Page 208 - CHEF Guide

Vapor Dispersions

Note: These apply only for rural release conditions and are developed based on limited data (see Figure
2.29 in [58]).

Figure 12-15 Dispersion coefficients for an instataneous release

Table 12-6 Neutrally Buoyant Puff Distribution Parameters for Calculation of x, Y and Z
(see Table 2.13 in [58])

Incorporating these distribution coefficients into the Neutrally Buoyant plume equation for maximum ground level
concentration for a ground elevation release yields for Class D atmospheric stability and Residential or Industrial surface
roughness (z0 = 1.0) yields Equation 12-14:
Y = a X = 0.128 X 0.905 and Z = c’ X = 0.395 X 0.701
d’
b
Cm = Q / ( Y Z u ) = 6.3 Q / ( u X 1.61 ) kg/m
3

Cm = 1.54x10 Q / ( Mw u X 1.61 ) ppm by volume Equation 12-14
8

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