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Kebisingan Industri
Definisi dan pengertian
 Bising = suara-suara yang tidak
dikehendaki
 Definisi secara ilmiah = sensasi yang
diterima telinga sebagai akibat fluktuasi
tekanan udara ‘superimposing’ tekanan
atmosfir/udara yang steady
 Bising = sejenis vibrasi/energi yang
dikonduksikan dalam media udara,
cairan, padatan, tidak tampak, dan dapat
memasuki telinga serta menimbulkan
sensasi pada alat dengar
Inside NOISE
What is noise?
– Definition, energy conducted and sensed, properties:
intensity/pressure, frequency, exposure,
Why unwanted?
– Health Effect, age, psychological: annoyed, concentration,
rest/relax problem, communication annoyance,
physiological: blood, heart, hearing loss, nausea, muscle
control, acoustic trauma (permanent) vs temporary,
Who are susceptible?
– Esp. Industrial workers, determining factors: sensitivity,
age,
How to evaluate & control?
What is noise?
Definisi:
 Suara-suara yang tidak dikehendaki (for
Who? Why?)
 Suara: sensasi yang diterima telinga
sebagai akibat fluktuasi tekanan udara
terhadap tekanan udara yang stabil.
 Telinga akan merespons fluktuasi-fluktuasi
kecil tersebut dengan sensitivitas yang
sangat besar.
Properties of noise?
Karakteristik bising
1.
Intensitas/tekanan (sound
pressure/intensity)
2. Frekuensi
3. Durasi eksposur terhadap bising
Ketiga karakteristik diperlukan karena:
 Semakin keras suara, semakin tinggi
intensitasnya
 Frekuensi tinggi lebih berbahaya
terhadap kemampuan dengar. Telinga
manusia lebih sensitif terhadap
frekuensi tinggi
 Semakin lama durasi eksposur semakin
besar kerusakan pada mekanisme
pendengaran
Jenis Bising
 Tergantung pada durasi dan frekuensi
 Steady wide band noise, bising yang meliputi
suatu jelajah frekuensi yang lebar (bising dalam
ruang mesin)
 Steady narrow band noise, bising dari sebagian
besar energi bunyi yang terpusat pada beberapa
frekuensi saja, contoh gergaji bundar.
 Impact noise, kejutan singkat berulang, contoh
riveting
 Intermitten noise, bising terputus, contoh lalu
lintas pesawat
Contoh…
Tekanan = Sound Pressure
 Manusia dapar mendengar suara pada tekanan
antara 0,0002 dynes/cm2 (ambang
dengar/threshold of hearing) sampai 2000
dynes/cm2  range besar sehingga satuan
yang dipakai dB (decibel): logaritmik
 Dinyatakan dalam decibel (dB) yang dilengkapi
skala A, B, dan C
 sesuai dengan berbagai kegunaan
 Skala A digunakan karena merupakan response
yang paling cocok dengan telinga manusia
(peka terhadap frekuensi tinggi)
 Skala B dan C untuk evaluasi kebisingan
mesin, dan cocok untuk kebisingan frekuensi
rendah
Intensitas
 Laju aliran energi tiap satuan luas yang dinyatakan dalam
desibell (dB) – Alexander Graham Bell dB adalah merupakan satuan yang dihasilkan dari
perhitungan yang membandingkan suatu tekanan suara
yang terukur terhadap suatu tekanan acuan (sebesar
0,0002 dyne/cm2).
 B = log (int.terukur/int.acuan) untuk mendapatkan angka
yang lebih akurat ditentukan dengan angka kelipatan 10
(desi)
 Intensity level dB=10 Log (IT/IA)
 Sound pressure level (tekanan bunyi) = 20 log (IT/IA),
karena intensitas sebanding dengan kuadrat tekanan
bunyi.






