Acquisition Safety - Noise Control Aboard Navy Ships
For the more than 107,000 Sailors living and working aboard U.S. Navy ships, noise is a fact of everyday life. In addition to flight operation noise, there are numerous noise sources on deck and throughout Navy ships that exceed safe limits for all but the shortest exposures. Long-term exposure to high levels of noise is a source of permanent hearing loss. Shipboard noise control is critical to the preservation of crew health, mission success, and personnel retention.
Noise-induced hearing loss is the Fleet's number one occupational health expense. The economic consequences to the Navy of hearing impairment include lost time and decreased productivity, loss of qualified workers through medical disqualification, military disability settlements, retraining, and expenses related to medical treatment, such as for hearing aids.
Disability payments to veterans for hearing loss show a continuing upward trend, as demonstrated in the graph below. In 2004, the Veterans Administration (VA) spent $108 million dollars in disability payments to 15,800 former Navy personnel for hearing loss - an increase of $65 million in VA spending on Navy hearing disability payments since 1999.
Given the enormity of the increase in spending by the VA on hearing loss disability payments to former Navy personnel, it is important to find the sources of hearing loss in the Navy and then investigate ways to reverse this trend. For example, a recent study by the Centers for Naval Analyses (CNA) - Statistical Analysis of Hearing Loss Among Navy Personnel, CRM D0011228.A2/Final February 2005, Geoffrey B. Shaw and Robert P. Trost - demonstrated a clear correlation between long term assignment aboard surface warships (e.g., carriers, surface combatants, and amphibious ships) and an increased rate of hearing loss.
Figure 1. VA Disability Payments Chart
This section of the Acquisition Safety website concentrates on the occupational safety and health challenges encountered while working in high noise level environments onboard Naval surface warships. Specifications and guidelines for permissible noise levels and noise control measures can be found in the Resources Section.
Background & Discussion
Noise exposure can be described by the intensity of the noise, its frequency, and its duration. Intensity of noise reflects the loudness of the sound while the frequency of the noise is reflected in how high or low pitched the noise is. The duration or length of time an individual is exposed to noise may have a significant detrimental impact on that person's hearing. Exposure to loud noise levels for short periods of time may cause temporary hearing loss (hearing is usually restored within 24 hours). Long-term exposure to hazardous noise levels, however, can cause permanent hearing damage.
Noise may be described as continuous or impulse (impact).
Because the range of sound intensity is so great, noise is usually measured in units called decibels, or dB using the "A" weighting scale. Measurements obtained using the A-weighting scale provides a better estimation of the threat to human hearing than do other weighting scales.
The decibel scale uses powers of ten; an increase of ten decibels represents a ten fold increase in sound power. The faintest sound humans with normal hearing can detect has a value between 0 and 10 decibels, and the loudest sound the human ear can tolerate without pain is about 120 decibels. Examples of decibel levels produced during a typical workday aboard a Navy ship include: normal conversation (60dB), an operating forklift (85dB), a paint chipper (100dB), and carrier deck operations (greater than 145dB). [For more information explaining acoustics, click here http://www.answers.com/topic/acoustics?cat=health]
The Navy considers any sound above 84dB as noise hazardous, or having the potential to cause hearing loss. Prolonged noise at levels greater than 84dB over an eight-hour period may result in temporary, and gradually permanent, hearing loss. The louder the sound and more prolonged the exposure, the shorter amount of time it takes to cause permanent hearing loss. Temporary (short-term) hearing loss is often considered an indicator of the risk of permanent hearing loss with continued exposure. This temporary threshold shift is often captured on periodic audiograms (hearing tests) and used to provide workers and medical staff with an early warning of potential permanent hearing loss.
