Noise Control
A guide for workers and employers
U.S. Department of Labor
Occupational Safety and Health Administration
Contents
Noise.
It can destroy hearing.
It can create physical and psychological stress.
And it can contribute to accidents by making it impossible to hear warning signals.
An estimated 14 million workers in the U.S. are exposed to hazardous noise.
Luckily, noise exposure can be controlled. No matter what the noise problems may be in a particular workplace, technology exists to reduce the hazard.
It may be possible to:
In the field of noise control, where there's a will, there's a way.
The Occupational Safety and Health Administration (OSHA) was established by the U.S. Congress to help eliminate job safety and health hazards such as noise.
This book is presented by OSHA for workers and employers interested in reducing workplace noise. OSHA believes that highly technical training is not generally necessary in order to understand the basic principles of noise control. Noise problems can often be solved by the workers and employers who are directly affected.
The book contains five major sections.
First, a brief overview of the effects of noise on human health
Second, a discussion of some of the key words and concepts involved in noise control.
Third, an explanation of specific principles of noise control which the reader can apply in his or her workplace.
Fourth, a discussion of particular techniques for controlling noise.
Fifth, a description of the ways OSHA can help employers and employees, including an explanation of the legal requirements for noise control which employers must follow.
OSHA hopes that the information in this book will be discussed by employers, workers, and union representatives. If more help is needed, contact the nearest OSHA area office listed in the back of the book.
1
The ability to hear is one of our most precious gifts. Without it, it is very difficult to lead a full life either on or off the job.
Excessive noise can destroy the ability to hear, and may also put stress on other parts of the body, including the heart.
For most effects of noise, there is no cure, so that prevention of excessive noise exposure is the only way to avoid health damage.
Hearing
The damage done by noise depends mainly on how loud it is and on the length of exposure. The frequency or pitch can also have some effect, since high-pitched sounds are more damaging than low-pitched ones.
Noise may tire out the inner ear, causing temporary hearing loss. After a period of time off, hearing may be restored. Some workers who suffer temporary hearing loss may find that by the time their hearing returns to normal, it is time for another work shift, so, in that sense, the problem is "permanent."
With continual noise exposure, the ear will lose its ability to recover from temporary hearing loss, and the damage will become permanent. Permanent hearing loss results from the destruction of cells in the inner ear-cells which can never be replaced or repaired. Such damage can be cause by long-term exposure to loud noise or, in some cases, by brief exposures to very loud noises.
Normally, workplace noise first affects the ability to hear high frequency (high-pitched) sounds.
This means that even though a person can still hear some noise, speech or other sounds may be unclear or distorted.
Workers with hearing impairment typically say "I can hear you, but I can't understand you." Distortion occurs especially when there are background noises or many people talking. As conversation becomes more difficult to understand, the person becomes isolated from family and friends. music and the sounds of nature become impossible to enjoy.
A hearing aid can make speech louder, but cannot make it clearer, and is rarely a satisfactory remedy for hearing loss.
Workers suffering from noise-induced hearing loss may also experience continual ringing in their ears, called "tinnitus." At this time there is no cure for tinnitus, although some doctors are experimenting with treatment.
Other effects
Although research on the effects of noise is not complete, it appears that noise can cause quickened pulse rate, increased blood pressure and a narrowing of the blood vessels. Over a long period of time, these may place an added burden on the heart.
Noise may also put stress on other parts of the body by causing the abnormal secretion of hormones and tensing of muscles (see Figure 1).
Workers exposed to noise sometimes complain of nervousness, sleeplessness and fatigue. Excessive noise exposure also can reduce job performance and may cause high rates of absenteeism.
2
Figure 1. In addition to causing hearing loss by destroying the inner ear, noise apparently can put stress on other parts of the body by causing reactions such as those shown at left.
Figure 2. Severe destruction of the hair cells in the hearing organ. Top picture: normal hair cells, lower picture: hair cells destroyed by noise.
3
Noise control: Basic concepts and terms
There are a number of words and concepts which must be understood before beginning a discussion of noise control methods.
Sound
Sound is produced when a sound source sets the air nearest to it in wave motion. The motion spreads to air particles far from the sound source. Sound travels in air at a speed of about 340 meters per second. The rate of travel is greater in liquids and solids; for example, 1,500 m/s in water and 5,000 m/s in steel.
(Note: Measurements in this book are generally given in the metric system. To convert, one meter equals about 39.4 inches, and one millimeter equals 0.04 inches, and one kilogram equals about 2.2 pounds.)
Frequency (Hz)
The frequency of a sound wave refers to the number of vibrations per second, measured in units of hertz (Hz). Sound is found within a large frequency range; audible sound for young [continued on next page]
Figure 3. The sound source vibrates and affects air particles, which strike the ear drum.
Figure 4. A pure tone is marked by a single column indicating the frequency and the sound level or intensity. Musical notes contain several tones of different frequencies and intensities.
4
persons is between about 20 Hz and 20,000 Hz.
The boundary between high and low frequencies is generally established at 1,000 Hz.
Sound may consist of a single pure tone, but in general it is made up of several tones of varying intensities.
Noise
It is customary to call any undesirable sound "noise." [sic] The disturbing effects of noise depend both on the intensity and the frequency of the tones. For example, higher frequencies are more disturbing than low ones. Pure tones are more disturbing than a sound made up of many tones.
Infrasound and ultrasound
Sound with frequencies below 20 Hz is called infrasound, and sound with more than 20,000 Hz is called ultrasound. There is some evidence that these sounds which cannot be heard can under certain conditions be hazardous to workers' health. This book deals only with noise which can be heard.
Figure 5. Noise is a disorderly mixture of tones at many frequencies.
5
Figure 6. At the same intensity, the noise from a truck is less disturbing than the sound of air blowing or suction because it is at a lower frequency.
6
Decibel (dB)
Sound levels are measured in units of decibels (dB). If sound is intensified by 10 dB, it seems to the ears approximately as if the sound intensity has doubled. A reduction by 10 dB makes it seem as if the intensity has been reduced by half.
Noise level measurement
In measuring sound levels, instruments are used which resemble the human ear in sensitivity to noise composed of varying frequencies. The instruments measure the "A-weighted sound level" in units called dB(A).
Workplace noise measurements indicated the combined sound levels of tool noise from a number of sources (machinery and materials handling) and background noise (from ventilation systems, cooling compressors, circulation pumps, etc.).
Figure 7.
7
In order to accurately identify all workplace noise problems, the noise from each source should also be measured separately. Measurements at various production rates may be useful in considering possible control measures. A number of manuals for noise measurements are commercially available.
Adding noise levels
Decibel levels for two or more sounds cannot simply be added. Figure 8 shows how the combined effect of two sounds depends on the difference in their levels. Two or more sounds of the same level combine to make a higher noise level.
Octave band
It is common practice to divide the range of frequencies we can hear into eight octave bands. The sound level is then listed for each octave band. The top frequency in an octave band is always twice the bottom one. The octave band may be referred to by a center frequency. For example, 500 Hz is the center frequency for the octave band 354-708 Hz.
| number of decibels to add to higher of two levels |  |
Figure 8. A fan produces a sound level of 50 dB(A). Another fan produces 56 dB(A). The difference is 6 dB(A), and according to the diagram, 1 dB(A) will be added to the highest level. Operating together, the fans will result in a level of 57 dB(A).
