When noises occur, sound waves are produced and travel through the air. After these waves enter the outer ear, they travel through the ear canal and make their way toward the middle ear. When sound waves travel into the ear and reach the eardrum, they cause the eardrum to vibrate. These sound vibrations are carried to the three tiny bones of the middle ear - hammer to anvil to stirrup - as they travel through the middle ear. After sound waves get changed into vibrations in the middle ear, they enter the inner ear . The vibrations go into a small, curled tube in the inner ear called the cochlea. The cochlea is filled with liquid and lined with cells that have thousands of tiny hairs on their surface . The vibrations then cause the tiny hairs in the cells to move. The more vibrations, the more the hairs in will move. As these sensory hairs move, sound vibrations are transformed into nerve signals, the language of the brain. Once sound becomes nerve signals, only then can the brain understand what the ears are hearing
Because loud noise doesn't cause pain until the sound reaches high decibels, people generally don't recognize noise as damaging until after the fact. If the ears hurt or bled when noise rose above a safe level, everyone would be more aware of the threat. But it doesn't take much to start a gradual damaging effect that can lead to partial or total hearing loss Most people lose their hearing slowly -- over a 15- to 20-year period -- because regular and repeated noise exposure damages the hair cells of the inner ear that interpret sound vibrations as words, music or other sounds. Men are more likely to start being hearing impaired about a decade before women, since they have commonly held more industrial and transportation jobs, which produce consistently high noise levels
Almost everyone has experienced being temporarily “deafened” by a loud noise, such as concert music or driving long distance with the window open. This condition is usually accompanied by ringing in the ears and sounds become “muffled” for the duration of this deafness. Most people consider this condition to be a minor inconvenience as they know their hearing will return eventually. BUT exposure to this type of noise at a rate of eight hours a day five days a week could result in permanent hearing loss. And the noise level does not even have to be that loud. A person simply yelling in close proximity to a person’s ear threatens that individuals ability to hear properly.
According to a report by the Board of Health in the city of Toronto, March 2000, noise affects millions of people worldwide on a daily basis. &quot;Evidence indicates indirect health effects including an increased risk for cardiovascular disease, negative effects on mood, sleep, performance, reading and memory acquisition.&quot; The report also states,&quot; More people are affected by noise exposure than any other environmental stressor. However, because its associated health effects are not as life-threatening as those for air, water and hazardous waste, noise has been on the bottom of most environmental priority lists.&quot; Last year alone, WSIB paid out more than $20 million in hearing-loss benefits to some 2,500 claimants. Noise claims are on the increase mainly because they’re being identified more, and also because there’s such a backlog of individuals who have been working in noise for 30 or 40 years.”
This has increased the need for strict policies on allowable noise levels in the workplace. Although these regulations are specifically for Ontario Other provinces have legislation for maximum sound levels for an eight-hour period. For instance, British Columbia, Alberta, Saskatchewan, New Brunswick, Nova Scotia, Prince Edward Island, Newfoundland, Northwest Territories and Yukon all permit a maximum exposure level of 85 decibels per eight-hour shift. Federally, the maximum sound level a worker can be exposed to is 87 decibels. You will note Ontario has the highest level allowable for an eight hour period of 90.
But even with these regulations, sometimes that is not enough. Solutions for hearing loss must be found through other methods such as. Eliminate the noise hazards at the source Design Quieter Equipment Modify Existing Equipment Isolate Vibrating or noisy parts in a machine Substitute noise devices with quieter solutions.
