The 4 most costly blasting mistakes you can make

By |  April 9, 2021
Richard Ash presented key ratios 56 years ago that could be applied throughout surface blasting conditions to give comparisons between multiple types of operations. Photo:

Violence factor has been shown to be an excellent and simple tool to determine how a blast is breaking, the potential effects on ground vibration and flyrock, the potential effects on fragmentation, and the magnitude of backbreak expected. Photo:

No drilling and blasting operation is perfect. Mistakes will undoubtedly be made from time to time, but some are more costly than others. Here are four that will ultimately impact your bottom line and cut into profits.

1. Powder Factor Design

The costliest mistake companies make in their blasting is using a powder factor-based blast design.

The powder factor of a blast is nothing more than the pounds of explosive per volume or tons of rock, yet this has been expanded today to be a blast design philosophy some try to adopt to their mine.

The general understanding sounds like it makes sense: the more explosive we use, the better fragmentation we will have. It is not this simple, though, because the geometry and timing of the charge are the dominant factors in developing good fragmentation.

Two examples can illustrate this concept. One is an old Soviet Union (USSR) research program, and the second is from practical experience.

The Soviet Union needed to stop potential revolutions from occurring, and it dramatically sought solutions. During this process, it learned something that would permanently change its policy direction.

The major revolutions mostly came from universities where professors could get students to band together to fight oppression. If the USSR wanted to stop revolutions, it had to make professors happy. It knew the best way to get the support of the professors was to give them money – and lots of it. This money came in the form of research grants that would fund decade-long research projects that would be impossible without the government support.

A researcher named Kuznetsov was awarded a decade-long study on the fragmentation of rock from blasting. Kuznetsov’s goal was to find the perfect powder factor for every rock type. His research included small-scale experiments, as well as full-scale blasts where every piece of rock was sieved afterward to determine the exact fragmentation sizing of the blasts.

In the end, Kuznetsov found that powder factor had no real impact on the fragmentation from blasting. The geometry of the charge was at least an order of magnitude more important than powder factor. This concept later became the pivotal model for the fragmentation models that are used today.

This bit of academic research is interesting, but is it true practically?

I was called into a project in the Middle East to work with a mining operation and help with fragmentation. The mines in certain localities are interesting, because the regulations are widely different than countries such as the U.S., Canada and Australia.

In this case, the mine had a maximum powder factor it could use – and it was already at the maximum. The fragmentation was very poor, and the cost of handling oversize was extremely high.

To fix the situation, a two-stage process was used. Stage 1 was to abandon powder factor design. Stage 2 was to adopt a multivariate blast design. The result was an increase in fragmentation and a reduction in oversize by 500 percent to 1,000 percent.

Powder factor is not a design tool; it’s an economic tool or a key performance indicator (KPI) that can be used in relation to other KPIs to determine the economic cost of blasting to the performance.

When the powder factor is raised, the cost is raised – and that is the only guaranteed change in the blasting. The industry as a whole has absolutely no metric to evaluate how powder factor changes will affect the performance of a blast – and the research by Kuznetsov and others shows that no metric could exist.

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