Hearing Protection: How Do We Know When it Works? Session 208 April 28, 2014 AOHC San Antonio TX Presenter Disclosures Ted Madison Ted Madison, M.A., CCC-A 3M Personal Safety Division 1 St Paul, MN 2 Financial Employed by the 3M Personal Safety Division A manufacturer of noise monitoring and hearing protection devices. Salary and travel expenses paid by 3M Non-financial Represents the American Speech-Language-Hearing Association (ASHA) on the Council for Accreditation in Occupational Hearing Conservation (CAOHC) CAOHC course director and instructor at the University of Minnesota School of Public Health OSHA Requirements 29 CFR 1910.95 When Must Hearing Protection be Worn? When TWA is 85 dba and higher: Employer must provide Suitable variety of HPDs at no charge Replace them as necessary When TWA is higher than 90 dba: Employees must wear HPDs OSHA Requirements 29 CFR 1910.95 How much noise reduction is needed? HPDs must reduce employee s exposure to 90 dba or less Employees who have had a Standard Threshold Shift (STS) need more noise reduction; enough to lower exposure to 85 dba or less 3 4 Noise Monitoring Critical First Step When? Regulatory requirements Difficulty communicating Employee complaints about noise Change in equipment configuration Work shift changes Alerting devices Sampling Methods Representative sampling Individual sampling Area evaluations Maps 5 6 3M 2013. All rights reserved 1
Which Type of Hearing Protector Works Best? Real Ear Attenuation at Threshold (REAT) 7 The best hearing protector is the one that is: Worn correctly (fit) Worn consistently (wear time) 8 Human subject test in laboratory Measure hearing thresholds 10 Subjects / 3 Repeats Careful Fitting Motionless Subject Sounds presented using loudspeakers 1/3-Octave Noise Random Incidence Reverberant room Real-Ear Atte enuation (db) Typical Earmuff Attenuation Data 0 0 10 20 30 40 50.125.250.500 1.0 2.0 4.0 8.0 Frequency (khz) 10 Standa ard Deviation (db) Number of Oc ccurrences 6 4 2 0 Normal Distribution Mean = 40 db, sd = 3.0 db Theoretical Bell Curve Measured Data 32 34 36 38 40 42 44 46 48 Attenuation (db) Number of Oc ccurrences Normal Distribution Mean = 40 db, sd = 3.0 db 98% Protection 95% 68% Single Number Hearing Protector Ratings Combined attenuation minus variability All subjects, all frequencies 34 37 40 43 46 Attenuation (db) 12 3M 2013. All rights reserved 2
Noise Reduction Rating NRR Describes Best Fit of hearing protector when worn in laboratory How NRR Should Work In Theory Unprotected Noise Exposure HPD rating Protected Exposure 95 dbc TWA (29 db) 66 dba HPD Ratings Should Not be Used to Predict Protected Exposure of Individuals Only Groups 13 14 Using NRR with A-weighted TWA Unprotected Noise Exposure HPD rating Protected Exposure Noise Reduction Rating NRR Describes Best Fit of hearing protector when worn in laboratory 95 dbc TWA (29 db) 66 dba 95 dba TWA (29 7 db) 73 dba 7 db correction* 15 *U.S. OSHA 29 CFR 1910.95 16 In workplace, the average noise reduction obtained by groups of HPD wearers is much lower than the NRR Real-World vs. Laboratory NRR Factors That Effect HPD Performance Earplugs Earmuffs Comfort Communication Compatibility Readjustment Use Deterioration Fit Modification Wearing Time 17 Berger (2000) 18 3M 2013. All rights reserved 3
Derating Adjusting HPD Ratings In Workplace Unprotected Noise Exposure HPD rating Protected Exposure 95 dba (29 7 db) 84 dba 19 NIOSH 20 22 db x.5 50% derating* *U.S. OSHA 29 CFR 1910.95 For High Noise Exposures, Fit Earplugs Deeply Dual Protection 21 Effect of Insertion Depth on Attenuation Real-Ear Attenua ation (db) 0 10 Capping 20 30 40 50 Partial Standard Deep 125 250 500 1000 2000 4000 8000 Frequency (Hz) 22 Wearing earmuffs over earplugs boosts overall attenuation of earplugs by as much as 5-10 db Extra noise reduction varies by frequency Size & attenuation of earmuffs not critical Choose lightweight, comfortable earmuffs OSHA: Add 5 db to device with higher NRR Real-Ear Atte enuation (db) 10 20 30 40 50 60 Single vs. Dual Protection Earmuff Plug Plug + Muff Attenuation Limits.125.250.500 1.0 2.0 4.0 8.0 Frequency (khz) 24 Can We Assume They All Get the Same Protection? 3M 2013. All rights reserved 4
Real-World Results No Reliable Way to Use HPD Ratings RW NRR = 10 db RW NRR = 18 db Predicting individual performance from group average is not possible Derating does not account for individual employee differences 50% 26 Personal Attenuation Rating PAR The Solution Fit-Testing Hearing Protectors 27 28 Field Microphone In Real Ear F-MIRE Equipment Physical measurement of sound level Inside ear vs. outside ear Objective No need for worker to respond Fast External Mic Internal Mic Probed Earplugs 29 30 3M 2013. All rights reserved 5
Results Typical Earplug Fit Testing Results No Training 62% Needs Training Same Plug 21% New Plug 16% 31 32 Unfittable 1% Benefits of Fit Testing Earplugs NIOSH and OSHA: HPD Fit Testing is Best Practice Tool to train and motivate employees Provides means to train the trainer Permits appropriate assignment of HPDs OSHA Standard Threshold Shift follow up OSHA compliance in lieu of NRR Documentation for legal purposes https://c.ymcdn.com/sites/nhca.site-ym.com/resource/resmgr/imported/alliancerecommendationforfittesting_final.pdf 33 34 The Risks of Overprotection Communication Solutions Communication may be impaired Conversation Warning sounds Moderate attenuation devices Communication headsets Workers may fit HPDs incorrectly to enhance hearing Lower attenuation Workers may remove HPDs more often Reduced wear time 35 36 3M 2013. All rights reserved 6
Moderate & Low Attenuation HPDs Help Prevent Overprotection 37 38 Protective Communication Headsets Push-to-Listen 2-way radio Noise-reducing microphones Ambient listening Fast-acting impulse noise reduction Bluetooth wireless connections Localization Identifying which direction a sound is coming from may be easier with earplugs than with earmuffs 39 40 When wearers are allowed to choose from a variety of HPDs: Wear Time Increases More Effective Protection 41 3M 2013. All rights reserved 7