Sound transmission
The word "sound" usually means sound waves traveling in air. However, sound waves also travel in solids and liquids. These sound waves may be transmitted to air to make sound we can hear.
Resonance
Each object or volume of air will "resonate," or strengthen a sound, at one or more particular frequencies. The frequency depends on the size and construction of the object or air volume.
Sound reduction by distance
Sound spreading in open air and measured at a certain distance from the source is reduced by about 6 dB for each doubling of that distance. Sound is reduced less when spreading inside a room. (See Figure 9.)
8
Sound transmission loss (TL)
When a wall is struck by sound, only a small portion of the sound is transmitted through the wall, while most of it is reflected. The wall's ability to block transmission is indicated by its transmission loss (TL) rating, measured in decibels. The TL of a wall does not vary regardless of how it is used.
Noise reduction (NR)
Noise reduction is the number of decibels of sound reduction actually achieved by a particular enclosure or barrier. This can be measured by comparing the noise level before and after installing an enclosure over a noise source. NR and TL are not necessarily the same.
Sound absorption
Sound is absorbed when it strikes a porous material. Commercial sound-absorbing materials usually absorb 70 percent or more of the sound that strikes them.
Figure 9. If a small sound source produces a sound level of 90 dB at a distance of 1 meter, the sound level at a 2 meter distance is 84 dB, at 4 meters 78 dB, etc.
Figure 10. Part of the sound that strikes a wall is reflected, part is absorbed, and part is transmitted. The transmission loss (TL) of the wall is determined by the portion of the noise which is not transmitted through the wall.
9
Application of noise control principles
The following section explains how to apply basic noise control principles. In many cases, several principles must be applied and several control measures must be taken. Of course, these principles do not cover every possible noise problem.
The principles are discussed in eight sections:
A. Sound behavior
B. Sound from vibrating plates
C. Sound production in air or gases
D. Sound production in flowing liquids
E. Sound movement indoors
F. Sound movement in ducts
G. Sound from vibrating machines
H. Sound reduction in enclosure walls
A number of symbols are used throughout the drawings. For example, large black arrows indicate strong sound radiation and smaller ones show reduced radiation.
11
SOUND BEHAVIOR - CAUSES OF SOUND PRODUCTION - A1
Changes in force, pressure, or speed produce noise
Sound is always produced by changes in force, pressure, or speed. Great changes produce louder noises and small changes quieter ones. More noise is produced if a task is carried out with great force for a short time than with less force for a longer time.
Principle
12
Example
In a box machine, cardboard is cut with a knife blade. The knife must cut very rapidly and with great force in order for the cut to be perpendicular to the strip Much noise results.
Control Measure
Using a blade which travels across the strip, the cardboard can be scored with minimal force for a longer time. Since the cardboard strip continues to move, the knife must travel at an angle in order for the cut to be perpendicular. The cutting is practically noise free.
13
SOUND BEHAVIOR - CAUSES OF SOUND PRODUCTION - A2
Airborne sound is usually caused by vibration in solids or turbulence in fluids
For example, vibrations of the strings in a musical instrument are transmitted through the bridge to the sound box. When the sound box vibrates, sound is transmitted to the air. A circulation pump produces pressure variations in the water in a heating system. The sound waves are transmitted through the pipes to the radiators, whose large metal surfaces transmit airborne sound.
14
Example
Turbulent fluid flow within pipes produces sound which can be radiated from the pipes and even transmitted to the building structure.
Control measure
In addition to reducing the turbulence in the pipe, the pipe can be covered with sound absorbing material. The vibrations can be isolated from the wall or ceiling with flexible connecting mechanisms.
15
SOUND BEHAVIOR - CAUSES OF SOUND PRODUCTION - A3
Vibrations can produce sound after traveling great distances
Vibrations in solids and liquids can travel a great distance before producing airborne sound. Such vibrations can cause distant structures to resonate. The best solution is to stop the vibration as close to the source as possible.
Principle
16
Example
Vibrations from an elevator are transmitted throughout a building.
Control measure
The elevator drive can be isolated from the building structure.
17
SOUND BEHAVIOR - LOW AND HIGH FREQUENCIES - A4
The slower the repetition, the lower the frequency of the noise
The level of low frequency noise from a sound source is determined primarily by the rate at which the changes in force, pressure, and speed are repeated. The longer the time between changes, the lower the frequency of the noise generated. The level of noise depends on the amount of the change.
Principle
18
Example
Two gears have the same pitch diameter but different numbers of teeth. If they rotate at the same speed, the gear with fewer teeth will produce a lower frequency noise.
19
SOUND BEHAVIOR - LOW AND HIGH FREQUENCIES - A5
High frequency sound is strongly directional and more easily reflected
When high frequency sound strikes a hard surface, it is reflected much like light from a mirror. High frequency sound does not travel around corners easily.
Principle
20
Example
High frequency noise travels directly from the high-speed riveting machine to the worker's ears.
Control measure
A sound-insulating hood, open toward the bottom of the machine, is constructed above the hammer. The hood is coated on the inside with sound-absorbing material. The upper portion of the opening is covered with safety glass. As sound starts towards the ears, the glass reflects it against the sound-absorbing walls. The sound level for the machine operator is thus reduced.
21
SOUND BEHAVIOR - LOW AND HIGH FREQUENCIES - A6
Low frequency noise travels around objects and through openings
Low frequency noise radiates at approximately the same level in all directions. It travels around corners and through holes, and then continues to travel in all directions. A shield has little effect unless it is very large.
Principle
22
Example
Compressors and the diesel engines inside them both may produce strong low frequency noise, even if they are provided with effective mufflers at the intake and exhaust.
Control measure
A complete enclosure of damped material lined with sound absorbant will help. The air and exhaust gases must pass through mufflers which are partly made of channels with sound-absorbing walls. Doors for inspection must close tightly.
23
SOUND BEHAVIOR - REDUCTION IN AIR - A7
High frequency sound is greatly reduced by passing through air
High frequency sound is reduced more effectively than low frequency sound by passing through air. In addition, it is easier to insulate and shield. If the noise source does not cause problems in its immediate vicinity, it may therefore be worthwhile to shift the sound toward higher frequencies.
Principle
24
Example
The low frequency noise from roof fans in an industrial building disturbs residents of houses a quarter-mile away.
Control measure
The rooftop fan is replaced by another one of similar capacity but with a larger number of fan blades. This produces less low frequency noise and more high frequency noise. The low frequency noise no longer causes disturbances, and the high frequency noise is adequately reduced by the distance.
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SOUND BEHAVIOR - HOW DISTURBING? - A8
Low frequency noise is less disturbing
The Human ear is less sensitive to low frequency noise than to high frequency noise. If it is not possible to reduce the noise, it may be possible to change it so that more of it is at lower frequencies.
Principle
26
Example
The diesel engine in a ship operates at 125 rpm and is directly connected to the propeller. The noise from the propeller is extremely disturbing on board.
Control measure
Differential gear is installed between the motor and the propeller so that the motor can revolve at 75 rpm. The propeller is replaced by a larger one. The noise is shifted to a lower frequency, making it less disturbing.
27
SOUND FROM VIBRATING PLATES - SIZE AND THICKNESS - B1
Small vibrating surfaces give off less noise than large ones
An object with a small surface area may vibrate intensely without a great deal of noise radiation. The higher the frequencies, the smaller the surface must be to prevent disturbance. Since machines always will vibrate to some extent, noise control will be aided if the machines are kept as small as possible.
