPOSURE PATTERNS OF INDIVIDUALS
Levels of environmental noise for various defined areas
are provided for both the outdoor and indoor situation.
Examples are then used to illustrate how an individual's
daily dose accumulates from the exposure to such noise levels.
I. Ley e_j. s__ of En y i r on me n t a 1 N o i s e
A. Outdoor Sound Levels
The range of day-night sound levels (Ldn) in the United States
is very large, extending from the region of 20-30 dB estimated
for a quiet* wilderness area to the region of 80-90 dB in the
most noisy urban areas, and to still higher values within the
property boundaries of some governmental, industrial and
commercial areas which are not accessible to the general
public. The measured range of values of daylight sound
levels outside dwelling units extends from 44 dB on a farm
to 88.8 dB outside an apartment located adjacent to a freeway.
Some examples of these data are summarized in Figure B-I.
The dominant sources for outdoor noise in urban
residential areas are motor vehicles, aircraft and voices.
This conclusion has been found in several studies, including
B«l
a recent survey of 1200 people which is summarized in
Table B-I.
*Measurement approximately 25 feet from a mountain waterfall
on a small canyon stream in Wyoming gave an L<4n of approximately
85 dB. B-2
B-l
-------
DAY- NIGHT
SOUND LEVEL
QUALITATIVE
DESCRIPTIONS
_80_
CITY NOISE -t-
(DOWNTOWN MAJOR +C~
METROPOLIS )
VERY NOISY
NOISY URBAN
—70-
iMALL TOWN a
OUIET
SUBURBAN
— 40—
OUTDOOR LOCATIONS
LOS ANGELES- 3rd FLOOR APARTMENT NEXT TO
FREEWAY
LOS ANGELES- 3/4 MILE FROM TOUCH DOWN AT
MAJOR AIRPORT
LOS ANGELES- DOWNTOWN WITH SOME CON-
STRUCTION ACTIVITY
HARLEM- 2nd FLOOR APARTMENT
BOSTON-ROW HOUSING ON MAJOR AVENUE
WATTS-8 MILES FROM TOUCH DOWN
AT MAJOR AIRPORT
NEWPORT- 3.5 MILES FROM TAKEOFF AT
SMALL AIRPORT
LOS ANGELES- OLD RESIDENTIAL AREA
FILLMORE-SMALL TOWN CUL- de-SAC
SAN DIEGO- WOODED RESIDENTIAL
CALIFORNIA-TOMATO FIELD ON FARM
Figure B-l.
Examples of Outdoor Day-Night Sound. Level in dB
(re 20 micropascals) Measured at Various Locations B~4
B-2
-------
TABLE B-l
PERCENT CONTRIBUTION OF EACH SOURCE IDENTIFIED BY
RESPONDENTS CLASSIFYING THEIR NEIGHBORHOOD AS NOISY
(72% OF 1200 RESPONDENTS) B"3
Source
Percentage
Motor Vehicles
Aircraft
Voi ces
Radio and TV Sets
Home Maintenance Equipment
Construction
Industrial
Other Noises
Not Ascertained
55
15
12
2
2
1
1
6
8
B-3
-------
The cumulative number of people estimated to reside
in areas where the day-night sound level exceeds various values
is given in Table B-2. In the areas where the L^n exceeds 60 dB,
the proportion between the number of people residing in areas
where the outdoor noise environment is dominated by aircraft
and those residing in areas where motor vehicles dominate is
approximately one to four. This proportion is almost identical
to the proportion found in the survey, previously summarized in
Table B-l where people were asked to judge the principle
contributing sources of neighborhood noise. The estimates in
Table B-2 of the number of people living in areas which are
exposed to freeway and aircraft noise are taken from the EPA
B-4
ai rport/ai rcraft Noise report . They were based on
calculated noise contours and associated populations for a
few selected situations which formed the basis for extrapolation
to national values. The estimates for the number of people
living in areas in which the noise environment is dominated by
B-5
urban traffic were developed from a survey conducted in
Summer 1973 for EPA. The survey measured the outdoor 24-
hour noise environment at 100 sites located in 14 cities,
including at least one city in each of the ten EPA regions.
These data, supplemented with that from previous measure-
ments at 30 additional sites, were correlated with census tract
population density to obtain a general relationship between
Ldn and population density. This relationship was then utilized,
together with census data giving population in urban areas as
B-4
-------
TABLE B-2
ESTIMATED CUMULATIVE NUMBER OF PEOPLE IN MILLIONS IN
THE UNITED STATES RESIDING IN URBAN AREAS WHICH ARE EXPOSED
TO VARIOUS LEVELS OF OUTDOOR DAY/NIGHT AVERAGE SOUND
LEVEL, B-4 and B-5
Outdoor
L
-------
a function of population density, to derive the national
estimate given in Table B-2.
These data on urban noise enable an estimate of the
percentage urban population in terms of both noise levels
and the qualitative descriptions of urban residential areas
which were utilized in the Title IV EPA report to Congress in 1974 B>'
These estimates, summarized in Table B-3, show that
the majority of the 134 million people residing in urban areas
have outdoor Ldn values ranging from 13 dB to 72 dB with a median
value of 59 dB. The majority of the remainder of the population
residing in rural or other non-urban areas is estimated to have
outdoor Ldn values ranging between 35 and 50 dB.
B. Indoor Sound Levels
The majority of the existing data regarding levels
of environmental noise in residential areas has been obtained
outdoors. Such data are useful in characterizing the neighbor-
hood noise environment evaluating the noise of identifiable
sources and relating the measured values with those calculated
for planning purposes. For these purposes,the outdoor noise
levels have proved more useful than indoor noise levels
because the indoor noise levels contain the additional
variability of individual building sound level reduction. This
variability among dwelling units results from type of
construction, interior furnishings, orientation of rooms
relative to the noise, and the manner in which the dwellincr unit
is ventilated.
B-6
-------
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Data on the reduction of aircraft noise afforded by
B-7
a range of residential structures are available . These
data indicate that houses can be approximately categorized into
"warm climate" and "cold climate" types. Additionally, data
are available for typical open-window and closed-window con-
ditions. These data indicate that the sound level reduction
provided by buildings within a given community has a wide range
due to differences in the use of materials, building techniques,
and individual building plans. Nevertheless, for planning
purposes, the typical reduction in sound level from outside to
inside a house can be summarized as follows in Table B-4.
The approximate national average "window open" condition
corresponds to an opening of 2 square feet and a room absorption
of 300 sabins (typical average of bedrooms and living rooms).
This window open condition has been assumed throughout this
report in estimating conservative values of the sound levels
inside dwelling units which results from outdoor noise.
The sound levels inside dwelling units result from the
noise from the outside environment plus the noise generated
internally. The internally generated noise results from people
activity, appliances and heating and ventilating equipment.
Twenty-four hour continuous measurements were made in 12 living
rooms (living, family or dining room) in 12 houses during the
100-site EPA survey B~5of urban noise, exluding areas where the
noise resulted from freeways and aircraft. The results,
summarized below in TableB-5, show that the inside day-night
B-8
-------
TABLE B-4
SOUND LEVEL REDUCTION DUE TO HOUSES"' IN WARM AND
COLD CLIMATES, WITH WINDOWS OPEN AND CLOSED B~7
Warm climate
Cold, cl imate
Approx. national average
Windows
Open
12 dB
17 dB
15 dB
Windows
Closed
24 dB
27 dB
25 dB
* (Attenuation r i: outdoor noise by exterior a'.iell of the house)
B-9
-------
TABLE B-5
COMPARISON OF INTERNAL AND OUTDOOR SOUND LEVELS IN
LIVING AREAS AT 12 HOMES
Outdoors :
Average
Standard Deviation
Indoors:
Average
Standard Deviation
Difference (Outdoors
minus Indoors)
Daytime
Sound
Level
Ud)
in dB
57.7
3.1
59.4
5.6
1.7
Nighttime
Sound
Level
("-„)
in dB
49.8
4.6
46.9
8.7
2.9
DayrNight
Sound Level
Ldn in dB
58.8
3.6
60.4
5.9
- 1.6
B-10
-------
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B -11
-------
sound level in these homes was the result of internally
generated noise. In fact, the internal L^p and Ld values
were slightly higher than those measured outdoors, despite
the fact that the average house sound level reduction
appeared to exceed 18 dB. The pattern for the indoor
sound levels varies significantly among the homes, as
portrayed by the data in Figure B~2 The hourly equivalent
sound levels have an average minimum of approximately 36 dB
during the hours between 1 a.m. and 6 a.m. This minimum level is
probably governed by outdoor noise in the majority of
the situations. However, when people are active in the daytime,
the hourly equivalent sound levels have a range of over 30 dB,
depending on the type of activity. Thus, during the waking
hours, the outdoor noise sets a lower bound of indoor noise.
for the outdoor L^n range of 52-65 dB this lower bound is
significantly below the average level of the internally
generated noise.
II. Examples of Individual Noise Exposures
The noise exposures received by individuals are very
much a function of the individual's life style. The variation
in these exposures can be illustrated by examining several
typical daily activity patterns. While these patterns are
realistic, they should not be construed as applying to all
individuals following the particular life style depicted.
B-12
-------
The total daily exposure, L (24) is considered the sum
of the sound energy from all daily exposure, including
occupational exposures. Mathematically this can be interpreted
as:
Leq(24 hr) = 10 Log
-49.4
where: L(ti) is the Leq value for the appropriate time
periods, (tT-) and the summation of all the t^'s must equal
a total of 24 hours (i.e., y t, = 24 hours (86400 sec.).
i = l n
Five different exposure patterns for a 24-hour day are
depicted in Figures B-3 to B-7 . The patterns are representative
of the exposures that might be incurred by:
Factory worker - Figure B-3
Office worker - Figure B-4
Housewife - Figure B-5
School child - Figure B-6
Pre-school child - Figure B-7
Certain assumptions were made in determining the levels
shown in Figure B-3 to B-7, First, it was assumed that the
suburban environment was equal to an L^ of 50 (L^ = 50,
Ln = 40). For the urban environment,the Ldn value was 75
(Lj = 72, Ln = 68). The levels for the various activities
were determined from previous EPA reports on appliance noise,
transportation noise, as well as information contained in the EPA
Task Group #3 Report relating to aircraft noise. B~4
B-13
-------
FACTORY WORKER
cr
0)
100
90
80
70
60
50
40
30
i
Leq(24)
SUBURB
AM
m\i
URBAN
—
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Q.
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1
CO
1
12 3
MIDNIGHT
0 3
(—
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9
HOUR
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OF DAY
18 21
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Fiqure B-3. Typical Noise Exposure Pattern of a Factory Worker
B-l, B-4, B-8, B-9
B-14
-------
OFFICE WORKERS
90
80
70
60
50
40
30
SUBURBAN
URBAN
Q_
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LJ
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n
I I
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H
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cr
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72
70
1
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12 3 6
MIDNIGHT
036
9 12 3 6
NOON
9 12 15 18
HOUR OF DAY
9 12
MIDNIGHT
21 24
Figure B-4. Typical Noise Exposure Pattern of an Office Worker
B-l, B-4, B-8, B-9
B-15
-------
HOUSEWIFE
cr
o>
80
70
60
50
40
30
1
MIDr
Leq(24)
Cl IDI IDQAM - --.. .- - C/l
oUBUKDAINJ D'f
1 1
1 1
1
1
1
1
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y v *, ,y -,
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CO Q- X LU COXCJCLLUCJh-CO
1 II II
2369 12 36 9 12
JIGHT NOON MIDNIGHT
03 69 12 15 18 21 24
HOUR OF DAY
Figure B-5.
Apical Noise Exposure Pattern of a Housewife
B-l, B-4, B-8, B-9
B-16
-------
SCHOOL CHILD
cr
Q)
90
80
70
60
50
40
30
Leq(24)
SUBURBAN
URBAN
—
-
r~
_
—
fe
UJLJ CO
- a.
LU
LU
~J
^
oo o
1
9 1
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1
6
X »-
CL
LU
LU
-1
co
*
9 12
NOON
9 12
HOUR OF
15
DAY
18
MIDNIGHT
21 24
Figure B-6.
Typical Noise Exposure Pattern of a School Child
B-l, B-4, B-8, B-9
B-17
-------
PRE-SCHOOL CHILD
cr
o>
80
70
60
50
40
30
SUBURBAN
URBAN
0.
UJ
bJ
LJ
^
O
X
<
_J
CL
h-
LJ
Leq(24)
60
|
1
CO
o:
o
o
Q
o
; ^
< LJ
LJ a.
CO
1
12 3 6
MIDNIGHT
036
9 12 3 6
NOON
9 12 15 18
HOUR OF DAY
9 12
MIDNIGHT
21 24
Figure B-7.
Typical Noise Exposure Pattern of a Pre-School Child
B-l, B-4, B-8, B-9
B-18
-------
Values for the Equivalent Sound level (Leq(24))
experienced by the individual are computed from the basic
formulation of Leq. For each of these lifestyles, the
Leq(24) va^ue and tne Ldn values are equivalent as the
controlling noise dose normally does not occur at night.
This emphasizes that for most practical situations ,the
average individual L^n dose or Leq(24) individual dose are
i nterchangeable.
Noise levels for other lifestyles could also be generated,
However, it is important to remember that Leq(24) values
are,in most cases ,controlled by the 2-to 3-hour exposures to
relatively high level noise. For example, assume a motor-
cycle rider rode his vehicle for 2 hours a day at an exposure
of 100 dB producing an Leq(24) °f 89; if this were the
case/then other noise producing activities during the day
would have little effect on the l^n if they were at a level
of at least 15 dB below the level of the motorcycle.
B-19
-------
REFERENCES FOR APPENDIX B
B-l. Eldred, K. M., "Community Noise," Environmental Protection Agency
NTID 300.3, December 1971.
B-2. Garland, W. L., Hanna, S. J. and Lamb, D. R., "Anibient Noise, Wind
and Air Attentuation in Wyoming," Proceedings of Noise-Con 73,
Washington, D.C., October 1973.
B-3. Bolt Beranek and Nevnttan, Inc., "Survey of Annoyance from Motor
Vehicle Noise," Automobile Manufacturers Association, Inc.,
Report 2112, June 1971.
B-4. "Impact Characterization of Noise Including Implications of
Identifying and Achieving Levels of Cumulative Noise Exposure,"
Environmental Protection Agency NTID 73.4, July 27, 1973.
B-5. Galloway, D. and Eldred, K., 100-Site Report, in preparation as a
BBN Report for the Environmental Protection Agency.
B-6. "Report to the President and Congress on Noise," Environmental
Protection Agency NRC 500.1, December 31, 1971.
B-7. "House Noise - Reduction Measurements for Use in Studies of Aircraft
Flyover Noise," Society of Automotive Engineers, Inc., AIR 1081,
October 1971.
B-8. "Transportation Noise and Noise from Equipment Powered by Internal
Combustion Engines," Environmental Protection Agency NTID 300.13,
December 1971.
B-9. "Noise from Construction Equipment and Operations, Building Equipment
and Home Appliances," Environmental Protection Agency NTID 300.1,
December 1971.
B-20
-------
APPENDIX C
NOISE-INDUCED HEARING LOSS
*• Introduction
A considerable amount of hearing loss data have been collected
and analyzed. These data consist of measurements of hearing loss in
people with known histories of noise exposure. Much of the analysis
consists of collecting these measurements into populations of the same
age with the same history of noise exposure and determining the percen-
tile distribution of hearing loss for populations with the same noise
exposure. Thus, the evidence for noise-induced permanent threshold shift
can be clearly seen by comparing the distribution of a noise-exposed
population with that of a relatively non-noise-exposed population.
Most of these data are drawn from cross-sectional research rather
than longitudinal studies. That is, individuals or populations have
been tested at only one point in time. Because complete noise-exposure
histories do not exist, many conclusions are limited by the need to make
certain hypotheses about the onset and progression of noise-induced
hearing loss. Different hypotheses about the time history will lead
to different conclusions even from the same data base,although the range
of such conclusions is limited. Thus, in reaching conclusions about
hearing loss, reliance is made on assumptions, hypotheses, and extra-
polations which are not all universally accepted by the scientific
community. However, attempts have been made to consider differing opin-
ions and to insure that the methodology and conclusions in this section
are in the mainstream of current scientific thought.
c-1
-------
11. Bas i c AssjjmptiOJTS J*nd_Consj dj?rjjtjons
In order to proceed further^it is necessary to make the following
well-based assumptions:
1. Hearing shifts in the "non-noise-exposed" populations are
attributable to aging and other causes rather than to noise exposure.
2. As individuals approach the high end of the distribution and
their hearing becomes worse, they become less affected by noise exposure.
In other words, there comes a point where one cannot be damaged by
sounds that one cannot hear.
In addition, there are some important considerations necessary for
the identification of a level to protect against hearing loss.
A. Preservation of High Frequency Hearing
The levels identified in this document for hearing conservation
purposes are those which have been shown to provide protection from any
measurable degradation of hearing acuity. This protection is provided
even for those portions of the hearing mechanism which respond to the
audiometric frequency at which noise-induced hearing impairment first
occurs, namely 4000 Hz. The definition of hearing handicap originated
by the American Academy of Opthalmology and Otolaryngology (AAOO)fand
currently incorporated in many hearing damage-risk criteria, is some-
what different from the definition used in this document. Hearing
handicap, (and later, hearing impairment) was defined by a formula which
used the average hearing level at 500 Hz, 1000 Hz and 2000 Hz.