Occupational hearing loss has human, economic, and readiness impacts. Hearing loss may result in diminished quality of life because of loss of ability to communicate and social isolation, as well as impaired and misinterpreted communication with family members, the public, and coworkers. On-the-job hearing loss can result in diminished ability to respond to warning signals in the work environment, which could lead to increased injuries resulting from impaired communication. Noisy work environments can also result in missed commands with dire consequences to personnel and equipment, such as running aground or firing a missile at the wrong time. Army studies show that noise-impaired communications affect combat performance (the likelihood of hitting the target and returning safely from a combat mission). The economic effects of hearing loss to the Navy include lost time and decreased productivity, loss of qualified workers through medical disqualification, civilian workers' compensation costs, and military disability settlements, retraining, and expenses related to medical intervention such as hearing aids and audiometric testing.
Noise induced hearing loss is an almost entirely preventable disability. Identification of hazardous noise areas; monitoring of workers' hearing acuity using regular audiometric testing; providing training to workers on the benefits of hearing protection; enforcing the use of personal protective equipment; administrative measures such as shorter work shifts in noise hazardous environments; and engineering controls are all measures used by the Navy to protect military and civilian employees from hearing loss.
Common High Noise Problems/Areas Onboard Navy Ships
• Older ships were not designed or constructed with any modern noise reduction requirements.
• On aircraft carrier flight decks, flight operations are confined to a 4.5-acre area as compared to land-based flight operations that are normally conducted on 10,000 acres. Noise levels on the flight deck can exceed 145dBA. Below the flight deck is the gallery deck in which approximately 1400 sailors live and work. The high noise levels directly above adversely impact most of the gallery deck. Gallery deck noise levels, often in excess of 100dBA, can have the effect of reducing cognitive skill levels and cause miscommunication problems, both causes of fatal accidents.
• Besides the high noise levels on the flight deck and in other workspaces, such as machinery spaces and laundries, the crew of aircraft carrier and other Navy vessels can also be exposed to noise during off duty hours. It is commonly recognized that a quiet recovery time is essential to provide the "rest" needed by the ears to "recuperate" from noise exposures. However, under conditions of hazardous noise levels in both occupational and recreational activities, there is limited or no audiological recovery time.
• Poor ship design provides transmission paths (e.g., through ventilation ducts) for noise to travel from the noisy machinery spaces to berthing accommodations and workspaces.
• Improper ventilation system design and modifications often create noise sources.
Common Noise Sources
• On aircraft carriers, jet noise is transmitted to the gallery deck through several paths. Acoustic energy can be transmitted directly through the flight deck and immediately re-radiated. Jet noise also excites (forces vibration on a system by its surroundings) ship structure (overheads, bulkheads, catapult trough, and deck), which then radiate acoustically into the gallery spaces (see Figure 3). Other paths for structural excitation are jet exhaust impingement on the Jet Blast Deflector (JBD) and vibration transmission through the airplane tires, the catapult tow bar, and the catapult restraint bar.
• Other significant sources of airborne noise on the gallery deck are the catapult, JBD, and arresting gear equipment. This machinery produces high airborne noise levels and also excites ship structure. Typical airborne noise levels from various locations on the gallery deck are shown in Figure 4 above.
Figure 4: Aircraft Carrier Airborne Noise.
Notes: Single = Single Hearing Protection. Double = Double Hearing Protection.
• A major shipboard noise source comes from the ship's propeller excitation of the ship structure. The excited structure then re-radiates as airborne noise.
• Structure-borne noise associated with operation of auxiliary equipment (e.g., hydraulic pumps, fans, motors, transformers, generators, compressors) can also excite ship's structure, and re-radiate as airborne energy.
• Ventilation systems are often a significant source of shipboard noise. Because of space constraints, air ducts used aboard ships are often very small and have sharp curves and bends. This results in air moving through the ducts at very high velocities, causing noise and vibration in the ventilation system. Fans can also project noise throughout the ventilation system if they are poorly mounted, not properly isolated from air ducts, and/or are the wrong size. Finally, noise may be generated at the air duct outlets that distribute air in the work environment if proper design parameters are not followed.