Principle
28
Example
Too much noise is radiated from the control panel of a hydraulic system.
Control measure
The panel is detached from the system itself, the vibrating surface is reduced, and therefore the noise level is decreased.
29
SOUND FROM VIBRATING PLATES - SIZE AND THICKNESS - B2
Densely perforated plates produce less noise
Large vibrating surfaces cannot always be avoided. The vibrating surface pumps air back and forth like the piston of a pump, causing sound radiation. If the panel is perforated, the "piston" leaks, and the pumping functions poorly. Alternatives to perforated plates include mesh, gratings and expanded metal.
Principle
30
Example
The protective cover over the flywheel and belt drive of a press is a major noise source. The cover is made of solid sheet metal.
Control measure
A new cover is made of perforated sheet metal and wire mesh. Sound radiation is reduced.
31
SOUND FROM VIBRATING PLATES - SIZE AND THICKNESS - B3
A long, narrow plate produces less sound than a square one
When a plate is set into vibration, excess air pressure forms on one side of the plate and then the other. Sound comes from both sides. The pressure difference balances out close to the edges, so the noise radiation there is slight. Therefore, a long, narrow plate radiates less sound.
Principle
32
Example
A belt drive provides a large amount of low frequency noise because of the vibration of the broad belt.
Control measure
The broad drive belt is replaced by narrower belts, separated by spacers. This reduces the noise problem.
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SOUND FROM VIBRATING PLATES - SIZE AND THICKNESS - B4
Plates with free edges produce less low frequency noise
If a plate vibrates with free edges, pressure equalization takes place between the two sides of the plate, thus reducing sound emissions. Clamping the corners prevents pressure equalization and the sound emission is greater, especially at low frequencies. For example, speakers produce more bass if they are enclosed in a cabinet.
Principle
34
Example
Bumps in the floor produce noise from the bottom and side plates of a cart when the cart is pushed. Sound is also emitted when material is slid down the cart walls. Pressure equalization only takes place at the top edges of the side plates.
Control measure
The walls are replaced by new ones, constructed with a pipe frame. Plates are fastened with a gap between the plates and the frame. Pressure equalization takes place along all the edges, and the low frequency noise is reduced.
35
SOUND FROM VIBRATING PLATES - COLLISION AND IMPACT - B5
Light objects and low speed produce the least impact noise
When a plate is struck by an object, the plate vibrates and makes noise. The sound level is determined by the weight of the object and its striking speed. If the dropping height of an object is reduced from 5 meters (about 16 feet) to 5 centimeters (2 inches), the sound level drops about 20 dB.
Principle
36
Example
Steel parts are transported from a machine to a storage bin. When the bin is empty, the dropping height is large and the noise is loud.
Control measure
A hydraulic system is installed so that the conveyor belt can be raised and lowered. The belt ends in a drum equipped with rubber plates to break the fall of the parts. The drum is raised automatically.
37
SOUND FROM VIBRATING PLATES - INTERNAL DAMPING - B6
A damped surface gives off less sound
As vibration moves throughout a plate, it gradually decreases as it travels, but in most plates, this reduction is rather small. In such cases, the material is said to have low internal damping. Internal damping in steel, for example, is extremely poor. Good damping can be achieved by adding coatings or intermediate layers with better internal damping.
Principle
38
Example
The loudest noise from a pump system comes from the coupling guard which is made of sheet metal.
Control measure
The noise level is reduced by vibration isolating the guard or constructing it of damped metal. If the coupling creates a siren-type noise, the guard may need acoustical lining.
39
SOUND FROM VIBRATING PLATES - RESONANCE - B7
Resonance increases noise but it can be damped
Resonance greatly increases noise from a vibrating plate, but it can be suppressed or prevented by damping the plate. It may often be sufficient to damp only part of the surface, and, in some rare cases, damping of a single point is effective.
Principle
40
Example
An automatic tooth cutter for circular saw blades produces intense resonance sound.
Control measure
A urethane rubber coating clamped to the saw blade damps the resonance.
41
SOUND FROM VIBRATING PLATES - RESONANCE - B8
Resonance shifted to higher frequency is more easily damped
Large vibrating plates often have low frequency resonance which can be difficult to damp. If the plate is stiffened, the resonance shifts to higher frequency, which can be more easily damped.
Principle
42
Example
The greatest low frequency sound from this machine comes from the side surfaces of the machine stand.
Control measure
The side plates on the machine are stiffened with iron straps. A damped plate is installed over the braces.
43
SOUND PRODUCTION IN AIR OR
GASES - WIND TONES - C1
When air passes by an object at certain speeds, a strong pure tone,
known as a Karman tone, can be produced. This can be prevented by making
the object longer in the direction of flow, such as with a "tail,"
or by making the object's shape irregular.
Wind tones can be eliminated
Principle
44
Example
At certain wind speeds, loud sounds can form around smoke stacks, causing disturbances.
Control measure
A strip of sheet metal is mounted on the smoke stack in a spiral. The pitch of the spiral must not be constant. Regardless of the wind's direction, it encounters an irregular object.
45
SOUND PRODUCTION IN AIR OR GASES - WIND TONES - C2
Air flow past hollow openings should be avoided
When air or another gas blows across the edges of an opening to a hole, loud, pure tones are formed. This is how a wind instrument operates. The greater the volume of the hole and the smaller the number of openings, the lower the frequency of the tone will be.
Principle
46
Example
When a cutter wheel revolves under no-load conditions, sound can arise from the track for holding the plane blade. An air stream is being chopped, creating a siren (pure tone) noise.
Control measure
Minimizing the cavities by filling the empty space in the track with a rubber plate reduces the pumping action and the noise.
47
SOUND PRODUCTION IN AIR OR GASES - DUCTS - C3
Ducts without impediments produce the least amount of noise from turbulence
During flow in ducts or pipes there is always some turbulence against the duct walls. The noise from turbulence is increased if the flow must rapidly change direction, if the flow moves at a fast rate, and if objects blocking the flow are close together.
Principle
48
Example
A branch of a steam line has three valves which produce a loud shrieking sound. The branch has two sharp bends which also produce a lot of noise.
Control measure
A new branch is created with softer bends. Tubing pieces are placed between the valves, so that turbulence will be reduced or eliminated before the stream reaches the next valve.
49
SOUND PRODUCTION IN AIR OR GASES - DUCTS - C4
Undisturbed flow produces the smallest amount of exit noise
When a flowing gas mixes with a non-moving gas, noise may be produced, especially if the flow is disturbed before the outlet. A lower outflow speed will produce a lower sound level. For speeds below 325 feet/sec., reduction of the speed by half will mean that the sound will be about 15 dB weaker.
Principle
50
Example
The exhaust air from a compressed air-driven grinding machine produces a loud noise. The air becomes turbulent while leaving the machine through the side handle.
Control measure
A new handle is developed, filled with a porous sound-absorbing material between two fine-meshed gauzes. Passage through the porous materials breaks up the turbulence. The air stream leaving the handle is less disturbed, and the exhaust noise is weaker. A straight lined duct-type muffler may also be used.
