Page 535 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Applied Process Design 501

Table 7-26 [ 49] has been developed by ratio of relative partrnent No. 2 and, by the same analysis, this increased
heats of explosion. For close explosion, i.e., (Z < 3.0 pressure in No. 2 becomes the starting pressure for an
ft./lb 1 and for shapes other than spherical, the TNT explosion in No. 3. This pressure buildup under these
1 3)
equivalent factor can be much greater than those from types of conditions is known as pressure piling [ 40]. From
relative heats of explosion [ 49]. a pressure buildup standpoint,

Pressure Piling
1. when the initial pressure in compartment No. 1 is Pr-
If two or more systems are connected together (such as the final pressure will be (p 1) (x).
a pipe length with an orifice plate, two or more vessels 2. the final pressure in compartment No. 2 could be
connected with pipe or duct, or a compartmented vessel) X2PI·
and an explosion develops in No. 1 area, which generally 3. the final pressure in compartment No. 3 could be
may be at equilibrium pressure with compartments No. 2 X3Pl·
and 3 in equilibrium with No. 2, it can cause a pressure
rise in front of the flame front in the unburnt gases in the Where x = ratio of pressure increase, often with a value
interconnecting spaces (pipe, compartment). The between 2 and 8 for a deflagration.
increased pressure in compartment or area No. 1
becomes the starting pressure for an explosion in com- For example: If p1 = 20 psig + 14. 7 = 34. 7 psi a, assume
x = 6.5.
Thus, final pressures in compartment No. 2 would be
Table 7-26 (6.5)2 (34.7) = 1466 psia.
TNT Equivalence Factors for Chemical Explosives
Thus, it is easy to recognize that the pressure buildup
e, in a process system can be dangerously large and
Explosive (TNT Equivalent)
requires attention to both pressure relieving and to the
Amato! 60/40 design pressures for vessels/ equipment. This also helps
(60% ammonium nitrate, 40% TNT) 0.586 explain why some process vesseis fragment during an
Barona! (50% barium nitrate, explosion and fragments impact on personnel, build-
35% TNT, 15% aluminum) 1.051
Comp B (60% RDX, 40% TNT) 1.148 ings, etc., to do damage. It also helps to explain the shock
C-4 (91 % ROX, 9% plasticizer) 1.078 wave effects.
Explosive D (ammonium picrate) 0.740
H-6 (45% ROX, 30% T'.'JT, 20% Al,
5% D-2 wax) 0.854 Example 7-14: Estimating Blast Pressures and
HBX-1 (40% RDX, 38% TNT, 17% Al, Destruction
5% D-2 wa .. x ) 0.851
HMX l .256 A process petrochemical plant producing a synthesis
Lead Azide 0.340 gas high in hydrogen experiences an explosion that
Lead Sryphriate 0.423 results in the destruction of a 1500 cubic foot storage ves-
Mercury Fulminate 0.395 sel normally held at 50 psig. Unprotected glass windows
Nitroglyccrlnc (liquid) 1.481 (i.e., no wire mesh reinforcing, nor tempered) in the
Ni troguanidinc 0.668 plant area 150 feet away from the tank are broken. What
Octol, 70/30 (70% HMX, 30% TNT) 0.994 pressures were involved?
PETN 1.282
Pentolitc, 50/50
(5C% PETN, 50% TNT) 1.129 Using the equation for isen tropic expansion of an ideal
Picric Acid 0.926 gas:
RDX (Cyc!onite) 1.185
Silver Azide 0.419
Tetryl 1.00 (7-60)
Tl\T 1.00
Torpex (42% R.DX, 40% TNT, 18% Al) 1.667 V 1 = 1500 cu ft
Tri tonal (80% TNT, 20% Al) 1.639 k = l.41 for hydrogen

(Refs. 3-1 and 3-4 in original source) P1 = 50 + 14.7 = 64.7 psia
2
By permission, U.S. Anny Corps of Engineers, Report HN[Ji\l[.J J I0-1-2 P1 = 64.7 psia (144 in /ft 2) = 9316.8 lb/ft 2
(1977) [49] P 2 = 14.7 psia final pressure