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4) To determine the % of area of the settlement, which will be in the
forecasted chemical pollution zone, using the next relation:
(S forecasted *100%)/S settlement .
5) To calculate the population of the settlement, which will be live in the
forecasted chemical pollution zone, using the next relation: (P settlement * % of area of
the settlement, which will be in the forecasted chemical pollution zone)/100%.
6) To calculate the possible losses of workers, employees and the population
from potent toxic substances, using table 6.5.
7) To determine time of approach of a cloud with a toxic substance to

settlement, using the next relation: , where L – distance from the chemically

dangerous object to settlement, m; V – velocity of transport of the front edge of the
cloud of contaminated air, km/h (see table 6.4).
8) To calculate area of the possible and forecasted chemical pollution zones,
using formulas 6.1 and 6.2.
9) To make conclusions: on the one hand, give advice on how to avoid an
accident on a chemically hazardous facility or transport, on the other hand, if it is
impossible to avoid an accident, in this case, how to avoid an air pollution, losses
of population and how much forces and resources will be needed to attract to
eliminate the consequences of an accident and which work plans and other long-
term (reference) materials need to be prepared.

3.2 Emergency forecasting
Emergency forecasting is carried out at the time of an accident under the
intelligence data to determine the possible consequences of an accident and the
procedure of actions in the area of possible pollution.
For emergency forecasting, the following data is used:
- the total number of toxic substances at the time of an accident in the tank
(pipeline) where an accident occurred;
- the nature of the toxic substance spill on the underlying surface ("free" or
"in the tray"), the height of the bunding;
- real meteorological conditions: air temperature (°C), speed (m/s), wind
direction in the surface layer, degree of vertical air resistance (inversion,
convection, isotherm) (table 6.3)
- average population density for the district over which the cloud of toxic
substance spreads;
2
- area of the possible chemical pollution zone, km :

, (6.5)
where D – is the depth of the possible chemical pollution zone;
 – coefficient, which is conventionally equal to the angular size of the zone
and depends on wind speed (if V<1 m/s =360, if V=1 m/s =180, if V=2 m/s
=90, if V>2 m/s =45), for long-term forecasting =360.
2
- area of the forecasted chemical pollution zone, km :

, (6.6)

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