51
SOUND PRODUCTION IN AIR OR GASES - DUCTS - C5
Jet noise can be reduced by using an extra air stream
The term "jet stream" applies at flow speeds in excess of 325 ft/sec. Turbulence outside the outlet is great. Reducing the outflow speed by half may decrease the noise level by as much as 20 dB. Since the noise level is determined by the speed of the jet stream in relation to the speed of the surrounding air, noise production can be greatly reduced by using an air stream with a lower speed outside the jet stream.
Principle
52
Example
The cleaning of machine parts with compressed air after processing is often carried out with simple tubular mouthpieces. Very high exit speeds are required, and a strong high frequency noise develops.
Control measure
The simple tubular mouthpiece can be replaced by mouthpieces which produce less noise, such as a dual flow mouthpiece. In this mouthpiece, part of the compressed air moves at a lower speed outside the central stream.
53
SOUND PRODUCTION IN AIR OR GASES - DUCTS - C6
Low frequency jet noise is easier to reduce if converted to high frequency
If the diameter of a gas outlet is large, the noise will peak at the low frequency. If the diameter is small the noise will peak at high frequency. The low frequency noise can be reduced by replacing a large outlet with several small ones. To some extent this will increase the high frequency noise, but this is more easily controlled.
Principle
54
Example
Steam safety valves may discharge many times each day. Sound production during steam escape can produce high level, low frequency sound.
Control measure
A diffuser is formed as a perforated cone. The holes produce many small jet streams and high frequency noise which is absorbed in the down-stream pack.
55
SOUND PRODUCTION IN AIR OR GASES - FANS - C7
Fans make less noise if placed in smooth, undisturbed flow streams
A fan produces turbulence in air, which causes noise. If turbulence is already present in the incoming air, the sound will be more intense. The same principle applies, for example, to propellers in water.
Principle
56
Example
In one case the fan is located too close to a barrier, and in the other case too close to a sharp bend. The flow is disturbed and the noise at the outlet is intense.
Control measure
The control vanes are moved farther from the fan so that the turbulence has time to die down. In the other case, the bend is made smoother, and the fan is moved away from the bend. Turning vanes could also be used.
57
SOUND PRODUCTION IN FLOWING LIQUIDS - PIPE SYSTEMS - D1
Rapid pressure changes produce more noise
Turbulence will form if the pressure in a liquid system drops rapidly. Gas is released in the form of bubbles and produces a roaring noise. The pressure drop can be produced by a large, rapid change in volume. Noise is avoided by a slow change in volume.
Principle
58
Example
Control valves in liquid systems often have small valve seats, resulting in large flow speeds with large pressure changes. Twisted flow pathways and sharp edges produce intense turbulence. Sound radiates directly from valves and pipes, and solid sound is conducted to walls.
Control measure
Control valves with larger cone diameters, straighter flow pathways, and more rounded edges are used.
59
SOUND PRODUCTION IN FLOWING LIQUIDS - PIPE SYSTEMS - D2
Large and rapid changes in pressure produce "cavitation" sound
Noise production takes place at control valves, at pump pistons, and at propellers when large and rapid pressure drops occur in liquids. This so-called "cavitation" noise is most common in hydraulic systems. Cavitation can be reduced by bringing about the pressure reduction in several smaller steps
Principle
60
Example
In a hydraulic system, the full pump capacity is employed only in exceptional cases. The pressure is generally greatly reduced using a control valve. Cavitation can then arise, producing loud noise from the valve. The noise is conducted as solid-borne sound to connected machines and building structures
Control measure
A pressure reducing insert is placed in the same pipe as the control valve. The inset has removable plates with different perforations. The plates are selected so that the inset will not produce a greater pressure drop than that required to prevent cavitation.
61
SOUND MOVEMENT INDOORS - PLACEMENT OF SOUND SOURCE - E1
Sound sources should not be placed near corners
The closer to reflecting surfaces a sound source is placed, the greater the noise it will radiate to a given distance. The worst placement is in corners near three surfaces. The best placement is away from the walls.
Principle
62
Example
In an industrial shop, machines are placed in four rows with three aisles between them. This arrangement increases the noise from the machines in the two outermost rows.
Control measure
The machines are placed together, two by two, away from the walls and new aisles are set up along the walls.
63
SOUND MOVEMENT INDOORS - ABSORPTION - E2
Thick, porous layers absorb both high and low frequency sound
Porous material through which air can be pressed often makes a good sound absorbant. Examples of such materials include felt, foam rubber, foamed plastic, textile fibers and a number of sintered metals and ceramic materials. If the pores are closed, the absorption is slight. Thin porous absorbants handle high tones. For good effects below 100 Hz, the thickness required may become impractical. Low frequency absorption is improved with the aid of an air gap behind the absorbant.
Principle
64
Example
A workshop with intense low frequency noise is provided with absorbants that are effective for low tones. One part of the shop contains space for hanging absorption baffles, which provide good low frequency absorption and are easily installed. A traverse leaves no room for baffles in the other part of the shop. Instead, horizontal absorbant panels are installed above the traverse, 8 inches from the ceiling, to improve the low frequency absorption.
65
SOUND MOVEMENT INDOORS - ABSORPTION - E3
Cover layers with large perforations may be used without reducing absorption
For a variety of reasons, a covering material may be needed to protect a porous absorbant. This can be done without reducing the effectiveness of the absorbant if the cover material has a sufficient number of openings. The thicker the cover layer, the larger the number of perforations that will be required.
Principle
66
Example
Sound-absorbing material is required on many wall and ceiling surfaces in a building. To provide a more attractive environment, it is desirable to have many absorbants with different appearances.
Control measure
One material is used on all surfaces with varying thicknesses. Different covering materials provide the desired variation in appearance.
67
SOUND MOVEMENT INDOORS - ABSORPTION - E4
Panels on studs absorb low frequencies
Thin panels, fastened to a system of studs, absorb low frequencies. The absorption is effective in a narrow frequency range. This range is determined by the stiffness of the panels and the distance between the fastenings. If the panels are fastened to studs on a wall, the distance from the wall also has an effect. A panel with large internal damping absorbs in a larger frequency range. If a porous absorbing material is used at these low frequencies, it must be very thick.
Principle
68
Example
Low frequency resonance in an engine room produced a very loud hum
near the walls and in the center of the room. When the revolution speed
was significantly changed, the hum disappeared completely.
Control measure
The walls were coated with panels on studs to provide the greatest absorption in the range of the loudest tone. In order for the absorbant to continue to function even in the case of slight deviations from the normal rotation speed, a layer with good internal damping was used, which provided a more extensive range with good sound absorption. As a result, the resonance and the loud hum disappeared.
69
SOUND MOVEMENT INDOORS - ABSORPTION - E5
Sound shields may be combined with sound absorbing ceilings
High frequency noise can be reduced by using a shield. The shield is more effective the taller it is and the closer it is placed to the source. The effect of a shield is considerably reduced if the ceiling is not sound absorbant
Principle
70
Example
In an auto plant with several assembly lines, the work on one line is noisier than the other. Grinding work on the bodies produces a shrieking, high frequency sound, disturbing everyone in the plant.
Control measure
The other lines are protected from the grinding noise by means of shields on both sides of the line and sound absorbing baffles suspended above the open area.
71
SOUND MOVEMENT IN DUCTS - REACTIVE MUFFLERS - F1
All duct changes reduce sound transmission
With all changes in pathway, some sound energy is reflected back. In a duct this may apply to bends, branches, and changes in volume, shape, or wall materials.
