Transcript HEARING CONSERVATION & NOISE EXPOSURE

‫‪29 CFR 1910.95‬‬
‫برنامج الحفاظ على القوى السمعية‬
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‫‪Created By: C. Miterko‬‬
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What is Sound? ‫ما هو الصوت‬
•Sound is what we hear and
is produced by vibrating
objects and reaches the
listener’s ears as waves in the
air or other media.
•When an object vibrates it
causes slight changes in air
pressure. These air pressure
changes travel as waves
through the air and produce
sound.
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‫الصوت ينتج من إهتزاز األشياء‬
‫ويكون على هيئة موجات تصل‬
.‫إلى األذن‬
‫عندما تهتز األشياء يحدث نتيجة‬
‫لذلك تغيير بسيط فى ضغط‬
.‫الهواء‬
‫وهذا التغيير فى ضغط الهواء‬
‫ينتقل فى الهواء على شكل‬
‫موجات والتى بدورها تنتج‬
‫الصوت‬
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‫عندما يتم خبط الطبلة بواسطة العصاة ‪ ،‬يهتز سطح الطبلة وعندما يتحرك‬
‫سطح الطبلة لألمام يحدث تغيير موجب فى ضغط الهواء وعندما يتحرك‬
‫سطح الطبلة للوراء يحث تغيير سلبى فى ضغط الهواء وهكذا يتحرك هذا‬
‫الضغط على شكل موجات حتى يصل لألذن ونسمع الصوت‪.‬‬
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‫?‪What is Noise‬‬
‫الضوضاء هى األصوات غير‬
‫المرغوب بها‬
‫)‪Hertz (Hz‬‬
‫يقاس بوحدة الهيرتز وهى عدد‬
‫الذبذبات التى تنتج من تغيير ضغط‬
‫الهواء فى الثانية الواحدة‬
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‫‪Frequency‬‬
‫‪Humans can typically hear‬‬
‫‪between 20 - 20,000 Hz‬‬
‫تسمع األذن البشرية األصوات بين ‪– 20‬‬
‫‪ 20000‬هيرتز‬
‫التردد الخاص بالحديث العادى يكون فى‬
‫حدود ‪ 3000‬هيرتز‬
‫اإلنسان ذو الصحة الجيدة يمكنه أن يسمع‬
‫األصوات التى تحدث تغيير فى ضغط‬
‫الهواء يبلغ ‪0.00002 Pa‬‬
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‫ونظرا لصغر وحدات التغيير فى ضغط الهواء فقد تم إستعمال وحدة أكبر‬
‫تسمى الديسيبل ‪ dB‬وهى وحدة لوغاريتمية‪.‬‬
‫ولتحويل وحدات الضوضاء من باسكال إلى ديسيبل يتم إستخدام‬
‫المعادلة األتية‪:‬‬
‫‪dB = 20 log {sound pressure/Ref. Pressure (0.00002‬‬
‫})‪Pa‬‬
‫‪Sound pressure level in very quite room where the‬‬
‫‪sound pressure is 0.002 Pa is:‬‬
‫‪Lp (dB) = 20 log (0.002/0.00002) = 20 log 100 = 40 dB‬‬
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Common Sounds
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0 dB
Threshold of Hearing
30 dB
Soft Whisper
40 dB
Quiet Office
60 dB
Conversational Speech
80 dB
Very noisy restaurant
90 dB
Subway
110 dB
Woodworking
120 dB
Hydraulic press
140 dB
Threshold of Pain – Jet plane
180 dB
Rocket
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‫?‪How do we Hear‬‬
‫‪ -1‬األذن الخارجية تلتقط موجات الصوت‬
‫‪ -2‬تقوم الموجات بخبط طبلة األذن فتسبب إهتزازها‬
‫‪ -3‬تنتقل اإلهتزازات من طبلة األذن خالل المطرقة والسندان والركاب‬
‫‪ -4‬بعد ذلك تنتقل هذه الذبذبات إلى األذن الداخلية حيث توجد‬
‫الكوكيالة وبها ماليين الشعيرات الدقيقة التى تنقل هذه الذبذبات على‬
‫شكل نبضات إلى المخ وبالتالى نسمع الصوت‬
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Example
In the field, we determined the loudness of
two compressors right next to each other
89 dB
87 dB
How loud is this area?
– Do we add?
– Do we add and take the average?
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Neither, because it is a log scale
We use the following chart
Difference in dB
Values
Add to Higher
Level
0-1 dB
3 dB
2-3 dB
2 dB
4-9 dB
1 dB
10 dB or more
0 dB
82 dB + 83 dB = 86 dB
87 dB + 89 dB = 91 dB
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How does the Safety Person
determine noise levels
Sound level meter
– Determine the
loudness (dB) of
noise at any given
moment
‫يتم قياس الضوضاء بالمنطقة‬
‫بواسطة جهاز قياس‬
‫مستوى الضوضاء‬
‫القياس يكون لحظى‬
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Personal Dosimeters
– Worn by employees
– Measures the average
loudness in an 8 hour
work shift
“8hr. TWA” (Time
Weighted Average)
‫– يتم القياس بواسطة الدوزيميتر‬
‫ ساعات‬8 ‫– القياس يكون خالل‬
‫متوسط‬
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What does OSHA say?