Environmental Noise Projection
Environmental noise is a concern with regard to environmental compliance and encroachment of military operations on adjacent civilian activities.
Adopt Total Systems Engineering Approach
A total systems engineering approach should be conducted in order to have effective acoustic solutions. Total ship systems engineering evaluates what is appropriate to integrate, as a function of location, into the acoustic design of a ship.
Develop Effective Design Guidance
By teaming decades of Navy quiet ship design experience with ship builders' construction experience, a more effective noise proof ship design can be executed. This approach entails developing effective design guidance to evaluate and recommend the appropriate amount of acoustic treatment for specific areas of the ship. The ideal way to develop this design guidance is to perform shipboard testing of various acoustic solutions. Shipboard testing will evaluate the effectiveness of the various acoustic treatment options and will assist in determining which areas require treatment. The data generated by this effort will help control the business risk that shipbuilders will assume to meet the new design criteria.
Identify and Consider All Noise Sources
All sources of shipboard noise will potentially contribute to the overall shipboard noise level. Therefore, the entire ship should be measured and mapped for noise levels and their sources. Before any course of action is adopted to maximize noise reduction, the vessel must be analyzed completely and a Computer Aided Design-based model should be constructed to depict structure, vibrational, and acoustical pathways.
Evaluate Appropriate Noise Technologies
There are a variety of methods to reduce airborne noise levels. Many such methods can be leveraged from existing surface ship and submarine acoustic programs. A total ship engineering approach will include evaluation of the appropriate noise technologies and their integration into the ship design.
Determine Most Effective Noise Control MethodsThere are four basic methods to deal with noise aboard ship:
• Reduce noise at the source.
• Isolate and insulate the noise source from the structure and/or living/workspaces from the noise source or structure.
• Improve personal hearing protection when the crew must be exposed to a high noise environment such as the flight deck.
• Limit crew exposure to high noise levels (change current mode of operation or provide for remote sensing devices and acoustical enclosures to limit crew exposures).
Noise control techniques can be classified into two categories:
• Active Noise Control
• Passive Noise Control
Reduce Noise at the Source
Once vibrational energy disseminates into the surrounding environment (i.e., structure-borne vibration or airborne noise), more resources will be required to control it - this usually means the penalty of added weight in the form of insulation. The most effective and efficient noise control method is the prevention or reduction of noise generation at the source. This preventive approach avoids the need to redesign at a later stage and is more cost effective. An additional benefit of reducing noise at its source is usually a commensurate increase in energy efficiency and machinery longevity.
Purchase Quiet Equipment
The US Navy has a "Buy Quiet" policy for equipment aboard ship. Selecting quiet equipment, systems, tools, etc. at the earliest stages of acquisition is the best way to reduce noise at the source.
The "Buy Quiet" approach requires designers and engineers to obtain noise emission data before purchasing to choose the quietest available and affordable equipment. Noise emission values obtained from various suppliers can be compared with each other, and can be used for prediction of the noise levels in the area where equipment is to be placed.
Even though quieter equipment generally can be more expensive to purchase, the equipment is usually better built and has high efficiency. It also can require a simpler noise control installation. These features help to reduce the operating and maintenance costs of the equipment, reducing its total life cycle cost.
Design Integrated Power Systems - Electric Drive Propulsion
The US Navy's DDX destroyers are being designed and built to be powered by an electric drive featuring integrated power system (IPS) architecture. The IPS helps to reduce noise and vibration aboard ship due to the elimination of the drive shaft and reduction gears found in traditional Navy ships.
Use a Hydraulics System Noise Suppression Kit - BIMORF System
There are a number of distributive systems onboard Navy ships (e.g., chilled water, compressed air, firemain), which can generate and/or transmit noise throughout large portions of the ship. One of the distributive system airborne noise sources which runs through a significant area of aircraft carriers is the Jet Blast Deflector (JBD) hydraulic system on the gallery deck. To dampen the noise generated by raising and lowering the hydraulic JBD, a "bimorf" (bi-directional multi-orifice) muffler (see Figure 6) has been developed to replace the existing orifices in the JBD hydraulic system.
