Noise in Industry - Fundamentals and Assessment Tools for Occupational Ergonomics - page 626

to 7 a.m. The rationale for the penalty is that humans are more disturbed by noise, especially due to sleep
arousal, during nighttime periods.
The equation for the OSHA average noise level,orL OSHA , which uses a 5-dB exchange rate, is

" #

T X

N

1

10 (L iA =16:61) L OSHA (5) ¼ 16 : 61 log 10 t i

i ¼ 1

(where L iA is in dBA, slow response) (31 : 10)

OSHA's TWA is a special case of L OSHA , which requires that the total time period always be 8 h, that time
is expressed in hours, and that sound levels below 80 dBA, termed the threshold level, are not included in
the measurement:

" #

8 X

N

1

10 (L iA =16:61) TWA ¼ 16 : 61 log 10 t i

i ¼ 1

(where L iA is in dBA, slow response; T is always 8 h;
only L iA 80 dBA is included) (31 : 11)

OSHA's noise dose is a percentage representation of the noise exposure, where 100% is the maximum
allowable dose, corresponding to a 90-dBA TWA referenced to 8 h. Dose utilizes a criterion sound
level, which is presently 90 dBA, and a criterion exposure period, which is presently 8 h. A noise dose
of 50% corresponds to a TWA of 85 dBA, and this is known as the OSHA action level. Calculation of
dose, D, is as follows:

T c X

N

100

10 ((L iA L c )=q)

D ¼ t i

i ¼ 1

(where L iA is in dBA, slow response; L c is the criterion sound level;
T c is the criterion exposure duration; only L iA 80 dBA is included) (31 : 12)

Noise dose, D, can also be expressed as follows, for a constant sound level over the workday:

C 1
T 1 þ

C 2
T 2 þþ

C n
T n

D ¼ 100

(where C i is the total time (hours) of actual exposure at
L i ; T i is total time (hours) of reference allowed exposure at
L i , from TableG-16a of OSHA 19 ;
C i =

T i represents a partial dose at sound level i) (31 : 13)

T, the reference allowable exposure for a given sound level, can also, in lieu of consulting Table G-16a in
OSHA, 19 be computed as

8
2 (L90)=5

T ¼ (where L is the measured dBA level) (31 : 14)