myths and misconceptions about hearing protection e-a-r 11-13/hp...
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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 46268-1657 desk: 317-692-3031
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.
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.
Myths and MisconceptionsAbout Hearing Protection
National Hearing Conservation Assoc., New Orleans, February 25, 2011Elliott 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 suchas 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 tofive 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 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.
ANSI standards on how to measure attenuation
EPA labeling regulation that requires attenuation bemeasured 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 HPDs are not considered to be medical devices
CPSC no requirements with respect to HPD performance
HPDs must be ANSI certified or otherwise approved
Relevant Standards Groups and Federal Agencies
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.
ANSI standards on how to measure attenuation
EPA labeling regulation that requires attenuation bemeasured 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 HPDs are not considered to be medical devices
CPSC no requirements with respect to HPD performance
HPDs must be ANSI certified or otherwise approved
Relevant Standards Groups and Federal Agencies
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.
The actual adjustment factor as well as the math underlying the NRR derives from NIOSH 76-120
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
OSHA’s 7-dB adjustment is a real-world correction
Background information:
Patricia Kroes, Roy Fleming, and Barry Lempert
76-120 is the source document for the math underlying the NRR.
The adjustment appears in the OSHA HCA Appendix B.
workplace noise effective employee exposure
Using the NRRUsing the NRR
dBC - NRR = dBA´
Real-world derating is a separate issueand is often recommended
Using the NRRUsing the NRR
dBC - NRR = dBA´
dBA - (NRR – 7) = dBA´
A better approach is fit testing.
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 160 – 170 dB SPL
The attenuation of an earmuff and earplug as measured by REAT is a valid indicator of their relative performance
Earmuffs block bone-conducted energy better than earplugs, and REAT cannot measure that effect
The facts are these:
REAT is valid for the way in which the HPDs were fit for the testing that was conducted.
Foam plug + Lead Muff
Used lead muff plus deep-insert plug to estimate BC limits
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 S12.6-2008 in3M’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 holdingat 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
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, sound-transmission, and amplitude-sensitive
Conventional HPDs – no electronics, no moving parts, simple sound barriers – provide level-independent attenuation up to about 160-170 dB peak SPL
Passivelevel-dependent earplugs
Activelevel dependent earmuff
Combat Arms – 0.3-mm ID hole in a 0.1-mm thick plate
North – elastic element constricted between two metal plates
Incident Sound Level (dB)
Inse
rtio
n L
oss
(d
B)
Level-Dependency of an Orifice0
10
20
30
40
50
Actual SPL
IL of unmodified HPD
IL of orifice increases 5 dB/10 dB
Transition
Range
17016015014013012011010090
IL at low SPL Transition SPL
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 110 – 120 dB SPL.
PositiveProvides better hearing when noise not present,
and can sound more natural.
Impulse Hearing Protectors
Neutral or Possibly NegativeNever more protective than, and possibly not as
protective as, a conventional HPD
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 S3.19-1974 and labeling ARE required.
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), 97-105.
2. ANSI (1974). "Method for the Measurement of Real-Ear Protection of Hearing Protectors and Physical Attenuation of Earmuffs," American National Standards Institute, S3.19-1974 (ASA STD 1-1975), New York, NY.
3. ANSI (2008). "Methods for Measuring the Real-Ear Attenuation of Hearing Protectors," American National Standards Institute, S12.6-2008, 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), 1655-1687.
5. Berger, E. H. (2010). "History and Development of the E-A-R Foam Earplug," Canadian Hearing Rept. 5(1), 28-34.
6. 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), 1955-1967.
7. EPA (1979). "Noise Labeling Requirements for Hearing Protectors," Environmental Protection Agency, Fed. Regist. 44(190), 40CFR Part 211, 56130-56147.
8. Gauger, D. and Berger, E. H. (2004). “A New Hearing Protector Rating: The Noise Reduction Statistic for Use with A Weighting (NRSA),” E•A•R 04-01/HP, 3M, Indpls., IN <www.e-a-r.com/hearingconservation/journal_main.cfm>
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. 76-120, Cincinnati, OH.
10. OSHA (1983). "Occupational Noise Exposure; Hearing Conservation Amendment; Final Rule," Occupational Safety and Health Administration, 29CFR1910.95 Fed. Regist. 48(46), 9738-9785.
11. Zera, J. (2007). “Attenuation of high-level impulses by earmuffs,” J. Acoust. Soc. Am. 122(4), 2082-2096.
References
Questions?
[email protected] Zionsville, Rd., Indianapolis, IN 46260
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