At 85 dB (8hr. TWA) (Action level)
‫ متوسط‬8( ‫ ديسيبل‬85 ‫عندما تبلغ الضوضاء‬
‫ساعات) يعتبر هذا هو الحد الواجب إتخاذ قرار فيه‬
–
–
–
–
–
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Train employees
Make hearing protection available
Sample for noise levels
Do hearing tests
Notify employees of results
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Hearing Conservation Program
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Hearing Conservation Program
Monitoring:
Employers should monitor noise exposure
levels to identify employees who are
exposed to noise levels at or above 85
dBA averaged over 8 working hours, or
an 8-hour time-weighted average (TWA).
Noise level meters & Noise Dosemeter are
used after being calibrated.
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When the daily noise exposure has two or more
noise exposures at different levels, their
combined values should be considered. (Use the
following formula)
F(e) = (T(1) divided by L(1) + (T(2) divided by
L(2(( + ……… )T)n( divided by L)n((
F(e)= The equivalent noise exposure factor
T= The period of noise exposure at any essentially
constant level.
L= The duration of the permissible noise
exposure at the constant level.
If the value of F(e) exceeds unity (the value 1), the
exposure exceeds PEL.
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Example:
110 dbA 0.25 hours
100 dbA 0.5 hours
90 dbA 1.5 Hours
F(e) = (0.25/0.5) +
(0.5/2)+(1.5/8)
F(e)=0.5+0.25+0.1888
F(e) = 0.938
Since F(e) does not exceed
unity (1), the exposure
limit is within
permissible limits
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Duration Per
Day, Hours
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Sound Level
dBA
90
6
92
4
95
3
97
2
100
1½
1
102
¾
½
107
¼
115
105
110
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Audiometric Testing
• Should the noise level monitoring determine
that employees are being subjected to levels
equaling or exceeding a TWA of 85 dBA, the
next step is to establish an audiometric testing
program for those exposed at no cost to the
employee.
• The important elements of an audiometric
program include: Baseline audiograms, Annual
audiograms, Control measures, Training, and
follow-up procedures.
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Baseline Audiograms
•It is the reference audiogram
against which future audiograms
are compared.
•Must be provided within 6
months of an employee’s first
exposure at or above 8-hour TWA
of 85 dBA. (Control measures
should be taken)
•Baseline Audiogram must be
preceded by 14 hours without
exposure to workplace noise.
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Annual Audiograms
• After baseline audiogram has been taken,
each employee exposed to noise levels at
the 85 dBA or above shall have annual
examination.
• Annual audiogram must be conducted
within 1 year of the baseline.
• Compared with baseline audiograms
results.
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Continued
• To determine whether an employee has
experienced any recordable hearing loss.
• The hearing loss is reffered to in the
OSHA standard as :Standard Threshold
Shift (STS).
• OSHA defines STS as “a change in
hearing threshold relative to the baseline
audiogram of an average of 10 dB or
more at 2000, 3000, and 4000, Hz in
either ear.
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Example Baseline Audiogram
125
250
500
1K
2K
10
0
10
20
30
40
50
Baseline Audiogram
(The initial audiogram
taken by worker when
first employed.)
3K
4K
6K
8K
Annual Audiogram (Showing STS)
125
250
500
1K
2K
3K
4K
6K
8K
10
0
BASELINE
10
16
20
30
40
50
16 + 9 + 8 = 33
33 / 3 = 11
Reportable Loss? NO
STS ?
YES
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ANNUAL
Control
• The standard states that if the 90 dB PEL
is being exceeded, “feasible
administrative or engineering controls
shall be utilized.
• If fails, PPE shall be provided and used
to reduce sound levels.
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Administrative Controls
* Are defined as, “Methods of controlling
employee exposures by job rotation,
work assignment, or time periods away
from the hazards.
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Engineering Control
• Are defined as “ Methods of controlling
employee exposures by modifying the
source or reducing the quantity of
contaminants released into the workroom
environment.
• Example: installing noise – absorbing
acoustical foam or baffles to capture and
deaden reverberating noise.
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Hearing Protectors
• Hearing protectors shall be made
available and shall be worn by all
employees exposed to an 8-hour TWA of
85 dBA or greaters.
• Types of hearing protectors:
• Ear muffs
• Ear plugs
• Ear canal
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Examples of Hearing Protectors
Earmuffs
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Earplugs
Canal Caps
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Hearing Protection
NRR - Noise reduction rating
– Express - 25 NRR
– Classic - 29 NRR
– Max Lite - 30 NRR
DO NOT Subtract the NRR from the
noise level
– WRONG (109 dB - 25 NRR = 84 dB)
You must use the “Safety Factor”
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Safety Factor
OSHA says the hearing protection is
designed to reduce the noise by the
NRR, but that is unlikely to happen
due to :
– Leaks in the seal
– Vibration
– Improper insertion
(NRR - 7)
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Example of NRR Protection
The noise at a large compressor is
109 dB
You are wearing the Express plugs with
an NRR of 25
Do you have enough protection to place
you below 90 dB level?
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Training - Recordkeeping
• Employees training is very important. All
employees exposed to noise at a TWA of
85 dBA or greater shall participate in a
hearing conservation training program.
• An accurate records shall maintained of
all employee exposure measurements.
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