Although hearing loss for frequencies above 2000 Hz is not
treated as significant by most of the existing occupational hearing
C-2
-------
damage-risk criteria, the ability to hear frequencies above 2000 Hz
is important for understanding speech and other signals. Despite
the traditional use of the term "speech frequencies" to apply to 500,
1000 and 2000 Hz, useful energy in speech sound ranges from about 200
to 6100 Hz.0"1 It has been known for many years that the equal dis-
criminability point in the speech spectrum is at about 1600 Hz. That
is, frequencies above 1600 Hz are equal in importance to those below
1600 Hz for understanding speech.c'l However, there are other reasons
for preserving the frequencies above 2000 Hz. Higher frequencies are
important for the localization and identification of faint, high-pitched
sounds in a variety of occupational and social situations. Detection of
soft, relatively high-frequency sounds can be especially important in
vigilance tasks, such as those which may occur in the military. In addi-
tion, good hearing for the higher frequencies is important to hear every-
day occurrences such as sounds indicative of deterioration in mechanical
equipment, crickets on a summer evening, bird song, and certain musical
sounds. In fact, high-fidelity sound reproducing equipment is often
promoted on the basis of its fidelity up to 15,000 Hz, or even 30,000 Hz.
Any measurable hearing loss at any frequency is unacceptable if
the goal is protection of health and welfare with an adequate margin of
safety. For most environmental noise, protection at 4000 Hz will insure
that all other frequencies are protected.0"2 Thus, the 4000 Hz frequency
has been selected as the most sensitive indicator of the auditory effects
of environmental noise.
C-3
-------
B. Significant Changes in Hearing
In this section an attempt will be made to determine the
relation between exposure level and noise-induced permanent threshold
shift (NIPTS). Before this is accomplished, however, the significance
of various amounts'of NIPTS needs to be addressed.
For the purposes of identifying the levels in this document,
it was necessary to adopt a criterion for an allowable amount of NIPTS.
Whereas a NIPTS of 0 dB would be ideal, it is not appropriate for the
following reasons:
1. Most audiometric equipment does not have the capability
to measure hearing levels in less than 5 dB steps.
2. There is no known evidence that NIPTS of less than 5 dB
are perceptible or have any practical significance for the individual.
3. Individual hearing thresholds are subject to minor
fluctuations due to transitory psychological or physiological phenomena.
NIPTS.of considerably larger amounts have been permitted in
various damage-risk criteria in the past. For instance, shifts of 10 dB
to 20 dB have been considered reasonable.0"3 However, the requirement
for an adequate margin of safety necessitates a highly conservative
approach. This approach dictates the prevention of any effect on
hearing, which is defined here as an essentially insignificant and
unmeasurable NIPTS, i.e., a NIPTS of less than 5 dB. The available
evidence consists of statistical distributions of hearing levels for
populations at various exposure levels. The evidence of NIPTS, then,
is the shift in the statistical distribution of hearing levels for a
noise-exposed population in comparison to that of a non-exposed population.
C-4
-------
III. Prediction of Noise-Induced Permanent Threshold Shift
A. Status of Hearing at 4000 Hz in the United States
Figure c-1 summarizes hearing levels of the general American
population at 4000 Hz. The data is from the Public Health Survey (PUS)
conducted in 1960-62 in the United States.0'4 Robinson's non-noise-
exposed and otologically screened population is shown for comparison.
Several points should be noted.
1. The hearing of a selected percentile of the population can
be determined for various age groups. As displayed here, the higher the
percentile point, the worse the hearing.
2. At age 11,there is no hearing difference due to sexc~6,
but for the 18-24 age group, a definite difference is evident, with men's
hearing considerably worse.
3. Considering that there is no evidence for any sex-inherent
differences in susceptibility to hearing impairment, it is most likely
that the differences displayed are due to noise exposure.
B. The Effect of Noise on Hearing
Table c-l summarizes the hearing changes expected for daily
exposures to various values of steady noise, for an eight-hour day, over
10- and 40-year periods. c~7
Four different measurement parameters are considered in Table c-l
1. Max NIPTS: The permanent change in hearing threshold
attributable to noise. NIPTS increases with exposure duration. Max
NIPTS is the maximum value during a 40-year exposure that starts at
age 20. Data from the 90th percentile point of the population will be
C-5
-------
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C-6
-------
TABLE C.I
SUMMARY OF THE PERMANENT HEARING DAMAGE EFFECTS
EXPECTED FOR CONTINUOUS NOISE EXPOSURE AT
VAPIOUS VALUES OF THE A-WEIGHTED AVERAGE
SOUND LEVEL c~7
75 dB for 8 hrs
av.0.5,1.2 kHz av.0.5,1,2,4 kHz 4. kHz.
Max NIPTS 90th percentlie
NIPTS at 10 yrs. 90th percentile 1 dB 2 dP
Average NIPTS 0 1
Max Nipts 10th percentile 0 0
^ __0 0 0. _
80 dB for 8 hrs
av.0.5,1,2 kHz av.0.5,1.2.4 kHz 4 kHz
Max NIPTS 90th percentile
NIPTS at 10 yrs. 90th percentile 1 dB 4 dB 11 <1;
Average NIPTS ] 3 9
Max NIPTS 10th percentile |j n ?
85 dB for 8 hrs
av.Q.5,1.2 kHz av.Q.5,1,2,4 kHz 4 kHz
Max NIPTS 90th percentile 4 dB 7 dB 19 c'P
NIPTS at 10 yrs. 90th percentile 2 6 16
Average NIPTS 1 3 9
Max NIPTS 10th percentile 1 2 5_
90 dB for 8 hrs
av.n.5.1.2 kHz av.n.5.1.2.4 kHz 4 kHz
Max NIPTS 90th percentile 7 dB 12 dB 28 dB
NIPTS at 10 yrs. 90 percentile 4 9 24
Average NIPTS 3 6 15
Max NIPTS 10th percentile 2 4 JJ
Example: For an exposure of 85 dB during an 8-hour working day, the
following effects are expected:
For the 90th percentile point, the Max NIPTS occurring typically
during a 40-year work lifetime, averaged over the four frequencies of 0.5,
1, 2 and 4 kHz, is 7 dB; averaged over the three frequencies of 0.5, 1, and
2 kHz is 4 dB and 19 dB at 4 kHz. For this same 90th percentile point of
the population, the expected NIPTS after only 10 years of exposure would be
6 dB averaged over the four frequencies, 2 dB averaged over three frequencies,
and 15 dB at 4 kHz.
C-7
-------
used to extrapolate to higher percent!les.
2. NIPTS at 10 years: The entries on this row also apply
to the 90th percentile point of the population for 10 years of exposure.
3. Average NIPTS: The value of NIPTS is averaged over all
the percent!les for all age groups. (This figure differs by only a couple
of decibels from the median NIPTS after 20 years of exposure for the
entire population.)
The values in Table c-1 are arithmetic averages of data found
in the reports of Passchier-Vermeer "8, Robinson°~5, and Baughn°"9.
IV. Derivation of Exposure Levels
A. Selection of the Percentile and Related Exposure Level
The estimation of NIPTS for a given percentile has been accom-
plished by subtracting the hearing level of that percentile of the non-
noise-exposed group from the hearing level of the respective percentile
of the noise-exposed group. People above the 90th percentile are those
whose hearing is worse than that of 90 percent of the population. Thus,
for example, if the group at the 90th percentile shows a shift of 10 dB
because of noise exposure, then it is considered that the group has a
NIPTS of 10 dB. Extrapolations above the 90th percentile can be made
from existing data, as done in Figure C-2. These extrapolations require
cautious interpretation. First, the data for the 75 dB exposure levels
in Table c-1 are themselves derived from extrapolations. The last firm
data are at 78 dB. Second, for many of the studies that serve as the
basis for the Passchier-Vermeer work, the 90th percentile is already
extrapolated from the 75th percentile.
c-8
-------
As stated earlier, the assumption has been made that if a
person's hearing loss is severe enough, noise exposure will not make
it worse. To bo more precise, a person will not incur a hearing loss
from a noise that he cannot (so long as it is within tho. audible
frefjuency range). Granting this assumption, it follows that nt sew
percentile, the amount of NIPTS for a given exposure level will approach
an asymptote. In order for further hearing loss to be incurred above
this critical percentile point, greater exposure levels must occur. In
the extreme, a person who is totally deaf cannot suffer noise-induced
hearing loss.
A study of the data provides a basis for a reasonable estimate
of this critical percentile. Baughn's data gives an indication that
the population with a hearing level greater than 60 dB after a 40-year
exposure begins to become less affected by noise (Figures 9, 10, and 11
of ref. c-2). For example, if a person has a hearing loss greater than
75 dB, it is not reasonable to expect that an A-weighted noise of 75 dB
(which normally means that only a level of 65 dB would be present at the
octave band centered at 4000 Hz) will cause a further increase of the
75 dB loss. Next, it is necessary to determine the distribution of
hearing levels of the non-noise-exposed population
at age 60. The best data available are the hearing levels of 60 year-old
women of the 1960-62 Public Health Survey^ ~4. While certainly some of
the women in the sample may be noise exposed, the noise exposure of that
population sample can be considered minor as compared to the apparent
noise exposure of men. The data from the Public Health Survey predict
the percentage of the population with hearing levels above 70, 75, and
80 dB.
C-9
-------
r_-r
CM
% a
0) "-1
to
to
in
o
+3
<
CM
6
HP "T SLdIN
C-1Q
-------
Figure C-3 shows the exposure levels at which no more than 5 dB
NIPTS at 4000 Hz will occur for various percentiles on the lowermost curve.
The curve labeled PHS-4000 Hz represents hearing levels by percentiles of
the non-noise exposed population. If a noise level that cannot be heard
by an individual is assumed not to change his hearing level, then the
extrapolated 5 dB NIPTS curve of Figure C-3 cannot cross the curve labeled
PHS. In fact, the 5 dB NIPTS curve must turn upward and merge with the
PHS curve, shown in Figure C-3 by the dotted line. The point of merqina is
seen to be at approximately the 96th percentile and the exposure level
required to protect this percentile from a shift of more than 5 dB is an
^eq(8) °^ ^ to 74 dB, or approximately 73 dB. It may be concluded
therefore, that a 40-year noise exposure below an Leq(g) of 73 is satis-
factory to prevent the entire statistical distribution of hearing levels
from shifting at any point by more than 5 dB. Generalizing from these
conclusions, the entire population exposed to Leq(gj Of 73 is protected
against a NIPTS of more than 5 dB.
A similar analysis can be made for 5 dB and 10 dB NIPTS at
the mid frequencies (Figurec-4). The upper PHS curve represents the
better ear data for the average of 500, 1000 and 2000 Hz of both men
C* A
and women from the Public Health Survey "4. Both men and women are
used since there is little difference due to sex and hearing levels
for these frequencies. Considering that the curves will merge in the
same manner as the 5 dB at 4000 Hz NIPTS and PHS curves, one can conclude that:
1- Leq(8) of 84 dB will cause no more than a 5 dB shift at
the critical percentile for the averaged frequencies 500, 1000 and 2000 Hz.
c-ll
-------
HEARING LEVEL FOR PHS CURVE RE 20 MICRDPASCALS
LU
UJ
O
CC
UJ
Q- ,
I o
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vap (Ava/aH 8) 13A31 3ansodxa UA
C-12
-------
HEARING LEVEL FOR PHS CURVES
RE 20 MTCRDPASCALS
8
o
o>
o
00
o
CO
o>
CO
(V9P) T3A31 3UnSOdX3 (AVQ/UH 8) HA Ofr
C-13
-------
2. Leq(8) of 89 dB will cause no more than a 10 dB shift at
the most critical percentile for the averaged frequencies 500, 1000 and
2000 Hz.
Although the data base used here is quite large, we cannot
be absolutely certain that it is representative of the whole population.
Any argument such as that presented above does not,in fact,provide 100%
protection of the entire population. Obviously, there are a few individ-
uals who might incur more than 5 dB NIPTS for an exposure level of 73 dB.
There is the possibility that individuals might shift from lower to
higher percentiles with a change in exposure level. In other words,
there may be individuals who experience greater shifts in hearing level
than those predicted here over periods of time much less than 40 years.
At this point,it may be useful to examine the same data in a slightly
different way, without utilizing the concept of the critical percentile.
Assuming that the NIPTS of the exposed population are distributed
normally, the exposure levels which produce various amounts of NIPTS
at the 50th and 90th percentiles may be extrapolated to levels which
produce NIPTS at the 99th percentile. Using this extrapolation, Figure
c-5 shows NIPTS as a function of exposure level for the 50th, 90th and
99th percentiles. The 99th percentile curve intersects the 5 dB NIPTS
point at 71.5 dB (which is only 1.5 dB below the level previously
identified). Thus, if one wishes to protect up to the 99th percentile
without employing the concept of the critical percentile, the exposure
level necessary to prevent more than 5 dB NIPTS is an Leq(8) of 71.5 dB.
The preceeding analysis utilizing the concept of the critical
percentile, concludes that an 8-hour per day exposure to a 73 dB steady
C-14
-------
p
I
I
Max NIPTS (.9)
MaxNIPTS^.99}/
/
''
Max NIPTS (.5)
Single extrapolation
Double extrapolation
65
70
95
75 80 85 90
40 YR (8 HR/DAY) EXPOSURE LEVEL IN dBA
FIGURE C-5 NIPTS as a Function of Exposure Level for the 50th, 90th and 99th
Percentiles.
C-15
-------
noise for 40 years will result in a noise-induced permanent threshold
shift of no more than 5 dB at 4000 Hz. This conclusion was reached
through the use of assumptions and considerations pointed out earlier
in this appendix. Similar analysis of the same and similar data may be
made using other assumptions and considerations. Some analyses lead to
essentially the same conclusion while others do not. However, no such
anlaysis has identified a level of much less than 65 dB or much greater
than 80 dB for the same conditions (i.e., 5 dB NIPTS at 4000 Hz for
40 years of exposure). While the discussion of these levels and their
derivations are a subject of great interest and activity in the scientific
community, the Administrator of the Environmental Protection Agency is
required to identify the level which,in his judgment,is requisite to
protect public health and welfare. For that purpose, the level of 73 dB
appears to be the most reasonable choice for the conservation of hearing
based on the present state of scientific knowledge.
B. Adjustments for Intermittency and Duration
The next step is to transpose this level into one which will
protect public health and welfare,in terms of environmental noise exposure,
with an adequate margin of safety. For this purpose, it is necessary to
correct for intermittency and to extrapolate to 24 hours. In order to do
this, two hypotheses are necessary -- the TTS Hypothesis and the Equal
Energy Hypothesis.
The TTS Hypothesis states that a temporary threshold shift
measured 2 minutes after cessation of an 8-hour noise exposure closely
approximates the NIPTS incurred after a 10- to 20-year exposure to that
c-16
-------
same level. There is a substantial body of data supporting this hypothesis,
The Equal Energy Hypothesis states that equal amounts of sound
energy will cause equal amounts of NIPTS regardless of the distribution
of the energy across time. While there is experimental confirmation and
general acceptance of this hypothesis, certain types of intermittency
limit its application.
1. Intermittency
The equal energy concept is considered by some to be a
conservative approach for short exposure periods. An alternative approach
may be necessary because there is little direct evidence to show the effect
of short exposure periods or intermittency on the development of NIPTS.
This approach implies the use of temporary threshold shift as a predictor
of NIPTS.
Even for a continuous noise, TTS is not predictable for
all possible durations using the equal energy rule. The equal energy
rule predicts, with reasonable accuracy, the TTS at 4000 Hz for durations
of 8 hours down to about 30 minutes. Effects from durations shorter than
this, however, are better predicted by a slight deviation from the equal
energy rule. While equal energy provides for a 3 dB increase in exposure
level for each halving of exposure duration, TTS for durations of less
than 30 minutes are better predicted by greater intensities for each
halving of time. For instance, TTS for durations of less than 15 minutes
are better predicted by a 6 dB rather than a 3 dB increase. For an
exposure of two minutes duration, the level required to produce an
expected TTS at 4000 HZ would be approximately 10 dB greater than the
C-17
-------
level predicted by the equal energy concept.
Investigations of environmental noise patterns reported
in the EPA document "Community Noise''^^ indicate that in most environ-
ments, noise fluctuates or is intermittent. Moreover, intermittent noise
for a given Leq having peak levels of 5 to 15 dB higher than the back-
ground level, may produce less hearing damage than a continuous noise
with the same energy.c'11 Also, noise levels which are below 65 dB for
c i ?
10 percent of the time tend to be less dangerous than continuous noise. "'
Therefore, intermittent noise as used in this document will be defined as
noise which is below 65 dB for about 10 percent of each hour (i.e., Lgg of
less than 65 dB), with peak levels of 5 to 15 dB higher than the background.
From the examples cited in "Community Noise", it is clear that most environ-
mental noise meets these criteria. For this reason, the L measured in
many situations can be expected to produce less harmful effects on hearing
than those depicted in Table C-l. Some correction factor is thus indicated
for l_eq values describing noise expected in a typical environmental situa-
tion in which the exposure is relatively intense but intermittent in
nature.
In order to determine an appropriate correction factor,
Figure c-6 has been drawn. Using an exposure of 73 dB for 8 hours as a
baseline, the sound pressure levels producing equal TTS to be expected
at 4000 Hz are plotted for durations of continuous noise as short as
c ^
1-1/2 minutes. "•* Plotted also (curve a),is the maximum intermittency
Q -I o
correction suggested by "Second Intersociety Committee" "' and discussed
in the NIOSH criteria document. c"11 This correction is for the mid
c-ia
-------
ZH OOOfr aoj sa/uro sil
LLJ
C
2
CD
O
3
»*-
O
co
(O
O
T3 m'
•s™
189
H
fa
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t^ ^~
P-
a_?
.1 <«
._
-------
frequencies. Recent work has indicated that for 4000 Hz the best inter-
mi ttency correction to produce equal TTS^ is represented by curve b.c-l4
Tho crosshntchod nro.i betweon the curves"a"and"c"siqnifies the dtrea of
uncertainty.
In addition, ITS curves for impulse noise are included in
Figure C-6. Appendix G contains the details of the modified CHABA limit
and the conversion necessary to derive from the peak sound pressure level
of a decaying impulse the continuous A-weighted noise of the same dura-
tion. The impulse noise data show that the equal energy concept is still
a reasonable approximation for very short durations. While certainly it
may be overly protective for some noise patterns, in general it predicts
the effects of noise on hearing reasonably well. Prediction is improved,
however, with a 5 dB allowance for intermittency.
