Safe distances during the blasting works

SAFE DISTANCES DURING THE BLASTING WORKS (EN: safe passing distance; DE: Sicherheitsabstand, Sicherheitsradius; FR: distance de securite; ES: aviso de distancia de seguridad; RU: безопасные расстояния) are the minimal distances from the charge of the explosive substances, at which the action of the explosion is safe for the people, mechanisms, buildings, and built structures, or does not cause the transfer of the detonation to another charge; it serves as the boundary for the dangerous zone of the explosion.

The calculation of the dangerous zones during the blasting works is performed in accordance with the "Unified safety rules during the blasting works", and also with the "Technical rules for the conducting of the blasting works on the daylight surface". Depending on the purpose and conditions during the conducting of the blasting works, they determine the safe distances (or the radii of the dangerous zones): according to the flying distance of the rock fragments, according to the action of the shock airwave, according to the transmission of detonation, according to the acceptable concentration of the poisonous gases, and according to the seismic action of the explosion. The safe distances according to the flying distances of the rock fragments exclude the possibility of the damage by the splinters and debris; they depend on the factor of the action of the explosion, on the maximal value of the line of the least resistance, on the method of the blasting, on the type of the blasting works, and on the local conditions. The safe distances according to the action of the shock airwave depend on the placement of the charges (open and buried charges), and are calculated according to the condition:

where

Q - the total mass of the explosive charge, kilograms;

kv - the coefficient of proportionality (0.5-150).

The properties of the explosive substances during the calculations of the safety distances are not taken into account. In the case, when the protected object is situated behind the obstacle, the safe distances decrease, but not more than by 2 times. The safe distances according to the transfer of the detonation exclude the possibility of the transfer of the detonation from one charge to another charge, and are determined according to the formula:

where

q1, q2, ..., qn - the masses of the various explosive substances (their sum is equal to the total mass of the explosive substances within the storage depot), kilograms;

kd1, ..., kdn - the coefficients, which are depending on the type of the explosive substances, and on the conditions of the blasting (the placements of the active and passive charges);

D - the smallest linear dimension of the passive charge, which is equal to the width of the charge, or to its height twice.

The safe distances according to the acceptable concentration of the poisonous gases are calculated according to the condition, that at the boundary of the dangerous zone the content of the poisonous gases (in terms of the CO gas), which are emitted during the explosion of the explosive substances, does not exceed 0.008%:

where

ke - the experimental coefficient (0.5-1.0);

s - the quantity of the poisonous gases, which is emitted by 1 kilogram of the explosive substances, litres. It depends on the climatic peculiarities of the region of the explosion (the direction and the speed of the wind).

The safe distances according to the seismic action of the explosion are calculated in such manner, that the oscillations of the ground, which are caused by the single explosion of the concentrated charge of the explosive substances (except the open charges on the surface), would be safe for the buildings and built structures:

where

kc - the coefficient, which is depending on the properties of the soil at the foundation of the protected built structure (for the hard dense rocks k = 3, for the water-saturated soils kc = 20);

a - the coefficient, which is depending on the factor of the action of the explosion.

In case of the the damages within the buildings, and of the conducting of the multiple explosions (at the open pit mines, and so on) near the same facilities, the calculated safe distance for the single explosions must be increased by at least 2 times; for the buildings and built structures of the unique character (the high-rise building, towers, and so on), complicated engineering built structures (bridges, radio towers, and others), there are being performed the special calculations.