Gas plume dispersal

Rule of thumb

From the point of release the plume will move with the actual wind speed in the prevailing wind direction in an area triangle with an angle of 30 – 60 degrees.

A gas plume will disperse in the air and become diluted as a result of the turbulence in the atmosphere. The extent of the turbulence depends on the roughness of the ground or sea over which the plume passes and on the stability of the atmosphere. Models have been developed for both instantaneous and continuous spills to enable assessments to be made about the amount of dilution that can take place in the air stream. The concentration in the plume at any point will be a function of the source strength (amount released per time unit), wind speed, distance from the source, atmospheric turbulence and time. The gas plume tends to broaden and become more diluted the further it travels, lessening the toxicity and the explosion risk. The danger zone associated with the plume will roughly elliptical or teardrop in shape reflecting the fact that the concentration contours follow this profile. In an instantaneous release, a given quantity of material is discharged immediately or released over a comparatively short period of time.