Page 537 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Applied Process Design 503

Blast Scaling When accounting for effective charge weight at ground
reflection the conversion is [ 49]:
The Universal Hopkinson-Cranz and Sachs Laws of
Blast Scaling have both been verified by experiment. (7-63)
These laws state that self-similar blast (shock) waves are
produced at identical scaled distances when two explosive We = effective charge weight in pounds of Tl\'T for estimating
charges of similar geometry and the same explosive com- surface burst effects with free air.
position, but of different size, are detonated in the same
atmosphere [ 49]. It is assumed that the energy reieased is proportional
to the mass of a specific explosive [ 40].
The scaled distance Z, which is a proportionately con-
stant, is: At times it is necessary to have a feei for overpressure
as it relates to shock front velocity [ 49]. (See Figure 7-60).
Note especially that for a reasonable detonation velocity
the peak overpressure could be in the range of 700 to
Z 1.'11. =--R-, forTNToniy, fl/lb 113 (7 - 61) 1000 psi and when referenced to Figure 7-60, the extent
1/3
.
IT!Tl\"T
of industrial damage would be catastrophic. The use of
scaled distance is illustrated in Ref. [ 41].
(7-62)
or Rexp = RoA Example 7-15: Blast Scaling
Compare two different explosive charge weights of the
where R,xp = distance from the center of the explosion same material. For an observed overpressure of 40 psi
source to the point of interest, ft from a specific charge using the scaling equation above,
mTNT = mass of TNT, lb the scaled distance is Z = 5 ft/lb 1 What is the distance
1 3.
0NT = scaled distance to the point of interest, for an overpressure of 40 psi with a charge of 500 lb?
feet/ (lb) 113
We = explosive charge weight, lb 1 1
1 3
A = yield factor= (W/V1 10) 1 Z = 5 = 5/(l lb) 1 3 = x/(500 lb) 1 3
Subscript, o, refers to reference value. x = (500) i/s (5) = 7.93 (5) = 39.6 ft

100

"'
,fr 50
""' o 30
OJ
"' �
Ul
"
0
ii
10
5

3
�
o
0
.s::
,:/]
1
0.5 1 3 5 10 30 so 100 300 500 1000 3000 5000 10,000
Peak Overpressure, psi
Figure 7-60. Shock front velocity as a function of peak overpressure at sea level. By permission, Report HNDM-1110-1-2, U.S. Army Corps of
Engineers, 1977, Huntsville, AL (49].