Myths and Misconceptions about Hearing Protection E-A-R 11-13/HP. E. H. Berger, M.S.

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1 Myths and Misconceptions about Hearing Protection E-A-R 11-13/HP E. H. Berger, M.S. M 3M Occupational Health & Environmental Safety Division E A RCAL Laboratory 7911 Zionsville Road Indianapolis, IN desk: Elliott.Berger@mmm.com October 6, 2011 Version 1.2 Presented at the National Hearing Conservation Association, New Orleans, LA, February 2012 Spectrum Vol 29, Supplement III, p. 34.

2 Myths and Misconceptions about Hearing Protection As someone who has kept up with the literature in the field of hearing conservation for over 30 years, I have had the opportunity to learn much, but also to observe common myths and misconceptions that cause confusion in the application of hearing protection devices (HPDs). This talk will address five common fallacies: 1) HPDs must be ANSI certified or otherwise approved (false in the U. S.); 2) The 7-dB correction used when applying the NRR is a real-world correction (false); 3) Earmuffs provide better protection than earplugs from sound that excites the bone-conduction pathways, and real-ear attenuation at thresholds tests cannot reveal these bone-conduction issues (mostly false); 4) For the best fit and protection, roll-down foam earplugs must be held in place during expansion in the earcanal (false); 5) Level-dependent HPDs are designed for impulse noise and therefore provide better protection from gun shots and blasts than conventional passive (non-electronic) HPDs (false). Explanations will be provided to unravel these statements and clarify the facts. Learning Objectives: 1. Understand the reason for and application of the 7-dB correction for use with the NRR. 2. Be able to describe the relative effectiveness of earplugs vs. earmuffs in blocking bone-conducted sound transmission. 3. Understand the limitations of level-dependent HPDs and which type of HPD provides the most protection from blast noise.

3 Myths and Misconceptions About Hearing Protection National Hearing Conservation Assoc., New Orleans, February 25, 2011 Elliott Berger, Indianapolis, IN Having worked in our field for many years, I have had the opportunity to read the literature, conduct my own research, collaborate with many bright people, and attend conferences such as this one. I have been able to sort the wheat from the chaff. My intent today is to share some of those learnings with respect to five common myths and misconceptions related to hearing protection.

Myths and Misconceptions HPDs must be ANSI certified or otherwise approved The OSHA 7-dB adjustment factor is a real-world correction Earmuffs block bone-conducted energy better than earplugs

4 Myths and Misconceptions HPDs must be ANSI certified or otherwise approved The OSHA 7-dB adjustment factor is a real-world correction Earmuffs block bone-conducted energy better than earplugs especially at high levels, and REAT cannot measure this effect Roll-down foam plugs must be held in place during expansion Level-dependent ( nonlinear ) HPDs provide more protection from impulse noise (gunshots) than do simple plugs or muffs The five topics to be discussed are outlined on this first slide.

5 HPDs must be ANSI certified or otherwise approved Relevant Standards Groups and Federal Agencies ANSI standards on how to measure attenuation EPA labeling regulation that requires attenuation be measured and reported OSHA specifies use of HPDs above Action Level, and defines how to determine HPD suitability MSHA specifies use of HPDs above Action Level NIOSH best practice guidance; no requirements or regulations NVLAP accredits laboratories, not their test results FDA CPSC HPDs are not considered to be medical devices no requirements with respect to HPD performance The most common representation of this assertion is in manufacturer s literature where sometimes it is implied or stated that their HPDs are ANSI or OSHA approved. Another issue is that customers may ask for or require use of approved or certified devices.

6 HPDs must be ANSI certified or otherwise approved Relevant Standards Groups and Federal Agencies ANSI standards on how to measure attenuation EPA labeling regulation that requires attenuation be measured and reported OSHA specifies use of HPDs above Action Level, and defines how to determine HPD suitability MSHA specifies use of HPDs above Action Level NIOSH best practice guidance; no requirements or regulations NVLAP accredits laboratories, not their test results FDA CPSC HPDs are not considered to be medical devices no requirements with respect to HPD performance The most common representation of this assertion is in manufacturer s literature where sometimes it is implied or stated that their HPDs are ANSI or OSHA approved. Another issue is that customers may ask for or require use of approved or certified devices.

7 OSHA s 7-dB adjustment is a real-world correction Background information: The actual adjustment factor as well as the math underlying the NRR derives from NIOSH The adjustment factor provides the best agreement, when used with dba, between a NIOSH-style single-number rating and a long-method octave-band computation The adjustment has nothing to do with real-world use/misuse of HPDs Patricia Kroes, Roy Fleming, and Barry Lempert is the source document for the math underlying the NRR. The adjustment appears in the OSHA HCA Appendix B.

8 Using the NRR dbc - NRR = dba workplace noise effective employee exposure

9 Using the NRR dbc - NRR = dba - (NRR 7) = dba dba Real-world derating is a separate issue and is often recommended A better approach is fit testing.

10 Earmuffs block bone-conducted energy better than earplugs, and REAT cannot measure that effect The facts are these: The small area of coverage of the skull by earmuff cushions does not substantially affect airborne excitation of those areas REAT (real-ear attenuation at threshold) is the gold standard for measuring HPD attenuation REAT is based on subjective thresholds, i.e., response of the cochlea; it accounts for all pathways including BC REAT is valid up to the point at which conventional HPDs become level-dependent, about db SPL The attenuation of an earmuff and earplug as measured by REAT is a valid indicator of their relative performance REAT is valid for the way in which the HPDs were fit for the testing that was conducted.

