TITLE. 3.3 Noise. Prepared by:

Transcription

1 PART 3: SHE ELEMENTS TITLE 3.3 Noise Prepared by:

2 Learning Objectives To define what is noise and sound. To discuss the nature of sound, the effects of noise exposure, noise control, and the human ear. To calculate the combined decibels and noise exposure according to OSHA.

3 Definitions: Noise: - defined as unwanted sound. Exposure to noise from machinery and equipment in the workplace can result in several forms of hearing impairment. Sound: - defined as any pressure variation in air, water or some other medium that the human ear can detect.

4 The Nature of Sound Sound is generated by the vibration of surfaces or turbulence in an air stream which sets up rapid pressure variations in the surrounding air. The rate at which variations occur (frequency) is expressed in cycles per second or Hertz (Hz). The human ear is sensitive to frequencies between 20 Hz and 20,000 Hz, being particularly sensitive in the range 1,000 Hz to 4,000 Hz (the frequencies of interest and progressively less sensitive at higher and lower frequencies.

5 Hertz (Hz) and Decibel (dba) HERTZ ( Hz ) = unit for frequency Human hearing frequency : Hz Human speech / communication : Hz DECIBEL ( dba ) = measurement of intensity 0 dba : lowest intensity heard 140 dba : Threshold of pain

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7 The Effects of Noise Exposure Exposure to noise can affect hearing in three ways: Short-term effect, that is, a temporary reduction in hearing acuity, which may follow exposure to noise. The condition is reversible and the effect depends, to some extent, on an individual s susceptibility to noise. Temporary Threshold Shift This takes place when the limit of tolerance is exceeded in terms of time, the level of noise and individual susceptibility to noise. Recovery from permanent threshold shift will not proceed to completion, but will effectively cease at some particular point in time after the end of the exposure. Permanent Threshold Shift This condition involves ear damage from short-term intense exposure or even from one single exposure. Explosive pressure rises are often responsible, such as that from gun fire, major explosions or even fireworks. Acoustic Trauma

8 Diagram of Human Ear The ear has 3 main parts (external, middle and inner ear)

9 Structure of the ear : a. Outer ear b. Middle ear c. Inner ear Parts of the ear: Outer ear : Pinna, auditory canal. Middle ear : Ossicle bone, Eustachian tube. Inner ear : Oval window, semicircular canal, cochlea & auditory nerves.

10 Controlling Noise In essence there are three components of a noise problem: o the source o the pathway o the receiver Therefore noise hazard management has three basic components: I. Minimise the hazard at its source. II. Isolate the hazard (break the path). III. Protect the worker.

11 Methods Of Noise Control

12 Combining Decibels Table 1 provides a scale for combining decibels to arrive at a total noise level from two sources. If there are three or more sources, two sources are combined until all sources have been combined into a single total.

13 Table 1: Scale For Combining Decibels Difference between two decibel levels to be added (db) Amount to be added to larger level to obtain decibel sum (db) Source: NIOSH (Industrial Noise Control Manual (NIOSH ), 1978).

14 Case Study 1 Q: Four machines contribute the following noise levels in db (A) to a worker s exposure: Machine A Machine B Machine C Machine D 86 db 86 db 82 db 78 db Calculate the combined noise levels exposure for the workers. Please use Table 1 to help you.

15 OSHA Noise Standard Noise is unusual in that it is a hazard for which OSHA has set both a PEL and AL. The best known is the PEL, which is set at 90 dba for an 8-hour TWA. AL is computed to be 50% of the maximum permissible PEL. Where: The formula used is: D = total shift noise exposure as a percent of PEL. Ci Ti n = time of exposure at noise level i. = max permissible exposure time at noise level i. = number of different noise levels observed.

16 Case Study 2 Noise level readings show that a worker exposure to noise in a given plant is as follows: 8.00 a.m a.m 90 dba a.m a.m 95 dba a.m p.m 75 dba p.m 1.30 p.m 85 dba 1.30 p.m 2.00 p.m 95 dba 2.00 p.m 4.00 p.m 90 dba

17 By referring to OSH Standard of Noise Standard: i) Compute a total shift noise exposure toward worker in percentage. ii) Have Permissible Exposure Limit (PELs) and Action Level (AL) have been exceeded the standard?