The basic instrument for objectively measuring sound is the sound level meter. In its simplest form it is calibrated to read sound level over a short period of time with a similar response to all frequencies, that is a 'linear' weighting. Since the human ear is not uniformly sensitive to all frequencies, several weighting scales have been developed to simulate the various sensitivities. These weightings are known as A, B, C or D weightings The A, B and C weightings mainly differ in the degree of sensitivity at lower frequencies, relative to 1000Hz. The least sensitivity to lower frequencies is provided by the A-scale, the most by the C-scale. The D-scale gives an indication of perceived noisiness and is used in aircraft noise measurements Measurements of sound pressure levels with a weighted response are usually referred to as 'sound levels with the appropriate suffix' (i.e. dB(A), dB(B), dB(C) or dB(D))
Sound is considerably more difficult to measure than temperature or pressure. Since it occurs over a range of distinct frequencies, or ƒ, its level must be measured (or predicted in the case of an analysis) at each frequency to understand how it will be perceived in a particular environment. Our ears can sense sounds at frequencies ranging from 20 to 16,000 Hertz (Hz), To make the amount of data more manageable, this spectrum is divided into octave bands. Each octave band is identified by its center frequency and is delimited such that the band's highest frequency is twice its lowest frequency. This weighting system assigns a weight that is related to how sensitive the human ear is to each sound frequency. Frequencies that are less sensitive to the human ear are weighted less than those for which the ear is more sensitive. The adjusted sounds are called A-weighted levels (dBA.) It has been found that the A-scale on a sound level measurement best approximates the frequency response of the human ear. C weighting provides a fairly flat frequency response with only slight attenuation of the very high and low frequencies. C weighting is intended to represent how the ear perceives sound at high decibel levels and is often used as a flat response when LINEAR is not available. C weighted measurements are often reported as dBC. In plain English, the dBC scale is what the approximated sound level is really at while the dBA scale is the sound level at which the human ear picks it up.
As you can imagine as our cities continue to grow and develop in rural areas, neighborhoods that were once quiet will soon be surrounded by the loud noises of industry. These high noise levels will begin to effect more than just an individual’s hearing and health. The ecology of mother nature is already being effected. Farmers are finding that their animals are producing fewer offspring and those that are produced are underweight and unhealthy. Cows are not producing enough milk to nourish their young and chickens are laying fewer eggs due to stress caused by high noise levels in the areas. Scientists believe high noise levels cause increased heart rates, and hormone fluctuation due stress caused by proximity to excessive noise. Research has also shown that animals which rely on their hearing for survival are at risk of becoming extinct because they are suffering hearing loss due to traffic and industry situated close to their habitat. And this ecological upset is not just occurring on land but also our oceans and lakes. Fish are producing fewer offspring and are susceptible to predators due to hearing loss caused by our boats and submarines in their habitat. So the question becomes what can be done about this?
The job of a silencer is to treat the noise at its source. .
Silencers may be placed either at the discharge of pipes for vent application, or placed in the path of a duct for heating and ventilation, or process applications. Silencers are also used at the air intake of engines, gas turbines, rotary blowers, compressors, and reciprocating engines. They are also used at the exhaust of reciprocating engines and vacuum pump discharges
In order to size a silencer for a piece of equipment or a specific application certain information is required. This information can differ depending on the type of silencer required or the silencer’s application but there are 6 main things required to size any silencer. Noise in a system is generally caused by a combination of flow and speed. Therefore a silencer must be designed to specifically contain that systems flow and speed capacities in order to get optimum noise reduction. Pressure Requirements are necessary so the silencer can be designed to withstand the pressure of the system. Temperature is required to aid in the designing of the silencers as well as to aid in determining what materials would be used in its construction. Connection size is necessary so the silencer can be fit into the system Required dBA enables the engineers to design a silencer to meet the customer’s noise requirements.
. Today, industrial blowers are the workhorses of the process industry. These high volume, low pressure air producers are found in many environments. Unfortunately the downside of this equipment is they produce a significant amount of noise, sometimes rivalling that of a jet engine. Despite the concern regarding noise output, most blower systems are often sold without any type of sound-absorbing device. There is little question that silencers are necessary on any blower installation. Regardless of the size or speed of the blower, there is a need for both inlet and discharge silencers.
A need for blower silencers can be found in any industry that uses pneumatic conveying. Pneumatic conveying is popular because it is energy efficient and requires little maintenance. But as discussed the blowers required to run the system tend to be very loud. Industries that rely on pneumatic conveying are the plastics industry, the printing industry,carpet cleaning, pulp and paper, and waste water treatment to name a few.