Principle
72
Example
An area is to be provided with mechanical ventilation. There is sufficient space for the fan, but not for the necessary muffler.
Control measure
In place of a single inlet into the room, several smaller inlets are used. The sound reflection which takes place with all changes in volume and at each bend replaces the muffler.
73
SOUND MOVEMENT IN DUCTS - REACTIVE MUFFLERS - F2
Expansion chambers are useful for reducing low frequency noise
If a duct is provided with an expanded section or chamber, the low frequency pressure variations in the duct are reduced. The lower the frequency which must be reduced, the greater the space required in the chamber.
Principle
74
Example
Using a jacket over the tip and a tubular outlet in the jacket, the high frequency noise given off by a jack hammer can be partially shielded. The low frequency noise in the exhaust air is effectively reduced. The enlarged are between the barrel and the jacket functions as an expansion chamber.
75
SOUND MOVEMENT IN DUCTS - REACTIVE MUFFLERS - F3
Reflection mufflers are effective in narrow frequency ranges
If noise is present in a limited frequency range, a reactive muffler may take up the least space. These are generally used at low frequencies. A large frequency range can be covered using several reactive chambers in succession. Perforated tubes are also employed in reflection dampers.
Principle
76
Example
The muffler shown here is primarily used in large piston engines.
77
SOUND MOVEMENT IN DUCTS - PACKED MUFFLERS - F4
Absorption mufflers are effective over a broad range of frequencies
The simplest form of absorption muffler is a duct with sound-absorbing material on the walls. The thicker the material, the lower the frequency that can be reduced. For higher frequencies, the space between the absorbing walls must be made smaller. A large duct must therefore be subdivided into many smaller ones.
Principle
78
Example
If a very large frequency range is to be reduced, it is generally necessary to employ absorption mufflers with thick and thin baffles.
79
SOUND MOVEMENT IF DUCTS - PACKED MUFFLERS - F5
Unused areas can be absorption chambers
The absorption chamber is simple muffler. One section of the duct is made up of a room whose walls are covered with a sound-absorbing material. When the sound is reflected against the chamber walls, sound energy is absorbed. To prevent the direct passage of high frequency, directed sound, the inlet and the outlet should not be located opposite one another. The greater the chamber volume and the thicker the absorbant used, the lower the frequency at which the muffler is effective.
Principle
80
Example
The shape of the absorption chamber is of little significance. Unused rooms can be simple converted to absorption chambers.
81
SOUND FROM VIBRATING MACHINES - MACHINE MOUNTING - G1
Machines which vibrate should be mounted on heavy, rigid bases
Knocking on a thin door produces more sound than knocking on a thick wall. For the same reason, noise sources should be mounted on heavy or rigid bases.
Principle
82
Example
A motor-driven oil pump is placed on the side wall of a hydraulic press. The vibrations are transmitted to all plates, which convert the solid-borne sound to loud airborne sound.
Control measure
The oil system is removed from the press and installed in a frame on a heavy base. Sound transmission in the oil line is controlled with an accumulator.
83
SOUND FROM VIBRATING MACHINES - MACHINE MOUNTING - G2
Machines should be vibration isolated
Vibration isolation of machines can reduced the area of excessive noise as shown below. Either the machine or the working area can be isolated.
Principle
84
Example
Vibration isolators are made of various materials and in various shapes.
85
SOUND FROM VIBRATING MACHINES - INSTALLATION - G3
Improperly selected springs can increase vibrations
A machine placed on springs has a so-called "fundamental frequency." Vibrations at or close to the fundamental frequency are greatly intensified. The machine may even break away from its fastenings. Vibrations with lower frequency that the fundamental frequency are not blocked. If the base is very heavy or very rigid, the fundamental frequency is determined entirely by the machine and base weights together with the rigidity of the spring. The lighter the machine and the more rigid the spring. the higher is the fundamental frequency. This reinforcement of vibrations can be avoided by using springs with good internal damping.
(Same fundamental frequency in the four examples.)
86
Example
Two fans are used in the same building. Both are vibration isolate with steel springs which have very poor internal damping. The isolation functions well for both fans during constant operation, but one of the fans is started and stopped frequently. When this happens, the vibration frequency corresponds for a short time with the fundamental frequency, which produces serious disturbance.
Control measure
On the fan with irregular operation, steel dampers are installed with pads which have good internal damping. The isolation is somewhat less, but the disturbance from starting and stopping disappears.
87
SOUND FROM VIBRATING MACHINES - INSTALLATION - G4
Isolating machines with low natural frequency may require a rigid floor
A machine and mount with low natural frequency are difficult to vibration isolate unless the floor is very rigid. As shown below, and extra heavy (stiff) or pile-reinforced floor might be necessary.
Principle
88
Example
A company is planning a building where a need for freedom from vibration and noise is great. It should also be possible to remove and interchange the machines.
Control measure
The building is constructed with large concrete plates on a pillar and beam system. The concrete plates which are expected to carry heavy machines are provided with strong reinforcements. If heavy machines are added later, the normal concrete plate is removed and replaced with a thicker one.
89
SOUND FROM VIBRATING MACHINES - MACHINE MOUNTING - G5
A separate base layer provides the best solid-borne sound barrier
A good way to isolate very heavy machines with low natural frequency vibration is to place them on a concrete base plate which rests directly on the ground. Even more effective protection is achieved if the base plate is separated from the remainder of the building by means of a joint. If the ground has a clay layer, it may be necessary to place pilings beneath the plate.
Principle
90
Example
Drive motors with gears and differentials connected to a paper-making machine cause both loud air noise and vibrations in the machines. They require only occasional maintenance which can generally be performed with the machines turned off. Therefore, the machines can be permitted to make large amounts of noise if the noise is prevented from entering the rest of the factory.
Control measure
The engine room has it's own thick base plate which is in good contact with the solid ground. The large base plate is also vibration isolated with corrugated rubber mats. Sound is prevented from entering other rooms by means of a brick wall. Holes in the wall for the axles to pass through are sealed with mufflers.
91
SOUND FROM VIBRATING MACHINES - MACHINE MOUNTING - G6
Sound through solid connections can be blocked
Vibration isolation of a machine may be ineffective if sound is transferred through connections for oil, electricity, water, etc. These connections must be made very flexible. The machine movements will be reduced if a heavy base is selected, and more rigid springs can be used.
92
Example
Cooling systems may be serious sources of noise as a result of intense pressure shocks in the liquid from compressors.
Control measure
Compressors may be vibration isolated with steel springs. In addition, flexible connections should be used for all inlet and discharge pipes.
93
SOUND REDUCTION IN ENCLOSURE WALLS - TL - H1
The TL of a single wall is estimated from its surface weight
"Transmission loss" (TL) indicate a wall's ability to absorb sound-producing vibrations. TL is expressed in decibels (dB). The TL of a homogeneous single layer wall can be estimated by its surface weight, that is, kilograms per square meter or pounds per square inch.
Principle
94
Example
A sand blast operation creates excess noise. A separate room is available, with a thin drape as a barrier.
Control measure
A separate room is constructed for this operation. The blasting equipment is separated from other work areas with a drapery of lead-rubber fabric, which is heavy, but flexible.
95
SOUND REDUCTION IN ENCLOSURE WALLS - TL - H2
A single wall will provide poor sound isolation at a certain frequency
A single wall has a "resonant frequency" at which the TL will be less than the figure indicated by the weight per unit of surface. This "coincidence valley" will disappear if the wall has good internal damping.