Ruang kelas: ?dB
Rumah
Restauran
Berbisik
Berteriak
Jet plane
The decibel
SOUND INTENSITY
SOUND SOURCE

LINEAR UNITS
Bel
LOGARITHMIC UNITS
Decibel
Lowest limit of hearing
1
0
0
Rustling leaf
10
1
10
Quiet farm setting
100
2
20
Whisper (5 feet)
1,000
3
30
Dripping faucet, quite office
10,000
4
40
Low conversation, residence
100,000
5
50
Ordinary conversation
1,000,000
6
60
Idling car
10,000,000
7
70
Silenced compressor, very noisy restaurant
100,000,000
8
80
Backhoe
1,000,000,000
9
90
Unsilenced compressor
10,000,000,000
10
100
Rock dril, woodworking
100,000,000,000
11
110
Pile driver*
1,000,000,000,000
12
120
Rivet gun*
10,000,000,000,000
13
130
Explosive-actuated tool*, jet plane
100,000,000,000,000
14
140
*Intermittent or "impulse" sound
Source: Construction Safety Association of Ontario, Hearing Protection for the Construction Industry, 1985, page 3
The decibel
 dB = 10 log10 (I1/I0)
dB = 20 log10 (P1/P0)
I = Intensitas
P= Tekanan = 0,0002
dynes/cm2
SP (microbar)
0,0002
0,002
SPL (dB)
0
20
Ratio Intensitas
100
102
Jadi bila SP berubah 10x, maka dB bertambah ? x
Pressure
Sound intensities
Pa
Bel (B) Decibel (dB)
Threshold of hearing
0,00002
0
0
Quiet office
0,002
4
40
Ringing alarm clock at 1 m
0,2
8
80
Ship's engine room
20
12
120
Turbo jet engine
2000
16
160
Frekuensi
Adalah jumlah getaran dalam tekanan
suara per satuan waktu (Hertz atau cycle
per detik), frekuensi dipengaruhi ukuran,
bentuk dan pergerakan sumber,
pendengaran normal orang dewasa dapat
menangkap bunyi dengan frekuensi 2015.000 Hz.
Frekuensi
 Dibagi dalam 8 octaf (octave bands), 37.5,
75, 150, 300, 600, 1200, 2400, 4800, 9600 Hz
 Telinga manusia bereaksi beda terhadap
berbagai frekuensi
 Kebisingan ‘rata-rata’ mencakup seluruh
taraf kebisingan dari setiap frekuensi 
dihitung Leq
Leq = ekuivalen noise level/ekuivalen energi
level
Leq = 10 log10 (Σ 10 Lpi/10)
Satuan (Konversi)
1bar=105Pa=105N/m2

=105.105dyne/104cm2

=106dyne/cm2 atau
1microbar = 1 dyne/cm2
Sumber > 1…..
dB=L=20 log(P1/P2)=10 log(P1/P2)2
L/10= log(P1/P2)2
10L/10= 10log(P1/P2)^2=(P1/P2)2
L=10 log(P1/P2)2
 =10 log 10L/10 (satu sumber)
L =10 log (Σ10Li/10) (sumber banyak)
 =10 log (10L1/10+ 10L2/10+…)
Sumber > 1….. (Contoh)
 =10 log (Σ10Li/10)
(banyak sumber)
 =10 log (10L1/10+
10L2/10+…)
Perbedaan
antara sumber
bunyi
ΣdBA yang turun
ditambah ke
bunyi terbesar
0
3,0
1
2,6
2
2,1
3
1,8
4
1,5
5
1,2
6
1,0
7
0,8
8
0,6
10
0,4
12
0,3
14
0,2
16
0,1
Satuan (Konversi)
1bar=105Pa=105N/m2

