Impact of Atmospheric Dispersion

If the released and dispersed materials are flammable, the dispersion calculation can serve to find out which part of the cloud lies within the limits of explosion and can therefore bum or explode. This is shown in Example 10.17. If the material is toxic it affects the health of people, as described in Sect 2.6. The effects can then be calculated using a probit relation. This is shown in Example 10.18. 

The fonnation of large clouds of flammable substances is an important problem in safety analyses for process plants. As already mentioned such clouds can be formed following instantaneous or continuous releases of flashing and/or vaporizing substances. 

The treatment of dispersion is based here on Eq. (10.94), which reads for spherical symmetry and constant a as follows 

The maximum hazard from a flammable material results if the concentration in the centre of the cloud is equal to the upper explosion limit (UEL) (vid. Sects. 2.1.1.1 and 2.1.1.2), i.e. there is no region within the cloud where the mixture is too rich. We then have 

Analogously one arrives at the radius at which the lower explosion limit (LEL) is reached, r , from Eq. (10.113) 

---