Schedule 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 "Gels" denoting such a ratio being the logarithm to the base of 10

of this ratio. The noise level (or the sound pressure level). Corresponds to a

reference pressure of 20X10-5 newtons per square or 0.0002 dynes per square

centimeter which is the schedule 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.- (1) In every factory suitable engineering control of

administrative measures shall be taken to ensure, so far as is reasonable practicable that no

worker is exposed to sound level exceeding the maximum permissible exposure levels

specified in Tables 1 and 2.

Table 1

Total time of Sounds pressure

exposure level in dBA

(Continuous or a

number of short

term exposures) per

day in hours.

8 90

6 92

4 95

3 97

2 100

1.5 102

1 105

0.75 107

0.5 110

Less than 0.5 115

Note: 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 Permitted number of

in in dB impulses or impacts per

day

140 100

135 315

130 1000

125 3160

120 10000

Note: 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

of impact per day is to be determined by extrapolation on a proportionate basis.

(2) For the purpose 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 shall apply. In other cases, the noise is to be considered as impulsive

or impact noise and the criteria given in table 2 shall apply.

(3) 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

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of each. The mixed exposure should be considered to exceed the limit value if the sum of the

fraction C /T + C /T +………… C /T exceeds unity,-

1 1 2 2 n n

Where the C , C etc. indicate the total time of actual exposure at a specified noise

1 2

level and T , T , etc. denote the time of exposure permissible at that level. Noise exposure of

1 2

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

(4) Where it is not possible to reduce the noise exposure to the levels specified in sub-clause

(1) above by reasonably practicable engineering control or administrative measures, the noise

exposure shall be reduced to the greatest extent feasible by such control measures, the each

worker so exposed shall be provided with suitable ear protectors so as to reduce the exposure

to noise to the levels specified in sub-clause (1), above.

(5) Where the ear protectors provided in accordance with sub-clause (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

sub- clause (1).

(6) (a) In all cases where the prevailing sound levels exceed the permissible levels specified

in sub- clause (1) there shall be ad-ministered 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 level or

by transferring them to place 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 sub-clause (1), above, shall be subjected to an auditory

examination by a Medical Officer within 14 days of his first employment thereafter, shall re-

examined at least once, every 12 months. Such initial the periodical examinations shall

include tests which the Medical Officer may consider appropriate, and shall include

determination of auditory thresholds for pure tones on 125, 250, 500, 1000, 2000, 4000 and

8000 cycles per second.