7.0 MITIGATION OF CONSTRUCTION NOISE (continued)

7.4 Mitigation at the Source

Source control is, in general, the most effective form of noise mitigation and involves controlling a noise source before it is able to emit potentially offensive noise levels. Construction noise (exclusive of blasting) is typically generated by two source types:

Stationary equipment; and
Mobile equipment.

Noise levels from both types of noise sources are dependent on equipment characteristics and their operation.

7.4.1 Equipment - All Types

The following discussions relate to both stationary and mobile construction equipment:

less noisy equipment: One of the most effective methods of diminishing the noise impacts caused by individual equipment is to use less noisy machinery. By specifying and/or using less noisy equipment, the impacts produced can be reduced or, in some cases, eliminated. Source control requirements may have the added benefits of promoting technological advances in the development of quieter equipment.

Several construction workers use a vibratory soil compacter on a roadway project. In comparison, the picture on the right is of the same roadway project with one construction worker using a typical soil compacter, which is much larger in

Several construction workers use a typical soil compacter on a roadway project. In comparison, the picture on the left is of the same roadway project with several construction workers using a vibratory soil compacter, which is much smaller in size.

Figure 7.12 In some instances, using a less noisy piece of equipment (right) may be possible, as opposed to using more conventional and sometimes noisier equipment (left) to perform the same operation (Photos #505 & #506)

Mufflers: Most construction noise originates from internal combustion engines. A large part of the noise emitted is due to the air intake and exhaust cycle. Specifying the use of adequate muffler systems can control much of this engine noise.

A stationary piece of recycling equipment uses a muffler system to reduce or eliminate noise. Mufflers can be used on the air intake and exhaust systems of stationary and mobile equipment.

Figure 7.13 Muffler system on recycling equipment (Photo #1287)

Shields: Employing shields that are physically attached to the particular piece of equipment is effective, particularly for stationary equipment and where considerable noise reduction is required.

A stationary piece of equipment that is unshielded and not baffled. Shielding on stationary equipment can be quite effective for noise reduction.

Figure 7.14 Unshielded, non-baffled equipment (Photo #74)

A compressor on a trailer is contained within a shell that shields the compressor noise.

Figure 7.15 Shielded compressor (Photo #18)

A 20 foot high, round dampener surrounds a pile driving hammer to minimize noise from the impact of the hammer on the pile.

Dampeners: Equipment modifications, such as dampening of metal surfaces, is effective in reducing noise due to vibration. Another possibility is the redesign of a particular piece of equipment to achieve quieter noise levels.

A 20 foot high, round dampener surrounds an underwater pile driving hammer to minimize noise from the impact of the hammer on the pile.

Figure 7.16 Examples of pile driver shielding and dampening (Photos #1277, #1281 & #1308)

A 20 foot high, square dampener surrounds a pile driving hammer to minimize noise from the impact of the hammer on the pile.

Bubble Curtains: Where piles are driven or drilled through water, bubble curtain technology may be employed. Bubble curtain techniques introduce specifically sized air bubbles into the water surrounding the pile in a controlled manner, thus dampening the shock waves and helping to minimize the effects on aquatic life. Air may be released in a variety of ways, including through a ring, as shown in Figure 7.18 below.

A construction worker stands near an underwater pile driving hammer with an operating bubble curtain surrounding the pile and hammer. The bubbles are visible at a few feet higher than the water surface at the top of the curtain.

Figure 7.17 Bubble curtain (Photo #57)

See References 030, 036, 046, 054, 060, 061, and 102 for information related to aquatic effects.

	Figure 7.18 Bubble curtain air release ring (Photo #51)
Figure 7.19 Bubble curtain (Photo #52)

Aprons: Sound aprons generally take the form of sound absorptive mats hung from the equipment or on frames attached to the equipment. The aprons can be constructed of rubber, lead-filled fabric, or PVC layers with possibly sound absorptive material covering the side facing the machine. Sound aprons are useful when the shielding must be frequently removed or if only partial covering is possible.

Enclosures: Enclosures for stationary work may be constructed of wood or any other suitable material and typically surround the specific operation area and equipment. The walls could be lined with sound absorptive material to prevent an increase of sound levels within the structure. They should be designed for ease of erection and dismantling.

