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:Sensitivity range: sound pressure variations ranging from 0.0002 µbar to 200 µbar (one µbar = one dyne per square centimeter).

– Frequency range: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

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).

–Example: –A large chipping hammer emits sound power equivalent to one watt (1w), what is this level in dB?

– Answer: 120 dB.

Permissible Noise Exposure

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

RMS Acceleration not to be Exceeded

4-8 hours 4 m/s2

2-4 hours 6 m/s2

1-2 hours 8 m/s2

< 1 hour 12 m/s2

Freq. (Hz) 0.42 hours 1 hour 2.5 hours 4 hours 8 hours 16 hours 24 hours

1 3.55 2.36 1.4 1.06 0.63 0.383 0.281.25 3.15 2.12 1.26 0.95 0.56 0.338 0.251.6 2.8 1.9 1.12 0.85 0.5 0.302 0.2242 2.5 1.7 1 0.75 0.45 0.27 0.2

2.5 2.24 1.5 0.9 0.67 0.4 0.239 0.183.15 2 1.32 0.8 0.6 0.355 0.212 0.16

4 1.8 1.18 0.71 0.53 0.315 0.192 0.145 1.8 1.18 0.71 0.53 0.315 0.192 0.14

6.3 1.8 1.18 0.71 0.53 0.315 0.192 0.148 1.8 1.18 0.71 0.53 0.315 0.192 0.14

10 2.24 1.5 0.9 0.67 0.4 0.239 0.1812.5 2.8 1.9 1.12 0.85 0.5 0.302 0.22416 3.55 2.36 1.4 1.06 0.63 0.383 0.2820 4.5 3 1.8 1.32 0.8 0.477 0.35525 5.6 3.75 2.24 1.7 1 0.605 0.45

31.5 7.1 4.75 2.8 2.12 1.25 0.765 0.5640 9 6 3.55 2.65 1.6 0.955 0.7150 11.2 7.5 4.5 3.35 2 1.19 0.963 14 9.5 5.6 4.25 2.5 1.53 1.1280 18 11.8 7.1 5.3 3.15 1.91 1.4

Threshold Limit Values for Whole Body Vibration

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.)

Vibration Collection (use accelerometers)

Types:

Piezoelectric– hand-arm vibration tool measurementsPiezoresistive– whole body vibration measurementStrain Guage – vehicle floors, large mass objects

Accelerometers collect data on...

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)

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)