Transcript NOISE AND ACOUSTICS Noise-Induced

STOPPING NOISE-INDUCED
HEARING LOSS
Presented by Brad Witt
STOPPING NOISE-INDUCED HEARING LOSS
NIOSH Safe-In-Sound Award Recipient
▪ “Measurable achievements in reducing or eliminating noiseinduced hearing loss”
▪ 2011 industrial recipient: Shaw Industries Group Plant WM
▪ Elimination of noise-induced hearing loss
(see www.safeinsound.us)
NOISE AND ACOUSTICS
Hazardous noise exposures are cumulative
on the job ..…
and off the job.
NOISE AND ACOUSTICS
Noise-Induced Hearing Loss

Causes no pain

Causes no visible trauma

Leaves no visible scars

Is unnoticeable in its earliest stages

Accumulates with each over-exposure
Is permanent and 100% preventable
NOISE AND ACOUSTICS
Noise-induced hearing loss
is the most common
permanent and preventable
occupational injury in the world.
~ World Health Organization
1997 Report on Occupational Noise
NOISE AND ACOUSTICS
NON-OCCUPATIONAL
► 140 dB
Immediate physical damage
► 120 dB
Pain threshold
► 85 dB
OSHA Action Level
Hearing damage possible
► 60 dB
Comfortable noise level
NOISE AND ACOUSTICS
The decibel scale is a logarithmic scale,
not a linear scale
If the noise source is doubled
83 dB
The noise level only goes up 3 dB
86 dB
Small increases in decibel level
89 dB
Represent enormous increases in
noise level and risk
92 dB
NOISE AND ACOUSTICS
95
dB
92
dB
89
dB
86
dB
83
dB
NOISE AND ACOUSTICS
Sound Level Meter
vs.
Noise Dosimeter
“Area Sampling”
“Personal Sampling”
Sound is measured
immediately in a specific area
Sound is ‘averaged’ throughout the
day for a sample employee or job
photos courtesy of Quest Technologies
NOISE AND ACOUSTICS ~ Hierarchy of Controls
ENGINEERING
CONTROLS
• Buy Quiet
• Vibration Pads
• Enclosures
ADMINISTRATIVE
CONTROLS
• Rotate Workers
• Barriers
• Extended
Breaks
• Isolation
•2nd/3rd Shift
PERSONAL
PROTECTIVE
EQUIPMENT
EVALUATING NOISE REDUCTION
Noise Level =
100 dB
Noise Reduction Rating =
30 dB
How much noise is reaching
the ear of the worker ?
That is completely unknown …
(55 – 104 dB)
0 dB
0 dB
Which ear is protected?
33 dB
EVALUATING NOISE REDUCTION
The Noise Reduction Rating (NRR)

A laboratory estimate of the
amount of attenuation achievable
by most users when properly fit

A population-based rating …
some users will get more
attenuation, some will get less
The NRR is only a population estimate,
not a predictor of individual attenuation.
EVALUATING NOISE REDUCTION
Developing the NRR

10 human subjects tested in a
simulated industrial room

Tested with ears open / occluded at
nine frequencies

Each subject tested 3x

NRR calculated to be population
average
A test subject in the Howard Leight
Acoustical Lab, San Diego, CA, accredited
by the National Voluntary Laboratory
Accreditation Program (NVLAP)
NOISE _
NRR
LEVEL
=
SAFE
NOISE
?
NOISE _ HUMAN
=
FACTOR
LEVEL
?
SAFE
NOISE
EVALUATING NOISE REDUCTION
Real-World Protection May Not Equal NRR
192 users of a flanged multiple-use 27 dB earplug
50
Attenuation in dB
Multiple-Use Earplug Rated for 27 dB
40
30
20
Retraining and
refitting resulted
in an average
10
14 dB
improvement
0
in attenuation for
this group
-10
From Kevin Michael, PhD and Cindy Bloyer “Hearing Protector Attenuation Measurement on the End-User”
EVALUATING NOISE REDUCTION
The Biggest Factors in Achieving the NRR
1.FIT
2. WEAR TIME
30
A worker who selects an
earmuff with an NRR of 30
but then removes that
HPD for just …
effectively reduced his
8-hour NRR to just …
dB
5 min
10 min
15 min
30 min
19 dB
17 dB
15 dB
12 dB
In noise exposures, small intervals of no protection
quickly cancel large intervals of adequate protection.
EVALUATING NOISE REDUCTION
100 dB
30 dB = 1000x
90 dB
20 dB = 100x
10 dB = 10x
80 dB
3 dB = 2x
70 dB
60 dB
0
1
2
3
4
8-Hour Workday
5
6
7
8
EVALUATING NOISE REDUCTION
The Hazards of Overprotection