Low cost straw bales are stacked like blocks in a four-sided enclosure. One corner is open so a worker may access the equipment. The access site can be blocked when worker is completed with task.

Figure 7.20 Straw bail enclosure for stationary equipment (Photo #58)

Blasting Mats: These mats are typically made with layers of used tires cabled together. They are commonly used as blankets for blasting operations to control and confine debris. These mats also provide a degree of noise attenuation from the blast. However, they do not mitigate vibration, which is usually more of a concern than noise.

Blasting mats constructed with black tires can be seen intermingled amongst a pile of large rocks post blast.

Figure 7.21 Blasting mats constructed with black tires (in foreground of photo) (Photo #261)

A blasting mat made of black tires is being placed into position with a excavator.

Figure 7.22 Blasting mats being placed into position (Photo #1341)

Selection of Equipment: Newer equipment is generally quieter than old equipment for many reasons, including technological advancements and the lack of worn, loose, or damaged components. Some equipment manufacturers have made their equipment quieter in recent years and have achieved significant reductions over older equipment. In some cases, the use of over- or under-powered equipment may be an unexpected source of excessive noise. The types of engines and power transfer methods also plays a significant roll in achieving lowered equipment noise. The use of electric powered equipment is typically quieter than diesel, and hydraulic powered equipment is quieter than pneumatic power.

A large, bulky, dirty, and rusty paver still functions well, but may emit louder noise than a newer piece of equivalent equipment.

Figure 7.23 Older equipment may be as efficient as new, but may not meet noise emission requirements (Photo #809)

Paving equipment that is small, efficient, and in good working condition is likely quieter than older equivalent equipment.

Figure 7.24 Newer paving equipment (Photo #813)

Maintenance Programs: Poor maintenance of equipment typically causes excessive noise levels. Faulty or damaged mufflers and loose engine parts such as screws, bolts, or metal plates contribute to increased noise levels. Removal of noise-reducing attachments and devices such as mufflers, silencers, covers, guards, vibration isolators, etc., will, to varying degrees, increase noise emission levels. Old equipment may be made quieter by simple modifications, such as adding new mufflers or sound absorbing materials. Loose and worn parts should be fixed as soon as possible.
Equipment Operation Training: Careless or improper operation or inappropriate use of equipment can increase noise levels. Poor loading, unloading, excavation, and hauling techniques are examples of how lack of adequate guidance and training may lead to increased noise levels.

A new, efficiently designed wheel loader appears to be clean and well maintained. Regular service of equipment is an essential to quietest operation possible. Equipment suppliers may also be valuable source of training related to proper use of equipment.

Figure 7.25 Regular service of equipment is an essential component to quietest operation possible. Equipment suppliers may also be valuable sources of training related to proper use of equipment. (Photo #827)

7.4.2 Stationary Equipment

Whenever possible, positioning stationary noise sources such as generators and compressors as far away as possible from noise sensitive areas should be considered. Temporary barriers can be employed and/or enclosures can be built around noisy equipment. These techniques can significantly reduce noise levels and, in many cases, are relatively inexpensive. These barriers can typically be constructed on the work site from common construction building material (plywood, block, stacks, or spoils). Enclosures are often constructed from commercial panels lined with sound absorbing material to achieve the maximum possible shielding effect.

To be effective, the length of a barrier should be greater than its height, the noise source should not be visible, and any barrier should be located as close as possible to either the noise source or the receiver. In addition, providing increased distance between a noise source and a noise receiver can also be considered a form of abatement.

Stationary equipment is enclosed on all six sides with a temporary barrier of plywood found on the construction site.

Figure 7.26 Temporary shielding of stationary equipment (Photo #1340)

A construction worker at his workstation is shielded by a seven foot tall U-shaped barrier of plastic or vinyl material that can be easily relocated.

Figure 7.27 Temporary barrier around stationary activity (Photo #1339)

7.4.3 Mobile Equipment

Many construction operations are mobile and tend to progress along the length of a project at varying rates. Noise levels at the receiver tend to vary considerably, not only as the speed and power of the equipment varies, but also as the equipment is constantly changing in terms of its distance from the receivers and its relative location. To address this, all the equipment noise mitigation techniques listed in Section 7.4.1 are worthy of consideration with the exception of the enclosures. Enclosing mobile equipment is usually not possible, unless the operation is slow moving and the enclosures can be easily moved.

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