The "bimorf" muffler gradually reduces the line pressure in the hydraulic system from 3000 psi to 800 psi, in contrast to existing orifices that drop the pressure suddenly. This seemingly small change reduces the noise level from the JBD hydraulic system by 30dB (see Figure 7) and costs less than $500.00 per unit. This relatively inexpensive fix reduces the amount of noise energy from the JBD hydraulics that enters the environment of the gallery deck and the ship's structure. The benefit of this system is that less acoustic insulation is needed to meet required noise standards
Reduce Aircraft Noise
Modern commercial aircraft, such as the Boeing 757 are designed to be quiet enough to enable them to meet commercial airport noise requirements for early morning departures or late evening arrivals. This is achieved by utilizing bypass air in the engine design. The Navy has allocated funding to research additional new designs to reduce military aircraft noise. The Naval Research Laboratory recently allocated $12.9 million to develop technology that will diminish helicopter rotor blade noise and vibration inside helicopter cabins.
Reduce Ventilation System Noise
In addition to ventilation systems designed for human comfort, large air ducts provide combustion (intake) and exhaust for ship propulsion systems, including boilers in older steam driven plants, main propulsion engines (found on certain classes of support ships) and auxiliary power diesel engines, and gas turbine power plants (common on most newer vessels). Design of intake and exhaust ducts is critical to provide for low noise signature and reduced noise in shipboard spaces. Placement of ducts is important to control adjacent noise. Configurations including largest feasible duct diameter, gradual turns, and use of turning veins at abrupt curves (particularly near fans) are important to control noise and vibration.
• HVAC Terminal Silencing - Active Tuned Dissipative Silencer. A resonator can be installed at fan inlet or discharge points and tuned to the fan's blade passage frequency. The resonator is often mounted into the cutoff of the fan casing. When the resonator is tuned to the blade passing frequency, the pressure changes at the cutoff at this frequency are reduced. Reducing pressure changes in turn reduces the noise level. A typical resonator is designed to achieve a 6 to 20dB reduction at tuned frequency.
• Turning Vanes and Splitter Silencers. Airflow noise is turbulence created when airflow is changing direction at a 90-degree angle. The dead air spot in the back corner of the 90-degree turn forms a vortex, creating an annoying air rumble. Turning vanes and splitter silencers can be installed at fan or turbine inlets and outlets to straighten the airflow to reduce noise and vibration on rotors/impellers.
• Correct HVAC Duct Size and Properly Balanced Airflow. Noise problems due to high air velocity in the ductwork and/or at the diffusers will be eliminated if the ductwork for shipboard ventilation systems is sized correctly and the airflow is balanced properly. The DDG-51 Class ships' laundry ventilation system ductwork was not designed and balanced properly. Noise levels near the duct diffusers ranged from 87 to 92dBA and had to be redesigned to reduce these hazardous noise levels to 84dBA. The ventilation system ductwork redesign is being retrofitted on some DDG-51 Class ships and will be incorporated into newly constructed DDG-51 Class ships. [for a fuller explanation go to http://www.public.navy.mil/navsafecen/Documents/SuccessStories/0022%20Noise%20DDG%2051%20Laundry.pdf]
• Proper Supports for Exhaust and Piping Systems. Secure ventilation ductwork piping systems will reduce vibration against shipboard structures.
Reduce Propulsion System Noise
As shown in Figure 9 below, a new and improved design in aircraft carrier fleet propellers reduces the propeller excitation of the ship structure.
Isolate and Insulate the Noise Source
When it is not possible to decrease the noise characteristics of a system or the cost of reducing noise at its source is too high in terms of system performance or overall expense, isolation or insulation may provide a viable noise mitigation alternative. The source can be isolated/insulated from the structure or the crew can be isolated/insulated from the transmitted noise. The classic treatment to noise control is the addition of insulation to absorb/attenuate acoustic energy.
