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h – thickness of the layer of toxic substance, m (equel to 0.05 m).
The width of forecasting zone of chemical pollution is determined as
follows:
0.6
for inversion W =0.3D , (6.9)
for isotherm W =0.3D 0.75 , (6.10)
for convection W=0.3D 0.95 , (6.11)
Evaporation time from the area of spilling, hour:

, (6.12)

The depth of the zone of contamination with the primary or secondary cloud
is determined depending on Q and Q and wind speed.
1e
2e
Full depth of contamination zone D :
full
D =D max +0.5D , (6.13)
min
full
where D max – is the biggest of the values D and D ;
2e
1e
D is the smallest of the values D and D .
min
1e
2e
The obtained value of D is compared with the maximum possible value of
full
transfer depth of air masses D .
air
D =N×V (6.14)
air
where V – is the speed of movement of the front of contaminated air, km/h.
For further work, choose the minimum of the last two values.
For emergency 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 (in
accordance to degree of vertical air resistance), using table 6.3 and 4.6 or 6.7, or
6.8.
2) To calculate equivalent amount of substance in the primary and secondary
clouds, using formula 6.7-6.8 and table 6.9-6.10.
3) To determine full depth of contamination zone and depth of air masses,
using formula 6.13, 6.14 and table 6.11.
4) To choose the minimum of the last two values from previous item for
further work.
5) To calculate area of the possible and forecasted chemical pollution zones,
using formulas 6.5 and 6.6.
6) To make conclusions: give advice on how to avoid an accident on a
chemically hazardous facility or transport, 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 need to be prepared.

Table 6.3 – Categories of stability of the atmosphere (degree of vertical
air resistance – DVAR)
Wind speed at a Day Night
height of 10 m
Cloudiness Cloudiness

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