Environmental Engineering FOURTH EDITION

Noise Pollution 445

22.8 If the SL were 80 dB(C) and 60 &(A), would you suspect that most of the

22.9 In addition to the data listed in Example 22.3 (Table 22-2), the following SL

noise was of high, medium, or low frequency? Why?

measurements were taken:

Time (s) WA) Time (s) dB(A)

110 80 160 95

120 82 170 98

130 78 180 82

140 87 190 88

150 92 200 75

Calculate the L50, ,510, and NPL by using all 20 data points.
22.10 If the pressure wave was 0.3 N/m2, what is the SPLin decibels? If this is all
the information about the sound you have, what can you say about the SL in dB(A)?
What data would you need to make a more accurate estimate of the SL in &(A)?
22.11 If you sing at a level 10,000 times greater than the power of the faintest
audible sound, at which decibel level are you singing?
22.12 How many times more powerful is a 120-dl3 sound than a 0-dl3 sound?
22.13 On a graph of decibels vs hertz (10 to 50,000), show a possible frequency
analysis for: (a) a passing freight train, (b) a dog whistle, and (c) “white noise.”
22.14 The OSHA standard for an 8-h exposure to noise is 90 &(A). The Environ-
mental Protection Agency (EPA) suggests that this should be 85 &(A). Show that the
OSHA level is almost 400% louder in terms of sound level than the EPA suggestion.
22.15 A machine with an overall noise level of 9OdB is placed in a room with
another machine putting out 95 dl3.

a. What will be the sound level in the room?

b. Based on OSHA criteria, how long should workers be in the room during one

22.16 What sound pressure level results from the combination of three sources:
68,78, and 72 dB?
22.17 If an occupational noise standard were set at 80 dl3 for an 8-h day, 5-day-
per-week working exposure, what standard would be appropriate for a 4-h day, 5-day-
per-week working exposure?
22.18 Carry a sound level meter with you for one entire day. Measure and record
the sound levels as &(A) in your classes, in your room, during sports events, in the
dining hall, or wherever you go during the day.
22.19 Seek out and measure the three most obnoxious noises you can think of.
Compare these with the noises in Table 22-5.
22.20 In your room measure and plot the sound level in dB(A) of an alarm clock
vs distance. At what distance will it still wake you if it requires 70 dB(A) to get you
up? Draw the same curve outside. What is the effect of your room on the sound level?
22.21 Construct a sound level frequency curve for a basketball game. Calculate
the noise pollution level.

working day?