|
|
| A to Z Index | Find It! in DOL | Advanced Search | Help |
|
VOLUME IV METAL AND NONMETAL MINES INTERPRETATION, APPLICATION AND GUIDELINES ON ENFORCEMENT OF 30 CFR MSHA considers the following engineering noise controls, or a combination of these controls, to be feasible and effective in most circumstances to reduce the noise exposure of employees operating surface self-propelled equipment (for example, dozers, front-end loaders, trucks, graders, scrapers, etc.): - acoustically treated cabs (primarily on equipment manufactured since the mid-1970s); Among these controls, a well designed and constructed acoustically treated cab and a properly treated exhaust system are the most effective and the most likely to reduce employee noise exposure to the PEL. MSHA generally considers acoustically treated cabs to be feasible provided: (1) a cab is available for that particular piece of equipment; (2) there are no significant technical or safety problems caused by the installation of a cab; (3) its installation would not require modification to, or alteration of, the equipment's roll-over protection (ROPs) in any way that would affect the ROP's certification; and (4) its use will significantly reduce the employee's noise exposure. A well designed and constructed acoustically treated factory cab can reduce employee noise exposure by more than 10 dBA. Generally, retro-fit cabs will exhibit somewhat less noise reduction. Although such cabs are the single most effective noise control, on some particularly noisy equipment an acoustically treated cab may not reduce noise levels to the PEL. In these cases, administrative controls or other engineering controls, such as an exhaust muffler and acoustical treatment of the firewall, would need to be evaluated to determine if they could further reduce the employee's noise exposure. If, after using all feasible controls, employee exposure still exceeds the PEL, then adequate hearing protection would have to be provided and worn. There may be limited applications, where, based upon the amount of time the equipment is used during the employee's work shift and the degree of noise overexposure, controls other than a cab may be able to reduce employee exposure to the PEL. Such controls are described below. However, if a mine operator chooses to use such controls and the employee's noise exposure remains significantly above the PEL, the mine operator shall be cited if a cab is feasible and has not been installed. On equipment manufactured before the mid-1970s, acoustically treated cabs become increasingly infeasible due to the following factors: lack of availability of retro-fit cabs; difficulties installing cabs given the equipment's design; decreased acoustic effectiveness; and cost considerations given these concerns. When it is determined that a cab is infeasible, engineering controls that are likely to be feasible include: (1) a windshield to block the engine noise from the employee; (2) an exhaust muffler along with redirecting the exhaust away from the employee; and (3) the placement of acoustic materials on the firewall and in the operator's compartment. Noise reduction of 5 to 10 dBA may be achievable by using these controls. The cost of the materials is approximately $2,000 per machine. A video tape demonstrating the installation of these controls is available for mine operators to review at their local MSHA office. Acoustically treated cabs are available as an option on most new equipment and on a retro-fit basis for most equipment manufactured since the mid-1970s. Retro-fit cabs are available from various manufacturers at costs ranging from approximately $5,000 to $13,000. For comparison, the retail price of a mid- 1970s D-9 Caterpillar dozer in serviceable condition is approximately $70,000 to $80,000. A cab installed at the factory when the unit is purchased may cost more than installing a retro-fit cab at a later date; however, the fit, durability and acoustic effectiveness of a factory installed cab is usually better. According to information received from Caterpillar, an acoustically treated air conditioned cab for a D-10N dozer costs $15,900, if ordered when the dozer is purchased. This represents 3.4 percent of the $470,617 cost of the D-10N. Noise levels inside a factory cab on a D10-N, during a standard work cycle, were reported by Caterpillar to be 88 dBA at the operator's position with the doors and windows closed. Commonly encountered complaints with cabs are inadequate ventilation and temperature control. If ventilation is inadequate, employees operating such equipment have been known to open cab doors or break out windows to provide the needed ventilation, thereby significantly reducing the cab's acoustical effectiveness. This may result in a citation if MSHA should sample at that time and find the employee overexposed. Particular attention should therefore be given to selecting or designing a cab with an adequate pressurized air filtration/ ventilation system or air conditioning. In addition to maintaining the acoustical effectiveness of the cab, it may also result in increased worker comfort and productivity, as well as protecting the worker from excessive dust exposure. Manufacturers are now offering more reliable and efficient air conditioners for mining