SECTION 3 - Department of mines, minerals and energy


SECTION 3


^ BASIC KNOWLEDGE OF BLASTING


This page intentionally left blank.

SECTION 3 – BASIC KNOWLEDGE OF BLASTING




^ BASIC SECTION 3 - Department of mines, minerals and energy KNOWLEDGE OF BLASTING

Explosive Properties


An explosive is a chemical compound, or mixture of compounds, initiated by heat, shock, impact, friction, or a combination of these conditions. Once initiated, it decomposes very SECTION 3 - Department of mines, minerals and energy rapidly in a detonation producing a rapid release of heat and large quantities of high-pressure gases. The gases produced expand rapidly with sufficient force to overcome confining forces, such as the SECTION 3 - Department of mines, minerals and energy rock surrounding a borehole. High explosives are categorized as being able to be initiated by a No. 8 test blasting cap, and which react at a speed greater than the speed of sound through the SECTION 3 - Department of mines, minerals and energy explosive medium.


If improperly or accidentally initiated, explosives may burn without the aid of atmospheric oxygen. The flame burning of explosives is called deflagration.


The energy released by the detonation of SECTION 3 - Department of mines, minerals and energy explosives manifests itself in four basic ways: 1) rock fragmentation; 2) rock displacement; 3) ground vibration; and 4) airblast. In addition, toxic and non-toxic fumes are also produced, and are released into the atmosphere.


All explosives have SECTION 3 - Department of mines, minerals and energy specific characteristics which differentiate them, and which can be measured to determine their performance under specific blasting conditions. A brief explanation of some of the more important explosive properties follows.


^ Detonation SECTION 3 - Department of mines, minerals and energy Velocity


Detonation velocity (DV) is the speed at which the detonation wave travels through a column of explosives. DV is typically measured in feet per second (fps), or meters per second (m/s), and SECTION 3 - Department of mines, minerals and energy may be affected by many factors including explosive type, diameter of the explosive column, confinement, and temperature. Most commercially available explosives in use today have detonation velocities in the SECTION 3 - Department of mines, minerals and energy range of 10,000-18,000-fps. Each explosive has an ideal velocity, which is dependent on the explosive’s composition and density.


Depending on the type of explosive, and how it is confined, the diameter of the product SECTION 3 - Department of mines, minerals and energy will influence the DV up to a certain charge diameter. Generally, the larger the diameter the greater the velocity until the explosive’s maximum (ideal) velocity is reached. DV is SECTION 3 - Department of mines, minerals and energy also strongly dependent on the density (packing density in a drill hole) of the explosive. All explosives also have a critical diameter, which is the smallest charge diameter at which the detonation process will SECTION 3 - Department of mines, minerals and energy support itself once initiated.


Confinement of the explosive charge will also affect the DV. Generally, the greater the confinement of the explosive, the higher the DV. For some explosive SECTION 3 - Department of mines, minerals and energy products such as ANFO, dynamites, emulsions, heavy ANFO, and water gels the effect of confinement can be significant in small diameter holes. Confinement usually has less influence on DV as the charge SECTION 3 - Department of mines, minerals and energy diameter increases.


Adequate priming of an explosive charge is critical in ensuring that the detonation will reach its maximum velocity as quickly as possible. If priming is inadequate the charge may fail SECTION 3 - Department of mines, minerals and energy to detonate, may build up slowly to its final velocity, or may initiate a low order detonation or deflagration. Blasters should always follow the explosive manufacturer’s recommendations for priming in order to SECTION 3 - Department of mines, minerals and energy ensure maximum velocities.

Density

The packing density of an explosive loaded in a borehole is one of its most critical properties. Density affects sensitivity, DV, and critical diameter of the explosive charge SECTION 3 - Department of mines, minerals and energy. It is defined as the weight per unit volume and is typically expressed in grams per cubic centimeter (g/cc). The density of most commercial explosives ranges from a low of SECTION 3 - Department of mines, minerals and energy about 0.8 g/cc to a high of about 1.6 g/cc. Free-flowing ANFO products are in the low density range of approximately 0.8 - 1.15 g/cc. Cartridge explosive products such as emulsions, water gels, and dynamites have SECTION 3 - Department of mines, minerals and energy densities in the range of 0.9 -1.6 g/cc. Since water is considered to have a density of 1.0 any product with a density of less than 1.0 will float. Blasters should also realize that muddy SECTION 3 - Department of mines, minerals and energy water or salt water in a borehole might have a density greater than 1.0 g/cc.

Sensitivity

Sensitivity is a loosely used term that indicates the absolute or relative ease with which an SECTION 3 - Department of mines, minerals and energy explosive can be induced to chemically react. Different explosives will show differing sensitivity to stimuli such as shock, low velocity impact, friction, electrostatic discharge, or other sources of energy SECTION 3 - Department of mines, minerals and energy. The shock initiation sensitivity is the ease with which an explosive can be induced to detonate. Some explosives require only a single detonator for initiation, while others require large booster charges.


