MODELING THE HAZARDS POSED BY SUDDEN RELEASE OF A QUANTITY OF CONTAMINANTS

The consequence of an accidental release of toxic, flammable or noxiou s material into an environmental flow needs to be assessed in terms of the territory that is subjected to the contaminant at unacceptable co ncentration levels. Environmental flows are turbulent and generally un steady and inhomogeneous such that the contaminant concentration value s in question are non-stationary, inhomogeneous random variables. Thus the practically important, basic, problem of describing the evolution of the concentration field in a contaminant cloud presents some serio us theoretical and experimental challenges. A new approach is develope d to describe the diffusion of a contaminant cloud in terms of its loc ation, size and state. The state of the cloud will characterize the di lution of the contaminant concentration values within the cloud. A new measure-the 'expected mass fraction' function-is introduced to descri be the state of cloud dilution. The advantages of this approach are di scussed in terms of the experimental difficulties associated with taki ng averages. The theoretical advantages that follow from this new appr oach are illustrated in terms of recent, simple, models of the evoluti on of the moments of the one-point probability density function of con centration. (C) 1997 Elsevier Science Ltd.