=105.105dyne/104cm2

=106dyne/cm2 atau
1microbar = 1 dyne/cm2
Sumber > 1…..
dB=L=20 log(P1/P2)=10 log(P1/P2)2
L/10= log(P1/P2)2
10L/10= 10log(P1/P2)^2=(P1/P2)2
L=10 log(P1/P2)2
 =10 log 10L/10 (satu sumber)
L =10 log (Σ10Li/10) (sumber banyak)
 =10 log (10L1/10+ 10L2/10+…)
Sumber > 1….. (Contoh)
 =10 log (Σ10Li/10)
(banyak sumber)
 =10 log (10L1/10+
10L2/10+…)
Perbedaan
antara sumber
bunyi
ΣdBA yang turun
ditambah ke
bunyi terbesar
0
3,0
1
2,6
2
2,1
3
1,8
4
1,5
5
1,2
6
1,0
7
0,8
8
0,6
10
0,4
12
0,3
14
0,2
16
0,1
Decibel yang ditambahkan pada
tingkat kebisingan lebih tinggi
Kebisingan dari 2 sumber
3
2,5
2
Perbedaan
(dB)
Tambah pada yg
lebih tinggi
0 atau 1
3
2 atau 3
2
4–9
1
10+
0
1,5
1
0,5
2
4
6
8
10
12
14
Perbedaan antara 2 tingkat bising, dB(A)
Why unwanted?
Health Effect, age, psychological:
annoyed, concentration, rest/relax
problem, communication annoyance,
physiological: blood, heart, hearing loss,
nausea, muscle control, acoustic trauma
(permanent) vs temporary,
Efek bising pada manusia
 Psikologis, terkejut, mengganggu dan
memutuskan konsentrasi, tidur dan saat
istirahat
 Fisiologis, seperti menaikkan tekanan
darah dan detak jantung, mengurangi
ketajaman pendengaran, sakit telinga,
mual, kendali otot terganggu, dll.
 Gangguan komunikasi yang
mempengaruhi kenyamanan kerja dan
keselamatan.
Interference with communication by
speech
 When background or ambient noise levels are
sufficiently high enough, the background noise can
mask the sound levels of speech that wish to be
heard.
 Restaurants can often be classic examples of
excessive noise interference due to lack of
sufficient quality or quantity of sound absorbing
materials that prevent excessive noise buildup.
 Diners have to speak louder and louder to be heard
and in doing so compete with one another, thereby
increasing the sound levels to even greater levels.
Appropriate acoustical treatment will prevent the
reflected noise buildup and significantly reduce the
necessity for diners to speak louder to enjoy
conversations with one another.
Mechanics of hearing

Mekanisme pendengaran
• Terdiri dari 3 bagian: telinga luar (daun telinga
sampai membran timpani) meneruskan
gelombang ke telinga tengah
• Telinga tengah: membran timpani (yang
melekat pada 3 tulang kecil sampai membrana
ovale)  getaran diteruskan
• Telinga dalam: tube berspiral seperti rumah
siput berisi cairan  cairan bervibrasi 
stimulasi rambut sel  impuls syaraf otak
Gangguan pendengaran
Pemaparan pada suara tinggi dan
periode/durasi yang lama akan
menyebabkan sel syaraf pendengar dan
rambut pada corti over aktif sehingga
menimbulkan kehilangan pendengaran
permanen
Pengukuran kebisingan
• Mengukur overall level  sound level
meter (satuan dBA)
• Mengukur kebisingan pada setiap level
frekuensi  SLM dengan frequency
analyzer
• Penentuan eksposur kebisingan pada
pekerja  noise dosimeter (satuan dBA)
Alat ukur
 Sound level meter, mencatat keseluruhan
suara yang dihasilkan tanpa memperhatikan
frekuensi yang berhubungan dengan bising
total (30-130 d) – (20-20.000Hz)
 Sound level meter dengan octave band
analyzer, mengukur level bising pada berbagai
batas oktaf di atas range pendengaran manusia
dengan mempergunakan filter menurut oktaf
yang diinginkan (narrow band analyzers untuk
spektrum sempit 2-200 Hz)
NOISE
MEASUREMENT
KIT
NOISE KALIBRATOR
SOUND
LEVEL
METER
NOISE DOSIMETER
PENGUKURAN PADA
PEKERJA
DOSEBADGER
Pneumatic
chip hammer
103-113
Crane
90-96
Jackhammer
102-111
Hammer
87-95
Concrete joint
cutter
99-102
Gradeall
87-94
Skilsaw
88-102
Front-end
loader
86-94
Stud welder
101
Backhoe
84-93
Bulldozer
93-96
Garbage
disposal (at 3
ft.)
80
Earth Tamper
90-96
Vacuum
cleaner
70

Pengukuran akibat bising
Untuk mengevaluasi akibat pemaparan
terhadap kehilangan pendengaran,
kenyamanan, interferensi komunikasi
dan mengumpulkan informasi untuk
pengontrolan.
How Does Excessive Noise
Damage Your Ears?
 Microscopic hair cells of the cochlea are
exposed to intense noise over time
 Hair cells become fatigued and less responsive,
losing their ability to recover.
 Damage becomes permanent resulting in noiseinduced permanent threshold shift.
 Risk of Hearing Loss
 Estimated Risk of Incurring Material Hearing
Impairment as a Function of Average Daily
Noise Exposure Over a 40-year Working
Lifetime (source: NIOSH)
 Average Exposure 90 dBA 29%
 Average Exposure 85 dBA 15%
 Average Exposure 80 dBA 3%
Ketulian
= berkurangnya
ketajaman pendengaran
dibanding/terhadap orang normal (15 dB)/ gol usia
• Ada 2 macam:
- permanen: karena penyakit, usia tua, obat, trauma, dan
kebisingan
- temporer: akibat ekposur bising, dapat pulih setelah
istirahat beberapa saat tergantung keparahan
• Ketulian temporer akan menjadi permanen bila terus
terekpos bising (dari rumah, tempat umum, rekreasi,
musik, industri, dll.)
• Secara mekanisme: ketulian ada 2:
- konduktif: peralatan konduksi suara rusak akibat
trauma atau sakit
- sensorinueral: akibat persyarafan pendengaran rusak
Audiometric test