In terms of blower silencers there are basically three types. Chamber, Absorption and Chamber-Absorption Blower speed plays an important part in the selection of a silencer. For slow speed blowers chamber type silencers perform best for all sizes. For applications not requiring this degree of silencing on all small size blowers, the absorption type of silencer has been used successfully for many years. For high speed blowers a chamber absorption type is required. This combination design is necessary to reduce the increased high frequency noise energy that is developed above the transition speed and also treats the energy contained in the low frequency
Stoddard produces a number of blower silencers to accommodate different applications. Our D13’s and D33’s are usually purchased by the blower packaging distributors. More information regarding our “D” models can be found in our catalogue under bulleting D. The L21, C23, & C26 models can be found in the centrifugal blower industry which is a different kind of blower used for pneumatic conveying. A centrifugal blower is multi-staged and requires a different silencer application. These blowers are commonly found in the wastewater treatment industry. Some customers use the L21 models specifically for truck mounted pneumatic conveying blowers. These
Another silencer commonly used in the blower industry is the vacuum type silencer. These models are obviously used on vacuum blowers and can be found in such industries as the printing industry, carpet cleaning, vacuum trucks, pulp and paper, and the plastics industry. Dry vacuum silencers are designed to primarily handle a gas such as air. They normally operate with an open discharge to atmosphere. Wet Vacuum Silencers are used with vacuum pumps. Since the vacuum pump discharges both air and water to the atmosphere there are two problems involved. Discarding the water and silencing the air noise flowing from the discharge. Intake silencers are seldom required in vacuum pump operations unless removal of process liquid is required prior to entry into the pump. A pump or biometric leg is required to remove the liquid from the intake separator because of vacuum conditions. All intake silencers are designed for full vacuum service. Discharge separator silencers are normally used on wet vacuum systems to reduce the discharge noise and simultaneously separate the liquid which can be recovered or piped to a drain. Information on our Vacuum blower silencers can be found in our bulletins D and V.
The fan silencer industry is wide reaching. Any industry that uses fans for exhausting fumes require a fan silencer. Such industries as steel manufacturers, casting plants and the pulp and paper companies use fans. They are also required in places where large volumes of air are required. For example for ventilation in mines for the miners. Large centrifugal fans produce highlevels of noise and require inlet and outlet silencers or some acoustical equipment. Fan noise varies with static pressure, equipment efficiency, air flow and speed. Major sources of fan noise are air inlet and outlet of a primary air fan, inlet of forced draft fan, and outlet of an induced fan, fan casing and drive motor.
Stoddard offers two types of fan silencers, the C24 model and the C26 model. As you can see the only difference visually is the flat head vs the dished head. The reason for the two different models is quite simple. The flat head model is usually used in doors while the dished model is used outdoors. The reason for this is the flat head in an outdoor environment would tend to corrode very quickly due to the fact the rain would gather in the flat head surface and rust the unit out. The dished head does not present that problem.
Electric Motors can be found in almost every industry. The motors are predominantly noisy due to the rotation of the cooling fan which contributes to the overall noise in our industrial plants. A silencer can be added to the motor cowling to reduce noise levels by as much as 10dBA. They are easily mounted to the cowling with an adaptor provided with the silencer for installation.
Exhaust silencers are necessary in a variety of industries such as Natural Gas, Genset, marine and construction. This is due to the fact that the engines used to tend to operate at very loud levels.
In the engine silencer business the different models are broken down into a number of grades depending on the application and required noise attenuation. Industrial and semi-residential grade units are usually recommended for use on intake or exhaust of internal combustion engines in industrial areas where the surrounding noise levels are comparatively high and exhaust silencing is not critical. Residential grade silencers are used on intake or exhaust of internal combustion engines in residential areas which surround light industry. Critical Grade silencers are used on engines situated in residential and school areas. Hospital Grade silencers in highly critical areas where the surrounding noise levels are extremely low and maximum silencing is required. For example in a hospital. Hospital plus units are used in intensely critical areas where noise levels are extremely low and superior silencing is required. For example in a convalescence homes. Depending on the required noise attenuation these units can be interchangeable. More detailed information on each unit can be found in our E Bulletins.
