7. Results case studies ‐ damping material and silencers.
| Damping material and silencers | |||||||||
| Noise source | Intervention | Follow‐up | Initialnoise level | Noise level after | 8 h TWA before | 8 h TWA after | Dose before | Dose after | Reference ID |
| Confetti machine | Damped machine surfaces: Replaced vacuums with small cyclones that were quieter and had fewer clogs, Installed conveyors to carry the paper into the disintegrators | not reported | 95 dB | 85 dB | Maling 2016 | ||||
| Production noise | Installation of sound absorbing panels, shields, covers, insulation, sheeting, installation of mufflers for fans and solenoids, reduction of compressed‐air pressure and volume in vents, use of vibrating personal alarms instead of audible alarms | not reported | 2 to 11 dB noise reduction | ||||||
| Helicopter | Cover of structural leaks with lightweight materials (e.g. new door seals) and damping of the structure (patches of constrained visco‐elastic materials that are bonded to the structure), optimised sound‐proofing panels (sandwich panels with “soft core”) and windows (thickened laminated windows with damping layer and double glazing), and Main Gear Box suspension devices (laminated ball joints at MGB support strut foot) | not reported | 7 dB noise reduction | Caillet 2012 | |||||
| Pump | Suppressor on palletizer hydraulic pump to minimize hydraulic banging, pump whine contained in sound‐insulated box | not reported | 88 dB | 83 dB | Morata 2015 | ||||
| Air‐rotary drill rig | Installation of hydraulic noise suppressors and a lead‐fiberglass blanket covering Ihe gap between the inside door and the cab frame | not reported | 98 dB | 95 dB | MSHA PEL 280%; NIOSH 3222% | MSHA PEL 210%: NIOSH 2585% | |||
| Air‐rotary drill rig | Installation of hydraulic noise suppressors | not reported | 98 dB | 97 dB | MSHA PEL 280%; NIOSH 3222% | MSHA PEL 249%; NIOSH 2951% | |||
| Pumps | Installing mufflers on pumps | not reported | 98.1 dB | 81.3 dB | |||||
| Haul trucks in underground metal/non‐metal mines | Improving the engine compartment noise barrier: the usual barrier material has been replaced with a barrier material part number Duracote 5356, manufactured by Durasonic | not reported | MSHA PEL 495% | MSHA PEL 416% | Thompson 2015 | ||||
| Chiller | Reduce noise from a chiller with a combination of acoustic absorbent and retro‐fit constrained layer damping | not reported | 8 dB noise reduction | Wilson 2016 | |||||
| High‐speed strip‐fed press | Normally the press legs are welded boxes, the press frame was isolated from the fabricated legs by inserting 6 mm composite pads between frame and legs | not reported | 101 dB | 92 dB | |||||
| Product impact on hoppers and chutes | Coated internally with food‐grade, sound‐deadening material | not reported | 96–98 dB | Noise reduced by 2‐8 dB | HSE 2013 | ||||
| Gas cylinder impact on metal table | Rubber matting on table | not reported | 110 dB peaks | removal of peak noises | |||||
| Product impact on ducting | Lagged ductwork with noise‐absorbent padding | not reported | 92 dB | 84 dB | |||||
| Product impact on vibrating components | Coated externally with sound‐deadening material | not reported | 92 dB | 84 dB | |||||
| Bread‐basket stacking machine | Fitted hydraulic dampers | not reported | 92 dB | 83 dB | |||||
| Hand‐crimping metal foil packages | Mounted on layers of rubber | not reported | 86–89 dB | 85–86 dB | |||||
| Keg impact on concrete floor | Fitted rubber matting on to floor | not reported | High noise levels | Noise levels reduced | |||||
| Gas cylinder impact on metal ‘A’ frame trolleys | Fitted rubber matting on to trolleys | not reported | 110 dB peaks | Peak noise levels reduced | |||||
| Road tanker degassing | Fitted silencers | not reported | 92 dB | 83 dB | |||||
| Evaporative condensers and refrigeration plant | Fitted silencers | not reported | 94 dB | 83–87 dB | |||||
| Number of cases: 20 | mean before | mean after | mean reduction | ||||||
| noise level dB | 93.6 | 86.5 | 7 | ||||||
| TWA dB | 101 | 92 | 9 | ||||||
| Dose % (MSHA PEL) [dosimeter settings: 90 dB Lt, 90 dB Lc, 5‐dB exchange rate] | 351.7 | 291.7 | 60 | ||||||
| Dose % (NIOSH) [dosimeter settings: 80 dB Lt, 85 dB Lc, 3‐dB exchange rate] | 3222 | 2768 | 454 | ||||||
MSHA = Mine safety and health administration
NIOSH = National Institute for Occupational Safety and Health
PEL = permissible exposure limit