Page 222 - CHEF Guide

Explosions

TNT Model
for Sperical Explosion at Sea Level
1000

100
Scaled Overpressure, P S = P 0 / P a 10 1

0.1
1 psi overpressure

0.01
0.01 0.1 1 10 Z = 18 100
Z = 18 1/3
Scaled Distance, Z = X / Kg TNT

Estimate the distance to 1 psi overpressure for a runaway reaction representing a deflagration or detonation. Use an
enthalpy of reaction of 1 X 10 kJ.
6
KgTNTeq = 1 X 10 / 4600 = 217 Kg
6
From the graph at 1 psi overpressure,
Scaled Distance, Z = 18 = X / 217
1/3
1/3
X = 18 (217 ) = 108 m
Note that some of the reaction energy is likely needed to heat the reacting material.

13.5 Baker-Strehlow-Tang Explosion Model

Blast modeling for flammable vapor is based on rapid combustion. Correlation of Blast Overpressure for combustion
related explosions requires a more complex model than the simple TNT Model. The TNO Multi-Energy Method may also
used to evaluate combustion related explosions. This technique, however, requires an estimate of the source strength. The
Baker-Strehlow-Tang method relates explosion efficiency to three parameters: Fuel Reactivity, Obstacle Density, and
Degree of Confinement.

Blast energy for the Baker-Strehlow-Tang Model is correlated to flame speed (expressed in Mach number units) and
related to:
• Fuel Reactivity (categorized as high, medium or low)
• Obstacle Density or Congestion (categorized as high, medium or low).
• Degree of Confinement (categorized as 1D, 2D, or 3D)

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