Consequence Analysis 2.1

Source Model To determine the form of material released (solid, liquid or vapor); To determine the total quantity of material released; To determine the rate at which it is released.

Atmospheric Dispersion of Vapors Vapor could behavior Neutrally buoyant gas (Positively) buoyant gas Dense (or negatively) buoyant gas Duration of release Instantaneous release (puffs) Continuous release (plumes) Time varying continuous

Parameters Affecting Atmospheric Dispersion Wind speed Atmospheric stability Ground conditions, buildings, water, trees Height of the release above ground level Momentum and buoyancy of the initial material released

Atmospheric Stability Turbulence is estimated from atmospheric stability; stable conditions leads to the least amount of mixing and unstable to the most. Stability is commonly defined in terms of the atmospheric vertical temperature gradient. During the day, the air temperature decreases rapidly with height, encouraging vertical motion. At night the temperature decrease is less, resulting in less vertical motion. Sometimes an inversion will occur.

Wind Speed In the absence of detailed meteorological data for a particular site, two common weather combinations used in many CPQRA studies are D at 5 m/s (daytime) and F at 2 m/s (nighttime). Wind data are normally quoted on the basis of 10 m height. A simple power law correction can be used