Principle
96
Example
Behind one end wall in a long factory room are a number of machines with an intense noise level peak around 1000 Hz. The end of the room is isolated with a wall of 25 mm chipboard and 6 mm glass. The isolation is ineffective since the chipboard has its coincidence valley at 1000 Hz.
Control measure
The chipboard is replaced by two layers of 9 mm plasterboard. The isolation is improved by about 10 dB. The plasterboard weighs about the same as one 25 mm chipboard, but is less than one-fourth as rigid. The coincidence valley is located at 2500 Hz. (Absorptive material could also be added to the machines side of the wall.
97
SOUND REDUCTION IN ENCLOSURE WALLS - TL - H3
Rigidity and weight are both important in thick walls
In most single layer walls, the coincidence valley is close to 100 Hz for a thickness of about 20 cm. At higher frequencies, both increased weight and increased rigidity greater TL. A cast concrete wall has greater rigidity than a brick wall, and therefore provides greater TL if the two walls weights are equal.
98
Example
Machines in a large open area in an industrial building create a noise hazard .
Control measure
The are containing the machines is surrounded by a brick wall.
99
SOUND REDUCTION IN ENCLOSURE WALLS - TL - H4
Light double walls provide good TL
Two light walls separated by an air gap provide good TL, increasing with the distance between them up to about 15 cm. With sound-absorbing material in between, the TL further increases as the distance between increases. Double walls may provide the same TL as single walls that are five to ten times as heavy.
Principle
100
Example
Extremely noisy machines disturb workers in two work areas separated by a thin wall.
Control measure
The machines are brought together and placed in one end of the factory. This is separated off with a light double wall which provides 60 dB of insulation. A passageway is created with doors to the two quiet areas. The insulation between the areas is at least 35 dB even if one of the doors is open.
101
SOUND REDUCTION IN ENCLOSURE WALLS - TL - H5
Double walls should have few connections
A double wall provides the best TL if each layer is connected to heavy walls or if there are open joints on both ends. If the layers are fastened to shared studs, the TL is greatly reduced if the studs are close together. The thicker the layers, the farther apart the studs must be in order to avoid substantial reduction of TL.
Principle
102
Example
The control room for a machine in a paper factory is noisy, and telephone conversation is practically impossible.
Control measure
A well-insulated room is created with thin panels on common studs. The floor plate of the room is isolated from vibration from the floor of the factory.
103
The following is a survey of noise control methods which have been applied with good results in various types of workplaces. Many noise sources produce airborne sound and sound from vibrating surfaces at the same time, so in many cases several noise control measures must be applied.
Changes in machinery and equipment
The machines or machine pars to be controlled must be identified. Methods of maintenance and servicing must be taken into account in noise control design. Attempts should be made to:
Designers should be encouraged to:
Noise of existing equipment can often be controlled as effectively as new equipment without complicated procedures. Common control measures include:
In a new plant, it is sometimes possible to make more extensive changes such as:
104
Various types of air and solid-borne noise control measures in a tool-making machine
105
Existing workplaces may be changed to prevent impact and collision during manual and mechanical materials handling.
If new transportation equipment is being purchased, consideration should be given to creating a system for quiet materials handling.
The following may be considered:
If it is not possible to prevent noise, it may be necessary to enclose the machines.
Plates dropping from a great height off of a roller belt onto a stacking platform produce loud noise. By using a board whose height can be raised and lowered, the drop can be reduced and the noise decreased.
Enclosure of a hydraulic system requires muffled ventilation openings. Electric motors release both sound and heat, as do the pump and the oil tank.
106
Control of noise from vibrating surfaces
Vibration in machines often results from slippage or loosened bolts. In such cases, the disturbance can be reduced by repair or replacement.
In the case of heavily vibrating machines, a separate machine base may be used as well as a separating joint to prevent the spread of sound. Here, two joints are used for separation.
All joints are equipped with double 10mm layers of cellular plastic projecting shields prior to concrete pouring.
After pouring, clean or burn out the joints, inspect, and reclean if necessary. No pieces of stone or the like should be present in the joints.
Seal the joint with a piece of rubber tubing, etc., which is pressed down. Then close off the surface with elastic sealing compound.
107
In a workplace with hard materials on the ceiling, walls, and floor, almost all of the sound which strikes the surfaces is reflected. The sound level goes down at first as you move away from the machine, but after a certain point it remains practically unchanged. A better sound environment can be obtained by coating the ceilings and walls with effective sound-absorbing material.
How sound levels vary at different distances from a sound source before and after application of absorbent materials to the entire ceiling surface.
108
Sound insulating separate rooms
With automation of machines and processes, remote control from a separate room may become desirable. Some control measures may include:
Sound disturbances in an operating room or shop office may be caused by direct transmission (leakage through the door opening, etc.) from the machine or by radiation from the common floor.
109
In some cases, a noise hazard will be created or made worse by a lack of maintenance. Parts may become loose, creating more noise because of improper operation or scraping against other parts. Grinding noises may also occur as the result of inadequate lubrication.
It is especially important to provide proper maintenance of noise control devices which are added or built into machinery. If a muffler becomes loose or worn out, for example, it should be fixed or replaced as soon as possible.
Noise control should be taken into account from the beginning of the planning process for a new building:
110
Example of noise control measures which can be carried out in an industrial building to avoid the spread of noise.
111
How OSHA can help employers and employees
Legal limits on noise
Under the Occupational Safety and Health Act, every employer is legally responsible for providing a workplace free of such hazards as excessive noise.
OSHA regulations require every employer to limit workers' exposure to 90 "decibels," of dB(A), averaged over an 8-hour period. There are shorter time limits for higher noise levels (see chart). Measurements must be made under normal working conditions.
If noise exposure rises above these levels, the employer must use "engineering controls"-changes in the physical work environment-or "administrative controls"-limits on individual employees' exposure time-in order to comply with the law. While such controls are being implemented, workers must be provided with personal protective equipment, such as earmuffs or plugs, to protect their hearing.
Personal protective devices are generally not a good permanent solution for a number of reasons. They may cause infections or discomfort. They may not work effectively because of the difficulty in getting acceptable fit for each individual. In some cases-particularly when noise is intermittent and below 85 dB(A)- they may make communication more difficult, which can contribute to accidents and make jobs more difficult to perform. If ear protection equipment is not effective or comfortable, the worker should discuss the problem with his or her employer. Other devices may be more satisfactory, and perhaps permanent noise control measures may be installed more quickly.
If sound levels are above the OSHA limits, it is a serious violation of OSHA standards if the employer does not maintain an adequate hearing conservation program. The program must include periodic
| Hours of exposure | Sound level, dB(A) |
| 8 | 90 |
| 6 | 92 |
| 4 | 95 |
| 3 | 97 |
| 2 | 100 |
| 1 ½ | 102 |
| 1 | 105 |
| ½ | 110 |
| ¼ or less | 115
|
OSHA standards establish limits on workplace noise exposure for given time periods. The limit for average exposure during an 8-hour shift is 90 decibels, or dB(a). Exposure to impulse noise should never exceed 140 decibels.
112
hearing tests (audiograms) for each overexposed employee and retesting or referral to a qualified physician if an employee's hearing ability is reduced by 20 decibels at any frequency
When insert ear plugs or custom-molded hearing protection devices other than self-fitted, malleable plugs are being used, OSHA requires that individual employee fitting be conducted by a trained person, and that employees be instructed in the care and use of the devices.
