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. 2017 Jul 7;2017(7):CD006396. doi: 10.1002/14651858.CD006396.pub4

8. Results case studies ‐ design changes.

Design changes
Noise source Intervention Follow‐up Initial noise level Noise level after 8 h TWA before 8 h TWA after Dose before Dose after Reference ID
Roof bolting machine at underground coal mines New drill bit isolator immediate       reduced by 3.2 dB MSHA PEL per hole 0.85% MSHA PEL per hole 0.57% Azman 2012
short term (after 253 holes and 628 m)       reduced by 2.2 dB MSHA PEL per hole 0.9% MSHA PEL per hole 0.66%
4‐roll calender in a tire manufacturing facility "calender operator" Replacing the piercer brackets, optimising alignment and improving preventative maintenance (increased and more frequent lubrication of the piercer and other areas of the equipment with high friction or pressure) not reported     87.7 dB 86.3 dB OSHA dose 72.8% OSHA dose 59.6% Cockrell 2015
4‐roll calender in a tire manufacturing facility "wind up operator" Replacing the piercer brackets, optimising alignment and improving preventative maintenance (increased and more frequent lubrication of the piercer and other areas of the equipment with high friction or pressure) not reported     93.1 dB 89 dB OSHA dose 153% OSHA dose 87.3%
Heavy metal arms which drove the reciprocating blade on the machines Alternative linkage using flexible nylon straps not reported 95 dB 75 dB         HSE 2015
Tobacco filter making machine Machine design improvements on a tobacco filter making machine and room improvements not reported   9 dB reduction         Maling 2016
Weaving machines Use of different spindle not reported 100 dB 90 dB        
Locomotive for mining Active noise control immediate             Pan 2016
Mining truck Active noise control immediate            
Mining truck active noise control and damping material immediate            
Filler Filler outfeed: line shaft removed, individual drives installed not reported 107 dB 81 dB         Morata 2015
Con‐air dryer Machine set on vibration mounts, quieter blower not reported 94 dB 85 dB        
Transfer cart not reported not reported 94 dB 79 dB        
Trimmer rReplacing nozzles from trimmer with in feed decline drive belt not reported 98 to 113 dB 86 to 104 dB        
Continuous mining machine Exchange of a single sprocket chain for a dual sprocket chain on a continuous mining machine (CMM, Joy Mining Machine 14CM‐15) not reported     93.4 to 93.3 dB 92 dB MSHA PEL 159 % MSHA PEL 132.5%
Moen case former Exchange of pneumatic cylinder for servo‐mandrel not reported 97 dB 87 dB        
Cart Exchange of cart wheels not reported 88 dB 72 dB        
Standard longwall cutting drums (mining) Modified set of longwall cutting drums instead of a set of standard (baseline) drums not reported 98 dB 92 dB 95.7 dB 93.1 dB MSHA PEL 220.5% MSHA PEL 158.6% Thompson 2015
Haul trucks in underground metal/non‐metal mines Improving the engine compartment noise barrier and changing the fan type, size, and rotation speed (larger fan of different design and different fan pulley to reduce the fan rotation speed to 90%) not reported     102 dB 93 dB MSHA PEL 495% MSHA PEL 158%
Load‐haul‐dumps (LHDs) in underground metal/non‐metal mines Improving the engine compartment noise barrier and changing the fan type, size, and rotation speed (larger fan of a different design and a different fan hub to reduce the fan rotation speed to roughly 87% and new noise barrier material (Duracote Durasonic 5356)) not reported     98 dB 96 dB MSHA PEL 289% MSHA PEL 231%
Load‐haul‐dumps (LHDs) in underground metal/non‐metal mines Improving the engine compartment noise barrier and changing the fan type, size, and rotation speed (a larger fan of a different design was installed as well as a different fan hub to reduce the fan rotation speed to roughly 95%) not reported     98 dB 93 dB MSHA PEL 289% MSHA PEL 142%
Standard camshaft washer drying nozzles (pneumatic) Pneumatic nozzles replaced with suitable entraining units not reported   12 dB reduction         Wilson 2016
Drier fan Retro‐fitting aerodynamic and acoustic elements inside fan casings and the associated ductwork not reported   9 dB reduction        
Aluminium can extract and chopper fans Fitting aerodynamic inserts inside the fan casing not reported   22 dB reduction        
Separator (large thin sheet distribution dome) alteration to a vibratory separator: forming this component in stainless sound deadened steel not reported 105 dB 89 dB        
Metal trays Replacing metal trays with plastic trays not reported 89 dB 84‐85 dB         HSE 2013
Metal wheels on baking racks Replacing baking rack wheels with resin wheels not reported above 100 dB 86‐92 dB        
Loosening product from baking tins with air knives Air knives modified to operate with a diffuse air jet not reported above 90 dB below 85 dB        
Bottles and cans banging together on conveyors Fitted a pressureless combiner conveyor system not reported above 90 dB below 90 dB        
Baking tins banging together on chain or slat conveyors Installing ‘tin‐friendly’ conveyors not reported above 90 dB below 85 dB        
Manual changeover of baking tins on conveyor Installed robots to handle pans not reported 94‐96 dB below 90 dB        
Water pumps on filling machines Replaced with air pumps and fitted silencers not reported 90 dB 84 dB        
Filling sachets and cups New design of horizontal powder‐feeder and enclosed machine not reported 83‐84 dB 80 dB        
Bottle manufacture, filling and packing lines Acoustic panels fitted to walls, high ceiling installed not reported Above 90 dB 83 dB        
Contact between metal trays and metal tracking Replaced with plastic tracking not reported 94 dB 87 dB        
Product impact on metal chutes Replaced with plastic chutes not reported 96‐98 dB 90 dB        
Electrically powered sausage‐spooling machines Replaced with compressed‐air spooler not reported 86‐90 dB below 80 dB        
Tray‐indexing arm Plastic caps on fingers of indexing arm not reported 94 dB 87‐89 dB        
Vibratory conveyor Ensured conveyor only used at least noisy speed not reported above 90 dB below 85        
Glass bottles on conveyor New design of conveyor with different chain speeds not reported 101 dB 84 dB        
Lidding and de‐lidding tins Installed robots to lid and de‐lid baking tins not reported 90‐93 dB 88 dB        
  Number of cases: 41 mean before mean after mean reduction  
Noise level dB 94.5 dB 85.3 dB 9.6 dB  
TWA dB 95.4 91.8 3.4 dB  
Dose % (OSHA) 112.9 73.5 39.5  
Dose % (MSHA PEL) 207.8 117.6 90.1  

MSHA = Mine Safety and Health Administration

OSHA = Occupational Safety and Health Administration

PEL = permissible exposure limit