Transcript Environment and HF

Environment and HF
INSY3020/7976/ENH670
Noise
•What is noise?
– Any unwanted sound
•Safety Hazards Associated with Noise
- distracting
- disrupt verbal communication
- facilitate hearing loss
Sound
•SOUND:
– An object that is set into vibration causes
the air adjacent to it to be compressed at a
frequency equivalent to the vibration.
– The sound pressure waves travel out from
the source of vibration in a spherical
fashion as more surrounding air becomes
compressed.
Hearing Capacity
– Sensitivity range: sound pressure
variations ranging from 0.0002 µbar to
200 µbar (one µbar = one dyne per square
centimeter).
– Frequency range: 20 Hz to 20,000 Hz,
with the greatest sensitivity in the 1,000
Hz to 3,000 Hz range.
1. Outer Ear
2. Middle Ear
3. Inner Ear
Energy Transfer:
Sound
Mechanical
Electro Chemical
Sound Power
•Sound power (in watts) can be
expressed as sound power level (Lw) in
decibels (dB).
– LW is the TOTAL AMOUNT OF POWER
radiated by a sound source, referenced to
1X10-12 watts (W0).
W
LW  10 log
W0
Example
–Example:
–A large chipping
hammer emits sound
power equivalent to one
watt (1w), what is this
level in dB?
– Answer: 120 dB.
Solution :
W
LW  10 log
W0
1
LW  10 log
12
1x10
LW  10 log 1012
LW  10 x12
LW  120 dB
Permissible Noise Exposure
T(min) =
480
2(L-90)/5
Auditory Defects – Hearing Loss
1. Temporary Hearing Loss
– Drug Induced
– Sound Induced (TTS)
•
•
•
•
Noise levels > 60 dB
Noise frequency > 2000 Hz
Exposure duration lasting 10-12 hrs
Narrow bandwidth noise
2. Permanent Hearing Loss (NIPTS)
– Conductive Hearing Loss: impact or impulse noises
– Neural Hearing Loss: continuous exposure to noise
Hearing loss is not simply a loss of amplification or gain
Psychological/Performance Based Effects of Noise
1. Noise may induce mental stress when it:
– Indicates danger
– Interferes with desired auditory input or speech
– Creates irritation or annoyance (especially when it is intermittent,
unpredictable)
2. Performance Effects:
– Worker learning degraded
– Mental fatigue
– Learned helplessness
3. Subjective Associations with Noise
– Noise = power (e.g. vacuum cleaner)
– Sound =quality (GM’s car door studies)
Vibration
Periodic motion of an object in alternatively
opposite directions from its position of equilibrium
a.) sinusoidal vibration - regular, repeating waveform
b.) random vibration -
irregular and unpredictable
(most common is the real world)
Vibration Descriptors






frequency - cycles per second
displacement
amplitude
velocity
acceleration
jerk - rate of change in acceleration
Root-mean-square acceleration (RMS):
 Defines the total energy of the vibration source
 Used to express the intensity of vibration
 m/s2
The worker can be exposed to two types
of mechanical vibration
1. Segmental-
usually referring to vibration applied
locally to specific body parts, such
as the limbs, by hand tools
(e.g. hand / arm vibration)
2. Whole body - vibration transmitted to the entire
body through some supporting
structure such as a vehicle seat in
a truck, bus, or in farm machinery
Physiological Effects of Whole Body Vibration
1.
muscular activity and maintenance of posture
2.
cardiovascular system effects
3.
cardiopulmonary effects
4.
metabolic and endocrinological effects
5.
central nervous system effects
6.
gastrointenstinal system effects
7.
motion sickness effects
Performance Effects of Whole Body Vibration
• Tracking Performance
• Cognitive Skills
• Discomfort
• Resistant Tasks
Threshold Limit Values for
Hand Arm Vibration (ACGIH, 2001, ISO 2631)
Total Daily Exposure
Duration
4-8 hours
RMS Acceleration not
to be Exceeded
4 m/s2
2-4 hours
6 m/s2
1-2 hours
8 m/s2
< 1 hour
12 m/s2
Threshold Limit Values for Whole Body Vibration
Freq. (Hz) 0.42 hours
1
1.25
1.6
2
2.5
3.15
4
5
6.3
8
10
12.5
16
20
25
31.5
40
50
63
80
3.55
3.15
2.8
2.5
2.24
2
1.8
1.8
1.8
1.8
2.24
2.8
3.55
4.5
5.6
7.1
9
11.2
14
18
1 hour
2.36
2.12
1.9
1.7
1.5
1.32
1.18
1.18
1.18
1.18
1.5
1.9
2.36
3
3.75
4.75
6
7.5
9.5
11.8
2.5 hours
1.4
1.26
1.12
1
0.9
0.8
0.71
0.71
0.71
0.71
0.9
1.12
1.4
1.8
2.24
2.8
3.55
4.5
5.6
7.1
4 hours
1.06
0.95
0.85
0.75
0.67
0.6
0.53
0.53
0.53
0.53
0.67
0.85
1.06
1.32
1.7
2.12
2.65
3.35
4.25
5.3
8 hours
0.63
0.56
0.5
0.45
0.4
0.355
0.315
0.315
0.315
0.315
0.4
0.5
0.63
0.8
1
1.25
1.6
2
2.5
3.15
16 hours
0.383
0.338
0.302
0.27
0.239
0.212
0.192
0.192
0.192
0.192
0.239
0.302
0.383
0.477
0.605
0.765
0.955
1.19
1.53
1.91
24 hours
0.28
0.25
0.224
0.2
0.18
0.16
0.14
0.14
0.14
0.14
0.18
0.224
0.28
0.355
0.45
0.56
0.71
0.9
1.12
1.4
Risk Factors for Whole Body Vibration: Resonance

all objects have a resonance frequency

when a source of vibration matches an object's
resonance frequency...

at resonance the object will...

various body parts resonate at different frequencies

the resonance frequency of a body part will
depend upon ...

greatest decrement in performance and
most pronounced physiological effects occur.
Controls for Vibration Exposure
First Step: Job Documentation
a.)
Perform a work place walk-through of the entire
work process
b.)
Record work performances of workers
c.)
Review video, taking note of job components
involving vibration exposure
d.)
If possible, take vibration samples of workers
doing their jobs after their work-shift
Vibration Collection (use accelerometers)
Types:
Piezoelectric– hand-arm vibration tool measurements
Piezoresistive– whole body vibration measurement
Strain Guage – vehicle floors, large mass objects
Accelerometers collect data on...
 Duration vibration exposure
 RMS of vibration acceleration
 Frequency of vibrational source
 Fourier Spectrum Analysis
Control of Vibration
1. The SOURCE - engineering or administrative changes
to the source of vibration that:
(a)
Reduce the root mean square acceleration
(b)
Shift the frequency outside the resonance
(c)
Reduce the duration of exposure to the vibration
(d)
Mechanically isolate the sources of vibration in
the workplace
Control of Vibration
2. The PATH - engineering or administrative changes
to the path that the vibration takes from it’s source
(a) Structural support for vibrating tools
(b) Reduction in manual grip force requirements
(c) Coating to vibrating surfaces
Control of Vibration
3. The RECEIVER - engineering or administrative
changes designed to directly protect the worker
from vibration
(a) Have the worker wear anti-vibrational gloves
(AV gloves)
(b) Avoid smoking and cooling of the hands
(c) Periodic rest breaks