equipment. Problems with their use can be avoided to a large extent by adhering to a good preventive maintenance program. Costs to install an air conditioner on units like a D-10N dozer could range from $2,500 to $4,500. Other measures could be taken to reduce the heat load in cabs, such as: putting shielding or insulation on the firewall, floorboard and cab roof; painting the outside of the cab roof with a reflective paint; and using tinted safety glass. MSHA considers the following engineering noise controls to be feasible and effective in most circumstances to reduce the noise exposure of employees operating underground diesel powered haulage equipment (for example, LHDs, shuttle cars, haul trucks, etc.): - exhaust mufflers and redirecting the exhaust away from the employee; Total noise reduction of 3 to 5 dBA could be anticipated from the combined use of an exhaust muffler and acoustic materials, at a cost of less than $1,000 per machine. Although this reduction is significant, employee exposure may still exceed the PEL, requiring the continued wearing of adequate hearing protection. MSHA testing has indicated that certain exhaust mufflers on underground diesel powered haulage equipment are particularly effective in reducing low frequency noise, whereas personal hearing protection is generally more effective in reducing high frequency levels. When an exhaust muffler is used along with personal hearing protection their combined attenuation can significantly reduce noise levels measured underneath the personal hearing protection. Results of MSHA in-mine testing have shown that levels measured underneath personal hearing protection, with no exhaust mufflers installed, exceeded 90 dBA in seven out of nine tests. The average level was 98 dBA. The use of an exhaust muffler reduced the average level to 87 dBA. It should be emphasized that exhaust mufflers must be of proper design and construction to maximize noise reduction and minimize back pressure in the exhaust system. Some diesel powered haulage units are equipped with various devices to control exhaust emissions, such as: scrubbers, catalysts, filters and exhaust gas recirculation systems. These devices, though not as effective as mufflers, will provide some noise reduction. A muffler should not be added when such emission control devices are used because the combination may increase exhaust system back pressure beyond the unit's design specification. An exhaust muffler is also not recommended on diesel powered haulage units used in mines classified as gassy where their exhaust system must meet the approval requirements in 30 CFR Part 36. In these cases the exhaust pipe can be directed away from the employee. The effectiveness of acoustic materials in reducing noise levels beyond that obtained by the use of an exhaust muffler will vary depending upon the make and model of the unit, engine size, mechanical condition and mining conditions. Such treatments may include: the use of barrier and absorptive material to reduce the noise coming from the engine and transmission compartments; increased mass applied to the firewall; or sealing any openings between the employee and transmission. Particular care must be taken in the application of acoustic materials to avoid engine overheating. Materials selected should not absorb oil which could create a fire hazard. In some underground mines, conditions permit using full-size surface haulage equipment. If environmental conditions are such that the use of an acoustically treated cab does not present a safety hazard due to impaired visibility, such cabs may be considered feasible on this equipment. Refer to the discussion of noise controls for "surface self-propelled equipment" for additional factors to be considered in determining the feasibility of cabs on such equipment. Noise levels on an untreated pneumatic jumbo drill can typically exceed 115 dBA at the operator's position. Hydraulic drills are usually about 5 to 10 dBA quieter. Noise controls for pneumatic and hydraulic jumbo drills were discussed in a February 1, 1984, MSHA memorandum to district and subdistrict managers, which indicated that acoustically treated cabs and partial barriers were, in general, considered to be feasible controls for this equipment. A well designed and constructed acoustically treated cab is more effective than a partial barrier and may reduce employee noise exposure to the PEL. Such cabs should be utilized instead of partial barriers wherever drill design and mining conditions permit. If an acoustically treated cab is not feasible, a partial barrier can yield significant noise reduction. However, because of the high noise levels produced by these drills, it is unlikely that a partial barrier will reduce employee exposure to the PEL, thereby requiring the continued use of personal hearing protection. Dual hearing protection (ear plugs under ear muffs) may be required if noise levels are particularly high and the attenuation of a single pair of hearing protectors is inadequate. Commonly encountered complaints with cabs are inadequate ventilation and temperature control. In such instances, employees operating the equipment have been known to open cab doors or break out windows to provide the needed ventilation, thereby significantly reducing the cab's