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where k – coefficient that depends on the degree of vertical air resistance (for
inversion k=0.081, for isotherm k=0.133, for convection k=0.235);
N – time, which is taken for determination the depth of spreading of a cloud
with a toxic substance in forecasted chemical pollution zone (equel to 4 hours).
- forecasting is carried out for period of time no more than 4 hours, after
which the forecast should be clarified.
The primary cloud of toxic substance is a vapor-like part of toxic substance,
which is in any tank above the surface of liquefied toxic substance and which
enters the atmosphere directly in the destruction of tanks without evaporation from
the underlying surface.
The secondary cloud of toxic substance is a cloud of toxic substance, which
is formed during a certain time due to the evaporation of toxic substance from the
underlying surface (for volatile substances, the time of formation of a secondary
cloud after the end of the primary cloud is absent; for other substances, it depends
on the properties of toxic substance, the state of the tanks bunding and air
temperature).
The methodology provides for calculations for planning measures to protect
the population only at altitudes up to 10 m above the surface of the earth (the
surface layer of air).
Equivalent amount of substance in the primary cloud, t:
, (6.7)

Equivalent amount of substance in the secondary cloud, t:

, (6.8)

where Q – amount of spilled toxic substance, t;
0
K – depends on the storage conditions of toxic substances (for compressed
1
gases K = 1);
1
K – depends on the physical and chemical properties of toxic substances;
2
K – is qual to the ratio threshold of toxic dose of chlorine to threshold doses
3
of other toxic substances;
K – takes into account the speed of the wind;
4
K – depends on the degree of vertical air resistance:
5
for inversion K =1;
5
for isotherm K =0.23;
5
for convection K =0.08.
5
K – depends on the time N, which has passed since the beginning of an
6
accident:
0.8
К = N , if N < T;
6
0.8
К = T , if N > T ,
6
where Т – duration of substance evaporation per hour.
K – takes into account the influence of air temperature (for compressed
7
gases K = 1);
7
3
d – density of toxic substance, t/m ;
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