WEAPONS EFFECTS 3

3.1 DESCRIPTION OF EXPLOSION FORCES 
An explosion is an extremely rapid release of energy in the form of light, heat, sound, 
and a shock wave. The shock wave consists of highly compressed air that wave-reflects 
off the ground surface to produce a hemispherical propagation of the wave that 
travels outward from the source at supersonic velocities (see Figure 2-1). As the shock 
wave expands, the incident or over-pressures decrease. When it encounters a surface 
that is in line-of-sight of the explosion, the wave is reflected, resulting in a 
tremendous amplification of pressure. Unlike acoustical waves, which reflect with an 
amplification factor of two, shock waves can reflect with an amplification factor of up 
to thirteen, due to the supersonic velocity of the shock wave at impact. The 
magnitude of the reflection factor is a function of the proximity of the explosion and 
the angle of incidence of the shock wave on the surface. 
The pressures decay rapidly with time (i.e., exponentially), measured typically in 
thousandths of a second (milliseconds). Diffraction effects, caused by building 
features such as re-entrant corners and overhangs of the building may act to confine 
the air blast, prolonging its duration. Late in the explosive event, the shock wave 
becomes negative, followed by a partial vacuum, which creates suction behind the 
shock wave(see Figure 3-1). Immediately following the vacuum, air rushes in, creating 
a powerful wind or drag pressure on all surfaces of the building. This wind picks up 
and carries flying debris in the vicinity of the detonation. In an external explosion, a 
portion of the energy is also imparted to the ground, creating a crater and generating 
a ground shock wave analogous to a high-intensity, short-duration earthquake. 
The peak pressure is a function of the weapon size or yield, and the cube of the 
distance (see Figure 3-2). For an explosive threat defined by its charge weight and 
standoff, the peak incident and reflected pressures of the shock wave and other useful 
parameters such as the incident and reflected impulse, shock velocity, and time of 
arrival are evaluated using charts available in military handbooks. 
WEAPONS EFFECTS 
WEAPONS EFFECTS


3.2 FURTHER READING 
These references provide charts for evaluating explosive loads as well as extensive 
information regarding the structural design of buildings to resist explosive attack. 
U.S. Air Force, 1989, ESL-TR-87-57, Protective Construction Design Manual, Contact Airbus 
Technologies Division (AFRL/MLQ) at Tyndall Air Force Base, Florida, via e-mail to 
techinfo@afrl.af.mil. [Superseded by Army Technical Manual TM 5-855-1 (Air Force 
Pamphlet AFPAM 32-1147(I), Navy Manual NAVFAC P-1080, DSWA Manual DAH-
SCWEMAN-97), December 1997] 
U.S. Army Corps of Engineers, 1990, TM 5-1300, Structures to Resist Accidental Explosions, 
U.S. Army Corps of Engineers, Washington, D.C., (also Navy NAVFAC (Naval 
Facilities) P-397, Air Force Regulation 88-2); Contact David Hyde, U.S. Army Engineer 
Research and Development Center, 3909 Halls Ferry Road, Vicksburg, Mississippi 
39180 or via e-mail to hyded@ex1.wes.army.mil 
U.S. Department of Energy, 1992, DOE/TIC 11268, A Manual for the Prediction of Blast and 
Fragment Loadings on Structures, Southwest Research Institute, Albuquerque, New 
Mexico. 

WEAPONS EFFECTS 
WEAPONS EFFECTS