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forecasting, the spilling "freely" is taken when the toxic substance spills on the
ground surface with the height of the layer of this spill (h) not exceeding 0,05 m.
The "tray" spilling is taken if toxic substance spills by a surface that has bunding,
with the height of the layer of toxic substance h = H - 0.2 m, where H is the height
of the bunding.
- meteorological data: the wind speed in the surface layer is 1 m/s, the air
temperature is 20 °C, the degree of vertical air resistance (DVAR) is inversion, the
direction of wind is not taken into account, and the spread of the cloud of
contaminated air is taken within a radius 360°;
- average population density for this area;
2
- area of the possible chemical pollution zone, km :
2
S possible = 3.14D , (6.3)
2
- area of the forecasted chemical pollution zone, km :
2
S forecasted = 0.11D , (6.4),
where D – is the depth of the possible chemical pollution zone.
Possible chemical pollution zone is an area within which, under the
influence of a change in the direction of the wind, the movement of the clouds with
dangerous for human concentrations of toxic substances may occur. Forecasted
chemical pollution zone is a calculated zone within the limits of the possible
chemical pollution zone, the parameters of which are approximately determined in
the form of an ellipse (see Figure 6.1).

Figure 6.1 – Possible and forecasted chemical pollution zones

For long-term forecasting the calculation algorithm is determined by using
the theoretical positions and include next steps:
1) To find the depth of spreading of a cloud with a toxic substance in the
event of an accident on chemically dangerous object or transport – D (for constant
conditions of long-term forecasting: degree of vertical air resistance – inversion,
temperature +200C, wind speed 1 m/s) using table 6.6.
2) To calculate the width – W of distribution of a cloud with a toxic
substance for inversion, using formula 6.9.

3) To find the area of the forecasted chemical pollution zone, which pass
throught the settlement, using width of this zone from previous item and depth of
the settlement.

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