The chamber resonator silencer are designed for two cycle turbocharged engines and recommended for applications that have low pressure drop requirements where background noise levels are fairly high. The spark arrestor silencer are recommended for use on exhaust of engines used in marine applications or areas where fire hazards may exist. The spark arrestor silencer removes burning carbon particles from the exhaust gas going to atmosphere. Information regarding these models can also be found in our E Bulletins.
These systems are ideal for environments with simple cycle turbines where the need to control emissions below turbine exhaust levels are critical and noise control is top priority. These catalytic silencer combinations offer the benefit of noise and emissions reductions all in one unit for both diesel and natural gas engines
Gas turbines require silencers for all simple cycle and bypass operations where the turbine exhausts directly to atmosphere. Silencers are also needed when there are strict noise requirements on combined cycle or heat recovery applications. Generally inlet silencers are required on all turbine systems. Turbine inlet noise is predominantly a high frequency whine corresponding to the blade passing frequency of the turbine’s air inlet. The turbine exhaust noise is predominantly low frequency resulting from mass flow and high temperature and combustion process. The normal operating life of an inlet and exhaust silencer on gas turbines is between 24000 and 160,000 hours depending on design, installation and material of construction.
Vent Silencers are found in a number of industries such as petrochemical, mining, pulp and paper, refineries and Power generation. This is because due to the processes used in these industries, they release high pressure gases to the atmosphere which generates noise due to the high velocity flow through the valve and turbulence created when the vented steam mixes with the atmosphere. The process is a very very loud one which needs to be silenced to protect workers safety and prevent complaints from neighbouring communities.
Most pressure regulators applications are for regulation of natural gas at city gates and steam used for heating or other processes. Regulator noise is caused by the rapid expansion of gas or steam as in high pressure vents and blowdowns to atmosphere. In critical flow applications both the gas flow and the noise increases until the critical pressure ratio is reached. The critical pressure ratio occurs when the flow through the opening is at sonic velocity. Once critical pressure is reached the noise increases only with an increase in flow. All vent silencers are custom designed and constructed for the pressure service requirements.
Stoddard manufactures a number of different vent silencer models depending on required application. Our B13, B14 & B15 model silencers employ a single or multi stage diffuser and contain an acoustic core to decrease high frequency noise levels. The difference between the three models is levels of attenuation. The B34 model is a multi chamber silencer employing a single stage diffuser and absorption section to effectively treat both high and low frequency. Models are determined by parameters as well as attenuation requirements.
Stoddard acoustic enclosures can be made to reduce more than just noise. They can aid in the controlling of fumes, dust and excessive moisture or temperature in a plant. Acoustic enclosures thus compliment the airborne noise control measures provided by Stoddard’s silencers to form a comprehensive noise control package. They can be equipped with access doors and windows for easy cleaning or access to equipment inside and when necessary fans and filters can be added to the enclosure to solve additional heat and noise problems.
Detailed information on our acoustic enclosures can be found in our bulletin NE
Stoddard offers a number of accessories to accompany our engine silencers. We can provide flexible connectors in whatever size is required as well as mounting brackets when necessary with connections to meet the specifications of the various engine manufacturers.
Stoddard also offers a range of accessories for our other silencers such as Rain caps, mounting brackets for both horizontal and vertical mounting, legs for a “standing” application. Lifting lugs for easy transportation as well as manways if necessary for maintenance.
Stoddard Presentation English (Miguel) 2009
STODDARD SILENCERS OF CANADA INC. Enjoy the Silence…
Who We Are We at Stoddard Silencers are dedicated to the manufacturing and supplying of products that combat noise pollution as well as vibration and aid in the creation of a safe environment for people in the workplace.
