Schedule B XXIV

Operations involving high noise levels

1. Application.—This schedule shall apply to all

operations in any

manufacturing process having high noise level.

2. Definitions.For the purpose of this schedule, -

a. "Noise" means any unwanted sound.

b. "High noise level" means any noise level measured on the A-weighted

scale is 90 dB or above.

c. "Decibel" means one-tenth of "Bel" which is the fundamental division

of a logarithmic scale used to express the ratio of two specified or

implied quantities, the number of "Bels" denoting such a ratio being

the logarithm to the base 10 of this ratio. The noise level (or the sound

pressure level) 6 corresponds to a reference pressure of 20 x 10

power(-6) Newton per square meter or 0.0002 dynes per square

centimetre which is the threshold of hearing, that is, the lowest sound

pressure level necessary to produce the sensation of hearing in

average healthy listeners. The decibel in abbreviated form is dB.

d. "Frequency" is the rate of pressure variations expressed in cycles per

second or hertz.

e. "dBA" refers to sound level in decibels as measured on a sound level

meter operating on the A-weighting net work with slow meter

response.

f. "A-weighting" means making graded adjustments in the intensities of

sound of various frequencies for the purpose of noise measurement, so

that the sound pressure level measured by an instrument reflects the

actual response of the human ear to the sound measured.

3. Protection against noise. -

mn in osh ala oe ua en ao e o re so ear as is ering conte or ore art raiee

worker is exposed to sound levels exceeding the maximum permissible noise

exposure levels specified in Tables 1 and 2.

Table 1

Permissible exposure in cases of continuous noise

Total time of exposure (continuous dBA Sound pressure level in or a per day, in

hours number of short term exposures) :

6 92

4 95

3 97

2100

1 ½ 102

1 105

¾ 107

½ 110

¼ 115

Notes :- 1. No exposure in excess of 115 dBA is to be permitted.

2. For any period of exposure falling in between any figure and the next higher

or lower figure as indicated in column 1, the permissible sound pressure level

is to be determined by extrapolation on a proportionate basis.

Table 2

Permissible exposure levels of impulsive or impact noise

Peak sound pressure level in dB Permitted number of impulses or impact per day :

140 100

135 315

130 1,000

125 3,160

120 10,000

Notes :- 1. No exposure in excess of 140 dB peak sound pressure level is

permitted.

2. For any peak sound pressure level falling in between any figure and the next

higher or lower figure as indicated in column 1, the permitted number of

impulses or impacts per day is to be determined by extrapolation on a

proportionate basis.

3. For the purposes of this schedule, if the variations in the noise level involve

maximum at intervals of one second or less, the noise is to be considered as a

continuous one and the criteria given in Table 1 would apply. In other cases,

the noise is to be considered as impulsive or impact noise and the criteria

given in Table 2 would apply.

4. When the daily exposure is composed of two or more periods of noise

exposure at different levels their combined effect should be considered, rather

than the individual effect of each. The mixed exposure should be considered

to exceed the limit value if the sum of the fractions C1/T1 + C2/T2

+....... Cn/Tn exceeds unity, - Where the C1, C2 etc. indicate the total

time of actual exposure at a specified noise level and T1, T2, etc. denote the

time of exposure of less than 90 dBA may be ignored in the above calculation.

5. Where it is not possible to reduce the noise exposure to the levels specified in

Point (1) of the Note by reasonably practicable engineering control or

administrative measures, the noise exposure shall be reduced to the greatest

extent feasible by such control measures, and each worker so exposed shall

be provided with suitable ear protectors so as to reduce the exposure to noise

to the levels specified in Point (1) of the Note.

6. Where the ear protectors provided in accordance with sub- paragraph (2) and

worn by a worker cannot still attenuate the noise reaching near his ear, as

determined by subtracting the attenuation value in dBA of the ear protectors

concerned from the measured sound pressure level, to a level permissible

under Table 1 or Table 2 as the case may be, the noise exposure period shall

be suitably reduced to correspond to the permissible noise exposures

specified in point (1) of the Note.

7. (a) In all cases where the prevailing sound levels exceed the permissible

levels specified in point (1) of the Note there shall be administered an

effective hearing conservation programme which shall include among other

hearing conservation measures, pre-employment and periodical auditory

surveys conducted on workers exposed to noise exceeding the permissible

levels, and rehabilitation of such workers either by reducing the exposure to

the noise levels or by transferring them to places where noise levels are

relatively less or by any other suitable means ;

(b) Every worker employed in areas where the noise exceeds the maximum

permissible exposure levels specified in point (1) of the Note shall be subjected to

any auditory examination by a Medical Officer within 14 days of his first employment

and thereafter, shall be re-examined at least once every 12 months. Such initial and

periodical examinations shall include tests which the Medical Officer may consider

appropriate and shall include determination of auditory thresholds for pure tones of

125,250,500, 1000, 2000,4000 and 8000 cycles per second.