The average correction for intermittency suggested by
Figure c-6 is 5 dB (i.e., placing the origin of the equal energy line at
78 dB for 8 hours). This correction should be used only if the noise
level between events is less than 65 dBA for at least 10 percent of the
time (Lgg<65 dBA). Since most environmental noise exposures will meet
this requirement during any 8-hour period, it is further suggested that
environmental noise should be considered intermittent unless shown
otherwise. Using the 5 dB correction factor, the area of uncertainty
(crosshatched) of Figure c-6 is approximately bisected. Further support
for such a 5 dB correction factor is found in a recent Swedish study
where exposure to continuous noise of L 85 to 90 caused a hearing
loss which corresponded to an intermittent noise of L go to 95. The
C-20
-------
authors conclude that a 5 dB correction factor is appropriate.1^5
For certain noise situations, a larger intermittency
correction might be justified. However, the use of large corrections
when only part of the total noise exposure pattern is known entails a
considerably higher chance of error. Therefore, the use of correction
factors higher than 5 dB for intermittency are not considered con-
sistent with the concept of an adequate margin of safety.
2. Conversion of 8-Hour to 24-Hour Exposure Levels
The TTS after 24 hours of exposure generally exceeds that
c 9
after 8 hours of exposure by about 5 dB. "^ Thus the use of a 5 dB
correction factor is suggested to extrapolate from the 8-hour exposure
data to 24-hour exposure. ? For example, the predicted effects of an
exposure to 75 dB steady-state noise for a 24-hour duration are equiva-
lent to the effects estimated from industrial studies for an 8-hour
exposure to a continuous noise with a level of 80 dB. This 5 dB correction
is consistent with the equal-energy trade-off between exposure duration
and noise level. That is, the equal-energy rule in this case also dictates
a correction of 5 dB for 24 hours.
It appears that exposures over a period longer than 24 hours
need not be considered in this case. Various studies of TTS ' > "' » ^
have shown that, for an exposure to a specific noise level, TTS will not
exceed a limiting value regardless of exposure duration. This limit is
reached at approximately 24 hours of exposure. However, this concept
applies only to exposure levels less than 85 dB.
-------
3. Conversion^ of Occupational Dose to a FulJ_Ye_ar
r250'To 365 DaysT
The applicability of occupational data to non-occupational
exposure is questional in several ways. One concern is the use of the
occupational exposure data to predict the general effects on populations
composed of people who, for a variety of reasons, do not work. However,
there are no data from which to derive approximate correction factors.
Another concern is the fact that the occupational data are based on a
250-day working year. When predicting the effect of a known noise
exposure over the 365-day year, certainly some correction is in order.
The equal energy concept would predict at least a 1.6 dB lowering of the
exposure level,and such a correction should be used when the concept of
an annual exposure dose is used.
To summarize the adjustments, the following exposures
over 40 years will result in the same effect:
Leq of 73 dB continuous noise during the 8-hour
working day with relative quiet for the remaining
16 hours, 5 days per week. (See discussion of quiet
requirements below).
Leq of 78 dB intermittent noise during the 8-hour
working day with relative quiet for the remaining
16 hours, 5 days per week.
73 + 5 = 78
L of 76.4 dB intermittent noise for 8 hours a day,
with relative quiet for the remaining 16 hours, for
the 365-day year.
78 - 1.6 = 76.4
c-22
-------
Leq of 71-4 dB intermittent noise for 24 hours
a day, 365 days a year.
76.4 - 5 = 71.4
In view of possible uncertainties in the analysis of thp data, it is
considered reasonable to round down from 71.4 dB to 70 dB. These uncertain-
ties will be discussed in the next section.
V. Considerations for Practical Application
A. The Data Base
In viewing the data in this appendix, and elsewhere in the hear-
ing impairment literature, a number of fundamental considerations must be
noted:
1. Few, if any, of the various "classic studies" (e.g., those
of Robinson, Baughn, and Passchier-Vermeer) are on comparable populations.
In addition, some of the data are derived from populations for which noise
exposure histories are sketchy, if not absent (e.g., the 1960-62 U.S.
Public Health Survey data).
2. There are major questions regarding the comparability of
the audiometric techniques used in the various surveys.
3. There are a great number of unanswered questions and areas
of uncertainty with regard to the relationship of individual physiological
and metabolic state to hearing ability. The role of the adequacy of the
blood supply to the ear (and the possible influence of changes in that
blood supply resulting from cardio-vascular respiratory disease or the
process of aging),as well as the fundamentals of cellular physiology
involved in adverse effects within the organ of Corti,simply cannot be
-------
stated with any degree of reliability at this time. There is some evidence
that these non-noise related influences may be of major significance.
Moreover, part of the adverse effect of noise on hearing may be attribut-
able indirectly to these influences.
4. There are no large-scale longitudinal studies on hearing
loss in selected and carefully followed populations, whose physical state
and noise exposure has also been carefully detailed.
B. Accuracy of Estimated Effects
There is imperfect agreement among various studies as to the
exact relationship between sound exposure level and noise-induced hearing
loss. The range of error involved is on the order of 5 dBc"^ when examin-
ing the difference between the values in any single study and the values
presented in Table c-1. Furthermore, the intermittency correction of
5 dB is only an approximation. It has been proposed that a correction
as high as 15 dB could be used in some cases. Thus, the true intermittency
correction for a particular noise exposure situation could be from 0 - 15 dB
The selection of alternative population percentiles to be pro-
tected would cause relatively small changes. For instance, there is only
a 7 dB difference in protecting the 50th percentile against incurring a
5 dB hearing loss instead of the 96th percentile.
Using the assumption that the noise is of broadband character
can lead to errors of 5 to 10 dB by which the risk of the sound exposure
is underestimated. This could lead to greater possible errors if a sub-
stantial portion of the exposure is to noise with intense pure tone
components. These conditions, however, are rare in the environmental
situation.
C-9A
-------
There are apt to be errors in extrapolating beyond the 90th
porcentile in order to predict effects at higher percentiles. Likewise,
thpro might, ho errors in extrapolating from known exposure data at nn and
80 dB to estimated effects at 73 dB for an 8-hour exposure to continuous
noise.
One final potential source of error inherent in using the occupa-
tional data is the need to compare the population which has received an
occupational noise exposure to population that has not received an occupa-
tional noise exposure. This latter population may, however, have been
exposed to levels of environmental noise (other than occupational). As a
consequence in comparing the two groups, occupational exposures may very
well show negligible effects below a certain level because other environ-
mental noises predominate. The direction of the possible error is not
unequivocally clear, as certainly the adverse effect of many industrial
exposures may very well have been due to an unfortunate combination with
non-occupational exposures. At this time, it is impossible to properly
analyze the possible bias that the non-occupational noise exposure
introduces into the data of Table C-l. At present it is assumed to be
negligible. This assumption will require ultimate verification by experi-
mentally relating the annual exposure dose of individuals to their
hearing level. Only such studies will show how much of what we now tend
to contribute to the physiological aging process of the hearing mechanism
could be reduced by further reducing what we consider today as "normal"
or "quiet" environmental noise levels associated with present-day living
in our society.
C-25
-------
C. Quiet Requirements
It has been shown that the quiet intervals between high intensity
noise-bursts must be below 60 dB SPL for the octave band centered at 4000 Hz
if recovery from temporary threshold shift at 4000 Hz is to be independent
C- 20
of the resting sound pressure level. In this document, sound pressure
level of 50 dB in the 4000 Hz octave band is suggested as a goal for "effec-
tive quiet" For typical spectra of community noise, 50 dB SPL in the
4000 Hz octave band translates to an A-weighted sound level of approximately
60 dB. Thus, for purposes of hearing conservation, the noise level where
an individual sleeps should not be above an L of 60 dB, based on the
following considerations:
1. Total TTS recovery is required to prevent TTS from
becoming NIPTS.
2. For some individuals, an 8-hour nighttime period is the
only available recovery period.
3. In order to be consistent with the identified level of
Leq(24) = 70, an 8-hour exposure of 75 dB would require an exposure of
60 dB or less for the remaining 16 hours.
It should be noted that this level would be too high to protect
against other effects. (See Appendix D)
D. Contribution of Outdoor Noise to the Total Exposure in
Residential Areas
A person's 24-hour exposure to outdoor noise will typically
include both outdoor and indoor exposures. Since a building reduces the
level of most intruding outdoor environmental noises by 15 dB or more
(windows partially open), an outdoor Leq will not adequately predict
C-26
-------
hearing effects, because the corresponding NIPTS estimates win be too
high. Consider a situation where the average sound level is 70 dB out-
doors and 55 dB indoors. The effective noise exposures
for some of the possible exposure situations are:
24-hour Leq in dB
Indoor Time
(55 dB)
24 hrs
23
22
21
20
16
8
0
Outdoor Time
(70 dB)
0 hrs
1
2
3
4
8
16
24
Combined
Indoor &
Outdoor
55.0
58.6
60.5
61.8
62.9
65.5
68.3
70
Outdoor
Only
-
56.2
59.2
61.0
62.2
65.2
68.2
70
(assuming the noise
is generated out-
doors)
The 24-hour value of the combined L is essentially unchanged from the
outdoor value (less than one dB) by the indoor noise exposure, so long as
the outdoor exposure exceeds 3 hours. Thus, as long as the criterion is
established with respect to outdoor noise exposure exceeding 3 hours per
day, the contribution of the indoor level of intruding outdoor noise may
be neglected in computing the 24 hour Leq. This conclusion does not
depend greatly on the actual noise attenuation provided by the house
so long as the attenuation is greater than 10 dB.
E. Relation of l_dn to Lgq in Residential Areas
Although in residential areas, or in areas where individuals
may be expected to be present for prolonged periods of time, it would
C-27
-------
appear desirable for practical considerations to use only one measure of
noise, such as l_dn, u may be misleading to do so. The difficulty arises
from the fact that to relate hearing loss to noise exposure, the basic
element to consider is the actual energy (not weighted) entering the ear
during a twenty-four hour period. L measures the actual energy enter-
ing the ear whereas L^ includes a 10 dB weighting for the nighttime
period. Thus, Ldn values corresponding to actual L values are dependent
upon the distribution in noise levels occurring during the total twenty-
four hour period and could be misleading. For example, the L^p values
corresponding to Leq(g) are between 0 to 6 dB greater than the L values.
The lower value corresponds to a situation where the average sound level
during the night is 10 dB lower than that occurring during the dayfwhere-
as the higher value corresponds to the situation when the average sound
level during the night equals that occurring during the day. In residen-
tial areas, the difference in Leg values for the daytime and nighttime
period often is approximately 4 dB based on community noise measure-
p ?n
ments. In this particular case, this difference in Leq values leads
to an Lc|n value which is three decibels above the Leq value for the day-
time period.
C-28
-------
REFERENCES FOR APPENDIX C
C-l. French, N. R. and Steinberg, J. C., "Factors Governing the
Intelligibility of Speech Sounds," Journal of Acoustical Society
of America, 19:90-119, 1947.
C-2. Johnson, D. L., "Prediction of NIPTS Due to Continuous Noise
Exposure," EPA-550/9-73-001-B or AMRL-TR-73-91, July 1973.
C-3. Kryter, K. D., Ward, W. D., Miller, J. D. and Eldredge, D. H.,
"Hazardous Exposure to Intermittent and Steady-State Noise,"
Journal of Acoustical Society of America, 39:451-464, 1966.
C-4. National Center for Health Statistics, Hearing Levels of Adults
by Age and Sex, United States, 1960-1972. Vital and Health
Statistics, PHS Pub. No. 1000-Series 11-No.ll. Public Health
Service, Washington, D.C., U.S. Government Printing Office,
October 1965.
C-5. Robinson, D. W., "The Relationship Between Hearing Loss and
Noise Exposure," Aero Report Ae 32, National Physical Laboratory,
England, 1968.
C-6. National Center for Health Statistics, Hearing Levels of Children
by Age and Sex. Vital and Health Statistics. PHS Pub. No. 1000
Series 11-No. 102. Public Health Service, Washington, D.C.,
February 1970.
C-7. Guignard, J. C., "A Basis for Limiting Noise Exposure for Hearing
Conservation," EPA 550/9-73-001-A for AMRL TR-73-90, Julv 1973.
C-3. Passchier-Vermeer, W., "Hearing Loss Due to Steady-State Broadband
Noise," Report No. 35, Institute for Public Health Engineering,
The Netherlands, 1968.
C-9. Baughn,W. L., "Relation Between Daily Noise Exposure and Hearing
Loss as Based on the Evaluation of 6835 Industrial Noise Exposure
Cases," In publication as AMRL-TR-73-53, Wright-Patterson Air
Force Base, Ohio.
C-10. Eldred, K. M., "Conmunity Noise," EPA NTID 300.3, December 1971.
C-ll. "Occupational Exposure to Noise, Criteria for a Reconraended
Standard," U.S. Department of Health, Education and Welfare,
National Institute for Occupational Safety and Health, 1972.
C-12. Kryter, K. D., Effects of Noise on Man, Academic Press, New York,
1970.
C-13. Guideline for Noise Exposure Control, Sound and
Vibration, Vol. 4, pp. 21-24, Noveittoer 1970.
C-14. Ward, W. D., "On the Trading Relation Between Time and Intensity
for Intermittent Noise Exposures," presented at 86th Meeting of
Acoustical Society of America, October 1973.
C-29
-------
C-15. Johansson, B., Kylin, B., and Reppstorff, S., "Evaluation of
the Hearing Damage Risk from Intermittent Noise According to
the ISO Reoommendations," Proceedings of the International
Congress of Noise as a Pv±>lic Health Problem, Dubrovnik, Yugoslavia,
EPA 550/9-73-008, May 1973.
C-lf). Carder, H. M. and Miller, J. D., "Temporary Threshold Shifts
from Prolonged Exposure to Noise," Journal of Speech and Hearing
Research, 13:603-623, 1972.
C-17. Mills, J. H. and Talo, S. A., "Temporary Threshold Shifts
Produced by Exposure to Noise," Journal of Speech and Hearing
ftssearch, 15:624-631, 1972.
C-18. Melnick, W., "Investigation of Human Temporary Threshold Shift
(TTS) from Noise Exposure of 16 Hours Duration," paper presented
at Meeting of Acoustical Society of America, 1972.
C-19. Ward, W. D., "The Concept of 'Effective Quiet1," presented at
the 85th Meeting of the Acoustical Society of America, April 1973.
C-20. "Impact Characterization of Noise Including Implications of
Identifying and Achieving Levels of Cumulative Noise Exposure,"
Environmental Protection Agency,NTID 73.4, July 27, 1973-
C-30
-------
APPENDIX »
NOISE INTERFERENCLWJJH HUMAN ACTIVITIES AND RESULTING
ANNOYANCE/HEALTH 'EFFECTS '
Environmental noise may interfere with a broad range of human
activities in a way which degrades public health and welfare. Such
activities include:
1. Speech Communication in Conversation and Teaching •
2. Telephone Communication .
3. Listening to TV and Radio Broadcasts.
4. Listening to Music.
5. Concentration During Mental Activities .
6. Relaxation.
7 . Sleep .
Interference with listening situations (1-4) can be directly
quantified in terms of the absolute level of the environmental noise
and its characteristics. The amount of interference in non-listening
situations ( e,^.,) is often dependent upon factors other than the
physical characteristics of the noise. These may include attitude
towards the source of an identifiable noise, familiarity with the
noise, characteristics of the exposed individual, and the intrusiveness
of the noise.
The combination of the various interference effects results in
an overall degradation of total well-being. Maximum noise levels
that do not affect human well-being must be derived from the body
D-l
-------
of information on human behavioral response to various noise
environments.
I. Speech Interference
Speech communication has long been recognized as an
important requirement of any human society. It is one of the
chief distinctions between humans and other species. Interference
with speech communication disturbs normal domestic or educational
activities, creates an undesirable living environment*and can
sometimes, for these reasons, be a source of extreme annoyance.
Continued long-term annoyance is considered to affect individual
as well as public health and welfare in a variety of ways.
Noise can disturb speech communication in situations
encountered at work, in vehicles, at home,and in other settings.
Of chief concern for the purposes of this report, is the effect
of noise on face-to-face conversation indoors and outdoors, telephone
use>and radio or television enjoyment.
The extent to which environmental noise affects speech
communication depends on the location (whether indoors or outdoors),
the amount of noise attenuation provided by the exterior walls
when indoors (including windows and doors)>and the vocal effort of
the talkers. Certainly, it is possible to maintain communication
in the face of intruding noise if the voice level is raised, but
in an ideal environment, one should not have to increase the voice
D-2
-------
level above that which is comfortable in order to communicate
p»r. i 1 y.
!<«••,c.ir< h '.line l.hc l
-------
measure of the speech interference potential of intruding noise.
A-weighting gives greatest weight to those components of the noise
that lie in the frequency range where most of the speech information
resides, and, thus, yields higher readings (A-weighted levels) for
noises in most of the 200 to 6000 Hz range than does the overall
sound pressure level. A-weighted sound levels will be used
throughout this appendix unless otherwise noted.
The principal results of relevant speech research can be
utilized for practical application to provide the levels of noise
that will produce varying degrees of masking as a function of average
noise level and the distance between talkers and listeners. Other
factors such as the talker's enunciation, the familiarity of the
listener with the talker's language, the listener's motivation and,
of course, the normality of the listener's hearing also influence
intelligibility. This value is consistent with the upper end of
the range of levels of steady state sound recommended by prior authors
in Table D-10 (to be discussed later) as "acceptable" for design
purposes for homes, hotels, motels, small offices,and similar spaces
where speech communication is an expected and important human activity.