acoustical effective- ness. Particular attention should, therefore, be given to selecting or designing a cab with an adequate pressurized air filtration/ventilation system. Such systems may also increase worker comfort and productivity, as well as protecting the worker from excessive dust exposure. Acoustically treated cabs may be available from the drill manufacturers or from suppliers of retro-fit cabs. Mine operators have also constructed retro-fit cabs of their own design, many of which were as effective as factory cabs and less costly. Noise levels on an untreated track drill can typically exceed 115 dBA at the operator's position. MSHA issued guidance on noise controls for pneumatic and hydraulic track drills in a June 30, 1986 memorandum to district and subdistrict managers. As indicated in that memorandum, the preferred noise control for such drills is an acoustically treated cab, provided that the drill design permits its installation. A well designed and constructed acoustically treated cab can reduce employee noise exposure to the PEL. On some very small pneumatic track drills it may not be feasible to install a cab. A cab may also be infeasible if the driller has to change steels frequently. Acoustically treated cabs may be available from the drill manufacturers or suppliers of retro-fit cabs. Mine operators have also constructed retro-fit cabs of their own design, many of which were as effective as factory cabs and less costly. Where a cab is infeasible, a partial barrier can usually be constructed and erected vertically along the length of the drill's mast. This barrier blocks the employee from noise coming from the drill and drill steel while standing at the operating controls. Such a barrier can be installed on almost any track drill and will not interfere with steel changing. The partial barrier can be constructed at minimal cost out of angle iron and used conveyor belting. The barrier has achieved an average of 8 dBA noise reduction. However, noise levels at the drill operator's position are still likely to exceed 100 dBA with the barrier in place, requiring the continued use of adequate hearing protection. A video tape demonstrating the installation of a partial barrier is available for mine operators to review at their local MSHA office. The use of an exhaust muffler or long exhaust hose directing the exhaust away from the drill, along with a cab or barrier, may provide additional noise reduction on pneumatic drills, particularly at times when the drill operator may be outside the cab or out from behind the barrier. Acoustically treating or isolating the drill's compressor may also be of some benefit if the noise from it contributes to an employee's overexposure. If a cab is used, and it is determined that doors and windows must be kept closed to keep employee exposure within the PEL, then it may be necessary to provide an adequate pressurized air filtration/ventilation system or air conditioning. In addition to maintaining acoustical effectiveness, this may result in increased worker comfort and productivity, as well as protecting the worker from excessive dust exposure. Noise levels on unmuffled pneumatically operated hand-held percussive drills can typically exceed 115 dBA. In the late 1970s, exhaust mufflers began to be available for hand-held pneumatic drills (such as, jackleg drills, stopers and sinkers). Since that time, many drill manufacturers have offered either integrally muffled drills or retro-fit mufflers for their drills. In 1979, MSHA developed a muffler made from a section of rubber tire which was both economical and effective in reducing noise levels. Noise reduction with this muffler averages 6 dBA. MSHA considers exhaust mufflers to be feasible controls for nearly all hand-held pneumatic drills used at both surface and underground mining operations. They are widely used throughout the mining industry. There may be a few drills where, due to their design and/or application, a muffler may not be feasible. If such a problem is encountered, it should be brought to the attention of Metal and Nonmetal's Division of Health. A video tape and a T-Gram technical report (TD 1), which describe the design and installation of the rubber tire muffler, are available for mine operators to review at their local MSHA office. Although exhaust mufflers are effective, it is likely that noise levels while drilling will exceed 105 dBA, requiring the continued use of hearing protection. At such high noise levels, it becomes increasingly important to evaluate the effectiveness of the hearing protection being worn. In some cases, dual hearing protection (ear plugs under ear muffs) may be needed to ensure adequate protection. The most commonly used feasible control to reduce employee noise exposure on draglines and shovels involves the following: - placement of a lead vinyl curtain or a solid barrier with a door behind the operator to shield the employee from engine noise; This method of control should cost less than $700 in materials and can yield 6 to 8 dBA reduction. A video tape demonstrating the installation of this control on a dragline is available for mine operators to review at their local MSHA office. The most effective and frequently used noise control for employees operating a portable crusher