Peak Positive Pressure

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(1) Peak Positive Pressure.  The peak positive pressure, Pso,
outside a partially vented cubicle can be expressed as
EQUATION:
Pso = 290(A/V2/3)0.401(R/W1/3) -1.496
(19)
Equation (19) was derived from experimental data involving a cube-shaped
cubicle and the following conditions:
0.063 < /= W/V < /= 0.375 lb/ft3
0.0198 < /= A/V2/3 < /= 1.000
1.59 < /= R/W1/3 < /= 63.0 ft/lb3
(a) As indicated by Keenan and Tancreto, exercise caution in
applying Equation (19) to other conditions.  This equation was used to
construct Figure 11, based on Composition B explosive, cylindrical
charges, and cube-shaped cubicles with the charge at the geometric center
of the cubicle.  However, changes in these parameters would introduce only
small errors.
(b) Equation (19) and Figure 11 were constructed for the
pressures outside a 4-wall cubicle on a horizontal plane located at the
elevation of the vent area.  When the location of interest lies at a
different location other than that of the vent area, the procedure
outlined in Appendix C of Blast Environment from Fully and Partially Vented
Explosions in Cubicles by Keenan and Tancreto should be followed.
(2) Peak Positive Impulse.  Figure 12 taken from Blast Environment
from Fully and Partially Vented Explosions in Cubicles is useful for
selecting the vent area needed to limit the peak positive impulse at any
range outside a 4-wall cubicle.  The chart probably yields reasonable
values of is/W1/3 (scaled impulse) within the range of the test data;
that is, 0.072 < W/V < 0.289 and 0.008 < AW1/3/V < 0.721.  Except at very
close-in ranges (R/W1/3 < 10), the peak positive impulse outside a 4-wall
cubicle without a roof is about the same as that from an unconfined
surface burst.
(3) Duration of Positive Pressure.  For design purposes, the actual
pressure pulse is approximated by a equivalent triangular pressure-time
pulse with the duration expressed as
EQUATION:
t'o/W1/3 = 2(is/W1/3)/Pso
(20)
The scaled duration of the impulse, to/W1/3, is underestimated by the
equation above for small degrees of venting and scaled distances.  In such
cases, engineering judgment should be exercised.
6.
FULLY VENTED EXPLOSIONS.
a.  Definition.  According to Keenan and Tancreto, a fully vented
explosion is one that occurs in a environment where A/V2/3 >/= 0.6.
2.08-26