A. Indoor Speech Interference Due to Steady Noise
The effects of masking normally-voiced speech indoors
are summarized in Figure D-l, which assumes the existence of a
reverberant field in the room. This reverberant field is the
D-4
-------
result of reflections from the walls and other boundaries of the
room. These reflections enhance speech sounds so that the decrease
of speech level with distance found outdoors occurs only for spaces
close to the talker indoors. At distances greater than 1.1 meters
from the talker, the level of the speech is more or less constant
throughout the room. The distance from the talker at which the
level of the speech decreases to a constant level in the reverberant
part of the room is a function of the acoustic absorption in the
room. The greater the absorption, the greater the distance over
which the speech will decrease and the lower the level in the
reverberant field for a given vocal effort. The absorption in a
home will vary with the type and amount of furnishings, carpets,
drapes and other absorbent materials. It is generally least in
bathrooms and kitchens and greatest in living rooms, with typical
values ranging between 150 and 450 sabins. A typical value for
living rooms and bedrooms is 300 sabins. For this value of absorption,
the distance to the reverberant field from the talker is slightly
greater than one meter, as stated above.
As shown in Figure o-l, the maximum sound level that
~w
will permit relaxed conversation with 100% sentence intelligibility
throughout the room (talker-listener separation greater than
approximately 1.1 meter) is 45 dB.
D-5
-------
CO
I—I
C3
o
LU
0.
STEAD? A-WEIGHTED SOUND LEVEL IN dB (re 20 micropascals)
NDTE: Assumes 300 sabins absorption typical of living rooms
and bedrooms and is valid for distances greater than
one meter.
Figure D-l. Normal Voice Sentence Intelligibility as a
Function of the Steady Background Sound Level
in an Indoor Situation ®~1> °~2' &
D-6
-------
B. Outdoor Speech Interference Due to Steady Noise
The sound level of speech outdoors generally continues
to decrease with increasing distance between talker and listener
with the absence of reflecting walls which provide the reverberance
found indoors. Figure D-2 presents the distances between talker
and listener for satisfactory outdoor conversations, in different
steady background noise levels (A-weighted), for three degrees of
vocal effort. This presentation depends on the fact that the voice
level at the listener's ear (outdoors) decreases at a predictable
rate as the distance between talker and listener is increased.
In a steady background noise there comes a point, as the talker
and listener increase their separation, where the decreasing speech
signal is masked by the noise.
The levels for normal and raised-voice "satisfactory
conversation" plotted in the figure do not permit perfect sentence
intelligibility at the indicated distances; instead, the sentence
intelligibility at each distance is 95 percent, meaning that 95 percent
of the key words in a group of sentences would be correctly understood.
Ninety-five percent sentence intelligibility usually permits reliable
communication because of the redundancy in normal conversation.
That is, in normal conversation, some unheard words can be inferred
if they occur in particular, familiar contexts. Moreover, the
vocabulary is often restricted, which also helps understanding.
n-7
-------
Therefore, 95 percent intelligibility is satsifactory for most
situations.
D-8
-------
.3 .4 .6
.8 1 1.5 2 34 6
Communicating Distance In Meters
8 10 15 20
Figure D-2. Maximum Distances Outdoors Over Which Conversation
is Considered to be Satisfactorily Intelligible
in Steady Noise.D-'. D-2
D-9
-------
The levels given in Figure D-2 for relaxed conversation
permit 100% speech intelligibility when communicating in a normal
voice. This situation represents an ideal environment for speech
communication and is considered necessary for acceptable conversation
in the indoor environment. However, it does not define the situation
outdoors where 95% intelligibility is adequate,and communication
outdoors generally takes place between people who are walking or
standing relatively close tegether, about 1 to 2 meters. Moreover,
these levels appear to be consistent with the need for speech
privacy.
The data for normal and raised voice of Figure D-2
are tabulated for convenience below;
«
TABLE D-1
STEADY A-WEIGHTED NOISE LEVELS THAT ALLOW COMMUNICATION WITH
95 PERCENT SENTENCE INTELLIGIBILITY OVER VARIOUS DISTANCES
OUTDOORS FDR DIFFERENT VOICE LEVELS (Ref. D-2)
VOICE LEVEL
COMMUNICATION DISTANCE (meters).
Normal Voice (dB)
Raised Voice (dB)
0.5
72
78
1
66
72
2
60
66
3
56
62
4
54
60
5
52
58
D-10
-------
If the noise levels in Figure D-2 and Table D-l are exceeded, the
speaker and listener must either move closer together or expect
reduced intelligibility. For example, consider a conversation at
a distance of 3 meters in a steady background noise of 56 dB using
normal voice levels. If this background level is increased from
56 to 66 dR, the speakers will either need to move from 3 to 1 meter
separation to maintain the same intelligibility, or alternatively,
to raise their voices well above the raised-voice effort, if they
remain 3 meters apart without raising their voices, the intelligi-
bility would drop from 95 to 65 percent.
0-11
-------
C. Speech Interference in the Presence of Fluctuating Sound
Levels
The data in Figures o-l and D-2 are based on tests
involving steady, continuous sound. It might be questioned whether
these results would apply to sounds which have fluctuating levels.
For example, when intermittent noise intrusions, such as those from
aircraft flyovers or truck passbys, are superimposed on a steady
noise background, the equivalent sound level is greater than the
level of the background alone. If the sound levels of Figures D-l
and 0-2 are interpreted as equivalent sound levels, it could be
argued that these values could be slightly increased (by an amount
r
depending on the statistics of the noise), because most of the
time the background noise level is actually lower than the equivalent
sound level.
The amount of this difference has been calculated for
the cases of urban noise and aircraft noise statistics shown in
Figure D-3. The data in this figure ^ include a wide range of
urban sites with different noise levels and an example of
aircraft noise at a site near a major airport. In each case the
speech intelligibility was calculated from the standard sentence
D-4
intelligibility curve for various values of Leq, first with
steady noise and then with the two specific fluctuating noises of
Figure D-3. The calculation consisted of determining the incremental
D-12
-------
20
10
03
C
o-
_l
I
-10
-20
-30
-40
Range of Urban Noise Samples
from Community Noise Study
(Excluding Aircraft Noise)
Example of Aircraft Noise
Near Major Airport
12 5 10 20 30 40 50 60 70 80 90 95 98 99
Percent of Time LX Value will be Exceeded
Figure D-3. Cumulative Distribution of Typical Community Noises During
the Daytime Relative to the Equivalent Sound Level.
0-13
-------
contribution to sentence intelligibility for each level (at
approximately 2 dB increments) and its associated percentage of
time of occurrence. The incremental contributions were then
summed to obtain the total value of intelligibility in each case.
The results, shown in Table D-2, demonstrate that, for
95 percent sentence intelligibility, normal vocal effort, and
2 meter separation between talker and listener outdoors, the
maximum Leq value associated with continuous noise is less than
the maximum value for an environmental noise whose magnitude varies
with time. It is therefore concluded that almost all time-varying
environmental noises with the same Leq would lead, averaged over
long time periods, to better intelligibility than the intelligibility
for the same Leg values of continuous noise.
Alternatively, for a fixed Leq value, the percentage of
interference with speech (defined as 100 minus the percentage
sentence intelligibility) is greater for steady noise than for
almost all types of environmental noise whose magnitude varies
with time. The relationship between L^p and the maximum percentage
sentence interference (i.e., for continuous noise) is given in
Figure D-4.
-------
Table D-2
;-';xl!-"JM EQUIVALENT SOUND LEVELS THAT ALLCW 9b PERCENT
SENTENCE INTELLIGIBILITY AT A DISTANCE OF 2 METERS,
USING NORMAL VOICE EFFORT OUTDOORS
(PvSF: Figures D-2 and D-3)
Noise Type L in decibels
Steady
Urban Coraiunity Noise
Aircraft Noise
60
60 +
65
The extreme example of a fluctuating noise is a series of
noise pulses of constant level that are of sufficient magnitude relative
to the background to control the equivalent sound level. For example,
there could be a case where the background noise during the off-cycle
is assumed negligible, so that when the noise pulses are not present,
the speech intelligibility is 100 percent. Table D-3 shows how the
percentage interference with sentence intelligibility varies as a
function of the level and on-time for a cycled steady noise whose
level and duration are always adjusted to yield a fixed value for
the equivalent sound level. Two situations are envisaged: indoors,
relaxed conversation, Le = 45 dB, leading to 100 percent sentence
intelligibility in the steady, continuous noise; and outdoors, normal
voice effort at 2 meters separation* Leq = 60 dB, leading to 95
percent sentence intelligibility in the steady, continuous noise.
D-15
-------
OUTDOORS
(NORMAL
VOICE
LEVEL AND
2 METERS
SEPARATION)
INDOORS
(15 dB attenuation)
65
70
75
80
OH7T/11 :.AV .IIG.'.T ."A'E;V\?E SC'J.:: LEVEL, !_dr, IM
(re 20 micropascals)
NOTE: Percentage interference equals 10O minus percentage
intelligibility, and L. is based on L, + 3. D~39
on d
Figure D-40 Maximum Percentage Interference with Sentences as a
Function of the Day-Night Average Noise Level.
D-16
-------
TABLE D-3
PERCENTAGE INTERFERENCE WITH SENTENCE INTELLIGIBILITY IN THE
PRESENCE OF A STEADY INTRUDING NOISE CYCLED ON AND OFF
PERIODICALLY IN SUCH A WAY AS TO MAINTAIN
CONSTANT EQUIVALENT SOUND LEVEL, AS A FUNCTION OF THC
D-39
MAX I MUM NOISE LEVEL AND DURATION
(Assumes 1007" intelligibility during the off-cycle)
A-Weighted
IPVP! of in-
truding noise
during "on-cycle,"
Situation decibels
Duration
of intru-
ding noise
as per-
cent of
total time
Percent
inter-
ference
if intru-
ding noise
were con-
tinuous
Average
percent
interfer-
ence in.
cycled noise
INDOORS
Relaxed conversa-
tion, background i
Leq = 45dB,
100% intelligibility
if background
noise were
continuous at 35 dG
OUTDOORS
Normal voice at 2
meters, background
Leq = 60dB,
9% intelligibility
if background
45
50
55
60
65
70
75
80
1
60
65
70
75
100
32
10
3
1
0.3
0.1
0.03
100
32
"10
3
0 0
0.5 0.16
1 0.10
2
0.06
6 0.06
40
100
100
5
7.7
53
100
j 80 1 100
0.12
0.10
0.03
5.0
2.5
5.3
3.0
1.0
noise were continuous at 60
(REF: Task Group #3 Report)
D-17
-------
The combination of level in the first column and duration
in'the second column are such as to maintain constant L for each
situation, 45 dB indoors and 60 dB outdoors. The third column gives
the percent interference with sentence .intelligibility that would apply
if the noise were steady and continuous with the level indicated in
column 1. The fourth column gives the percent interference for the
cycled noise in each case.
The results for this extreme case indicate that no matter
how extreme the noise fluctuation for the indoor case, on the average
there is negligible speech interference for L = 45 dB. On the other
hand, with L = 60 dB outdoors, the average speech interference tends to
decrease as the fluctuations of the noise become more extreme.
However, it should be recognized that if the duration of the intruding
noise were to take place in one continuous period, and if its
percentage interference (column 3) were equal to 100, then it would
blot out all communication for the duration of its "on-cycle".
The following sections relating to activity interference,
annoyance, and community reaction utilize equivalent sound level
with a nighttime weighting (Ljjn) which is discussed more fully in
Appendix A. However, for the speech interference effects of noise,
a similar measure without the nighttime weighting Ueq) has been
employed. To allow comparison between the various effects stated
above, some relationships are necessary to allow at least approximate
D-18
-------
conversion from l_eq to L^. For indoor levels such as those
described in Appendix A for various lifestyles, levels during
the day are at least 10 dB higher than those during the night.
Thus Leq is virtually the same as L^n for normal indoor situations,
For an outdoor l^n of 55 dB or less, day time levels
(l_d) are generally 8 dB higher than the nighttime levels (l_n).
For this situation, L(jn is still quite close to Leq during the
day. The correction is less than one dB. For levels greater
than L^ 65 dB, the nighttime levels are generally only 4 dB
less than during the day time. For these cases, L(jn is 3 dB
higher than Leq during the day.
For values of L^ between 55 and 65, further inter-
polation is necessary using Figure A-7.
II. Activity Interference
Activity interference due to noise is not new. The
recent EPA document concerning public health and welfare criteria
D-5
for noise mentions an ordinance enacted 2500 years ago by the
ancient Greek community of Sybaris, banning metal works and the
keeping of roosters within the city to protect against noise
that interfered with speech and might disturb sleep. History
contains other examples indicating speech and sleep interference
due to various types of noises, ranging from wagon noise to the
noise of blacksmiths.
D-19
-------
1 Startles
2 Keeps From
Going to Sleep
3 Wakes Up
4 Disturbs Rest
or Relaxation
-~30 ... . 4_6. Percentage of People Disturbed by Aircraft Noise for
Various Tynes of Reasons Concerned With Domestic
Factors D~*
D-20
-------
More recently, surveys have been conducted which further
demonstrate that noise does interfere with various types of activity.
For example, Figures D-5 and D-6, based on research done in England,
give activity interference reported by the people who were
disturbed by aircraft noise for various types of activities as a
function of the approximate L . associated with noise from aircraft
flyovers (for explanation of the term L(jn see Appendix A).
Thus, for an outside L^n of approximately 55 dB, over 50% of the
people who were disturbed reported some interference with TV sound,
and 45% reported some interference with conversation. At the same
level, about 45% reported that noise occasionally woke them up,
while 30% claimed it sometimes disturbed their relaxation. The
figures also indicate that at higher noise levels,greater percentages
of people who were disturbed have reported activity interference.
Later research in the USA D~ provides the information
on activity interference shown in Table D-4. This table gives the
activity disturbance percentages of those who reported that they were
extremely disturbed by the noise, which accounts in part for
the low percentage values. It was reported that the daily activities
of 98.6% of those questioned (about 4000 people) were disrupted
one or more times by aircraft noise. More activities are mentioned
in Table D-4 than in the previous tables. For example, telephone
use, reading, listening to tapes and records,and eating were
reported to have been disturbed by noise.
D-21
-------
TABLE D-4
PERCENT OF THOSE PEOPLE WHO WERE EXTREMELY DISTURBED
BY AIRCRAFT NOISE*, BY ACTIVITY DISTURBED0"7
Activi ty
Percent
TV/Radio reception
Conversation
Telephone
Relaxing outside
Relaxing inside
Listening to records/tapes
Sleep
Reading
Eating
20.6
14.5
13.8
12.5
10.7
9.1
7.7
6.3
3.5
*Percent scoring 4 or 5 on a 1-5 scale,
n-22
-------
D ft
A study performed in the Netherlands gives further
evidence that activity interference is associated with noise (see
Table i>5). The data were taken in the urban/suburban areas in the
vicinity of the Amsterdam Airport where the L£jn ranged from 45 to
85 dB. Activity interference is shown by percentage of people
interviewed who have been frequently or sometimes disrupted in
various activities. Also reported are the estimated tolerance
limits for various portions of the exposed population. Thus,
in an area where noise produces "predominantly moderate nuisance,"
the "tolerance limit" is reached for one-third of the population.
Thirty-one percent report being sometimes disturbed by noise
during conversation,and 21% report being sometimes disturbed by
noise during sleep; occupational disturbance was reported by 122.
(The judgment of "admissibility" with respect to well-being in
Table D-5 is the result of the referenced study and not a
conclusion of this report.)
A recent study °~9 in the USA found that 46% of the 1200
respondents were annoyed by surface vehicle noise at some time.
Activities which were reported disturbed are indicated by
percentages shown in Table D-6. Here we see that sleeping is the
activity most disturbed by surface vehicle noise, followed in
order by listening to TV, radio or recordings; mental activity,
such as reading, writing or thinking; driving; conversing; resting
and walking.
D-23
-------
From the studies reported here,it is clear that noise does
indeed interfere with various activities in our everyday lives.
Unfortunately,most of the studies do not provide activity inter-
ference as a function of noise exposure. However, the activity
which is most sensitive to noise in most of the studies is speech
communication (including listening to TV), which can be directly
related to the level of the intruding noise.
-------
TABLE D-5
p t E OF PERSONS INTERROGATED WHO FEEL THAT THEY HAVE FREQUENTLY,
or Someti"METIMES' (s) BEEN D15™1®120 IN CONVERSATION, RADIO LISTENING,
' OCCUPATIONS, SLEEP; FEEL AFRAID, AND OF PERSONS IN WHOSE
ON THESE OCCASIONS THE HOUSE VIBRATES. AT MEAN VALUE OF
.loan
nuioonoo .
ocora I
«
0
1
2
3
4
5-
6
•
7
DiBtU
of
convorc
p *
0
7
16
27
39
56
67
93
rbfcnco
sation
S*
0
12
24
31
35
37
31
U
DioUi
of rfi
H_D(.i
P
0
2
5
10
18
27
38
56
irb » ••
idlo
j ning,
3
0
4
8
15
22
30
36
44
Mot
or t
vic
P
0
6
12
20
31
42
57
72
urb.
olo-
lon
B
0
A
10
18
23
25
• 26
26
28
Dlstui
OCCUpL
•
P
0
1
3
7
11
19
%
34
55
b.of
ilionn
a
0
3
7
12
19
28
39
45
Afraid
YtS
0
25
48
66
76
91
94
100
.* F denotes "frequently" S denotes "sometimes"
D-25
-------
TABLE D-5 (Continued)
House
Vibra.
f
Yr.i
0
21
41
'56
12
03
92
100
Distu
of SI
?
0
3
*
6
12
20
31
44
72
rb.
eep
S
0
7
14
21
20
33
42
20
Nuisance Felt
Subjectively
No nuioanco
Slight nui ounce
Slight to modo-
rute rfuioanco
i
Prodoiiiinantly
modor.ito
nuioanco
Predominantly
coriouc
nuiounco
^"fiouc
•nuiaancc
Inlolorublo
Intolo'rablo
l
Admissibility from point of view of
physical, mental and social well being,
in regard to which the stress is laid
on disturbance of sleep, disturbance
of conversation and feeling afraid.
Admissible
Admissible; the tolerance limit is
reached for about one-fifth of the
population.
Limit of admissibility; the tolerance
limit is reached for about one-third
of the population.
Inadmissible; the tolerance limit is
exceeded for about half of the
population
Inadmissible; the tolerance limit is
exceeded for about two-thirds of the
population.