More information about OSHA requirements and procedures for enforcing noise standards is contained in OSHA's Industrial Hygiene Field Operation Manual.
If an employer fails to comply with OSHA standards, and the problem cannot be resolved at the workplace, workers should contact the nearest OSHA are office.
Consultation for employers
In all states, free consultation services are available to help employers identify job safety and health hazards, such as excessive noise exposure, and to recommend solutions. All information gathered by the consultant, including the employer's identity, is completely confidential and is not made available to OSHA enforcement personnel - with one very rare exception. If a consultant observes a serious violation of OSHA standards and the employer fails to correct it within the time period recommended by the consultant, OSHA or the responsible state agency will be notified.
Employers may on an anonymous basis contact the nearest OSHA office to find out how to take advantage of the free consultation services.
Loans for small businesses
The Small Business Administration (SBA), in cooperation with OSHA, provides loans to small businesses which are "likely to suffer substantial economic injury" in meeting OSHA safety and health standards.
Small business employers can obtain more information from the nearest SBA office or may write for a copy of SBA Loans for OSHA Compliance (OSHA 2005) from OSHA Office of Publications, Room S-1212, Department of Labor, Washington, D.C. 20210.
Workers' rights under OSHA
With its small staff of inspectors, OSHA obviously cannot prevent every hazard in every workplace. It is essential that workers and employers cooperate on job safety and health programs. In particular, OSHA encourages the formation of workplace health and safety committees. Health and safety committees can keep on top of job hazards such as noise, day in and day out. And if properly set up, they can make sure both employers and workers are involved in eliminating hazards.
(For more information on health and safety committees and the workers' rights described below, contact the nearest OSHA office.)
Whenever possible, safety and health problems should be resolved at the workplace. If they can't be, here are some ways workers can use the laws:
113
OSHA can seek an order from a federal court.
Workers' right to insist on job safety and health
Section 11(c) of OSHA's law says an employer cannot punish or discriminate against an employee for job safety and health activities, such as:
144
115
U.S. Department of Labor Regional Offices for Occupational Safety and Health Administration
Region I
(CT, ME, MA, NH, RI, VT) 16-18 North Street
1 Dock Square, 4th Floor
Boston, Ma 02109
Telephone: (617) 223-6710
Region II
(NY, NJ, PR, VI, CZ)
Room 3445, 1 Astor Plaza
1515 Broadway
New York, NY 10036
Telephone: (212) 944-3426
Region III
(DE, DC, MD, PA, VA, WV)
Gateway BLDG., Suite 2100
3535 Market Street
Philadelphia, PA 19104
Telephone: (215) 596-1201
Region IV
(AL, FL, GA, KY, MS, NC, SC, TN )
1375 Peachtree Street, N.E.
Suite 587
Atlanta, GA 30309
Telephone: (404) 881-3573
Region V
(IL, IN, MN, MI, OH, WI)
230 South Dearborn Street
32nd Floor, Room 3263
Chicago, IL 60604
Telephone: (312) 353-2220
Region VI
(AR, LA, NM, OK, TX)
555 Griffin Square, Room 602
Dallas, TX 75202
Telephone: (214) 767-4731
Region VII
(IA, KS, MO, NE)
911 Walnut Street, Room 3000
Kansas City, MO 64106
Telephone: (816) 374-5861
Region VIII
(CO, MT, ND, SD, UT, WY)
Federal Bldg., Room 1554
1961 Stout Street
Denver, CO 80294
Telephone: (303) 837-3883
Region IX
(CA, AZ, NV, HI)
Box 36017
450 Golden Gate Avenue
San Francisco, CA 94102
Telephone: (415) 556-0584
Region X
(AK, ID, OR, WA)
Federal Office Bldg., Room 6003
909 First Avenue
Seattle, WA 98174
Telephone: (206) 442-5930
U.S. Department of Labor Area Offices for Occupational Safety and Health Administration
