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3.2 The calculation of the limit of the object stability to the influence of
the air shock wave
As a quantitative indicator of the stability of industrial object to the air shock
wave, to take into account the value of overpressure at which buildings, structures,
equipment and utility energy network of the object, are conserved or have a light or
moderate destruction. This value of overpressure is considered as limit of stability
of the object to the air shock wave – ΔP f lim. . An object is stable if ΔP f lim. ≥ ΔP fmax. .
The method of assessing the object resistance to the action of air shock wave
includes:
- calculation the maximum overpressure value of air shockwave, what is
expected in region of the object ΔP fmax. ;
- calculation the limits of the object stability to the action of air shock wave
ΔP f lim. ;
- analysis the results of estimation: conclusion – stable object or not;
- definition of measures to improve the sustainability of the facility.
The calculation algorithm is determined by using the theoretical positions,
considered above and include next steps:
1) Find out in which of the zones (I, II or III) of the hearth of explosion of
the gas-air mixture is placed the investigated object of economic activity (compare
distance L from the tank with calculated radius of this zone r, using theoretical
material and/or formula 7.2 or 7.3).
2) Determine the value of overpressure of the air shock wave ΔР , using
f
theoretical material, considered above and/or formula 7.4 or 7.6, 7.7.
3) More of the two values, calculated or according to the graph (using Figure
5.2), are accepted for ΔP fmax.
4) Calculate the limits of the object stability to the action of air shock wave

ΔP f lim. :
a) determine which elements of the object are the weakest (with small values
of ΔP f lim. );
b) determine the degree of destruction of the object as a whole using the
smallest value of ΔP f lim. from all elements of the object.
5) Assessing the stability of the shop to the influence of overpressure of the
air shock wave, it is necessary to draw up a table (an example in table 7.1), on the
left part of which to list all the main elements of the object of economic activity
(the stability of which depends on the stability of the entire facility), and on the
right side indicate the values for low, medium and strong degree of destruction of
these elements, depending on the overpressure at the front of the shock wave ΔР f
max. . Data for this is taken from table 7.3. The values of the degree of destruction of
the object as a whole are noted down into the last column.

Table 7.1 – The results of estimation of the object stability to the action
of the air shock wave
Elements of object Degree of destruction The The limits
depending on ΔР f max. , limits of of the

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