Basics of open cast blasting

1.  Rock usually takes "60 ms(milli-second )" to move around "1 m".
2. A blasting is said to healthy when it is free from fly rocks, with minimum vibration and boulders up to 1 %.
3. Drilling and blasting cost should be within 22 % of the contract price.
4. Minimum stemming of 3.5 meter should always be maintained.
5. Efforts should be made to complete the blasting within 800 ms.
6. Range of burden/spacing should be between 0.5 and 1.0.
7. For optimum breakage, bench height/burden should be around 2.5.
8. For satisfactory throw, bench height/burden should be greater than 2.5.
9. Bench height should be between 10 and 12 m. 
10. If the stemming height is 1.2 to 1.5 times the burden then fly-rock can easily be controlled.

• bold parts are thumb rules.

Rock type(based on RMR)	Burden(in meter)(B)	Spacing(in meter)	Stemming(in meter)
Very poor	51 X D*	1.45 X B	1 X B
Poor	44 X D	1.34 X B	0.95 X B
Medium	37 X D	1.25 X B	0.95 X B
High	29 X D	1.19 X B	1.1 X B
Very high	23 X D	1.14 X B	1.1 X B

• D: diameter of hole in mm (100,160,…..)