Choosing a protector with an NRR higher than necessary may
result in overprotection
 Verbal communication may be hindered
 Warning alarms, telephones, machine noises may not be heard
Insufficient Protection
Acceptable Protection
Optimal Protection
Acceptable Protection
Over Protection
dB
-85
-80
-75
-70
Worker Exposure
at the Ear With
Protectors
EVALUATING NOISE REDUCTION
The Noise Reduction Rating (NRR)
Current NRR Label
80th %
20th %
Minimallytrained
Proficient
Users
Mock-up of New Label
REDUCING COSTS & CLAIMS
REDUCING CLAIMS
Lagging Indicators vs Leading Indicators
REDUCING CLAIMS
Fit Testing
In-Ear Dosimetry
REDUCING CLAIMS
Variation from Published Rating
10
Published
Rating
0
-5
-10
-15
-20
Distribution of PARs
-25
12
-30
0
10
20
30
40
50
Workers
6010
Workers
Difference in dB
5
70
80
90
100
8
6
4
2
0
-30
-25
-20
-15
-10
-5
0
5
10
Variation from Published SNR
15
20
25
30
REDUCING CLAIMS
Personal Factors
Gender
What predicts a good fit?
Age
Years in Noise
Distribution of PARs
12
Ear Canal Size
Workers
10
8
Familiarity
6
Model of Earplug
4
2
Program Factors
0
-30
-25
-20
-15
-10
-5
0
5
10
Variation from Published NRR
15
20
25
30
# Group Trainings
# Personal Trainings
REDUCING CLAIMS
Difference on 2nd / 3rd Test
10
Variation from NRR
5
Published
Rating
0
-5
-10
-15
-20
-25
-30
Subjects
Trying a second earplug often improves attenuation
FIT TESTING
Complete
Check
● 5 freqs in
each ear
● Best for
new users,
reliability
checks
● ↑ accuracy,
↑ test time
Quick
Check
Report
Mode
● 1 critical
freq in each
ear
● Individual
● ↓ accuracy,
↓ test time
● Results
by freq
● Can use
with severe
hrg loss
● Historical
Fit Training
● Videos
REDUCING CLAIMS
Fit Testing
In-Ear Dosimetry

In-ear dosimetry measures actual noise dose,
with and without protection

Alerts when worker approaches safe limits

Only metric to measure and prevent further
progression of occupational hearing loss
IN-EAR DOSIMETRY
Dosimeter records …
• Good fit
• Bad fit
• No fit
Indicator lights give
immediate feedback of
noise level and dose
IN-EAR DOSIMETRY
Research > Alcoa Intalco Works
hearing threshold
and4kHz):
4 kHz) 2000 – 2007 (N = 46)
Mean HearingMean
Threshold
(2k,(2,3,3k,
Employees using continuous ESP starting in 2005
2000 - 2007 (N=46)
Employees using continuous in-ear dosimetry starting in 2005
50
ESP Introduced
Mean HTL 3,4,6kHz
45
trend line
40
35
30
25
20
15
10
5
0
2000
2001
2002
2003
2004
Year of test
2005
2006
2007
REDUCING CLAIMS
In practice, identifying a shift in hearing is not a preventive action ….
It is documentation of a hearing loss after the fact.
How soon will an employee suffering NIHL be re-fit / re-trained ?
“Best case scenario” per annual audiometric testing
In-ear dosimetry “worst case” scenario …
1 Day
0
2
• Retest
• Audiometric test
4
6
8
10
Months
12
14
• Notification
16
REDUCING CLAIMS
PROS
- Estimate
Measure
CONS
- Cost
- NRR obsolete
- Time Investment
- Eliminates need for de-ratings
- Not standardized
- Medico-legal cases
- Delineates non-occupational
- Eliminates double protection
- Provides employee feedback
REDUCING CLAIMS
Off-job + On-job
=
Shift
CASE STUDIES - CARPET MILL
NIOSH Safe-In-Sound Award Recipient
1. Engineering controls
Brought noise levels down to 100-104 dBA.
2. Annual fit-testing and training
Documented successful reduction of noise exposures
under the hearing protector below 85 dBA for all
employees.
3. End result: reduction of STS to zero in the most
recent years of annual audiometric testing.
CASE STUDIES – MILITARY INSTALLATION
U.S. Navy
▪ 60 sailors experienced in earplug use
- command-issued standard foam earplug
OR
- a second earplug of their choosing
▪ Prior to testing with the “variety” earplug, sailors received brief training
(less than one minute in duration) by someone modeling the correct fit of
that style of earplug.
▪ Despite no prior experience with the “variety” earplug, 45 of the 60 sailors
(75%) achieved higher attenuation with the variety earplug over the
command-issued earplug.
Median attenuation for ‘variety’ earplugs = 18 dB
Median attenuation for command-issued earplugs = 9 dB
CASE STUDIES - AEROSPACE
Fit-Testing / 1:1 Training
for 337 noise-exposed workers
Number of Employees
350
Did not meet 15 dB criterion
300
250
197
Met 15 dB criterion
200
150
110
100
50
75
140
87
0
1st Test
42% pass
2nd Test
44% pass
63
35
12
3rd Test
32% pass
4th Test
16% pass
60
3
5th Test
5% pass
CASE STUDIES - AEROSPACE
Pre-Test
Post-Test
1.
1.
Which type of hearing protectors do you normally
use on the job?
After this fit-test, are you better able to fit your
earplugs?
Don’t normally use
on-the-job, 16% Earmuffs, 8% -
Not sure, 1% No, 6% -
- Earplugs, 76%
2. How would you rate your ability to fit your earplugs?
2.
- Yes, 93%
Did you change your choice of earplugs as a
result of the fit-test?
Expert, 10% Don’t know how, 2% Poor, 1% Okay, 36% -
- Good, 51%
No, 37% -
- Yes, 63%
Hearing Loss Due To
Noise Exposure Is …
Painless
Permanent
Progressive
… and very Preventable!