What We Do <ul><li>We combat Noise Pollution and for that we design & manufacture Industrial Silencers </li></ul><ul><li>All our products are custom-made to meet the criteria specified by the customer, no silencer can be too small or not big enough. </li></ul><ul><li>To Us, every project is unique and we take pride in our work from the beginning to the end. </li></ul>
What We Don’t Make!!! Gun Silencers Automotive Silencers
What Causes Hearing Loss Healthy cochlea. This person would have normal hearing Damaged cochlea. This person would be suffering severe hearing loss
How Loud is Loud EFFECT ON PEOPLE SOUND LEVEL (in dbA) SOUND SOURCE High Injurious ------------------------- Injurious Irritating ------------------------- ------------------------- 140 130 120 110 100 85 80 70 60 50 40 30 20 10 0 Jet engine Jack hammer PAIN THRESHOLD Chain Saw Sheet-metal workshop GENERAL STANDARD FOR 8 HRS Heavy traffic Normal conversation Low conversation Quiet radio music Whispering Quiet urban room Rustling leaves HEARING THRESHOLD
Effects <ul><li>Hearing loss </li></ul><ul><li>Increased risk of cardiovascular disease </li></ul><ul><li>Mood swings </li></ul><ul><li>Irritability </li></ul><ul><li>Insomnia </li></ul><ul><li>Performance </li></ul><ul><li>Reading & memory </li></ul>
How To Control Noise Induced Hearing Loss <ul><li>Eliminate noise hazards at the source. </li></ul><ul><li>Design quieter equipment. </li></ul><ul><li>Modify existing equipment. </li></ul><ul><li>Isolate vibrating or noisy parts in a machine. </li></ul><ul><li>Substitute noisy device with a quieter solution. </li></ul>
The Science of Noise <ul><li>Noise unit of measurement is a decibel. </li></ul><ul><li>Three scales of measurement (A,B,C and D) most commonly used is dbA. </li></ul><ul><li>Noise measurements usually taken with a sound meter. </li></ul>
Silencer Applications <ul><li>Discharge of pipes for vents </li></ul><ul><li>Path of a duct for heating and ventilation </li></ul><ul><li>On air intake of engines, gas turbines, rotary blowers and compressors </li></ul><ul><li>On exhaust of reciprocating engines and vacuum pump discharges </li></ul>
How a Silencer is Sized <ul><li>Flow </li></ul><ul><li>Speed </li></ul><ul><li>Pressure requirements </li></ul><ul><li>Temperature </li></ul><ul><li>Connection size </li></ul><ul><li>Required dbA level </li></ul>
Required Sizing Information <ul><li>Type of Gas </li></ul><ul><li>Weight or gravity of gas </li></ul><ul><li>Mass flow </li></ul><ul><li>Upstream pressure and temperature </li></ul><ul><li>Valve type and size </li></ul><ul><li>Allowable pressure drop </li></ul><ul><li>Installation (Vertical or Horizontal) </li></ul><ul><li>Piping Size and Arrangement </li></ul>
Types of Vent Silencers <ul><li>B13 </li></ul><ul><li>B14 </li></ul><ul><li>B15 </li></ul><ul><li>B34 </li></ul>
Enclosure Applications <ul><li>Control noise </li></ul><ul><li>Control contaminants such as fumes </li></ul><ul><li>Contain excessive moisture or temperature </li></ul>
Sizing an Enclosure <ul><li>Height, Length and Width of the equipment to be enclosed. </li></ul><ul><li>Noise level requirements </li></ul><ul><li>Whether the installation is inside or outside. </li></ul><ul><li>Operating conditions of equipment to be enclosed </li></ul><ul><li>Inlet and Outlet piping size </li></ul>
Warranty & Disclaimer WARRANTY: Material and workmanship are guaranteed for one year from date of invoice. We will repair or replace any article proving defective when used for the purpose intended, but no claims for loss, damage or labour will be allowed. Disclaimer: The warranty stated above is expressly in lieu of all other warranties ,expressed or implied, and in lieu of all other obligations and liabilities on the part of Stoddard Silencers of Canada Inc. that has been altered or repaired by others without its written authorization, nor to any product that has been subject to misuse, negligence or accident.
Contact Information Contact information <ul><li>Miguel Castro </li></ul><ul><li>Regional Sales Manager </li></ul><ul><li>Canada & Latin America </li></ul><ul><li>(416) 291-4390 </li></ul><ul><li>Toll Free 1-888-291-4390 </li></ul><ul><li>[email_address] </li></ul>