12 Foam plug + Lead Muff Used lead muff plus deep-insert plug to estimate BC limits

14 Roll-down foam plugs must be held during expansion This idea originated in the early 1970s Another potential reason for the misconception is illustrated in the next slide.

Key Experimental Details Laboratory testing according to ANSI S12.

16 Key Experimental Details Laboratory testing according to ANSI S in 3M s E A RCAL facility Test conditions: Method A, w/pinna pull (trained fit, n = 16) Method B (inexperienced-subject fit, n = 15) In each test the same subjects did both the hold and the no-hold Presentation order was counter balanced Paired t-tests indicated no significant effect of holding at any frequency Illustration of the Method-B Instructions Only about ½ of Method-B subjects followed instructions About ½ of Method-B subjects pulled pinna

17 More important is to teach correct tight, smooth, and crease-free roll downs and the correct pinna pull

Level-dependent HPDs provide better protection from impulse noise than simple earplugs or earmuffs Other common terms describing level dependency are, nonlinear,

18 Level-dependent HPDs provide better protection from impulse noise than simple earplugs or earmuffs Other common terms describing level dependency are, nonlinear, sound-transmission, and amplitude-sensitive Conventional HPDs no electronics, no moving parts, simple sound barriers provide level-independent attenuation up to about db peak SPL

19 Active level dependent earmuff Passive level-dependent earplugs Combat Arms 0.3-mm ID hole in a 0.1-mm thick plate North elastic element constricted between two metal plates

20 Insertion Loss (db) Level-Dependency of an Orifice IL at low SPL Transition Range 120 Transition SPL IL of unmodified HPD Incident Sound Level (db) Actual SPL IL of orifice increases 5 db/10 db NOTE: Level-dependent HPD may reach, but will never exceed the attenuation of conventional HPD Level-dependent HPDs include a sound bypass to let sound in at lower levels This can be accomplished passively (by mechanical design) or actively (by electronics using a power source such as a battery) Sound = movement of air molecules; orifice create turbulent air flow Key point level dependency in passive HPDs does not begin until about db SPL.

21 Impulse Hearing Protectors Positive Provides better hearing when noise not present, and can sound more natural. Neutral or Possibly Negative Never more protective than, and possibly not as protective as, a conventional HPD

22 Summary Remarks In North America HPDs do not require certification OSHA s 7-dB adjustment is not a correction for real-world performance, rather it is a function of using the NRR with dba vs. dbc Muffs and plugs are about equal in blocking bone-conducted sound, and their relative performance can be properly measured via the standardized REAT procedure No evidence was found for the need to hold a roll-down earplug during expansion; key factors for fit are the roll down and the pinna pull Level-dependent HPDs do not provide more protection from impulses than conventional HPDs, rather they let you hear better between the impulses, that is, during the quiet times Though certification is not required testing to ANSI S and labeling ARE required.

23 References 1. Allen, C. H. and Berger, E. H. (1990). "Development of a Unique Passive Hearing Protector with Level-Dependent and Flat Attenuation Characteristics," Noise Control Eng. J. 34(3), ANSI (1974). "Method for the Measurement of Real-Ear Protection of Hearing Protectors and Physical Attenuation of Earmuffs," American National Standards Institute, S (ASA STD ), New York, NY. 3. ANSI (2008). "Methods for Measuring the Real-Ear Attenuation of Hearing Protectors," American National Standards Institute, S , New York, NY. 4. Berger, E. H. (1986). "Review and Tutorial - Methods of Measuring the Attenuation of Hearing Protection Devices," J. Acoust. Soc. Am. 79(6), Berger, E. H. (2010). "History and Development of the E-A-R Foam Earplug," Canadian Hearing Rept. 5(1), Berger, E. H., Kieper, R. W., and Gauger, D. (2003). "Hearing Protection: Surpassing the Limits to Attenuation Imposed by the Bone-Conduction Pathways," J. Acoust. Soc. Am. 114(4), EPA (1979). "Noise Labeling Requirements for Hearing Protectors," Environmental Protection Agency, Fed. Regist. 44(190), 40CFR Part 211, Gauger, D. and Berger, E. H. (2004). A New Hearing Protector Rating: The Noise Reduction Statistic for Use with A Weighting (NRS A ), E A R 04-01/HP, 3M, Indpls., IN < 9. Kroes, P., Fleming, R., and Lempert, B. (1975). "List of Personal Hearing Protectors and Attenuation Data," National Institute for Occupational Safety and Health, U.S. Dept. of HEW, Rept. No , Cincinnati, OH. 10. OSHA (1983). "Occupational Noise Exposure; Hearing Conservation Amendment; Final Rule," Occupational Safety and Health Administration, 29CFR Fed. Regist. 48(46), Zera, J. (2007). Attenuation of high-level impulses by earmuffs, J. Acoust. Soc. Am. 122(4),

Questions? elliott.berger@mmm.com 7911 Zionsville, Rd.

24 Questions? 7911 Zionsville, Rd., Indianapolis, IN M, E-A-R, Classic, TaperFit and the color yellow for earplugs are trademarks of 3M Company, used under license in Canada. Peltor is a trademark of 3M Svenska AB, used under license in Canada.

Introducing F-MIRE Testing - Background and Concepts E-A-R 06-29/HP. E. H. Berger, M.S.

Introducing F-MIRE Testing - Background and Concepts E-A-R 06-29/HP E. H. Berger, M.S. E A R / Aearo Technologies E A RCAL SM Laboratory 7911 Zionsville Road Indianapolis, IN 46268-1657 phone: 317-692-1111