Alabama
Birmingham, AL 35216
2047 Canyon Road - Todd Mall
Telephone: (205) 822-7100
Mobile, AL 36602
Commerce Building - Room 600
118 North Royal Street
Telephone: (205) 690-2131
Alaska
Anchorage, AK 99501
Federal Bldg.-U.S. Courthouse
701 "C" Street
Telephone: (907) 271-5152
Arizona
Phoenix, AZ 85004
Amerco Towers - Suite 300
2721 North Central Avenue
Telephone: (602) 241-2007
Arkansas
Little Rock, AR 72205
West Mark Bldg., - Suite 212
4120 West Markham
Telephone: (501) 378-6291
California
Long Beach, CA 90802
400 Oceangate-Suite 530
Telephone: (213) 432-3434
San Fransisco, CA 94105
211 Main Street
Telephone: (415) 556-7260
Colorado
Lakewood, Co 80204
Tremont Center-1st Floor
333 West Colfax
Telephone: (303) 837-5285
Connecticut
Hartford, CT 06103
555 Main Street
Telephone: (203) 244-2294
District of Columbia
Washington, DC 20215
400 First Street, N.W. - Room 602
Telephone: (202) 523-5224
Florida
Fort Lauderdale, FL 33301
299 East Broward Blvd. - Room 301
Telephone: (305) 527-7292
Jacksonville, FL 32207
2809 Art Museum Drive - Suite 4
Telephone: (904) 791-2895
Tampa, FL 33602
700 Twiggs Street - Room 624
Telephone: (813) 228-2821
Georgia
Macon, GA 31201
152 New Street
Telephone: (912) 746-5143
Savannah, GA 31405
Enterprise Bldg. - Suite 210
6605 Abercorn Street
Telephone: (912) 354-0733
Tucker, GA 30084
Building 10 - Suite 33
La Vista Perimeter Office Park
Telephone: (404) 221-4767
Hawaii
Honolulu, HI 96850
300 Ala Moana Blvd. - Suite 5122
Telephone: (808) 546-3157
Idaho
Boise, ID 83706
1315 West Idaho Street
Telephone: (208) 384-1867
Illinois
Aurora, IL 60542
344 Smoke Tree Business Park
Telephone: (312) 896-8700
Calumet City, IL 60409
1400 Torrence Ave. - 2nd Floor
Telephone: (312) 891-3800
Niles, IL 60648
6000 W. Touhy Avenue
Telephone: (312) 631-8200
Indiana
Indianapolis, IN 46204
U.S. Post Office and Courthouse
46 East Ohio Street - Room 423
Telephone: (317) 269-7290
Iowa
Des Moines, IA 50309
210 Walnut Street - Room 815
Telephone: (515) 284-4794
Kansas
Wichita, KS 67202
216 N. Waco - Suite B
Telephone: (316) 267-6311, Ext. 644
Kentucky
Louisville, KY 40202
600 Federal Place - Suite 554-E
Telephone: (502) 582-6111
Louisiana
Baton Rouge, LA 70806
2156 Wooddale Blvd.
Hoover Annex, Suite 200
Telephone: (504) 923-0718, Ext. 474
New Orleans, LA 70130
600 South Street - Room 337
Telephone: (504) 589-2451
Maine
Augusta, ME 04330
U.S. Federal Bldg. - Room 1110
40 Western Avenue
Telephone: (207) 662-6171
Maryland
Baltimore, MD 21201
Charles Center, 31 Hopkins Plaza
Telephone: (301) 962-2840
Massachusetts
Springfield, MA 01103
1200 Main Street - Suite 513
Telephone: (413) 781-2420, Ext. 522
Waltham, MA 02154
400-2 Totten Pond Road
Telephone: (617) 890-1239
Michigan
Detroit, MI 48226
231 West Lafeyette-Room 628
Telephone: (313) 226-6720
Minnesota
Minneapolis, MN 55403
100 North 6th Street-Room 801
Telephone: (612) 725-2571
Mississippi
Jackson, MS 39201
Federal Bldg. - Suite 1445
100 West Capitol Street
Telephone: (601) 969-4606
Missouri
Kansas City, MO 64106
1150 Grand Avenue - 6th Floor
12 Grand Bldg.
Telephone: (816) 374-2756
St. Louis, MO 63101
210 North 12th Blvd. - Room 520
Telephone: (314) 425-5461
Montana
Billings, MT 59101
Petroleum Bldg. - Suite 525
2812 1st Avenue North
Telephone: (406) 657-6649
Nebraska
Omaha, NE 68106
Overland-Wolf Bldg. - Room 100
6910 Pacific Street
Telephone: (402) 221-9341
Nevada
Carson City, NV 89701
1100 East William Street - Suite 222
Telephone: (702) 883-1226
New Hampshire
Concord, NH 03301
Federal Bldg. - Room 334
55 Pleasant Street
Telephone: (603) 224-1995
New Jersey
Belle Mead, NJ 08502
Belle Mead GSA Depot - Bldg. T3
Telephone: (201) 359-2777
Camden, NJ 08104
2101 Ferry Ave. - Room 403
Telephone: (609) 757-5181
Dover, NJ 07801
2 E Blackwell Street
Telephone: (201) 361-4050
Hasbrouck Heights, NJ 07604
Teterboro Airport Professional Bldg.
377 Route 17 - Room 206
Telephone: (201) 288-1700
Newark, NJ 07102
970 Broad Street - Room 1435C
Telephone: (201) 645-5930
New Mexico
Albuquerque, NM 87102
Western Bank Bldg. - Room 1125
505 Marquette Avenue NW
Telephone: (505) 766-3411
New York
Albany, NY 12207
Leo W. O'Brien Federal Building
Clinton Ave. & N. Pearl St. - Room 132
Telephone: (518) 472-6085
Brooklyn, NY 11201
185 Montague Street
Telephone: (212) 330-7667
Buffalo, NY 14202
220 Delaware Ave. - Suite 509
Telephone: (716) 846-4881
Flushing, NY 11354
136-21 Roosevelt Avenue
Telephone: (212) 445-5005
New York, NY 10007
90 Church Street - Room 1405
Telephone: (212) 264-9840
Rochester, NY 14614
Federal Office Bldg. - Room 608
100 State Street
Telephone: (716) 263-6755
Syracuse, NY 13260
100 South Clinton Street - Room 1267
Telephone: (315) 423-4188
Westbury, NY 11590
990 Westbury Road
Telephone: (516) 334-3344
White Plains, NY 10601
200 Mamaroneck Avenue - Room 403
Telephone: (914) 946-2510
North Carolina
Raleigh, NC 27601
Federal Bldg. - Room 406
310 New Bern Avenue
Telephone: (919) 755-4770
North Dakota
Bismarck, ND 58501
Federal Bldg. - Room 348
P.O. Box 2439
Telephone: (701) 255-4011, Ext. 521
Ohio
Cincinnati, OH 45202
Federal Office Bldg. - Room 4028
550 Main Street
Telephone: (523) 684-2354
Cleveland, OH 44199
Federal Office Bldg. - Room 847
1240 East Ninth Street
Telephone: (216) 522-3818
Columbus, OH 43215
Federal Office Bldg. - Room 634
200 North High Street
Telephone: (614) 469-5582
Toledo, OH 43604
Federal Office Bldg. - Room 734
234 North Summit Street
Telephone: (419) 259-7542
Oklahoma
Oklahoma City, OK 73118
50 Penn Place - Suite 408
Telephone: (405) 231-5351
Tulsa, OK 74127
717- South Houston - Suite 304
Telephone: (918) 581-7676
Oregon
Portland, OR 97204
1220 S.W. Third Street - Room 640
Telephone: (503) 221-2251
Pennsylvania
Erie, PA 16501
147 West 18th Street
Telephone: (814) 453-4351
Harrisburg, PA 17109
Progress Plaza
49 North Progress Avenue
Telephone: (717) 782-3902
Philadelphia, PA 19106
Wm. J. Green, Jr. Federal Bldg.
600 Arch Street - Room 4256
Telephone: (215) 597-4955
Pittsburgh, PA 15235
400 Penn Center Blvd. - Suite 600
Telephone: (412) 644-2905
Wilkes-Barre, PA 18701
Penn Place - Room 2005
20 North Pennsylvania Avenue
Telephone: (809) 753-4457
Puerto Rico
Hato Rey, PR 00918
U.S. Courthouse & FOB
Carlos Chardon - Room 555
Telephone: (809) 753-4457
Rhode Island
Providence, RI 02903
Federal Bldg. & U.S. Post Office -
Room 204
Telephone: (401) 528-4466
South Carolina
Columbia, SC 29204
Kittrell Center - Suite 102
2711 Middleburg Drive
Telephone: (803) 765-5904
South Dakota
Sioux Falls, SD 57102
Court House Plaza Bldg. - Room 408
300 North Dakota Avenue
Telephone: (605) 336-2980, Ext. 425
Tennessee
Nashville, TN 37203
1600 Hayes Street - Suite 302
Telephone: (615) 251-5313
Texas
Austin, TX 78701
American Bank Tower - Suite 310
221 West 6th Street
Telephone: (512) 397-5783
Fort Worth, TX 76115
Fort Worth Federal Center
4900 Hemphill Bldg. 24 - Room 145
Telephone: (817) 334-5274
Harlingen, TX 78550
Riverview Professional Bldg.
1325 South 77 Sunshine Strip - Suite 9
Telephone: (512) 425-6811
Houston, TX 77004
2320 La Branch Street - Room 2118
Telephone: (713) 226-4357
Irving, TX 75061
1425 West Pioneer Drive
Telephone: (214) 767-5347
Lubbock, TX 79401
Federal Bldg. - Room 421
1205 Texas Avenue
Telephone: (806) 762-7681
Tyler, TX 75701
FOB - USPO & Courthouse - Room 208
211 West Ferguson Street
Telephone: (214) 595-1404
Utah
Salt Lake City, UT 84101
U.S. Post Office Bldg. - Room 451
350 South Main Street
Telephone: (801) 524-5080
Virginia
Richmond, VA 23240
Federal Bldg. - Room 6226
400 North 8th Street
Telephone: (804) 782-2864
Washington
Bellevue, WA 98004
121 107th Street, N.E.
Telephone: (206) 442-7520
West Virginia
Charleston, WV 25301
Charleston National Plaza - Room 1726
700 Virgina Street
Telephone: (304) 343-6181, Ext. 420
Wisconsin
Appleton, WI 54911
2618 North Ballard Road
Telephone: (414) 734-4521
Milwaukee, WI 53203
Clark Building - Room 400
633 West Wisconsin Avenue
Telephone: (414) 291-3315
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