Audiometric test

Audiometric test
Current OSHA Standards
•1926.52 Occupational Noise Exposure
•TABLE D-2 - PERMISSIBLE NOISE EXPOSURES
Duration per day, hours
Sound Level dBA slow
response
8
90
6
92
4
95
3
97
2
100
1 1/2
102
1
105
1/2
110
1/4 or less
115
What Is The Purpose of Having a
Hearing Test on a Regular Basis?
 An audiometric testing program is used to track
your ability to hear over time.
– Baseline and annual
 Test records provide the only data that can be
used to determine whether the program is
preventing noise-induced permanent threshold
shifts. It is an integral part of the hearing
conservation program.
 Case Study 1. Teenage Girl
From the American Academy of Family
Physicians website, Rabinowitz article
FIGURE 1. Audiogram findings in the patient in
case 1.
The area below the curves represents sound levels that the patient could still
hear.
(X = left ear; O = right ear)
Case Study 1 Conclusion
 "Temporary threshold shift" example
 Common in persons exposed to high
noise
 Represents transient hair cell
dysfunction
 Complete recovery can occur
 Repeated episodes of such shifts
causes permanent threshold shifts
because hair cells in the cochlea are
progressively lost.
Case Study 2 Factory Worker Age 55
Case Study 2 Conclusion
 Noise Induced Hearing Loss
– Speech discrimination and social function
interference
– Difficulty in perceiving and differentiating consonant
sounds
– Sounds such as a baby crying or a distant telephone
ringing, may not be heard at all.
 Tinnitus
– Common symptom of noise overexposure
– Further interferes with hearing acuity, sleep and
concentration.
 These impairments have been associated with
depression and an increased risk of accidents.
Carpenter Hearing Losses by Age
Damage risk criteria
 Variation in individual susceptibility
 The total energy of the sound
 The frequency distribution of the sound
 Other characteristics of the noise
exposure, such as whether it is
continuous, intermittent, or made up of a
series of impacts
 The total daily time of exposure
 The length of employment in the noise
environment.
Noise control
A source radiating sound energy
A path along which the sound
energy travels
A receiver such as the human ear
Pengendalian kebisingan
SUMBER
PATHWAY/MEDIA
PENERIMA/RECEIVER
Pengendalian dilakukan di 3 bagian: SUMBER, RUANG
ANTARA sumber dan penerima/pekerja, pada
PENERIMA/PEKERJA
Urutan pengendalian paling efektif:
• Kurangi/hilangkan sumber bising
• Pengendalian pathway: jarak diperjauh dengan
perisai/isolator/automatisasi
• Perlindungan penerima dari bising (APD)
•Cara teknis:
SUMBER
PATHWAY
PENERIMA
Substitusi
Absorpsi/damping
Isolasi pekerja
Insulasi sumber
Perisai
Reduksi waktu
Perpanjang jarak
APD
•Cara medis:
Pemeriksaan ketajaman pendengaran secara periodik
Penempatan pekerja sesuai dengan kepekaan thd bising
Monitor ketulian temporer
•Cara manajemen:
Reduksi waktu eksposur
Diklat pemakaian dan pemeliharaan APD
Noise control
Source: modification or
redesigning of the source.
–
–
The modification of compressed air jets for parts
ejection, to reduce noise by altering the jet flow.
Multiple-opening air ejection nozzel: less noise than
single-opening.
Noise control
 Noise can be controlled at the source, along the
path or at the worker.
 At the source, equipment may be replaced by
quieter models, or less noisy work procedures
can be adopted.
- In general, less friction and vibration mean
less noise. Maintenance procedures such as
lubrication may sometimes reduce noise by
reducing friction.
- Equipment can sometimes be modified to
reduce the amount of noise that is generated.
Sound-absorbing material may be attached to
the noise source. Or the frequency of the noise
may be shifted to one that is less hazardous.
Noise control
 Noise can often be controlled along the
path to the worker with:
- the use of sound-absorbing paneling
on walls or ceilings, and
- enclosures around noisy machinery.
 Controls at the worker include both
administrative controls and personal
protective equipment.
– Administrative controls modify how the work
is carried out.
– The time employees spend in noisy areas
may be reduced.
– Workers in noisy areas may be rotated to
less noisy areas.
As the distance from the noise source increases, the
pressure (or intensity) of the noise decreases faster than its
sound level.
Noise control
Noisy operations may be
conducted outside normal working
hours to reduce the number of
people exposed.
Where noise exposures cannot be
reduced by other methods, hearing
protection is required. This
includes ear plugs and ear muffs.
Insulation of the workers
A separate noise insulated room
provides effective control (up to 30
dB noise reduction).
Machine insulation
Machine: on floors and walls
vibrate themsound radiation
proper use of machine mountings
insulates the machine and reduce
the transmission of vibration
