Methods for predicting the atmospheric dispersion of massive releases of flammable vapour

b Nominal plume radius c Local concentration in plume Ca Drag coefficient D Drag force H Cloud depth k Constant in spreading equation L Semi-width of cloud L, Briggs' lift-off parameter l Characteristic length scale Q Total mass released (instantaneous release cases) or mass release rate (continuous release cases) Qe Volume of air entrained per unit time Ri Richardson Number r Radial distance from plume centreline t Time U Wind speed U e Entrainment velocity u Local velocity in plume u' Characteristic turbulence velocity u. Friction velocity u* Plume centreline velocity relative to surrounding air ul, u3 Horizontal and vertical rms. turbulence velocities x, y, z Along wind, crosswind and vertical coordinates c~ Constant in entrainment equation • 1 Jet mixing entrainment coefficient ~2 Buoyancy mixing entrainment coefficient ~3 Ambient turbulence entrainment coefficient p~ Air density Ap Density difference between plume and air ax, ay, az Dispersion parameters 0 Plume trajectory angle above horizontal