• Acoustic Absorption. Absorptive treatments reduce noise in all accommodation compartments or spaces that house loud machinery. They absorb noise that would have been reflected through applied surfaces. This treatment is very important for ships, because most surfaces can be reflective. Materials such as absorbent ceiling panels, floor carpeting, drapes, or special absorbent wall coverings will reduce noise by reducing the reflected sound. Protective shielding for the absorbing material should generally be perforated. Acoustic absorptive treatments are only effective for attenuating the noise within a space by preventing reflections; they do little for reducing airborne or structure borne noise generated in and transmitted from other compartments.
• Acoustic Insulation (Cladding). This treatment is applied to provide sound insulation for an area or a compartment. An example is the application of acoustic sound insulation for control booths in the propulsion spaces. As illustrated in Figure 11, this treatment is primarily for controlling airborne noise as opposed to structure-borne noise in a controlling path. Cladding treatments take various forms such as rigid or semi rigid boards and blankets depending on the application. Some versions can be layered with a noise barrier material, technically referred to as a "limp mass" or "limp mass barrier," sandwiched between fiberglass or foam. The limp mass helps block noise transmission though the material.
• Floating Floor/Floating Room Treatments. Instead of isolating the machinery, these treatments isolate the compartment. These treatments vary in details of composition, but fundamentally consist of a dense rigid false floor, isolated from the structural deck by fibrous glass batts or resilient supports. For a floating room, false bulkheads are attached to the false floor and are only connected to ship structure by flexible supports at the top. Acoustic absorptive material, such as fibrous glass, is attached to the structural bulkheads behind the false bulkheads. Floating floor treatments are often used for engineers' control rooms or audiometric test booths aboard ships.
• Integrated Joiner Bulkhead System. These prefabricated cabins have been proposed as a fabrication cost saving measure for future Navy ship construction. By prefabricating complete cabin modules on land, a substantial reduction in the cost and time factors is achieved. The prefabricated cabins have been utilized on commercial cruise ships. According to the manufacturers for these prefabricated cabins, a sound reduction up to 40 dB can be achieved. The cabin sound partition walls are about two inches thick and often constructed with layers of steel and noncombustible reinforced fiber glass materials.
• Advanced Acoustic Materials
• Viscoelastic Laminated Sheet Metal. Viscoelastic laminated sheet metal has a sandwich layer of damping material that can be used to control noise transmission by damping the structure and removing energy from the resonant vibration. The Viscoelastic laminated sheet can be applied to exterior surfaces or placed between surfaces of structures or equipment.
• Viscoelastic Polymer Coating. This soundproof coating material has been incorporated into Sea Fighter, the Office of Naval Research's experimental craft for the Navy's Littoral Combat Ship. The soundproof coating material is applied to the hull and mission bay of Sea Fighter to reduce vibration and noise. According to its manufacturer, the soundproof coating material helps to reduce noise on the Sea Fighter by 15 decibels.
Improve Hearing Protection
When noise levels cannot be reduced at the source or personnel can't be isolated from the noise, proper personal protective gear must be used to provide hearing protection. Improved hearing protection for crewmembers may be the only cost effective solution for environments such as the aircraft carrier's flight deck. Currently, work is underway at both the government and contractor levels to design higher performance crew protective equipment.
• Active Headsets. Commercially available active noise cancellation headsets can provide low frequency (less than 750 Hz) attenuation for engine room and flight deck crews. The current helmets provide roughly 20dB of attenuation. In addition to providing passive hearing protection, these headsets allow improved speech intelligibility in high noise environments. In order to cover the audible frequency, both active and passive noise control treatments are needed for an integrated solution.
