Civil Engineering Reference
In-Depth Information
Many of the common noise sources in a plant (from manufacturing processes and
machinery, air intake, and other equipment) are illustrated in Figure 13.4. Several
measures have been taken to reduce noise, including the following: using vibration
isolation mounts, placing heavy vibrating equipment on a separate rigid structure, and
using an air intake muffler with laminar flow of air. The structure-borne transmissions
have been reduced, for example, by use of flexible pipe on the air intake and sound
isolating joints between the vibrating equipment and the floor. Finally,
TABLE 13.3
Approaches to Reducing Noise
Control Target
Measures
Noise source
Use vibration isolation mounts Fasten members to rigid structures Use mufflers
on exhaust/intake Change direction of sound emission Reduce the radiating or
vibrating efficiency of sound sources; e.g., by drilling holes in plates or covers
Structure-borne
transmissions
Decouple source from transmitting solid Isolate using spring steel or rubber
plate Use flexible couplings on shafts Use damping materials in ducts and
conveyors
Air-borne
transmissions
Increase distance between source and worker Rotate noise source Use barriers
and baffles Enclose noise source and/or workers Apply damping material Use
ear protection
the airborne transmission has been reduced by using sound absorbing ceilings and
shields, and by enclosing noise sources in a control room and in the basement.
Most of the engineering measures listed in Table 13.3 are equally effective in reducing
vibrations as well as noise. In fact, vibrations and noise are concomitant; noise and sound
are vibrations of the air mass introduced by compressions and rarefactions of the density
of air molecules. A vibrating plate will vibrate air masses and produce noise.
13.7
EFFECTS OF NOISE ON HUMAN PERFORMANCE
There are no clear-cut effects of noise on performance. In fact, this has been a much
debated topic among researchers (Broadbent, 1978; Poulton, 1978; Kryter, 1985).
Gawron (1982) reviewed 58 noise experiments and found that 29 showed a reduction in
performance, 22 showed no effect, and 7 showed that noise improved task performance.
Part of the problem in research is to provide a theory of the effects of noise on
performance. If a viable theory exists, experiments could be undertaken and the theory
tested. A problem in formulating a theory is that there are many types of noise and many
types of task. Noise can be anything from intermittent to continuous and from music to
white noise. The task can be skill-based (manual automatic behavior), rule-based (if
scenario A, then do X; if B, then do Y, etc.), or knowledgebased (requiring deep thinking
and pondering of alternatives) (Rasmussen, 1986).
