Equipment and Shelters

Ear Protection

Molded and pliable earplugs, cup-type protectors, and helmets are commercially available as hearing protectors. Such devices provide noise reductions from 15 to 35 dB (Figure 6.8.1). Earplugs are effective only if they are properly fitted by medical personnel. As shown in Figure 6.8.1, maximum protection can be obtained when both plugs and muffs are used. Only muffs with certification that stipulates the attenuation should be used.

Individual Enclosures or Noise Shelters

In an industrial plant, large areas where the noise level is too high for efficient work often exist. Any kind of office

Frequency, Hz (In Cycles per Second)

FIG. 6.8.1 Sound attenuation characteristics of various types of ear protectors.

Frequency, Hz (In Cycles per Second)

FIG. 6.8.1 Sound attenuation characteristics of various types of ear protectors.

FIG. 6.8.2 Principle of the labyrinth noise shelter.

work is impractical at such noise levels, yet inplant offices are needed.

Noise shelters provide an effective solution for these problems. They may be fully enclosed rooms with separate heating and ventilating systems, which protect from dust and odors as well as noise. Plant offices are often designed and constructed this way based on the principles described in Section 6.7.

When easy access to a noise shelter is needed, the labyrinth principle can be applied. This principle is useful in isolating areas where specialized work is done (such as, inspection and final adjustment) and where both people and work move continually in and out. Figure 6.8.2 shows how this principle is constructed. Such a noise shelter can be used for the operator's station when the machine controls are within the shelter and vision is through a large window area. In such construction, the wall surrounding the sheltered area should have a high-sound-transmission loss, and double glass suitably spaced and mounted to reduce noise transmission in the window.

Noise does not enter the space because it is reflected— preferably two or more times—from surfaces covered with absorbing material. At each reflection, appreciable noise reduction occurs. The noise shelter is also lined with absorbing material to absorb what noise does enter. The per formance quality of such enclosures depends on their design and construction.

The labyrinth principle effectively prevents the passage of noise from one work area to another. The labyrinth principle allows free passage between work areas without the interference of closed doors.

Other kinds of individual enclosures include the cabs used on agricultural and earth-moving machines. These cabs and motor trucks provide shelter from noise as well as weather conditions. Industrial crane cabs also provide this protection since safety in their areas depends on the alertness and ability of the operator.

Other Possibilities

When the noise within a confined area is too high to allow workers into it even with personal protection devices, the operation might be automated. An automated process is supervised from observation posts, that is, from remote-control stations where workers are adequately protected. A remote-control post receives information via a closed-circuit television, or it can be a highly insulated area within the department. Mechanical devices handle the production procedures under operator or computer control. For ex ample, rolling mills are controlled from soundproof cabins. The same is true of workshops for assembling and testing engines. The noise of such operations cannot normally be stifled at the source.

Noise-cancelling microphones and shielded microphones keep electrical communication operable at high-noise levels.

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