• Proper Hearing Protection Fit, Maintenance, and Training. In addition to better hardware, improved hearing protection includes improved crew training and enforcement of regulations. Testing has been conducted aboard Navy ships to demonstrate the importance of protective equipment fit, maintenance, and training. A 10dB loss in attenuation is common with ill-fitting gear, worn-out ear seals, or even the introduction of safety eye wear (the eyeglass frames break the ear cup seal). Ship personnel should be provided with personal protective gear that is individually fitted and assigned. They need to be trained to properly fit, use, and maintain their gear and be supplied with the tools and spares to accomplish the task. Workplace inspections should include an assessment of the condition of hearing protection, including seals on earmuffs and cranial helmets (pads should be pliable and intact), the manner in which earplugs are worn, and documentation of the need to order new or spare parts. The crew should also be trained and aware of the increased hazards of working in a high noise environment and of the potential for significant hearing loss.
Limit Crew Exposure
In some instances, hardware solutions may not present the complete answer or the most cost effective solution to noise reduction. Other options are the removal of personnel from hazardous environments or decreasing exposure times via automation or crew rotation. Currently, research indicates that a work rotation schedule using a sliding time scale based on known noise sources would be beneficial. A reduction in time spent in the highest noise environments and an increase in quiet, recovery time will improve auditory health, reduce crew fatigue, and improve morale.
The automation of some systems may be simple and affordable while other systems would be very expensive to automate and would still require the input of a trained professional. Crew functions will have to be analyzed on a case-by-case basis to determine the viability of reduced crew exposure times or automation.
Install Smart Signs
A Smart Sign, which lights up when ambient noise exceeds a predetermined level, can be utilized to provide a high noise level warning for ship personnel. A logic chip inside the sign senses the ambient noise levels. A green light indicates noise below 84dBA, a yellow light indicates noise levels between 84 and 104dBA (requiring single hearing protection - worker is required to wear hearing protection devices such as earplugs or earmuffs), and a red light indicates noise levels above 104dBA (requiring double hearing protection - worker is required to wear earplugs in combination with noise muffs or a helmet).
Provide Remote Monitoring for Equipment in Noisy Areas
Sensors can be used to remotely monitor machines and equipment in high noise level areas such as engine rooms. Proper design and placement of such remote monitors can help ship personnel to avoid entering high noise level environments for extended periods to manually monitor equipment.
Ensure Quality Maintenance
Equipment selection and maintenance plays an important role in noise control as well as longevity of systems. Poorly maintained equipment can be noisy due, for example, to vibrating parts, leaks, and impeded air flow. Equipment that is difficult to maintain will probably not be well accepted by users, receive less than optimal maintenance, require significant additional cost and time to care for and most likely not last as long as products that are easier to care for. Designers play an important role by ensuring that equipment is installed in configurations that support effective and safe maintenance (see the Acquisition Safety web pages Ergonomics/ Human Factors Engineering section). Maintenance and inspection personnel should ensure that replacement parts meet or exceed the noise attenuation properties of original equipment.Key areas include:
• Maintaining thermal and acoustic insulation after repairs and ensuring its maintenance after normal wear or damage.
• Ensuring that vibration spacers, isolators, and impedance mounting of machinery and equipment are replaced with comparable parts and that vibration isolation is not lost by simply bolting or welding units to the bulkhead or ventilation duct(s) without appropriate acoustic isolation.
• Controlling steam, pneumatic, water, and hydraulic pressures and systems to minimize leaks and use minimum required pressures. Additional pressure will typically waste energy, create additional noise, and create additional stress on the system with more potential leaks and additional maintenance. Leaky valves and damaged washers, packing, and valve seats are often resonant noise sources.
• Replacing and repairing ventilation ducts and equipment should ensure that vibration spacers are intact, that diffusers (duct outlets) are selected, installed to minimize transmitted vibration and turbulence, and ensure electrical conduits and cables are mounted via flexible connections to minimize transmitted vibration. In general, diffusers with sharp edges and rapid transitions and turns are likely to be noisy and inefficient.