Control of noise by absorption
Travels out in all direction
When encounter wallsreflected
Total noise exposure within the
room = direct + reflected noise
Application of sound absorption
material (However, limited: no
effect on direct noise).
Reduction of exposure time
Limiting the total daily exposure
reduces the noise hazard.
See TLV
Personal protection against noise
Many operations cannot be quieted
by engineering methods.
Therefore  protection: ear plugs
Properly worn: 25 – 400 dB
protection
Degree of discomfort  employee
education is adequate
Example….
 Durasi tingkat bising yang
diijinkan dapat dilihat dari
tabel di bawah ini:
 Kebisingan yang terukur di
suatu area adalah 90 dB
selama 2 jam sehari, 97 dB
selama 2 jam, dan sisa 4
jam berikutnya terdapat
variasi tingkat bising
secara bergantian 95 dB
selama 10 menit dan 80 dB
selama 10 menit.
Tentukan apakah tingkat
kebisingan yang terukur
masih dalam batas yang
diijinkan atau tidak.
Durasi per
hari
Tingkat
bising
8
6
4
3
2
1,5
1
¾
½
¼
90
92
95
97
100
102
105
107
110
115
Faktor-faktor yang mempengaruhi
bising
Tipe bising: menerus dan terputus
Lokasi pekerja
Waktu kerja
NAB Kebisingan di lingkungan kerja
USA (TLV ACGHI)
t (eksposur) jam dB(A)
8
90
6
92
4
95
3
97
2
100
1,5
102
1
105
0,5
110
<0,25
115
kebisingan impulsif < 140 dB
INDONESIA Permen 51/1999
t
dBA
8
85
4
88
2
91
1
94
30 mnt
97
15 mnt
100
7,5 mnt
103
3,75 mnt
106
1,88 mnt
109
dst
dilarang > 140 dB
Waktu pemaparan vs dB (TLV)
Waktu pemaparan (jam)
dB
8
6
4
2
1,5
1
0,5
<0,25
90
92
95
100
102
105
110
115
(Sumber: FHI)
Steps aiming to control noise at
work
 Assess risks to develop a noise control
plan
 Reduce risks for all employees
 Investigate and implement good practice
for control of noise
 Prioritise noise control measures
 Use hearing protection for residual risks
 Carry out a noise dosimetry program to
check the effectiveness of noise control
measures
Some simple noise control
techniques
 Application of damping material to
chutes, hoppers, machine guards etc.,
can give a 5-25 dB reduction in the noise
radiated
 Cabin internal noise can be reduced by
10-12 dB by applying damping pads and
sound barrier mats to floor and engine
bulkhead
 Reduce fan speed by 30% to achieve a
noise reduction of 8 dB
BARRIER-BARIER ATAU PANEL
ISOLASI PEKERJA/MESIN DI TEMPAT BISING
BAHAN ABSORBER
BAHAN BARRIER
Noise control can be complex
Engage
employees in
process
Use noise control
consultants to
help solve your
problems if
complex
Hearing protectors
 Selected for protection, user preference
and work activity
 Guard against over-protection — isolation
can lead to under-use and safety risks
 Require information, instruction,
training, supervision and motivation
 Will only protect if worn all the time and
properly
Rating hearing protectors
The sound level conversion (SLC80 ) rating of a
hearing protector, ear plugs or headset is a simple
number and class rating that is derived from a test
procedure as outlined in the Australian/New Zealand
Standard AS/NZS 1270:2002
Class and specification of
hearing protectors
Class
May be used up to this
noise exposure level
10 to 13
1
90 dB(A)
14 to 17
2
95 dB(A)
18 to 21
3
100 dB(A)
22 to 25
4
105 dB(A)
26 or
greater
5
110 dB(A)
SLC80
Ear plugs
Properly fitted
Wrongly fitted
Ear muffs
Proper clamping force
Worn-out head band
Reduction in protection provided by
hearing protectors with decreased
wearing time
Example:
Effectiveness of
wearing an ear
muff with a rating
of 30 dB for an
exposure time of
one hour
Wear time
Effective
attenuation
60 minutes
30 dB
55 minutes
11 dB
50 minutes
8 dB
45 minutes
6 dB
Our challenge
Away from …
 Noise assessment as the end point
 Reliance on hearing protection
Towards …
 Control of noise risks through prioritised
action plans
 Introducing equipment with good noise
and vibration characteristics – ‘Buy
Quiet’
TWA untuk kebisingan: berdasarkan standar
kebisingan.
STANDAR
KEBISING
AN
dB(A)
1 T ukur
Jumlah jam
dB(A)
Jumlah jam
dB(A)
8
90
1,5
102
6
92
1,0
105
4
95
0,75
107
3
97
0,5
110
2
100
0,25
115
80
2 jam
90
95
97
100
4 jam 2 jam
T TLV
tt
8 jam 4 jam 3 jam
TWA
0
4/8
2 T ukur
0
2
jam
T TLV
tt
TWA
0
2/4
= 1 < batas aman
2 jam 2 jam
8 jam 4 jam 3 jam
2/8
2/4
2/3
= 17/12 >batas aman
3.
4 orang pekerja printer di unit percetakan dimana
terdapat
offset press. Masing-masing terpapar sbb:
Noise
No. of presses
Average Sound
operating
Pressure Level (dBA)
Average daily
time in operation
(hours)
0
81
4.5
1
93
2.1
2
96
1.0
3
98
0.4
Berapa dosis harian yang diterimanya? dan Equivalent
8-hour Sound Pressure Level (SPL) yang dialami
pekerja percetakan tersebut?
Jawab:
8
Tmax 
2( L 90) / 5
Untuk SPL 81 dBA:
Tmax @ 81dBA 
8
2
( 8190) / 5
= 27.858 jam
Untuk SPL 93 dBA:
Tmax @ 93dBA 
8
2
( 9390) / 5
= 5.278 jam
Untuk SPL 96 dBA:
Tmax @ 96dBA 
Untuk SPL 98 dBA:
8
2
Tmax @ 98dBA 
( 9690) / 5
8
2(9890) / 5
= 3.482 jam
= 2.639 jam
Noise
n
Ci
Cn
C1
C2
D