is an acoustically treated control booth. Provided an employee's activities can be confined within the booth, a properly designed and constructed booth can reduce employee noise exposure to the PEL. If an employee's activities require leaving the booth, additional administrative or engineering controls may be needed to reduce the exposure when outside the booth. The effectiveness of an acoustically treated control booth is enhanced if it can be isolated from the crusher itself. A booth can be built on metal supports and connected to the crusher by a walkway. The booth and support structure can be made in such a manner that it can be easily transported to new mining sites. An MSHA T-Gram (TD 13) on the design of a mobile crusher booth is available at the local MSHA office. If doors and windows are closed in the control booth to keep the employee's exposure within the PEL, then it may be necessary to provide an adequate pressurized air filtration/ventilation system or air conditioning. In addition to maintaining the acoustical effectiveness of the booth, this may result in increased worker comfort and productivity, as well as protecting the worker from excessive dust exposure. Another alternative to reduce a crusher operator's noise exposure would be to move the employee to a quieter location where he can remotely control and view the operation. If the employee needs to stand near a conveyor belt to pick off oversize materials, a relatively inexpensive device can be constructed which will do this automatically or a partial barrier could be constructed to shelter the employee while performing this function. The channel burner is basically a jet burning tip, on a long handle, fueled by compressed air and diesel fuel. It produces an intensely hot flame that spalls the rock when directed against it. They are used in the dimension granite industry to cut granite blocks from the quarry. In a typical operation, the burner operator holds the handle and moves the burner back and forth, cutting a deep narrow channel in the granite. Noise exposures of miners operating hand-held air burners are among the highest in the mining industry. Noise levels produced by these burners commonly exceed 120 dBA. A noise level of 105 dBA was measured under muff-type hearing protectors worn by a burner operator. Such high noise levels can rapidly damage one's hearing. Exposure to silica bearing dust and to hot chips of granite from this process also pose additional hazards. Several types of equipment are currently used by the dimension granite industry as alternatives to using hand-held air burners. Among the most effective in reducing employee noise exposure is the diamond wire saw. The noise exposures of miners operating these saws are typically within permissible levels. Beyond its lower noise levels, the diamond wire saw can cut 20 to 40 square feet per hour compared to an optimum of 8 to 12 square feet per hour with a hand-held air burner. Additionally, compared to other methods, the diamond wire saw produces no harmful levels of dust and cuts a smooth face with minimal loss of granite. The saw works best in areas of low pressure and low quartz content. High pressure in the granite deposit can pinch the wire, and high quartz content (harder granite) can reduce cutting speed and wire life. It is also effective for cutting areas of fractured rock which are difficult to cut with a channel burner. When using the wire saw, adequate guarding or barricading must be provided to protect employees from inadvertently contacting moving parts. The diamond wire saw is commercially available from two manufacturers. The cost of the saw alone is approximately $50,000. The diamond wire costs approximately $85 per foot. Generally, 200 to 230 feet of diamond wire is needed for the average cut. Depending on the hardness of the granite and size of the cut, three to four cuts can be made before the wire needs to be replaced. Although the diamond wire saw can be used to make most cuts in a quarry, it will not entirely eliminate the need to use a channel burner or drill. Automated air burners are being used successfully at several granite quarries around the country. Miners operating these units can stand away from the burner, significantly reducing exposure to noise, dust, and hot chips of granite. It is also a faster and more economical method of cutting stone than a hand- held burner. Channel burners typically work best in harder granite. Although the use of the automated burner will result in significantly lower noise and dust exposures for the burner operator, other miners in the quarry may still be exposed to noise and dust generated from operating this unit. The automated air burner is currently commercially available from only one supplier. However, at least one quarry operator is using one of his own design and construction. The cost of an automated burner is approximately $19,000, but it should pay for itself in under 2 years due to reduced operating costs. A video tape demonstrating the automated burner is available in each MSHA field office. Hydraulic and pneumatic drills are also being used in lieu of hand-held air burners at several granite quarries. Slot drills, which use a guide bar to drill out the web left between holes, can be used to make an open