Absolutely inadmissible
Absolutely inadmissible
D-26
-------
TABLE D-6
ACTIVITIES OF RESPONDENTS DISTURBED BY SURFACE VEHICLE NOISE
(All Situations: Respondent's Usual Activity)
1 •
1 Category
r
Driving
Walking
Talking with people present
Working at home
! Reading, writing, thinking
Sleeping
Other
; Not relevant
Listening to TV, radio, records
Resting (awake)
Not ascertained
Total
!
No. of
Situations
47
16
42
12
30
155
13
179
92
35
22
693
Percentage
of total
Situations
7
2
6
2
12
22
2
26
13
5
3
100
D-2?
-------
3. Community Reaction to Environmental Noise
There are two methods of indirectly assessing the cumulative
effects of environmental noise on people. These are examining the
reactions of individuals or groups of individuals to specific intruding
noises, either (a) with respect to actions taken (complaints, suits, etc.),
or (b) in terns of responses made to social survey questionnaires.
The first category, involving overt action by individuals or groups,
is summarized in this section,and key data regarding the second category,
involving responses indicating annoyance, is summarized in the next
section.
In the last 25 years^rnany new types of noise sources have been
introduced into surburban and urban residential communities. These
sources, such as jet aircraft, urban freeways, new industrial plants,
and homeowner equipment, have created numerous community problems with
environmental noise. These problems have provided significant data
and insight relating to community reaction and annoyance and stimulated
the development of several indices for measurement of the magnitude of
intruding noises.
Various U.S. Governmental agencies began to investigate the
relationships between aircraft noise and its effect on people in
communities in the early 1950's. This early research resulted in the
proposal of a model by Bolt, Rosenblith and Stevens for relating
aircraft noise intrusion and the probable community reaction. This
D-?8
-------
model, first published by the Air Force, accounted for the following
seven factors:
1. Magnitude of the noise with a frequency weighting relating
to human response.
2. Duration of the intruding noise.
3. Time of year (windows open or closed).
4. Time of day noise occurs.
5. Outdoor noise level in community when the intruding noise
is not present.
6. History of prior exposure to the noise source and attitude
toward its owner.
7. Existence of pure-tone or impulsive character in the noise.
Correction for these factors v/ere initially made in 5 dB
intervals since the magnitudes of many of the corrections were based
solely on the intuition of the authors^md it was considered difficult
to assess the response to any greater degree of accuracy. This
model was incorporated in the first Air Force Land Use Planning Guide0'14
in 1957 and y/as later simplified for ease of application by the Air
Force and the Federal Aviation Administration.
Recently the day-night sound level has been derived for a
series of 55 community noise problems0" to relate the normalized
measured L . with the observed community reaction. The normalisation
procedure followed the Bolt, Rosenblith and Stevens method with a few
minor modifications. The correction factors which were added to the
measured L . to obtain the normalized L . are given in Table D-7.
D-29
-------
Table D-7
CORRECTIONS TO BE ADDED TO THE MEASURED DAY-NIGHT SOUND LEVEL (Ldn)
OF INTRUDING NOISE TO OBTAIN NORMALIZED Ldn °-3
Type of
Correction
Description
Amount of Correction
to be Added to Measured
Seasonal
Correction
Correction
for Out-
door Noise
Level
Measured
in Absence
of
Intruding
Noise
Correction
for
Previous
Exposure £
Community
Attitudes
Pure Tone
or Impulse
Summer (or year-round operation)
Winter only (or windows always closed)
Quiet suburban or rural community (remote
from large cities and from industrial activity
and trucking)
iiornal suburban community (not located near
industrial activity)
Urban residential community (not immediately
adjacent to heavily traveled roads and
industrial areas)
Noisy urban residential community (near
relatively busy roads or industrial areas)
Very noisy urban residential coimunity
No prior experience with the intruding noise
Community has had some previous exposure to
intruding noise but little effort is being
nade to control the noise. This correction
may also be applied in a situation where the
community has not been exposed to the noise
previously, but the people are aware that
bona fide efforts are being nade to control
the noise.
Community has had considerable previous
exposure to the intruding noise and the noise
maker's relations with the community are good
Community aware that operation causing noise i
very necessary and it will not continue
indefinitely. This correction can be aoplied
for an operation of limited duration and under
emergency circumstances.
flo pure tone or impulsive character
Pure tone or impulsive character present
0
-5
+10
+5
0
-5
-10
+5
0
-5
-10
0
+5
D-10
-------
The distribution of the cases among the various noise sources having
impact on the community are listed in Table D-8. The results are
summarized in Figure D-7.
The "no reaction" response in Figure D-7 corresponds to a
normalized outdoor day-night sound level which ranges between
50 and 61 dB with a mean of 55 dB. This mean value is 5 dB below
the value that was utilized for categorizing the day-night sound
level for a "residential urban community," which is the baseline
category for the data in the figure. Consequently, from these
results* it appears that no community reaction to an intruding
noise is expected, on the average,when the normalized day-night sound
level of an identifiable intruding noise is approximately 5 dB less
than the day-night sound level that exists in the absence of the identifiable
intruding noise. This conclusion is not surprising; it simply suggests
that people tend to judge the magnitude of an intrusion with reference
to the noise environment that exists without the presence of the
intruding noise source.
The data in Figure D-7 indicate that widespread complaints
may be expected when the normalized value of the outdoor day-night
sound level of the intruding noise exceeds that existing without the
intruding noise by approximately 5 dB, and vigorous community reaction
may be expected when the excess approaches 20 dB. The standard
deviation of these data is 3.3 dB about their maans and an envelope of
-------
+5 dB encloses approximately 90 percent of the cases. Hence, this
relationship between the normalized outdoor day-night sound level and
com/nunity reaction appears to be a reasonably accurate and useful tool
in assessing the probable reaction of a community to an intruding
noise and in obtaining one type of measure of the impact of an intruding
noise on a community.
D-32
-------
Table D-8
NUMBER OF COMMUNITY NOISE REACTION CASES AS A FUNCTION
OF NOISE SOURCE TYPE AND REACTION CATEGORY
Type of Source
Transportation vehicles, including:
Aircraft operations
Local traffic
Freeway
Rail
Auto race track
Total Transportation
Other single-event or inler-
mittent operations, including
circuit breaker testing, target
shooting, rocket testing and
body shop
Steady state neighborhood
sources, including transformer
substations, residential
air conditioning
Steady state industrial opera-
tions, including blowers,
general manufacturing, chemical,
oil refineries, et cetera
Total Cases
Community Reaction Categories
Vigorous
Threats of
Legal Action
6
1
2
9
5
1
7
22
Wide
Spread
Complaints
2
1
3
4
7
14
No Reaction
or Sporadic
Complaints
4
3
7
2
10
19
Total
Cases
12
3
1
1
2
19
7
24
55
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The methodology applied to arrive at the correlation between
normalized L^p and community complaint behavior illustrated in
Figure D-7 is probably the best available at present to predict
the most likely community reaction in the U.S. unfortunately,
readiness to complain and to take action is not necessarily an early
indicator of interference with activities and annoyance that the
noise creates. The fact that correction for the normal background
noise level without intruding noise results in better correlation
of the data points might be interpreted to mean that urban
communities have adapted to somewhat higher residual noise levels
that are not perceived as interfering or annoying. On the other
hand, it is more likely that the higher threshold for complaining
is caused by the feeling that higher residual noise is unavoidable
in an urban community and that complaining about "normal" noise
would be useless. For the present analysis*it might therefore be
more useful to look at the same data without any corrections for
background noise, attitude*and other subjective attributes of the
intruding noise. Figure D-8 gives these data for the same 55 cases.
The increase in spread of the data is apparent in comparing
Figures D-7 and D-8, and the standard deviation of the data about the
mean value for each reaction is increased from 3.3 dB for the normalized
data to 7.9 dB. The mean value of the outdoor day-night sound level
associated with "no reaction" is 55 dB; with vigorous reaction, 72 dB;
and, for the three intermediate degrees of reaction, 62 dB.
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There is no evidence in these 55 cases of even sporadic
complaints if the Ldn is less than 50 dB.
4. Annoyance
Annoyance discussed in this report is limited to the long-tern
integrated adverse responses of people to environmental noise. Studies
of annoyance in this context are largely based on the results of
sociological surveys. Such surveys have been conducted among residents
of a number of countries including the United States.^6' D"7' I>15' °"16
The short-term annoyance reaction to individual noise events,
which can be studied in the field as well as in the laboratory.is not
explicitly considered,si nee only the accumulating effects of repeated
annoyance by environmental stimuli can lead to environmental effects
on public health and welfare. Although it is known that the long-term
annoyance reaction to a certain environment can be influenced to some
extent by the experience of recent individual annoying events,the
sociological surveys are designed to reflect, as much as possible,the
integrated response to living in a certain environment and not the
response to isolated events.
The results of sociological surveys are generally stated in
terms of the percentage of respondents expressing differing degrees of
disturbance or dissatisfaction due to the noisiness of their environments.
Some of the surveys go into a complex procedure to construct a scale of
annoyance. Others report responses to the direct question of "how annoying
D-37
-------
is the noise?" Each social survey is related to some kind of measurement
of the noise levels (mostly from aircraft operations) to which the survey
respondents are exposed, enabling correlation between annoyance and
outdoor noise levels in residential areas.
The results of social surveys show that individual responses
vary widely for the same noise level. Borsky D ' has shown that these
variances are reduced substantially when groups of individuals having
similar attitudes about "fear" of aircraft crashes and "misfeasance"
of authorities are considered. Moreover, by averaging responses over
entire surveys, almost identical functional relationships between human
response and noise levels are obtained for the whole surveyed population
as are obtained for the groups of individuals having neutral attitudlnai
responses. Therefore, in deriving a generalized relationship between
reported annoyance and day-night sound level, it seems reasonable to
use the average overall group responses, recognizing that individuals
may vary considerably from the average, both positively and negatively
depending upon their particular attitudinal biases. In most cases* the
average group response can also be interpreted as the average
individual's response during his life period. That is to say, each
individual changes his attitudinal biases according to various factors
and personal experiences not necessarily connected to the noise or
even to the environment in general, which lead to fluctuations of
each individual's attitude. The average group response does, to some
extent, express the individual's response averaged over longer periods
of his life. Therefore, this response reflects the effects most likely
to affect his health over a longer time period.
D-36
-------
A comparison of the results of three of the most prominent
social surveys around airports are presented in the following
paragraphs. These are the first and second surveys around London's
Heathrow Airport, ' and the Tracer study D~7 around eight
major airports in the United States. The noise level data reported
for each survey were converted to outdoor day-night sound levels
for the purpose of this analysis. In addition, data are presented
r> 1R
from a survey of response to motor vehicles in U.S. urban areas. u~10
A. First London-Heathrow Survey
The first survey of about 2,000 residents in the vicinity of
Heathrow airport was conducted in ,1961 and reported in 1963.°~6 The
survey was conducted to obtain responses of residents exposed to a wida
range of aircraft flyover noise. A number of questions were
used in the interviews to derive measures of degrees of reported
annoyance. Two results of this survey are considered here.
A general summary of the data, aggregating all responses on a
category scale of annoyance ranging from "not at all" to "very much
annoying," is plotted as a function of approximate l_dn in Figure D-9.
This figure presents a relationship between word descriptors and
day-night sound level.
Among the respondents in every noise level category, a certain
percentage were classified in the "highly annoyed" category. This
percentage of each group is plotted as a function of approximate L,
on Figure D-10.
D-39
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Comparison of the data on the two figures reveals that, while
the average over the population would fit a word classification of
"little annoyed" at an L . value of approximately 60 dB, more than 20%
of the population would still be highly annoyed at this L, value.
In addition to the derivation of overall annoyance scales,
this study examined the attitude of the people towards their area and
their desire to move as a function of both noise level and several
other factors. The results are summarized in Figs. D-ll and D-12.
They indicate that when the approximate Ldn exceeded 66-68 dB,
aircraft noise became the reason most often cited by those who
either "liked their area less now than in the past" or "wanted to move".
Further, the data indicate that aircraft noise was of little importance,
compared to other environmental factors, when the approximate L(jn
was below 53 dB and was of average importance as a factor when the
approximate L . was 60 dB.
B. Results of Second London Survey and Tracer Surveys
D-15
In 1967, a second survey was taken around Heathrow
Airport in the same general area as the first survey. While
refinements were attempted over the first survey, the results were
generally the same. In 1971, the results of an intensive three
year program under NASA sponsorship which studies eight air carrier
airports in the United States were reported by Tracer. Since
each of these efforts is discussed in detail in the references,
-------
only an analysis of their combined results is considered here.
Borsky used the data from these studies to correlate
annoyance with noise exposure level for people having different
attitudinal characteristics and different degrees of annoyance.
Utilizing Borsky's data for "moderate" responses to the attitudes
of "fear" and "misfeasance", the relationship between percent highly
annoyed and noise exposure level is plotted on Figure D-13. Again,
noise levels have been converted to approximate L. values. It is
worth noting that more than 7590 respondents are included in the
data sets from which the computations were derived.
The comparison between the results shown on Figures D-10 and
D-13 is striking in the near identity of the two regression lines-
indistinguishable at any reasonable level of statistical confidence.
The importance of these two sets of data lies in the stability of the
results even though the data v/ere acquired 6 to 9 years apart, at nine
different airports in two different countries. This complete agreement
led to ihe .proposal of an average curve for the nominal relationship
between sound level and percc.icu&c. o." >>C:OHIe annoyed, which has
n 1Q
been coordinated among and used by various U.S. Government agencies,
applied in the studies of ICAO's coordinating committee on aircraft
noise; and verified by a recent analysis of British, French and
Dutch survey results conducted by the Organization for Economic
Cooperation and Development (OECD). D"20 According to the OECD work,
-------
0)
KEY
1 Aircraft Noise
2 Other Noise
3 Area Dirtier/
Overcrowded
4 Influx of
Undesirable
People
5 Want Change/
Been Here Too
Long
40 50 60 70
Approximate Day-Night Average Sound Level
Figure D-ll.
(Ldn>
in dB
Percentage of People Liking Their Area Less Now
than in the Past for Various Reasons
JKEY_
1 To Go Where
Climate is Better
2 To Go To Better
Living Accommodation
3 To Get Away From
Smoke/Dirt/SmeMs
4 To Be Nearer Work
5 To Get Away From
Aircraft Noise
40 50 60 70
Approximate Dav-Night Average Sound Level (L
dn
) in dB
Figure D-12.
Percentage of People Giving Particular Reasons
for Wanting to Move
D-kk
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25
Figure D-14. Percentage of Highly Annoyed AS A Function of
Percent Comnla1nant<: - D-v
Percent Complainants
-------
the percentage of annoyed people can be predicted as follows:
Percentage of annoyed people = 2 (Ldn - 50).
The results of the Tracer Study also give a relationship
between the number of people who indicate in a social survey that they
are highly annoyed and the number of people v/ho indicate that they
have ever complained about the noise to any one in authority. The
results, presented in Figure D-14, indicate that when 1% of the people
complain, 17% report being highly annoyed;and when 10% of the people
complain. 4-3Lare highly annoyed.
C- Judgement of noisiness at Urban Residential Sites
In 1972, a study of urban noise was conducted primarily to
evaluate motor vehicle noise for the Autonobile Manufacturers
Association.0" As part of this survey, 20 different urban-suburban
residential locations not in the vicinity of airports were studied in
Boston, Detroit, and Los Angeles. Noise measurements were acquired and
a social survey of 1200 respondents was conducted. Part of the survey
was directed towards obtaining the respondents' judgement^ on a category
scale, of the exterior noisiness at their places of residence.
The averaged judged noisiness values per site are plotted on
Figure D-15 as a function of measured L . values. The significance of
these "non-aircraft" data is the comparison they permit with other
survey data acquired exclusively around airports. Intcrccrnparison cf
-------
these data with previous data indicate that for an Ld value of
60 dB, the site would be judged "quite" noisy. The average
annoyance for a group would be classed as "little," but about
25% of the people would still claim to be highly annoyed.
When all respondents, irrespective of exposure site, were
asked whether they were annoyed by motor vehicle noise, 53% were
not annoyed, while 46% were, with an average intensity of
annoyance of 4.2 on a scale where 3 stood for "quite annoying,"
4 for "definitely annoying" and 5 "strongly annoying." Of the
46% of respondents who stated they were annoyed by motor vehicle
noise, 77% experienced annoying noises while in their homes,
12% while in transit, and only 5% at work.
This indication, that the principle annoyance with environmental
noise occurs in the residential situation is further confirmed in the
D_IO
results of the London City Noise Survey summarized in Table D-9.
D7~"Summary of Annoyance Survey Results
The relationships among percent complainants and percent highly
annoyed (Figure D-14) together with the combined results of the two
Heathrow surveys and the Tracer survey (Figures D-10 and D-13) have
been combined in Figure D-16 to produce a general summary relationship
between day-night sound level, percent complainants and percent highly
annoyed . Also included in the figure is a scale of the relative
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TABLE D-9
PERCENTAGE OF PEOPLE WHO WERE EVER DISTURBED BY NOISE AT HOME,
OUTDOORS AND AT WORK IN LONDON CITY SURVEY
D "*"
I
Disturbed from time to time
Notice but not disturbed
Do not notice
At Home
56
41
3
Outside
27
64
9
At Work
20
70
10
D-50
-------
importance of aircraft noise as a factor in disliking an area or wanting
to move (Figures C>-11 and D-12) and the average values of the three
main coraunity noise reaction categories (Figure D-7).
The results indicate that below an outdoor day-night sound
level of 55 dB, less than 1% of the households would be expected to
* ,,
complain, although 17% of the people may respond as highly annoyed
when questioned in a social survey- "No reaction" would be expected in
the average community, and noise would be the least important factor in
attitude towards neighborhood. When the outdoor L . is 60 dB,
approximately 2% of the households might be expected to complain* •
although 23% of the people may respond as highly annoyed when
questioned, and some reaction would be expected from an average community.
