Page 225 - CHEF Guide

Explosions

Table 13-3 is based on 2.5 D Confinement. 1D Confinement addressed as Mach >1 as transition to detonation is
assumed to occur [70]. Note that detonation is also assumed to occur for High Fuel Reactivity and Medium or High Obstacle
Density (or congestion) [70]. Note: The BST model has not been validated for dust explosions. However, the BST model
can provide a reasonable screening estimate of scaled overpressure versus scaled distance. This assumption could be
further refined using Computational Fluid Dynamic modeling, as needed.

The Baker-Strehlow-Tang (BST) model is also a correlation of Scaled Pressure versus Scaled Distance (Figure 13-5).
The Scaled Distance, R, is the distance from the Potential Explosion Site divided by (2 X Explosion Energy in kJ / 101.3
1/3
kPa) , with the “2” representing a reflected blast wave for ground elevation blasts [24, p. 184].

Baker-Strehlow-Tang Overpressure Curves
100
Mach > 1 represents a
Mach > 1 high explosion efficiency
and potential detonation.
Scaled Overpressure, P S = P 0 / P a 1 Mach 0.7
10

Mach 1.0

Mach 0.5
Mach 0.35
0.1
1 psi overpressure

0.01
0.1 1 10
Scaled Distance, R = X / (2 Q E / P a ) 1/3
[70]
Figure 13-5 Scaled overpressure vs scaled distance – BST model

The region of interest for explosion evaluation is generally a scaled overpressure less than 1 (or less than 14.7 psi)
where most buildings would be severely damaged or destroyed. Note that for Scaled Distance, the Explosion Energy is
multiplied by 2 to account for a reflected blast wave for ground elevation explosions.

13.6 Potential Explosion Site (PES)

A Potential Explosion Site (PES) represents a congested or confined volume that can be occupied by a flammable
vapor or, for screening, a dust cloud (Figure 13-6). Estimation of an indoor Potential Explosion Site volume is relatively
straight forward, merely the confined volume where a flammable release occurs. Evaluation of an outdoor PES is more
complex as a flammable cloud may fill one or more congested volumes. Differences between PES evaluations are as
follows:
• An indoor PES is the confined area, building or portion of a building in which a flammable release occurs.

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