Detonator, or cap sensitivity SECTION 3 - Department of mines, minerals and energy, is one measure commonly used to indicate product ease of initiation, and also to classify products for safety in transportation, storage, and use. The standard used is the explosives’ sensitivity to SECTION 3 - Department of mines, minerals and energy initiation by a No. 8 test blasting cap. Blasting agents are an example of an explosive product that will not initiate with the detonation of the No. 8 test cap, under test conditions.

Fumes SECTION 3 - Department of mines, minerals and energy

The chemical reaction resulting from the detonation of explosives produces water vapor, carbon dioxide, and nitrogen, and also, in smaller concentrations, poisonous gases such as carbon monoxide and nitrogen oxides. Fumes SECTION 3 - Department of mines, minerals and energy differ from smoke, in that smoke is mostly steam and the solid products of combustion and detonation. Exposure to smoke, especially that produced from dynamite, should be avoided as severe headaches SECTION 3 - Department of mines, minerals and energy may result from contact with small particles of unreacted nitroglycerin in the smoke. Some carbon monoxide and oxides of nitrogen will be produced from all detonations, with the amounts depending on the conditions SECTION 3 - Department of mines, minerals and energy of the detonation. It is imperative that adequate waiting periods be observed before allowing personnel to enter the blast area, as some toxic gases are both odorless and colorless. Absence of smoke is SECTION 3 - Department of mines, minerals and energy no guarantee that noxious gases are not present in the blast area; therefore, always ensure the area has been sufficiently ventilated before entering.


Flammability

Flammability refers to the ease with which an SECTION 3 - Department of mines, minerals and energy explosive or blasting agent can be ignited by heat. As you might suspect, most dynamites are easy to ignite and burn violently. If the burning takes place in a confined SECTION 3 - Department of mines, minerals and energy space the burning may transform into a detonation. Water gels and emulsions are more difficult to ignite than dynamite; however, after most of their water is evaporated by a heat source they can SECTION 3 - Department of mines, minerals and energy support combustion without confinement. Of the most common commercial explosives, ammonium nitrate products, emulsions and water gels have a lower tendency than dynamite to convert burning into a detonation.

^ Explosive Classification SECTION 3 - Department of mines, minerals and energy

The U.S. Dept. of Transportation (DOT) uses the United Nations explosives shipping classification system. This system is based on hazard in shipping only, versus the previous DOT system that considered both shipping SECTION 3 - Department of mines, minerals and energy and use hazards.


^ Division 1.1 explosives (with a mass explosion hazard): This class exhibits the maximum hazard potential and will affect the entire load almost instantaneously. Examples include such products as dynamite, black powder, certain SECTION 3 - Department of mines, minerals and energy watergels/slurries, certain blasting caps, electric and non-electric detonators, detonating cord, MS connectors, primers, boosters, etc. Other examples include shaped charges, grenades, mines, and nitroglycerin desensitized.


^ Division 1.2 explosives (with a projection SECTION 3 - Department of mines, minerals and energy hazard): This class exhibits a projection hazard but not a mass explosive hazard. Examples include rocket propellants, certain fireworks, aerial and surface flares.


Division 1.3 explosives (with predominantly a fire hazard): This class SECTION 3 - Department of mines, minerals and energy possesses a flammable hazard, and includes smokeless powder, fireworks (display), tracers for ammunition, projectiles.


Division 1.4 (minor explosion hazard): This class exhibits a minor explosion hazard with the explosive effects this SECTION 3 - Department of mines, minerals and energy material largely confined to the package and no projection of fragments of any appreciable size or range expected. Examples include some types of blasting caps and detonating cord, consumer fireworks, small SECTION 3 - Department of mines, minerals and energy arms ammunition.


Division 1.5 (very insensitive explosives): This class has a mass explosive hazard, but it is represented by a low probability of transition from burning to detonation while in normal transportation. Examples include primarily blasting SECTION 3 - Department of mines, minerals and energy agents, such as ANFO, and low sensitivity water gels.


^ Division 1.6 (extremely insensitive explosives, no mass explosions): This class contains only extremely insensitive detonating substances that demonstrate a negligible probability SECTION 3 - Department of mines, minerals and energy of accident initiation or propagation.



segodnya-ntv-16062012-1000-teleprogramma-segodnya-ntv-16062012-rossijskie-smi-o-mchs-monitoring-za-26-oktyabr-2013-g.html
segodnya-ntv-21062011-1300-teleprogramma-segodnya-ntv-21062011-rossijskie-smi-o-mchs-monitoring-za-22-iyunya-2011-g.html
segodnya-ntv-25082012-1900-teleprogramma-segodnya-ntv-25082012-rossijskie-smi-o-mchs-monitoring-za-27-avgusta-2012-g.html