If the levels increase over 65 dB, more than 5% may be expected to
complain, and over 33% would respond as highly annoyed. Increasingly,
vigorous community reaction could be expected,and noise becomes
the dominant factor in disliking an area.
It is important to keep in mind that the annoyance/tolerance
limits obtained from the social survey results have been found to be
based on relatively well defined health and welfare criteria: the
D-19
disturbance of essential daily activities.
D-51
-------
Relative Importance of Aircraft As A
Factor in Disliking Area or Wanting to
Move (Heathrow 1st Study) D-7f D-10, D-ll, D-12 and D-13
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INCREASING
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COMPLAINTS AND
THREATS OF
LEGAL ACTION
80
OUTDOOR DAY/NIGHT SOUND LEVEL( Ldn ) IN dB (RE 20 MICRO-
PASCALS)
Figure D-16. Summary of Annoyance Survey and Goranunity
Reaction Results
D-52
-------
V. Various Prior Recommendations for Acceptable Sound Levels
Recommended values for acceptable sound levels in various
types of spaces have been suggested by a number of authors over the
past two decades. These recommendations generally have taken into
consideration such factors as speech intelligibility and subjective
judgements by space occupants. However, the final values recommended
were largely the result of judgements on the part of the
authors, which in the case of acoustical consultants, have been
motivated by the need for design values which will be on the "safe"
side. One of the earliest publications providing recommended values
1n modern terminology was that of Knudsen and Harris in 1950. It
"is of interest to quote from the text to understand the reasoning used
to develop the recommended levels:
Acceptable Noise Levels in Buildings
The highest level of noise within a building that neither
disturbs its occupants nor impairs its acoustics is called the
acceptable noise level. It depends, to a large extent, on the
nature of the noise and on the type and customary use of the
building. The time fluctuation of the noise is one of the most
important factors in determining its tolerability. For example,
a bedroom with an average noise level of 35 dB, with no
instantaneous peak levels substantially higher, would be much
more conducive to sleep than would be a room with an average
noise level of only 25 dB but in which the stillness is pierced
by an occasional shriek. Furthermore, levels that are annoying
to one person are unnoticed by another. It is therefore
impossible to specify precise values within which the noise levels
should fall in order to be acceptable. It is useful, however,
to know the range of average noise levels that are acceptable
under average conditions. A compilation of such levels for
various types of rooms in which noise conditions are likely
to be a significant problem is given in [Table D-10.*] The
* These values are given in the first column of Table D-10.
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recommended acceptable noise levels in this table are
empirical values based on the experience of the authors
and others they have consulted. Local conditions or
cost considerations may make it impractical to meet
the high standards inherent in these relatively low
noise levels. In more than 80 percent of the rooms
of some of the types listed, the prevalent average noise
levels exceed the recommended acceptable levels. However,
it should be understood that the acceptance of higher noise
levels incurs a risk of impaired acoustics or of the comfort
of the individuals in the room.
Since 1950 recommendations by a number of authors, as well
as national standards, have been presented. Eighteen of these
D-21 through D-38
recommendations are tabulated in Table D-1Q.
It is encouraging to note the consistency displayed, although many
of the later recommendations may be based on the recommendations of
the earlier authors.
• *>. Summary of Noise Interference With Human Activities and
Resulting Health/Welfare Effects
The primary effect of noise on human health and welfare due to
interference with activity comes from its effect on speech communication.
The levels that interfere with human activities which do not
involve active listening cannot be quantified relative to the level of
a desired sound. Rather, the level of an intruding sound that will
cause an interference depends upon its relation to the level of the
other background sounds in the environment and the state of the human
auditor, e.q., the degree of concentration when endeavoring to
accomplish a mental task, or the depth of sleep, etc.
D-55
-------
The levels of environmental noise that are associated with
annoyance depend upon local conditions and attitudes. They cannot be
clearly identified in terms of the national public health and welfare.
The only levels which can be so identified are the levels which are
required to assure that speech communication in the home and outdoors
is adequate in terms of public health and welfare. Lower levels may
be desirable and appropriate for specific local situations.
The level identified lor the protection of speech communication
is 45 dB within the home. Allowing for the 15 dB reduction in sound
level between outdoors and indoors, this level becomes an outdoor day-
night sound level of 60 dB (re 20 micropascals) for residential areas.
For outdoor voice communication, the outdoor day-night level of
60 dB allows normal conversation at distances up to 2 meters with
95% sentence intelligibility.
Although speech•interference has been identified as the primary
interference of noise with human activities, and as one of the primary
reasons for adverse corrrnunity reactions to noise and long-term
annoyance, a margin of safety of 5 dB is applied to the maximum
outdoor level to give adequate weight to all of these other adverse
effects.
Therefore, the outdoor day-night sound level identified for
residential areas is a day-night sound level of 55 dB.
-------
The associated interior day-night sound level within a typical
home which results from outdoors is 15 dB less, or 40 dB. The
expected indoor daytime level for a typical neighborhood which has
an outdoor day-night sound level of 55 dB is approximately 40 dB,
whereas the nighttime level is approximately 32 d3 (see Figure A~?)•
This latter value is consistent with the limited available sleep
criteria (o-5). Additionally, these resulting indoor levels are
consistent with the background levels inside the home and which have
been recommended by acoustical consultants as "acceptable" for many
years (Table D-10).
The effects associated with an outdoor day-night sound
level of 55 dB are summarized in Table D-ll. The summary shows:
(1) satisfactory outdoor average sentence intelligibility
may be expected for normal voice conversations over
distances of up to 3.5 meters;
(2) depending on attitude and other factors non-
acoustical the average expected community reaction is
"none" although 1% may complain and 17% indicate
"highly annoyed" when responding to social survey
questions; and
(3) noise is the least important factor governing
attitude towards the area.
Identification of a level which is 5 dB higher than
the 55 dB identified above would significantly increase the
severity of the average community reaction, as well as the
expected percentage of complaints and annoyance. Conversely,
D-57
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TABLE D-11
SUMMARY OF HUMAN EFFECTS IN TERMS OF SPEECH COMMUNICATION, COMMUNITY
REACTION, COMPLAINTS, ANNOYANCE AND ATTITUDE TOWARDS AREA
ASSOCIATED WITH AN OUTDOOR DAY/NIGHT SOUND LEVEL
OF 55 dB re 20 MTCRDPASCALS
Type of Effect
Magnitude of Effect
Speech - Indoors
- Outdoors
Average Community Reaction
Complaints
Annoyance
Attitudes Towards Area
100% sentence intelligibility (average)
with a 5 dB margin of safety
100% sentence intelligibility (average)
at 0.35 meters
99% sentence intelligibility (average)
at 1.0 meters
95% sentence intelligibility (average)
at 3.5 meters
None, 7 dB below level of significant
"complaints and threats of legal action"
and at least 16 dB below "vigorous action"
(attitudes and other non-level related
factors may affect this result)
1% dependent on attitude and other non-
level related factors
17% dependent on attitude and other non-
acoustical factors
Noise essentially least important of
various factors
D-58
-------
identification of a level 5 dB lower than the 55 dB identified
above would reduce the indoor levels resulting from outdoor
noise well below the normal background indoors. It would
decrease speech privacy outdoors to marginal distance. Little
change in annoyance vrould be made since at levels below the
identified level, individual attitude and life style, as
well as local conditions, are more important factors in controlling
the resulting magnitude of the level of the intruding noise.
In conclusion, a L, level of 55 dB is identified as outdoor
level in residential areas compatible with the protection of public
health and welfare. The level of 55 dB is identified as maximum level
compatible with adequate speech communication indoors and outdoors.
With respect to complaints and long tern annoyance this level is
clearly a maximum satisfying the large majority of the population (see
Table D-ll). However, specific local situations, attitudes,and
conditions may make lower levels desirable for some locations. A noise
environment not annoying some percentage of the population cannot be
identified at the present time by specifying noise level alone.
D-59
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REFERENCES FOR APPEMDIX D
D-l "effects of IVoise on People," Environmental Protection Agency,
NTID 300.7, December 1971.
D-2 Webster, J. C., "Effects of ;;oise on Speech Intelligibility",
Noise as a Public Health Hazard, American Speech and Hearing
Association, '/o. 4, February 1969.
D-3 Eldred, K. .'!., "Community Noise," Environmental Protection
Agency f.'TID 300.3, December 1971.
D-4 "Method for the Calculation of the Articulation Index," American
National Standards Institute, ANSI 53.5-1969, New York.
D-5 "Public Health and Welfare Criteria for Noiso," Environmental
Protection Agency, 550/9-73-OO2, July 27, 1973.
D -6 ".'loise-rinal Report," H.M.S.O. , Crond. 2056, London, July 1963.
D .7 Connor, W.K. and Patterson, H.P., "Community Reaction to Aircraft
Noise Ar&und Smaller City Airports", NASA CR-2104, August 1972.
D-3 Bitter, C. , '"loise Nuisance Due to Aircraft," Institut Vour
Gezondheidstechniek TNO, 1968.
*
D -9 Bolt fteranek and ,','ewman, Inc., "Survey of Annoyance from Motor
Vehicle Noise," Automobile Manufacturers Association, Inc.,
Report 2112, Juno 1371.
D -10 Rosenblith, '.-I. A., Stevens, K. M., and the Staff of Dolt Beranek
and Newman, Inc., "Noise and Man," Handbook of Acoustic Noise
Control, Vol. 2, WADC TR-52-204, Wright-Patterson Air Force Base,
Ohio: I/right Air Development Center, U53.
D -11 Stevens, 1C. fj. , Rosenblith, !/. A., and LJolt, R. II., "A Community's
Reaction to 'toise: Can It De Forecast?" fJoise Control, 1 ; 63-71,
1955.
D-12 Stevens, K. N., and Baruch, J. J., "Community Noise and City
PI anni ng," Handbook _o_f_J.Joi s_e_ ContrpJ , Chapter 35, McGraw-lli 11
Book Co., 1957.
D-13 Parrack, H. 0., "Community Reaction to Noise," Handbook of Noise
Cj)jTtrpJ_, Chanter 3C, McGraw-Hill Book Co., 1057".
D-14 Stevens, K. 'V. and Pietrasanta, A. C., and the Staff of Bolt
Beranek and 'tewman, Inc., "Procedures for Estimating ,\'oise
Exposure and Resulting Community Reactions from Air Base Operation,"
I/ADC T;/-57-10, Wright-Patters on Air Force Base, Ohio: Wright Air
Development Center, 1957.
-------
D-15 "Second Survey of Aircraft Noise Annoyance Around London (Heathrow)
Airport," H.M.S.O., London, 1971.
D-16 Bitter, C., "Noise Nuisance Due to Aircraft," Collogue sur la
definition des exiqences hur.iain a 1'cqard du bruit, Paris,
November 136H.
D-17 Borsky, P. N., "A New Field-Laboratory Methodology for Assessing
Human Response to 'loise," NASA CR-2221, March 1973.
D-ia "Noise in Towns," IIOISE_, Chapter IV, 22-31, Presented to Parliament
by the Lord President of the Council and Minister for Science by
Committee on the Problem of Noise, July 1963; H.M.S.O., London,
Reprinted 1966.
D-19 "Safeer, Harvey B., "Community Response to Noise Relative to
Percent of Population Highly Annoyed by Noise," US Department of
Transportation, Office of Noise Abatement Tf1 72-1, June 6, 1972.
D -20 "Social and Economic Impact of Aircraft Noise," Sector Group on
the Urban environment, Organization for Economic Co-Operation
and Development, April 1973.
D-21 Knudsen, E. 0. andHarris, c.M.» Acous tical Cesijnirig 1 n
Architecture, New York: J. Wiley and Sons, 1950.
D-22 Geranek, L., Reynolds, J. L.,..and Wilson, K.E., "Apparatus and
Procedures for Predicting Ventilation System Noise," JASA, v. 25,
no. 2: 313 , 1953.
D-23 Ceranek, L ., 'Revised Criteria for !loise in Buildings," NoJ_se
C_o_ntro]_, v. 3, no. 1, 1957 .
D-24 Lawrence, A., Acous ti cs in 3uiJ d_1 ngs , Australian Building
Science Series 1, p 70, 1962.
D-25 Kosten, C. 'A. and van Os., G. J., "Community Reaction Criteria
for External Noises," National Physical Laboratory Symposium
to. 12, London, H.J1.S.O. 1902 .
D -26 ASHRAC: Guide and Data Book, Systems and Equipment, American
Society of Heating, Refrigerating and Air Conditioning Engineers,
p 379, 1967.
D -27 Denisov, E. I., "!]ew Health Norms on Noise", Institut Gigiyeny
Truda i Profzabolevaniy AM'I SSSR, Moscow, v. 14, no. 5:47, 1970.
D -23 Kryter, K., The Effects of Noise on Man, Academic Press,p 459,
1970.
D -29 ",'loises in Tokyo", Report on the Tokyo Conference on Environmental
Protection, November 8-11, 1971.
D-61
-------
D-30 "Sanitary 'lorris for Permissible Noise in Living Quarters and
Public Buildings and in Residential Construction Areas,"Main
Sanitary-Epidemioloqical Administration,USSR, 1971.
D-31 Beranek, I., .'|ojs_e_ and, Vjb_ratj_pn ,_CnntrpJ_, p 535, McGraw-Hill, 1071.
D-32 Doelle, L., ^ILvJLrPPEe-I1.tALAc-0JJ^A''£§-' P 186, McGraw-Hill, 1972.
D-33 Woods, R. I., "iloise Control in Mechanical Services," Published
jointly by Sound Attenuators Ltd and Sound Research Laboratories
Ltd, 1972.
D-34 Rettinger, 11., Acoustjc Dosign jnd ;'ipj._se Control, New York:
p 158, Chemical Publ". Co., Inc.,^1973.
D-35 Sweden National Board of Urban Planning, Samhallsplannerlng och
Vagtrafikbuller, Stockholm: 1971
D -36 Scnweizerfscher Ingenieur - und Architekten - Vereln, Empfehlung
fuer Schallschutz im Wohnungsbau, SIA No. 181, Zuericn, 1970
D -37 The Czech Ministry of Health; Rlchtlinien fuer Gesundheitsschutz
gegen unguenstige Wirkung von Laerm; Vorschriften der Hygiene,
Band 28, 1967, Prague : Staatsverlag fuer Medizinische Literatur
1967.
D -38 Der Bundesminister des Innen , Inventar der in der Bundesrepublik
Deutschland geltenden oder geplanten Rechts-und
Verwaltungsvorschriften ueber die Laermbekaempfung. Bonn
April 30, 1973.
0 -39 "Impact Characterization of Noise Including Implications of Identifying
and '.rh;(v/.'n ' •'<• r;7s of Cumulative Noise ^xnosure." EPA TV>cunent '"
73.-1, Jul 27, 1973.
D-62
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APPENDIX B
GENERAL EFFECTS OF NOISE NOT DIRECTLY USED IN IDENTIFYING LEVELS
OF NOISE REQUISITE TO PROTECT PUBLIC HEALTH AND WELFARE
There are a multitude of adverse effects that can be caused by noise
which may, both directly or indirectly, affect public health and welfare.
However, there are only three categories of adverse relationships in which
the cause/effect relationships are adequately known and can be justifiably
used to identify levels of environmental noise for protection of public
health and welfare. These are: (1) the effect of noise on hearing, (2) the
effect of noise on the general mental state as evidenced by annoyance, and
(3) the interference of noise with specific activities. These three cate-
gories of effects, discussed in detail in Appendices C and D, will serve as
the main basis for identifying the levels in Section 3 of this document.
Since a causal link between comnunity noise and extra-auditory disease
has not been established, this document proceeds on the assumption that pro-
tection against noise-induced hearing loss is sufficient for protection
against extra-auditory effects. However, the generation of most stress-
related disorders is somewhat longer than that required for noise-induced
hearing loss, and this time interval may have clouded a causal association.
Noise of lesser amplitude than that traditionally identified for the pro-
tection of hearing causes regular and dependable physiological rosponsos in
humans. Similar noise-induced physiological changes in sensitive animals
regularly leads to the development of stress-related disease. The implica-
tions of generalizing from these animal studies to humans is not clear. With
the availability of new information concerning the role of noise as a stressor
E-l
-------
in the pathogenessis of stress-related disease, the levels identified in
this document may require further review.
In the meantime, the question that is invariably asked is, "What is Iho
significance of omitting all other physiological effects?"
In answer to this question, most experts agree that, at present, there
is insufficient knowledge of the effect of noise on health except for noise-
induced hearing loss, (defining health in the more restricted sense, as the
B—1
absence of disease). In a recent review of this subject it was con-
cluded that: "if noise control sufficient to protect persons from ear damage
and hearing loss were instituted, then it is highly unlikely that the noises
of lower level and duration resulting from this effort could directly induce
non-auditory disease." Therefore, in this document, hearing loss will be
considered the controlling effect.
This is not to say that there are no indications to arouse concern in
the area of non-auditory effects, but substantial further research on these
effects of noise on health would be required to alter the above statanents.
Such research should be fostered,and the results should be carefully moni-
tored for any evidence indicating that the maximum sound levels identified
herein are excessive.
Although noise can affect people indirectly by disturbing the general
environment in which they live, the noise levels required to produce signifi-
cant non-auditory physiological effects are normally much higher than the
levels required to protect the public health and welfare from adverse effects
on hearing or interference with activities.
E-2
-------
However, for special conditions, certain effects which have not been
directly utilized in identifying the levels in this document, should be
examinixl. For this purpose, certain of the summary paragraphs of the I'PA
E—9
criteria document "Public Health and Welfare Criteria for Noise" ^ are
included in this appendix. Caution must be exercised when using such informa-
tion since, in many cases, there is no way to relate the exact exposure level
to the effect in question.
