of the N&V manual reviews briefly the history of
d. Step 4, noise control.
key studies on the influence of high-level, long-
(1) Most common methods of controlling indoor
time noise exposures on hearing damage, leading
noise by design considerations are set forth in the
up to the Occupational Safety and Health Act
N&V manual: the effectiveness (transmission loss)
(OSHA) of 1970. The principal noise requirements
of walls and structures in containing noise, and the
of the act are summarized. A slightly more con-
effectiveness of distance and sound absorption
servative and protective attitude toward hearing
(Room Constant) in reducing noise levels in the re-
conservation is contained in the DoD Instruction
verberant portion of a room. Special noise control
6055.3. This document is summarized in paragraph
treatments for use with engine installations are
34d of the N&V manual. In brief, this document
discussed in chapter 3 of this manual; they include
defines an exposure in excess of 84 dB(A) for 8
mufflers, lined ducts, vibration isolation, the use of
hours in any 24-hour period as hazardous and pro-
ear protection devices, and the use of nondisturb-
vides a formula for calculating the time limit of safe
ing warning or paging systems.
exposure to any A-weighted sound level (equation
(2) The influence of distance, outdoor barriers
34 and table 39 of the N&V manual). Other parts
and trees, and the" directivity of large sources are
of DoD Instruction 6055.3 refer to impulsive noise,
considered both as available noise control measures
noise-hazardous areas, labeling of noise-hazardous
as well as factors in normal outdoor sound propaga-
tools and areas, issuance and use of hearings pro-
tion (N&V manual).
tection devices, educational programs on the ef-
fects of noise, audiometric testing programs, and
23. Sound level criteria.
the importance of engineering noise control for pro-
a. Indoor noise criteria. Noise criterion (NC)
tecting personnel. from noise.
and preferred noise criterion (PNC) curves are
d. Application of criteria to power plant noise.
used to express octave-band sound pressure levels
Each of the above three criteria evaluations should
considered acceptable for a wide range of occupied
be applied to plants with engine installations, and
spaces. Paragraph 32 in the N&V manual dis-
the total design of each plant or engine installation
cusses these noise criterion curves, which are di-
rectly applicable here for setting design goals for
should contain features or noise control treatments
aimed at achieving acceptable noise levels for
noise levels from engine installations. Tables 31
nearby offices and work spaces, for community
and 32 of the N&V manual summarize the octive-
housing facilities on and off the base, and for per-
band sound pressure levels and the suggested ap-
plications of the NC and PNC curves. Also, in the
sonnel involved with the operation and mainte-
nance of the engines and plants.
N&V manual, paragraph 32d and 33 relate to
speech interference by noise, and paragraph 32e
offers criteria for telephone usage in the presence
2-4. Vibration criteria.
of noise.
Reciprocating engines produce large, impulsive,
b. Community noise criteria. A widely used
unbalanced forces that can produce vibration in the
method for estimating the relative acceptability of
floors on which they are mounted and in the build-
a noise that intrudes into a neighborhood is de-
ings in which they are housed, if suitable vibration
scribed in paragraph 33c of the N&V manual. It is
isolation mountings are not included in their de-
known as the Composite Noise Rating (CNR)
signs. High-speed turbine-driven equipment must
method, modified over the years to include addi-
be well balanced by design to operate at speeds
tional factors that are found to influence communi-
typically in the range of 3600 to 6000 rpm and, con-
ty attitudes toward noise. The method is readily
sequently, are much less of a potential vibration
applicable to the noise of engine installations
source in most installations, but they must have
(whether operating continuously or intermittently)
adequate isolation to reduce high-frequency vibra-
as heard by community residents (whether on-base
tion and noise. Chapter 4 of the N&V manual is de-
or off-base). Figures 33, 34, and 35 and tables
voted to vibration criteria and the radiation of au-
34 and 35 of the N&V manual provide relatively
dible noise from vibrating surfaces. Vibration
simple access to the method. If the analysis shows
control is less quantitative and predictable than
that the noise will produce an uncomfortable or
noise control, but suggestions for vibration isola-
unacceptable community reaction to the noise, the
tion of engine installations are given in paragraphs
method shows approximately how much noise re-
36, 37, and 38 of this manual.
duction is required to achieve an acceptable com-
2-5. Indoor sound distribution.
munity response to the noise.
c. Hearing conservation criteria. Paragraph 34
Sound from an indoor sound source spreads around
2-2
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