Casella CEL CEL-281 - Manual (Page 25)

Both terms are in common use, but the most recent international stand-
ards specify sound exposure.
The value of sound exposure measured (E A ) is normally defined as the
product of exposure time and the amount of A-weighted energy con-
tained in the sound. A similar relationship (E
C ) can be defined for expo-
sure to C-weighted sound energy.
Sound Energy is proportional to the square of sound pressure and has
the units Pascal-squared (Pa
2
), so that the units of sound exposure be-
come Pascal-squared seconds (as stipulated by the ISO Standard). How-
ever, Pascal-squared hours (Pa
2
h) are normally used in order to
obtain more manageable numbers (IEC Standard).
Therefore Sound Exposure E A can be defined as follows:
E A =
∫
t 1
t 2
P A
2 (t).dt
Where:
t 1 = Integration start time (hours),
t 2 = Integration end time (hours),
P A = Instantaneous A-weighted sound
pressure (Pa).
In the CEL-281, sound exposure is calculated and stored in Pa
2
h, while
sound levels are expressed in dB.
A sound exposure value of 1 Pa
2
h is equivalent to a continuous sound
level of approximately 85 dB(A) for eight hours (see Figure 1), while a
sound exposure value of 3.2 Pa
2
h is exactly equivalent to a continuous
sound level of 90 dB(A) for eight hours.
Recent European noise exposure legislation mentions three action levels
(which are also shown in Figure 1).
CEL-281 Operator's Handbook - Page 17
_Introduction