I. Effects of Noise on Humans
A, Performance and Work Efficiency
Continuous noise levels above 90 dBA appear to have potentially
detrimental effects on human performance, especially on what have been
described as noise-sensitive tasks such as vigilance tasks, information -
gathering and analytical processes. Effects of noise on routine-type tasks
appear to be much less important, although cumulative degrading effects have
been demonstrated by researchers. Noise levels of less than 90 dBA can be
disruptive, especially if they have predominantly high frequency components,
are intermittent, unexpected, or uncontrollable. The amount of disruption
is highly dependent on:
• The type of task.
• The state of the human organism.
• The state of morale and motivation.
Noise does not usually influence the overall rate of work, but high levels
of noise may increase the variability of the work rate. There may be "noise
pauses" or gaps in response, sometimes followed by compensating increases in
work rate. Noise is more likely to reduce the accuracy of work than to
B-3
-------
reduce the total quantity of work, Complex or demanding tasks are more likely
to be adversely affected than are simple tasks. Since laboratory studies
represent idealized situations, there is a pressing need for field studies
in real-life conditions.
Although these possibly adverse effects were not used in identifying
the noise levels in this document, employers or educational authorities
should consider their influence since it might provide additional motivation
to achieve the values seen in Table D-10 of Appendix D.
B. Effects of Noise on the Autonomic Nervous System and Other Non-Auditory
Physiological Effects
Noise can elicit many different physiological responses. However,
no clear evidence exists to indicate that the continued activation of these
responses leads to irreversible changes and permanent health problems. Sound
of sufficient intensity can cause pain to the auditory system, however, such
intense exposures are rarely encountered in the non-occupational environment.
Noise can also affect one's equilibrium, but the scarce data available indi-
cates that the intensities required to do so must be quite high, similar to
the intensities that produce pain.
Noise-induced orienting reflexes serve to locate the source of a
sudden sound and, in combination with the startle reflex, prepare the
individual to take appropriate action in the event of danger. Apart from
possibly increasing the chance of an accident in some situations, there
are no clear indications that the effects are harmful since these effects
are of short duration and do not cause long-term physiological changes.
E-4
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Noise can definitely interfere with sleep, however, relating noise-
exposure level to the quality of sleep is difficult. Even noise of moderate
levels can change the pattern of sleep, but the significance of these changes
is still an open question.
Noise exposure may cause fatigue, irritability, or insomnia in some
individuals, but the quantitative evidence in this regard is also unclear.
No firm relationships between noise and these factors can be established at
this time.
C. Interaction of Noise and Other Conditions or Influences
Determination of how various agents or conditions interact with noise
in producing a given effect requires three separate determinations: the
effect produced by the noise alone, the effect produced by the other agent
alone, and the effect produced by the combined action of the agent and the
noise. These results indicate whether the combined effect is indifferent,
additive, synergistic, or ameliorative.
Chemical agents may have a harmful effect when combined with noise.
Ototoxic drugs that are known to be damaging to the hearing mechamism can be
assumed to produce at least an additive effect on hearing when combined with
noise exposure. There are instances in which individuals using medication
temporarily suffer a hearing loss when exposed to noise, but there is no
definitive data on the interaction of ototoxic drugs and noise on humans.
Evidence linking hearing loss with the combination of noise and industrial
chemicals is also inconclusive.
The possibility of a synergistic effect exists when noise and vibra-
tion occur together. Vibration is usually more potent than noise in affecting
E-5
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physiological parameters. There appears to be consensus that vibration
increases the effect of noise on hearing, but such increases are probably
<]ui t.<> small.
Health disorders may interact with noiso to produce a hearing1 loss.
Mineral and vitamin deficiencies are one example but little research has
been done on the effect of such deficienceis on susceptibility to noise. A
reasonable hypothesis is that illness increases an individual's susceptibility
to the adverse effects of noise. However, as with the other hypotheses, con-
clusive evidence is lacking.
Noise exposure can be presumed to cause general stress by itself or
in conjunction with other stressors. Neither the relationship between noise
exposure and stress nor the noise level or duration at which stress may
appear have been resolved.
Exposure to moderate intensities of noise that are likely to be
found in the environment may affect the cardiovascular system in various
ways, but no definite permanent effects on the circulatory system have been
demonstrated. Noise of moderate intensity has been found to cause vasocon-
striction of the peripheral blood vessels and pupillary dilation. There
is no evidence that these reactions to noisy environments can lead to harmful
consequences over prolonged periods of noise exposure. However, speculation
that noise might be a contibuting factor to circulatory difficulties and
heart disease is not yet supported by scientific data.
II. Effects of Noise on Wildlife and Other Animals
Noise produces the same general types of effects on animals as it does
on humans, namely: hearing loss,masking of ccranunication, behavioral, and
non-auditory physiological effects.
B-6
-------
The most observable effects of noise on farm and wild animals seem to
be behavioral. Clearly, noise of sufficient intensity or noise of aversive
character can disrupt normal patterns of animal existence. Exploratory
behavior can be curtailed, avoidance behavior can limit access to food and
shelter, and breeding habits can be disrupted. Hearing loss and the masking
of auditory signals can further complicate an animal's efforts to recognize
its young, detect and locate prey, and evade predators. Competition for
food and space in an "ecological niche" results in complex interrelation-
ships and, hence, a complex balance.
Many laboratory studies have indicated temporary and permanent noise-
induced threshold shifts. However, damage-risk criteria for various species
have not yet been developed. Masking of auditory signals has been demonstrated
by commercial jamming signals, which are amplitude and frequency modulated.
Physiological effects of noise exposure, such as changes in blood
pressure and chemistry, hormonal balance and reproductivity have been
demonstrated in laboratory animals and, to some extent, in farm animals.
But these effects are understandably difficult to assess in wildlife. Also,
the amount of physiological and behavioral adaptation that occurs in response
to noise stimuli is as yet unknown.
Considerable research needs to be accomplished before more definitive
criteria can be developed. The basic needs are:
• More thorough investigations to determine the point at which
various species incur hearing loss.
• Studies to determine the effects on animals on low-level, chronic
noise exposures.
E-7
-------
• Comprehensive studies on the effects on animals in their natural
habitats. Such variables as the extent of aversive reactions,
physiological changes, and predator-prey relationships should be
examined.
Until more information exists, judgments of environmental impact must be
based on the existing information, however incomplete. The most simple
approach is to assume that animals will be at least partially protected
by application of maximum levels identified for hunan exposure.
III. Effect of Noise on Structures
Airborne sound normally encountered in real life does not usually
carry sufficient energy to cause damage to most structures. The major excep-
tions to this are sonic booms produced by supersonic aircarft, low frequency
sound produced by rocket engines and some construction equipment, and sonic
fatigue.
Prom an environmental point of view, the most significant effects are
those caused by sonic booms on the secondary components of structures. These
effects include the breaking of windows and cracking of plaster. Effects
such as these have led to the speculation that historical monuments and
archeological structures may age more rapidly when exposed to repeated
sonic booms. However, the levels identified in Appendix G to protect against
adverse effects on public health and welfare are low enough to protect
against damage to structures.
E-8
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REFERENCES FOR APPENDIX E
E-l. "Effect of Noise on People," Environmental Protection Agency/
NTID 300.7, December 1971.
E-2. "Public Health and Welfare Criteria for Noise," Environmental
Protection Agency, 550/9-73-002, July 27, 1973.
E-9
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APPENDIX F
EPA's Responsibility to Identify Safe Levels for Occupational Noise
Exposure
Although the workplace is a vital component of the human environ-
ment, the Environmental Protection Agency does not have jurisdiction
over most occupational health and safety matters. These matters have
traditionally been the responsibility of the Departments of Labor
and Health, Education and Welfare. Section 6(b)(5) of the Occupational
Safety and Health Act of 1972 specifies that the Secretary of Labor,
"...in promulgating standards dealing with toxic materials or harmful
physical agents ..., shall set the standard which most adequately assures,
to the extent feasible, on the basis of the best available evidence,
that no employee will suffer material impairment of health or functional
capacity even if such employee has regular exposure to the hazard dealt
with by such standard for the period of his working life ... In addition
to the attainment of the highest degree of health and safety protection
for the employee, other considerations shall be the latest available
scientific data in the field, the feasibility of the standards, and
experience gained under this and other health and safety laws."
In contrast, section 5(a)(2) of the Noise Control Act of 1972 directs
EPA's Administrator to "publish information on the levels of environmental
noise, the attainment and maintenance of which in defined areas under
various conditions are requisite to protecting the public health and
welfare with an adequate margin of safety."
-------
The words "public health and welfare" appear in a number of places
in the Noise Control Act, and have a broader reference than those defining
jurisdiction in the Occupational Safety and Health Act, namely, the
entire American public at all times rather than the American worker
during his workday. In addition, the requirement of an "adequate margin
of safety" does not appear in the Occupational Safety and Health Act,
which instead uses the phrase, "no employee will suffer material
impairment of health or functional capacity." These distinctions
indicate that EPA's duty to identify levels for exposure to noise
is broader in scope and more stringent than OSHA's duty to protect
in the occupational area. Furthermore, the intent of this document is
to identify safe levels for a variety of settings, whereas the responsibility
of HEW is to develop occupational exposure criteria and that of the
Department of Labor is to promulgate and enforce standards. In the
writing of such standards, the Labor Department must take feasibility
into account,a consideration omitted in the writing of this document.
EPA's responsibility to identify levels of exposure to noise "in
defined areas under various conditions" necessarily includes an identi-
fication of exposure levels in the workplace in order to satisfy the
intent of the law to consider total human exposure to noise. Working
hours are an inseparable part of the individual's 24-hour day, and they must
be considered in order to evaluate the contributions of nonoccupational
exposure to his daily and lifetime dose. For this reason, it is of utmost
importance that the levels specified for occupational and non-occupational
noise be compatible.
F-3
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APPENDIX G
IMPULSE NOISE AND SOME OTHER ^SPECIAL NOISES
I. Impulse Noise
Impulse noise is defined in various ways (G-i, G-2, G-ii] but
generally means a discrete noise (or a series of such noises) of short
duration (less than a second), in which the sound pressure level rises
very rapidly (less than 500 msec, sometimes less than 1 msec) to a
high peak level before decaying below the level of background noise.
The decay is frequently oscillatory, because of sound reflections and
reverberation (ringing) in which case the spectrum of the oscillation
may also be important in determining the hazard to hearing. Some
authors distinguish reverberant impulse noise as "impact" noise (typically
produced by metal to metal impact as in industrial forging), to distin-
guish it from simple oligophasic impulses (typified by a gunshot in the
open air) ( G-3).
The peak sound pressure level (SPL) is an important but not the
sole parameter determining hazard. Some typical values for disturbing
or hazardous impulse noises are given in Table G-l.
NOTE: Peak SPL for impulses cannot be properly measured with a standard
sound level meter, which is a time-averaging device. Oscillographic
techniques must be used.
G-3.
-------
TABLE G-l
SOME TYPICAL VALUES OF PEAK SPL FOR IMPULSE NOISE
(in dB re 0.00002 N/m2)
SPL
190+
160-180
140-170
125-160
120-140
110-130
EXAMPLE
Within blast zone of exploding bomb
Within crew area of heavy artillery piece or naval
gun when shooting
At shooter's ear when firing hand gun
At child's ear when detonating toy cap or firecracker
Metal to metal impacts in many industrial processes
(e.g., drop-forging; metal-beating)
On construction site during pile-driving
A. Effects of Impulse Noise on Man
(1) Cochlear Damage and Hearing Loss
Impulse noise can produce temporary (ITS) and permanent
threshold shift (PTS). The pattern essentially resembles that produced
by a continuous noise but may involve somewhat higher frequency losses
(maximal at 4 to 6 kHz) and recovery from impulse-NIPTS can be more
variable (G-9). A blow to the head can have a similar effect. ITS
(and, by inference, PTS) in man depends on many factors, the more
important of which are reviewed in more detail later. Impulse noise
(like continuous noise) can also be shown to produce pathological
changes in the inner ear (cochlea) of mammals, notably destruction and
degeneration of the haircells of the hearing organ, and atrophic changes
in related structures. A quantitative relationship between the amount
of visible damage to the cochlea and the amount of NIPTS has not yet
been clearly established (G-2, G-4, G-5).
G-2
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(2) Other Pathological Effects
Exposure to blast or to sustained or repeated impulsive airborne
over-pressures in the range 140 to 150 dB (5 to 15 psf) or higher can cause
generalized disturbance or damage to the body apart from the ear. This
is normally a problem for military personnel at war (e.g., artillerymen
firing field guns), and need not be considered further here. Transient
over-pressures of considerable magnitude can be experienced due to
sonic boom but are unlikely to be hazardous to the ear (see below).
(3) Startle and Awakening
Impulsive noises which are novel, unheralded,or unexpectedly
loud can startle people and animals. Even very mild impulsive noises
(classically, the dropping of a pin) can awaken sleepers. In some
circumstances (e.g., when a person is handling delicate or dangerous
objects or materials), startle can be hazardous. Because startle and
alerting responses depend very largely upon individual circumstances
and psychological factors unrelated to the intensity of the sound, it
is difficult to make any generalization about acceptable values of SPL
in this connection. A high degree of habituation, even to intense
impulse noises such as gunfire, is normally seen in animals and man when
the exposure in repeated, provided that the character of the stimulus
is not changed.
(4) Parameters of Impulse Noise Exposure
Impulse noise is characterized completely by the waveform
and spectrum. Various summary parameters are also useful in characteriz-
ing an impulsive noise, these include:
G-3
-------
(a) Peak SPL (in dB re 0.00002 N/m2)
(b) Effective duration (in milliseconds or microseconds)
(c) Rise time
In addition, the following are important for predicting the effects of the
impulse on man:
(d) Number of repeated impulses in a daily or other
cumulative exposure
(e) Intervals or average interval between repeated impulses
(or rate of impulse occurrence)
(f) Individual susceptibility to inner ear damage
(g) Orientation of the ear with respect to the noise
(h) Preceding or simultaneous exposure to continuous noise
at TTS-producing levels
(i) Action of acoustic reflex, if elicited
(j) Audiometric frequency
B. Impulse Noise Exposure Criteria and Limits
(1) Hearing Damage and Criteria for Impulse Noise
It is obvious from the above lists that limiting impulse
noise exposure for hearing conservation is not an easy matter. Existing
guidance in this matter in some spheres is seriously inadequate or
misleading (G-3). For instance, the Occupational Safety and Health Act
(OSHA) (and also the previous occupational noise regulations embodied
1 in Walsh-Healey) prescribes a limiting level of 140 dB SPL for industrial
impulse noise, with no allowance for any other parameter.
G-4
-------
In 1968, Working Group 57 of CHABA prepared a damage risk
criterion for gunfire noise, based essentially on the work of Coles
et. al. (G-6), which included procedures to allow for repetition of
impulses and some of the other parameters listed above (G-l). Some
modification has recently been proposed by Coles and Rice (G~7). The
CHABA proposal was intended to protect 95% of ears.
C. Guidelines for Evaluating Hazard from Impulse Noise Exposure
(1) Peak Level
The growth of TTS at 4 kHz with increase in peak level
above 130 dB SPL of impulses (clicks) presented at a steady rate has been
demonstrated by Ward et. al. (G*8). Based on TTS data from rifle shooters,
Kryter and Garinther (G-l8) estimated permanent hearing levels expected
to result from daily exposure to a nominal 100 rounds of rifle shooting
noise in selected percentiles. Their data are reproduced in Table G-2
below, showing the increasing hazard with increasing peak level and with
increasing audiometric frequency up to 6000 Hz.
CHABA's (G-l) 1968 DRC (See Figure G-l) recommended limits
to peak level as a function of impulse duration (discussed below) for a
nominal exposure of 100 impulses per day at normal incidence. These
limits were intended to protect 95% of the people according to an
implied criterion of NIPTS not exceeding 20 dB at 3 kHz or above, after 20 yrs
If 90% of the people were to be protected to a criterion of NIPTS
G-5
-------
TA.3LE G-2
ESTIMATED EXPECTED PERMANENT HEARING LEVEL (IN DB RE ASA: 1951)
IN SELECTED PEBCENTILES OF THE MOST SENSITIVE EARS
FOLLOWING NOMINAL DAILY EXPOSURE TO RIFLE NOISE
(DURING TYPICAL MILITARY SERVICE) ,
NAMELY, 100 ROUNDS AT ABOUT 5 SECOND INTERVALS
Peak
SPL*
idBj
170
165
160
150
140
Percentile
Exceeding HL
10
25
50
10
25
50
10
25
50
10
25
50
10
25
50
Audiometric Test Frequency (Hz)
1000 2000 3000 4000 6000
25
15
0
16
9
35
25
10
20
10
1 0 ' 0
70
55
35
62
32
12
15 16 25
7 8 18
0 I 0 .__0
10 1 15 ' 15
3
0
0
0
0
4 8
0
5
2
0
0
10
2
0
85
65
45
60
45
25
45
90
70
50
67
52
47
60
35 45
I 15 ; 25
35
25
50
40
10 20
30
18
5
,
45
30
10
*At the ear, grazing incidence.
not exceeding 5 dB at 4 kHz, it would be necessary to lower the CHABA
limits by 12 dB (15 dB reduction to meet the more stringent criterion,
assuming an approximately decibel to decibel relationship in the range of
interest (see Table G-2), less 3 dB elevation to apply the limit to the
90th percentile). This modified CHABA limit is shown in Figure G-I
(hatched lines).
G-6
-------
(2) Duration of Impulse
Hazard increases with the effective duration of impulses
(G-lo). Impulse duration is defined according to the type of impulse
(A, simple peak, or B, oscillatory decay) (G-l, G-6); and CHABA has
recommended separate limits for A- and B-durations (FigureG-1). For
effective durations much above 1 msec, a more stringent limit should be
applied to reverberant oscillations (e.g., metallic impacts in industry
or gunshots in a reverberant indoor range) than to simple A-type
impulses (e.g., gunshots in the open). When the type of impulse cannot
be determined, it is conservative to assume the B-duration.
f* T
CHABA 1968 warned that the 152 and 138 dB plateaux
are only "gross estimates": similar remarks apply to the modified
CHABA limit here proposed, in which the corresponding plateaux are 140
and 126 dB SPL.