• Replacing pipes, ducting, and other fluid conduits with properly sized equipment and minimizing sharp turns and abrupt transitions. In general, using the largest feasible pipe or duct for a given application will reduce pressure requirements and flow speed and related turbulence, pressure losses, and associated noise. [Note: Any significant modification from original design requires approval of relevant technical authorities.]
Occupational hearing loss has human, economic, and readiness impacts. Hearing loss may result in diminished quality of life of Navy personnel including isolation from social interaction. The economic effects of hearing loss to the Navy include lost time and decreased productivity, loss of qualified workers through medical disqualification, civilian workers' compensation costs and military disability settlements, retraining, and expenses related to medical intervention (e.g., costs of hearing aids and audiometric testing). Noise-impaired communications affect combat performance, and noisy ship systems mean a ship signature that is easily tracked.
Solving the noise issue aboard Navy ships will require a total system approach using a variety of technical and operational solutions. Effective design guidance should be developed by teaming Navy quiet ship design experience with the ship builders' construction experience and performing shipboard testing of various acoustic solutions.
The four basic noise control methods: 1) Reduce noise at the source, 2) Isolate and insulate the noise source, 3) Improve personal hearing protection, and 4) Limit crew noise exposure should be applied where appropriate.
Shipboard noise control is critical to preserving the hearing of ships' crews, ensuring mission readiness, and preserving a quiet ship signature. Design and acquisition of quiet systems, maintaining these systems, and continuing research into quieter ship designs and equipment make shipboard noise control achievable.
• General Information on Noise and Noise Control
• Research Studies on Effects of Noise
• Noise Control Technology
• Navy /DoD Instructions
• ISO and MIL Standards on Acoustics
• Acquisition Websites Containing Noise Control Information
General Information on Noise and Control
Best Practices in Hearing Noise Loss Prevention
NIOSH Proceedings - On October 28, 1999, leaders from industry, government, labor, professional and trade organizations, and academia met in Detroit to share best practices for preventing work-related hearing impairment. The symposium highlighted an array of proven strategies and advancements for protecting workers hearing.
Canadian Center for Occupational Health and Safety Physical Agents Page
Basic information, auditory and non-auditory effects of noise, exposure limits, measurement techniques (see left side bar)
Environmental Noise Management Program
U.S. Army Combat Systems Test Activity (Aberdeen Test Center) - Aberdeen, MD - Since 1984, CSTA has instituted several operational initiatives to reduce environmental noise impact to surrounding communities and to better balance CSTA's mission with community concerns.
Hearing Loss Prevention
National Institute for Occupational Safety & Health (NIOSH) articles, fact sheets, resources.
National Institute for Occupational Safety & Health (NIOSH) Noise Control Manual
DHHS (NIOSH) Publication 79-117 - Manual contains basic information on understanding, measuring, and controlling noise, and more than 60 actual case histories of industrial noise control projects. Included are sections on noise problem analysis, basic methods of noise control, and acoustical materials. Also contains an extensive, partially annotated bibliography of books and articles on noise.
NIOSH Power Tools Database
NIOSH recently released a Power Tool Database that can be used to find such information as sound power levels, sound pressure levels, and downloadable exposure and wave files related to commonly used power tools.
Noise Control - A Guide for Workers and Employers
Published by OSHA - brief overview of the effects of noise on human health; discussion of key words and concepts of noise control; specific principles of noise control, which can be applied in the workplace; discussion of particular techniques for controlling noise; description of ways OSHA can be of assistance including an explanation of employers' legal requirements for noise control.