 .... 
Tmax 1 Tmax 2
Tmax n
i 1 Tmax i
D pr int er 
4.5
2.1
1.0
0.4



27.858 5.278 3.482 2.639
= 0.998
Now, expressing this result as a percentage as required
by the problem statement, we have: Dprinter= 99.8%
The Printing Company that employs these four Printers
is not in violation of any established OSHA SPL dosage
standards.
Noise
Lequivalent = 90 + 16.61 log[D]
Lequivalent = 90 + 16.61 log[0.998]
= 89.987
~ 90 dBA
These Printers experience an equivalent SPL
of ~ 90 dBA
Noise
4. How much longer is an individual, without
hearing protection, permitted to work at a
location where the noise level has just been
reduced from 104 dBA to 92 dBA?
To answer this question, we must first determine the OSHA
permitted duration, in hours, for each of the two identified noise
levels.
Tmax = 8 / [2(L-90)/5]
For an SPL of 104 dBA: Tmax @ 104 dBA= 8 / [2(104-90)/5] = 1.149
hours
For an SPL of 92 dBA: Tmax @ 92 dBA= 8 / [2(92-90)/5] = 6.063
hours
The additional time permitted at the lesser noise level of 92
dBA, ΔTmax, is simply the difference between these two OSHA
permitted time intervals; thus:
ΔTmax=6.063 – 1.149 = 4.914 hours
This individual can spend an additional 4.9 hours at a 92 dBA
noise level