Rock Blasting

Charging

After drilling, drilled holes were blown to remove water and dust particles. Then required number of drill holes, were charged with explosives. We used chemical explosives for blasting according to the mining license. When we used Electric detonators as initiator, Gelatin Dynamite and ANFO (Ammonium + Fuel oil) were used as base charge and column charge respectively . If we use plane detonator as initiator, we used Black powder as column charge.   

 Electric Delay Detonators

Electric Delay Detonators  are the very safety initiating agent for the blast. There were nineteen accurately timed, static resistant, delay electric blasting caps designed for rugged blasting conditions in mines, tunnels, shafts and other underground construction projects. We used such caps which contain delay numbers starting from 0 to 9. The delay number has mentioned in the delay tag which is attached to the cord. It has an Aluminum or Copper tube and it includes a fuse head this has surrounded by coatings of flashing composition. This special composition is high heat sensitive is ignited by an electric current, which then initiates prime and base charges. The delay element is also a metal tube filled with a chemical composition that burns at a uniform rate. The length of the tube determines the duration of the delay. If tube is long, initiation is late. We were used 25ms delay electric detonators.

 ANFO (Ammonium Nitrate with Fuel oil)

ANFO was used as column charge in blasting. Normally Ammonia Nitrate was come as prills (Annex 07/P I) condition in 25Kg bags.ANFO was made mixing Ammonium Nitrate and Fuel oil (Diesel).For 25Kg Ammonium Nitrate was mixed with two liter of diesel. Water resistance of ANFO is very low.ANFO was highly soluble in water.Threfore in wet conditions we couldn’t used ANOF as loose condition. In wet condition we were used ANFO packets (Annex 07/P I) for charging.

Semi Gelatin Dynamite

GD was used as Base charge in blasting procedure.Gelatine Dynamite has high water resistance, therefore can be used for any wet condition. Normally Dynamite was come as cartridge type with 200mm long and 25mm in diameter (Annex 07/P I) When boulder blasting, Gelatin Dynamite was used separately with ED.  

 Charging Methods

Various types of blasts were done in quarry. Test Blast, Production Blast, Boulder blast were some of those. Before charging drilled holes we had to consider many factors. According to those conditions explosive quantity was changed. Those factors are,

1.      Delay Patten

2. Direction of delay Patten
3. Structures which was affected by blast
4. Rules and Regulations
5. Type of Blast