OHS - Physical Hazard - Noise

Noise

• unwanted sound

• hearing loss

• interfering with communication

• causing loss of sleep

• affecting human physiology

• annoyance

Noise Pollution

• It has characteristics and duration injurious to public health and welfare

• 2 categories

  • community noise

  • industrial noise/ noise from workplace

ambient noise

total noise in a given situation or environment

wavelength

• in meter

• distance between successive peaks or troughs

sinusoidal

rise and fall cyclic or wave pattern over a period of time

period

time between successive peaks or bet. successive troughs of oscillation

frequency

• number of times a peak arrives in one oscillation

• hertz Hz unit

amplitude

height of the peak or depth of the trough measured from the zero-pressure line

Pure tone

contain only one frequency

20 to 20,000Hz sonic category

young healthy ear can detect what frequencies?

1,000 to 6,000 Hz

sensitive hearing can detect what frequencies?

250 to 3,000 Hz

Normal speech frequencies

above 20,000 Hz

Frequency Category

Ultrasonic

below 20 Hz

Frequency Category

Infrasonic

Decibel dB

• dimensionless unit to express physical intensity or sound pressure levels

• one-tenth of a bell

• Alexander Graham Bell

• measurement: Sound Level Meter

0 dBA

Threshold of hearing for a young person w very good hearing

120 dBA

Threshold of pain for a young person w very good hearing

45 dB

According to WHO it is considered a safe noise level in a city

65 dB

According to international standards it can be tolerable noise level

Class A

Noise level is the weighted sound pressure level in dBA. What Weighted Scale used for

• human ear

• assessing regarding impact on humans

Class B

Noise level is the weighted sound pressure level in dBA. What Weighted Scale used for

• moderately loud sounds

Class C

Noise level is the weighted sound pressure level in dBA. What Weighted Scale used for

• very loud sound

Class D

Noise level is the weighted sound pressure level in dBA. What Weighted Scale used for

• measure and compare the effect of airplane noise on the human ear

Intensity

a sound wave is the energy transferred per unit time in secs through a unit area normal to the direction of propagation

• watts/ sq. cm

Loudness

• amplitude of sound is the sound level or sound pressure level as perceived by an observer

• 1 sone = 40 phons

• 2 sone = 50 phons (increasing by 10)

Noys

measure of the perceived noise level PNL in decibel in relation to the noisiness or acceptability of a sound level

Day Night Average Sound Level (DNL) System

• it is the 24hr average sound level expressed in decibels

Auditory Effect

Effect of Noise on People

include both hearing loss and speech interference

Threshold Shift

Effect of Noise on people: Auditory Effect

• increased sound pressure level required to achieve a new Hearing Threshold Level (HTL) scale

• it occurs during 2 hrs after exposure

• hearing losses may be either temporary or permanent

Temporary Threshold Shift TTS

Effect of Noise on people: Auditory Effect

• often accompanied by a ringing in the ear muffling of sound, or discomfort of the ears

• recovery Hearing Threshold Level (HTL) is attained within 16-24 hours after exposure

Permanent Threshold Shift PTS

Effect of Noise on people: Auditory Effect

• Acoustic Trauma

  • permanent hearing loss that results from very brief exposure to a very loud noise

Speech Interference or masking

Effect of Noise on people: Auditory Effect

• a function of the distance between the speaker and listener and the frequency components of the spoken words

Psychological/ Sociological Effects

Effect of Noise on People

• includes

  • annoyance

  • sleep interference

  • effects on performance

Steady State or continuous

Type of Sound

• an uninterrupted sound level that caries less than 5dB during the period of observation

• Ex. noise from a household fan

Intermittent

Type of Sound

• continuous noise that persists more than 1 sec that is interrupted for more than 1 sec

• Ex. dentist’s drilling

Impulse Noise

Type of Sound

• characterized by change of pressure of 40 dB or more within 0.5sec with a duration of less than 1 sec.

• a steady noise with interval between events of less than 0.5sec

• Ex. noise from firing a weapon

Presbycusis

hearing loss due to aging process

Permissible Noise Exposure Limits

Threshold Limit Values for Impulsive/ Impact Noise

Sound Level Motor

• measure the sound pressure level

• basic instrument for noise measurement

Noise Dosimeter (American)

Noise Dosemeter (British)

• measure the amount of potentially injurious noise to which an individual is exposed over a period of time

Sound Analyzer

• frequency analyzer may be necessary to measure complex sound and sound pressure according to frequency distribution

Cathode ray Oscillograph

• observing the wave form of a noise and pattern

• magnetic tape recorder makes possible the collection of noise information

Octave-band analyzer

• has filters that usually divide a noise into eight possible frequency categories

  • each category called octave band

Background Noise

• noise in the absence of the sound being measured that may contribute to and obscure the sound being measured

Methods of Noise Control

• controlled at the source

• building quieter machines

• use oof vibration isolators

• use of linings, seals