The 4 most costly blasting mistakes you can make

By |  April 9, 2021

2. KPIs

Photo by Pit & Quarry staff.

Insufficient burden on a blast occurs when the drill deviates toward the free face. Photo: P&Q Staff

The phrase “you can’t manage what you can’t measure” has become commonplace in the blasting community and throughout management literature.

Throughout the mining process, KPIs have been set up that can be measured and managed. The biggest issues with these KPIs is that you have to understand what the goals and appropriate levels are that represent a well-functioning system.

A frequent occurrence for me is that, when beginning work with a mine, about 50 percent have no KPIs or metric that are being tracked. The first step to improve blasting is to develop these systems and measurables. The KPIs should be measured, documented and recorded in a database or spreadsheet for each blast so they can be analyzed through time to observe the impacts of blast changes.

These KPIs should stay fairly consistent, as long as the long-term blast strategy stays consistent but will have minor changes based on the short-term strategy and daily blast modifications. The monitoring also develops a baseline from which changes to the blasting program can be evaluated for their effectiveness.

It is also critical that these KPIs are not solely based on the performance of the blast. Parameters such as peak particle velocity, the 50 percent passing (P50) and other metrics are important and valuable data. Still, KPIs must be established for the blast design (i.e., burden to spacing ratio, stiffness ratio) and the actual implementation of the blast design (i.e., drill deviation, minimum stemming in a hole). These can then be analyzed in a system to observe how changes in the design or the implementation of the design (the drilling and loading) affect the performance of the blast. All important aspects should have easy-to-manage KPIs set up.

After a KPI is set up, the next problem is that the management team can identify what results are achieved from the current system. But, the management team often does not know the full range of possibilities for the site.

For example, one site I consulted for was using powder factor as a KPI for cost of the blast and a boulder count (number of boulders larger than 3 ft. in diameter) as an oversize KPI. The issue was that the powder factor hardly ever changed, and the boulder count stayed within the same general range. The KPIs were eventually abandoned because they were just being used as data and not as a tool to manage the blasting.

Management then assumed that if the powder factor was decreased, boulders would increase – and vice versa. Through the consulting program, it was shown that the powder factor was reduced by about 75 percent while the boulder count was decreased – the opposite of what management thought would occur.

In this case, it becomes critical for management to use reference classes or general ranges of numbers that represent good, OK and bad performance for KPIs.

This goes one level further: It is not just a singular reference class for a KPI, but a function of reference classes for interrelated KPIs. For example, as the explosives per hole changes, what is the good range, OK range and poor range for ground vibration at a nearby structure?

Setting these KPIs up is one of the most critical parts of managing a successful blasting program. Put together expectations and measure the actual values on a per-blast basis. As blasting changes, identify what is causing these changes and what ranges are acceptable based on available or developed reference classes.

A great KPI being widely used today is violence factor, which is a comparison of the vertical height of flyrock to the bench height. This violence factor has been shown as an excellent and simple tool to determine how a blast is breaking, the potential effects on ground vibration, the flyrock, the potential effects on fragmentation and the magnitude of backbreak expected.

Violence factor can be used with other KPIs to determine what the different ranges of reference classes are based on the blasting. It is strongly related to the overall blast performance. A high violence factor leads to poor performance in every aspect, while a low violence factor leads to good overall performance.

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