Blasting sequence is the planned order in which explosive charges in a blast are detonated, while delay timing is the specific interval of time between sequential detonations. Together, they are critical for achieving finer rock fragmentation, controlling rock displacement, and minimizing ground vibrations by allowing seismic waves from each explosion to interfere constructively or destructively.
Key considerations in designing a blasting sequence and delay timing include:
Blast design parameters: these involve selecting the appropriate hole diameter, blast hole depth, burden (distance from the hole to the free face), spacing (distance between holes), bench height, and explosive type and quantity (powder factor). The pattern of the holes (square, staggered, rectangular) also impacts the blast design [1].
Initiation sequence and delay timing: the delay timing between holes in a row is generally between 1 to 5 milliseconds per foot of burden, with about 3 ms yielding good results. The delay between rows is typically two to three times longer than that between holes in a row. Corner holes often need extra delay due to the rock fixation at those points. Delay timing is critical for optimizing rock fragmentation, controlling flyrock, minimizing vibration, and ensuring effective rock movement [2].
Blast patterns and timing: common patterns include staggered (for row firing), square, and rectangular patterns often used for “V” (chevron) or echelon rounds. Millisecond delay blasting sequences are designed to ensure the blast progresses at an optimal rate for fragmentation and movement, reducing cut-off effects in explosive columns and preventing adjacent hole interaction issues like dead-pressing [3].
Optimal delay time also depends on the velocity of rock movement post-detonation and the size and burden of the blast holes, using rules of thumb like “2 milliseconds per foot of burden” for effective timing.
Additional considerations include specialized techniques such as presplitting and smooth blasting for perimeter control, especially where maintaining wall stability is critical.
To sum up, designing the blasting sequence and delay timing involves balancing explosive energy distribution, timing intervals related to hole spacing and burden, and desired rock fragmentation and displacement outcomes, while minimizing adverse effects such as vibration, flyrock, and overbreak. The use of millisecond delays and sequencing patterns plays a crucial role in achieving these objectives effectively.
Reference
[1] “High-Level Blast Design Basics Explained.” Accessed: Sep. 09, 2025. [Online]. Available: https://ergindustrial.com/high-level-blast-design-basics/
[2] P. D. Sharma, “ROCK BREAKAGE AND BLAST DESIGN CONSIDERATIONS IN OPENPIT,” Mining and Blasting. Accessed: Sep. 09, 2025. [Online]. Available: https://miningandblasting.wordpress.com/2012/10/12/rock-breakage-and-blast-design-considerations-in-openpit/
[3] C. J. Konya and E. Walter, “Surface Blast Design,” 1990. Accessed: May 15, 2025. [Online]. Available: https://www.semanticscholar.org/paper/Surface-Blast-Design-Konya-Walter/1f5ad0b76b760559079338b7c89053406a3a5755