(3) Rise Time
This parameter is usually correlated closely with peak
pressure. Present evidence as to its effect on hearing risk is in-
sufficient for allowance to be made for it in damage risk criteria.
(4) Spectrum (or Waveform)
Impulses with largely high frequency spectral components
(e.g., reverberant gunshots) are generally more hazardous to the hearing
mechanism than predominantly low-frequency impulses (e.g., distance-
degraded blast waves; sonic booms) of the same peak SPL. However,
G-7
-------
comparative data are as yet too scanty to serve as the basis of
differential damage risk criteria.
(5) Number of Repeated Impulses
ITS (and, by inference, NIPTS) grows linearly with the
number of impulses in a series, or linearly with time when the rate of
/*"* Q /"* n
impulses is constant . CHABA recommended an allowance of -5
dB for every tenfold increase in number of impulses in a daily exposure
G—7
(Figure G-2). Recently, Coles and Rice have contended that this
rule is underprotective for large numbers (N) of impulses and have
C1 *}
recommended a modification (see Figure G-2). In 1973, McRobert and Ward
questioned this modification, maintaining that it is probably
grossly overprotective for N>1000, and commented also on the CHABA rule
in the light of recent experiments. Figure G-2 reproduces a comparison
by McRobert and Ward of the CHABA rule with Coles and Rice G~7 and an
"equal-energy" rule (10 dB weighting for each tenfold increase in N)
originating at N = 100.
All in all, an "equal-energy" rule appears to fit the
existing data tolerably well and is easy to apply in practice, but
it may underestimate the hazard for values of N substantially less than
100 (isolated impulses).
(6) Interval Between or Rate of Occurrence of Impulses
Ward, et_. aj_. ^ showed that, when equal impulses occur at
more than I/sec, ITS development is slower than when the average interval
is in the range 1 to 9 sec, presumably because the acoustic reflex is
G-8
-------
maintained. When the interval is long (range 9-30 seconds), TTS again
develops more slowly, probably because the interval allows some
recovery. A conservative rule would be to apply a 5 dB penalty when
thn average impulse interval lies between 1 and 10 seconds: such an
!ril«-rv.il tiny I"' lyjiiiil "I MJ< h ,i
-------
"impulsiveness" in distributed noise, but the validity of this rule is
questionable. On present evidence, it is probably safest to evaluate
simultaneous impulsive and continuous noise separately, each according
to its own criterion.
(10) Action of the Acoustic Ref1 ex
This protective mechanism is valueless in the case of
brief single or isolated impulses because it has a latency of at least
10 msec and takes up to 200 msec before being fully effective. Rapidly
C* "7
repeated impulses , however, or simultaneous continuous noise , G"15
may activate it sufficiently to provide up to 10 dB of protection: but this
is too variable and uncertain to be allowed for in damage risk criteria.
(11) Audi ometri c Frequency
Generally speaking, impulse noise affects the hearing in much
the same way as does continuous noise, with ITS and PTS beginning and
growing most rapidly at 4 to 6 kHz. It is possible, however, that
impulse noise may have relatively more effect on high-frequency hearing
or affect hearing at higher frequencies. '
D. Use of Equivalent Continuous Sound I_eve1 (LefJ In Evaluation of
Impulse Noise
Support for the extension of the equal-energy (equivalent A-
weighted sound energy) concept of hearing hazard from continuous noise
exposure to include impulse noise exposure has recently been gaining
ground .G-19 At the 1970 Teddington Conference on "Occupational Hearing
Loss", it was suggested that a unifying rule based on this concept might
G-10
-------
be drawn up to link continuous and impulse noise exposure limits in a
single continuum relating A-weighted sound level to effective daily
exposure duration .G"20 An empirical formula enabling the A-weighted
Leq to be calculated from the peak sound pressure (ph) repetition
rate in impulses per second (N) and the decay constant of the impulse
envelope (k) in inverse seconds, was introduced as follows (G-21):
Leq = 85.3 + 20 log Ph + 10 log N - 10 log k + 10 log (l-e'2/ki'1)
where ph is absolute pressure in N/m^; not sound pressure level in dB.
For one impulse of the B- type, this formulation simplifies such that
the Le of an A-weighted continuous pulse of duration T is equal to
the peak sound Pressure Level (in dB) of an impulse which decays by
20 dB in time T minus 9 dB. The use of this formula assumes the
impulse is composed of broad-band noise that exponentially decays. This
relationship, at the present time, should not be used to evaluate impulse
data until it is further justified by more experimental research. How-
ever, it does provide further support of the equal energy concept out-
lined in Appendix c.
E. Summary and Conclusions
(1) Hearing Conservation
The following rules may be recommended if it is desired to
protect 90% of the people from significant impulse-NIPTS, that is, from
impulse-NIPTS exceeding 5 dB at 4 kHz after 10 years of repeated exposures:
G-il
-------
(a) Measure or predict the peak level (SPL) and A- or B-
type duration of the impulse, using proper oscillographic technique (NOTE:
if the noise is sufficiently rapidly repetitive to fit Coles and Rice's
category "C", it may be treated and measured as continuous noise
and evaluated accordingly in dBA. This usually means a repetition rate
exceeding 10/sec).
(b) Use the "modified CHABA limit" in FigureG -1 to
determine the maximum permissible peak SPL. If in doubt as to impulse
type, assume B-duration.
(c) If the number of similar impulses (N) experienced per
day exceeds 100, reduce the permissible level by 10 dB for every tenfold
increase in N (e.g., 10 dB when N = 1000, 20 dB when N = 10,000).
(d) If N is less than 100, a higher peak level may be
allowed in accordance with the same rule (e.g., 10 dB more when N = 10),
provided that an absolute maximum value of 167 dB for durations less
than 25 microseconds, grazing incidence (or 162 dB normal incidence) is
not exceeded.
(e) If the average repetition rate of impulses falls in
the range 0.1 to 1 per second (i.e., the average interval between
impulses is 1 to 10 seconds), reduce the permissible peak level by 5 dB.
(f) If the impulses are known to reach human ears in the
vicinity at grazing incidence, the permissible peak level may be raised
(3-12
-------
by 5 dB. NOTE: This allowance should be used with caution and must
not be applied if the surroundings are reverberant. If in doubt,
assume normal incidence.
(2) Effects Other Than on Hearing
See Section 3 in main document.
2. Special Noises
a. Infrasound G"26
Frequencies below 16 Hz are referred to as infrasonic frequencies.
Sources of infrasonic frequencies include earthquakes, winds, thunder,
and jet aircraft. Man-made infrasound occurs at higher intensity levels
than those found in nature. Complaints associated with high levels of
infrasound resemble mild stress reactions and bizarre auditory sensations,
such as pulsating and fluttering. It does not appear, however, that
exposure to infrasound, at intensities below 130 dB SPL, present a serious
health hazard. For the octave band centered at 16 Hz, the A-weighted
equivalent to 130 dB SPL is 76 dB(A).
b. Ultrasound G"26
Ultrasonic frequencies are those above 20,000 Hz. They are
produced by a variety of industrial equipment and jet engines. The
effects of exposure to high intensity ultrasound (above 105 dB SPL)
also the effects observed during stress. However, there are experimental
difficulties in assessing the effects of ultrasound since:
G-13
-------
CVI
^ 160
c\j
O
8 '55
q
o
2 150
CD
•o
J 145
UJ
UJ
LU
tt
UJ
or
a.
UJ
a.
140
135
130
125
T 1 1
CHABA(I968)
A-DURATION
MODIFIED
CHABA
LIMIT
^
I I J
I I J
1 I I
I I I
1
.025 .05 .1 .2
.512 5 10 20 50 1002005001000
DURATION IN MSEC
Figure G-l.
The 1968 CHABA G~1 Damage-Risk Criterion for Iinpulse Noise
Exposure (solid lines) and a Proposed Modification (hatched
lines). Peak Sound Pressure Level is Expressed as a Function
of A- or B- Duration in the Range 25 Microseconds to 1
Second.G"1
G-14
-------
20
CD
T>
cc
g
o
ui
cc
oc
o
o
10
"EQUAL-ENERGY"
-5
-10
-15
-20
-25
-30
CHABAU968)
COLES & RICE
(1971)
ill ill
10 20 50 100 200 500 1000 2000 5000
NUMBER OF IMPULSES
Figure G-2.
Cotparison of CHABA Weighting (Re: Zero at N = 100 Inpulses
per Day) for Number (N) of Impulses in Daily Exposure ^~1 with
the Proposed Modification by Coles and Rice G-~7 and an "Equal-
Energy" Rule. After McRoberts and Ward.0"3
G-15
"fr'*F~~' "30
<*<• ^ ' . ^JHB*
-------
(1) Ultrasonic waves are highly absorbed by air
(2) Ultrasonic waves are often accompanied by broad-band
noise and by sub-harmonics.
At levels below 105 dB SPL, however, there have been no observed adverse
effects.
3. Sonic Booms
Present day knowledge regarding the acceptability of sonic booms
by man is based on observations from both experimental field and
laboratory studies and observations of community response to actual
sonic boom exposures. Individual human response to sonic boom is very
complex and involves not only the physical stimulus, but various
characteristics of the environment as well as the experiences,
attitudes and opinions of the population exposed.0"22 One of the
most comprehensive studies to date on sonic boom exposure of a large
community over a relatively long period of time was the Oklahoma City
study conducted in 1964 .°~23' ^^ Eight sonic booms per day at a
median outdoor peak overpressure level of 1.2 psf N/rrr were experienced
by this community over a 6 month period. Some results of this study
are summarized in Figure G-3. For eight sonic booms/day, there is
clear evidence that the median peak overpressure must be well below
1 psf if no annoyance is reported. when interviewed, part of the
population considered eight sonic booms/day to be unacceptable. By
extrapolation, the level at which eight sonic booms per day should be
acceptable for the population is slightly less than 0.5 psf. But even
G-16
-------
at 0.5 psf N/m2, approximately 20% of the population consider themselves
annoyed by an exposure of eight sonic booms/day. Linear extrapolation
of the annoyance data of Figure G-3 indicates that annoyance will
disappear in the total population only when the 8 sonic booms oer day are less
than 0.1 psf. A linear extrapolation is orobablv not entirely justified,
however, as certainly for sonic booms much less than 0.1 to 0.2 psf, a
large percentage of the population is not even expected to sense the
boom. The fact that the extrapolation must curve is best illustrated by
the interference curve of Figure c-3. Unless the extrapolation is
curved as shown, interference would be predicted for about 70% of the
population even when the peak overpressure is zero, i.e., no boom at
all.
So far the discussion has been about eight sonic boom exposures per
day on a daily recurring basis. The more difficult question is how to
interpret the effect on public health and welfare of sonic booms that
are more infrequent than eight times per day. Kryter G~25 provides
a relationship which indicates that a sonic boom of 1.9 psf once a day
would be equal to 110 PNdB or a CNR of 98 dB. It further suggests
that the level (which is proportional to P^) should be reduced
by one half (3 dB) for each doubling of number of occurrences.
Prom Appendix A, L^n is approximately related to CNR by Ld = CNR
- 35 dB. Thus, a CNR of 98 equals an^Ldn of 63 dB. If the sonic
boom is made equivalent to an LJ = 55 dB, so as to be consistent
with the levels identified in the interference/annoyance section
of this document, the level of one daytime sonic boom per day must
be less than 0.75 psf. For more than eight sonic booms/day, the
G-17
-------
level should be less than 0.26 psf (0.75^V"N~). This result
is slightly lower than the data from Figure G-3. However,
extrapolating the annoyance line in the figure suggests that the
.26 psf level of 8 booms would annoy only 8% of the people and more
would find in unacceptable. Therefore, the relationship proposed is:
daytime peak over-pressure per day = (0.75 psf )^N~where N = number
of sonic booms/day. Thus, the peak over-pressure of a sonic boom
that occurs during the day should be no more than 0.75 psf if the
population is not to be annoyed or the general health and welfare
adversely affected.
The standard sound level meter, which is a time-averaging device, will
not properly measure the peak sound pressure level of sonic booms.
G-18
-------
100
1
1
u-
o
w
a
E-
80
60
1.0
20
#0*0***
0.0
ACTUAL COMPLAINTS
0.5
25
1.0 1.5
MEDIAN PEAK OVERPRESSURE, Ib/ft2'
50 75
MEDIAN PEAK OVERPRESSURE, N/m2
2.0
100
TSOTE: Data carpi led from Oklahoma City Study. Dashed lines are extrapola-
tions. All data for 8 sonic boonv/day. G-22
Figure G-3. Percentage of Respondents Reporting Adverse Reactions
to Sonic Boons
G-19
-------
REFERENCES FOR APPENDIX G
G-l. CHABA (Ward, et. al., (1968), "Proposed Damage-Risk Criterion for
Inpulse Noise (Gunfire)," (U) . Report of Working Group 57, NAS-NRC
Corrtnittee on Hearing, Bioacoustics, and Biomechanics (CHABA),
W. Dixon Ward, Chairman, Washington, D.C.: Office of Naval Research.
G-2. Guignard, J. C., "A Basis for Limiting Noise Exposure for Hearing
Conservation," Aerospace Medical Research Laboratory, Wright-
Patterson Air Force Base, Ohio and Environmental Protection Agency,
Washington, D.C.: Joint EPA/USAF Study AMRL-TR-73-90 and
EPA-550/9-73-001-A, 1973.
G-3. McRobert, H. and Ward, W. D., "Damage-Risk Criteria: The Trading
Relation Between Intensity and the Number of Nonreverberant Impulses,"
Journal of Acoustical Society of America, 53: 1297-1300, 1973.
G-4. Poche, L. B., Stockwell, C. W. and Ades, H. W., "Cochlear Hair-Cell
Damage in Guinea Pigs After Exposure to Impulse Noise," Journal of
Acoustical Society of America, 46: 947-951, 1969.
G-5. Majeau-Chargois,D. A., Berlin, C. I. and Whitehouse, G. D., "Sonic
Boom Effects on the Organ of Corti," Laryngoscope, 80, 620-630, 1970.
G-6. Coles, R. R. A., Garinther, G. R., Hodge, D. C. and Rice, C. G.,
"Hazardous Exposure to Impulse Noise," Journal of Acoustical Society
of America, 43: 336-343, 1968.
G-7. Coles, R. R. A. and Rice, C. G., "Assessment of Risk of Hearing Loss
Due to litpulse Noise," Occupational Hearing Loss, ed., Robinson, D. W.,
London & New York: Academic Press, 71-77, 1971.
G-8. Ward, W. D., Belters, W. and Glorig, A., "Exploratory Studies on
Temporary Threshold Shift from Impulses," Journal of Acoustical Society
of America, 33: 781-793, 1961.
G-9. Luz, G. A. and Hodge, D. C., "Recovery from 3Jrpulse-Noise Induced TTS
in Monkeys and Men: A Descriptive Model," Journal of Acoustical
Society of America, 49: 1770-1777, 1971.
G-10. Loeb, M. and Fletcher, J. L., "Impulse Duration and Temporary
Threshold Shift," Journal of Acoustical Society of America, 44:
1524-1528, 1968.
G-ll. Kryter, K. D., "Evaluation of Exposures to Impulse Noise," Archives
of Environmental Health, 20:624-635, 1970.
G-20
-------
<
i
G-12. Hodge, D. C. and McCormons, R. B., "Reliability of ITS from Impulse-
Noise Exposure," Journal of Acoustical Society of America, 40: 839-
846, 1966.
G-13. See Reference G-10.
G-14. Fletcher, J. L., "Effects of Non-Occupational Noise Exposure on a
Young Mult Population," Report for Department of Health, Education
and Welfare, NTOSH: HSM 099-71-52, Washington, D.C., HEW, 1972.
G-15. Cohen, A., Kylin, B. and La Benz, P. J. "Temporary Threshold Shifts
in Hearing from Exposure to Combined Impact/Steady-State Noise
Conditions," Journal of Acoustical Society of America, 40: 1371-1379,
1966.
G-16. Okada, A., Fukada, K. and Yamamura., K., "Growth and Recovery of
Temporary Threshold Shift at 4 kHz Due to a Steady State Noise and
Impulse Noises," Int z angew Physiol, 30: 105-111, 1972.
G-17. International Organization for Standardization (ISO), "Assessment
of Occupational Noise Exposure for Hearing Conservation Purposes,"
ISO Recommendation ISO/R1999, Geneva: ISO, 1971.
G-18. Kryter, K. D. and Garinther, G., "Auditory Effects of Acoustic
Impulses from Firearms," Acta Otolarying (Stockh), Supplement 211,
1965.
G-19. Coles, R. R. A., Rice, C. G. and Martin, A. M., "Noise-Induced
Hearing Loss from Impulse Noise: Present Status," Paper to Inter-
national Congress on Noise as a Public Health Hazard, Dubrovnik,
May 13-18, 1973.
G-20. Martin, A. M., In discussion, 1970 Teddington Conference on Occupa-
tional Hearing Loss, ed., Robinson, D. W., London and New York:
Academic Press, 89-90, 1971.
G-21. Martin, A. M. and Atherley, G. R. C., "A Method for the Assessment
of Impact Noise with Respect to Injury to Hearing," Annals of
Occupational Hygiene, 16:19-26, 1973.
G-22. von Gierke, H. E. and Nixon, C. W., "Human Responses to Sonic Boom
in the Laboratory and the Community," Journal of Acoustical Society
of America, 51:766-782.
G-23. "Noise as a Public Health Hazard," Proceedings of the National
Conference of the American Speech and Hearing Association,
June 13-14, 1968, Washington, D.C., Report 4, February 1969.
G-21
-------
>
1
G-24. Borsky, P. N., "Community Reactions to Sonic Booms in the Oklahoma
City Area," National Opinion Research Center, AMRL-TR-65-37, 1965.
G-25. Kryter, K. D., "Sonic Booms from Supersonic Transport," Science,
163: 359-367, January 24, 1969.
G-26. Public Health and Welfare Criteria for Noise, Environmental Protection
Agency, 550/9-73-002, July .27, 1973.
V, -
G-22
------- |