channel. The initial cost of such a drill is higher than that of an automated burner or diamond wire saw. The cutting rate using a slot drill is approximately 19 to 21 square feet per hour. Noise levels experienced by operators of such drills, though high, are significantly less than those experienced by hand-held air burner operators. Additionally, it may be possible to add noise controls to such drills to further reduce miner noise exposure (see Page A-8: "Track Drills"). Oxygen-fueled hand-held burners were used in the past, but never became popular due to the high price of liquid oxygen. However, significant decreases in the cost of liquid oxygen may now make its use an attractive alternative. Due to the oxygen burner's lower operating pressure, it produces less dust and approximately 5 dBA less noise than a hand-held air burner, with noise levels averaging about 115 to 117 dBA. Reportedly its hotter flame results in faster cutting rates than with an air burner. One disadvantage is that, due to its lower operating pressure, a blow pipe may be needed to clear spalling from the channel. Although the hand-held oxygen burner is less effective in reducing noise exposure than the other alternatives described in this appendix, it could be particularly promising if automated. One operator has developed and is using such a unit. Because rotation of the oxygen burner's tip is not needed, it should be easier to automate than an air burner and it may be possible for other mine operators to build their own units. Once the technology and equipment needed to construct an automated oxygen- fueled burner becomes readily available, MSHA will notify the industry and allow one year for mine operators using hand-held oxygen burners to automate their systems. MSHA will continue to evaluate developing technology in this area. Currently, MSHA is evaluating the use of water jets to cut granite. One operator is successfully using such a device as his sole means of cutting granite. Mine operators will be given until August 1, 1990, to evaluate the various alternatives to using hand-held air burners described in this policy. During this time period, MSHA will not cite mine operators when a miner's exposure exceeds the permissible level while operating a hand-held air burner, provided adequate hearing protection is worn. Due to the high noise exposure experienced by hand-held air burner operators, dual hearing protection (ear plugs under ear muffs) will be needed. After August 1, 1990, mine operators will be cited if MSHA finds a miner overexposed to noise while operating a hand-held air burner and MSHA determines that one of the described alternatives is feasible at that operation. Frequently, mining personnel are exposed to noise levels of up to 114 dBA from milling operations. The following engineering noise controls may be feasible for such operations: - resiliently backed liners; In order to determine which control, or combination of controls, are feasible and effective to reduce the noise exposure of employees working in mills, it is usually necessary to do a time study to pinpoint the locations and noise sources contributing to the employee's overexposure. In some situations an acoustically treated control booth may be all that is needed, in others more extensive treatments may be necessary. Administrative controls may also be feasible to limit employee exposure to particularly noisy areas of a mill. Control booths can be constructed and acoustically treated by mine operators or can be purchased from commercial sources. Resiliently backed liners can be put on chutes, bins and other drop or impact points to reduce noise from these sources. Although such material is available from a number of commercial suppliers, often old conveyor belting can be used with comparable results. In situations where numerous employees are exposed to the noise, full or partial topless enclosures around the mill may be feasible. Essentially, these enclosures create an acoustical shadow zone for the affected employees. The construction of such enclosures should incorporate the following considerations: - be of sufficient height so as to create the desired acoustical shadow zone; Dependent upon the noise reduction required to lower an employee's exposure to the PEL, acoustical absorptive material may be needed within and/or above the enclosure. When treating the interior of a mill enclosure, materials such as faced fiberglass or mineral board should be considered. The utilization of acoustical baffles suspended above such enclosures has proven to be an effective method of reducing the overall noise levels. The amount of absorptive materials necessary can be mathematically calculated. The cost for such enclosures is dependent on the type of materials utilized in its construction and the overall size of the enclosure. In three demonstrations of this technology, total material costs have ranged between $3500 and $7000. |
 Back to Top |
www.msha.gov | www.dol.gov |
|
| ||
|---|---|---|
|
| ||
|
Mine Safety and Health Administration (MSHA) 1100 Wilson Boulevard, 21st Floor Arlington, VA 22209-3939 |
Phone:
(202) 693-9400 Fax-on-demand: (202) 693-9401 Technical (web) questions: Webmaster On-line Filing Help: MSHAhelpdesk@dol.gov or call (877) 778-6055 Contact Us | |