Noise Exposure Assessment Tool (NEAT)
The Defense Safety Oversight Council Acquisition and Technology Task Force sponsored a project to help evaluate life-cycle costs and risk of noise exposure for military personnel. It provides acquisition programs and their reviewers with a tool to estimate the cost and risk avoidance associated with implementing noise controls in the design phase. The Noise Exposure Assessment Tool "NEAT" also describes personnel exposure risk in terms of Military Standard 882 System Safety categories and indicates the management risk acceptance level required for a given noise exposure and its reduction through control measures. The tool provides a method for calculating the effective protection provided by given types of protective equipment and de-rating their effectiveness according to accepted methodology. This discourages the use of protective equipment alone as the sole "control" for noise exposures. A related component of the tool estimates speech interference level, including some conditions which may be below occupational exposure limits, but still impair mission performance and safety due to communication issues.
• NEAT Briefing
• NEAT Tool Users Guide
• Noise Evaluation Acquisition Tool
Noise and Hearing Conservation - OSHA
Portion of web site containing fact sheets, articles, evaluations, attitudes on work-related hearing loss, noise monitors and meters, noise measurement techniques, establishing and evaluating hearing conservation programs, etc.
Preventable Noise Exposure Quick Reference Guide
Quiet Vehicle Acoustic Testing
Naval Undersea Warfare Center Division - Keyport, WA - The Dabob Bay range site is especially well suited for quiet vehicle testing due to its secluded location and quiet ambient noise. This site has a moderate depth and close industrial facilities. Data processing and analysis tools have been developed over the years to assist in meeting customer needs. Several radiated noise data acquisition systems are available; these systems include both bottom moored and boat deployed systems.
Research Studies on Effects of Noise
Center for Naval Analyses Hearing Loss Calculator
Center for Naval Analyses (CNA) Study: Computing the Return on Noise Reduction Investments in Navy Ships: A Life-Cycle Cost Approach
The Deputy Assistant Secretary of the Navy (Safety) asked CNA to analyze the factors that influence hearing loss rates among sailors, evaluate the long-term costs, and help identify strategies to reduce these rates.
Center for Naval Analyses (CNA) Study: Statistical Analysis of Hearing Loss Among Navy Personnel
Focus of this study was to find out how hearing loss relates to service time spent aboard ships, in order to reduce disabilities and costs.
Office of Naval Research (ONR) Hearing Conservation Workshop 2007
Presentations are available at website for download. To request access to the site, go to: Request access to "Noise and Hearing Protection Workshop" from the list of Public Projects.
Highlights of research on noise induced hearing loss.
System Safety Implications and Applications of Noise Evaluation and Control in Military Ships
Recommendations are made to address noise in the systems requirements and engineering management process and ensure risk evaluation and mitigation of noise generation and human exposures at a management level consistent with their severity.
Work-Related Hearing Loss
National Institute for Occupational Safety & Health (NIOSH) - Concise article on magnitude, costs and prevention of hearing loss.
Noise Control Technology
Techniques and applications - article by Ron Kurtus - "Some people have to work in noisy environments. I deviSe to protect their hearing and allow them to concentrate on what they are doing without the distraction of noise is an electronic noise cancellation or sound suppression device."
High Noise Control Plans:
The Defense Safety Oversight Council funded a project to identify optimal noise control for nine high noise sources and one promising technology. A poster summarizing this project is available in poster format. High Noise Source Reduction Poster.
Navy /DoD Instructions
Navy Occupational Safety and Health Program Manual for Forces Afloat - Chapter B4, Hearing Conservation.
Navy Safety & Occupational Health (SOH) Program Manual, Chapter 18, Hearing Conservation.
ISO and MIL Standards on Acoustics
International Organization for Standardization (ISO) Standards
For a listing of Acoustics-related Standards search under standards for "acoustics" - can be ordered from ISO website.
Preparation of Electronic Equipment Specifications: MIL-HDBK-2036
[Must register with ASSIST account to enter http://assist.daps.dla.mil/online/start/]
Acquisition Websites Containing Noise Control Information
Defense Acquisition University
Knowledge sharing system best practices, library, videos, etc. (search on noise topics).
Office of the Under Secretary of Defense (Acquisition, Technology and Logistics)/Interoperability
Search on "noise" topics of interest.
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Last Revision: 12 June 2013