The Problem
Explosive costs add up fast. Every hole, every shot, every shift.
A large coal miner in the Powder River Basin was spending big on bulk explosives for their overburden shots. And with commodity prices squeezing margins, they needed to find a way to use less product per hole without sacrificing results.
Here's the thing — cutting explosive doesn't help if fragmentation falls apart, overbreak gets worse, or digging slows down. The goal was simple: spend less on powder and keep everything else the same.
What They Tested
An independent consultant (Respec) ran 4 test blasts comparing traditional loading to 3 different air deck configurations using MTi BLASTBAGS™.
The setup was straightforward. They took the same blast design and replaced a portion of the explosive column with an air deck. The BLASTBAG™ sits between the stemming and the explosive, holding position so the stemming stays where it should.
They tested reducing the explosive column by 3 ft (0.9 m) in the first two designs and 5 ft (1.5 m) in the third, adjusting stemming height across all blasts.
Different air deck designs were placed in different sections of the test blasts, so results could be compared side by side.
A few things they did to make sure the data was solid:
- Checked explosive height in every hole after loading
- Compared as-drilled patterns to design — less than 2% variance across the board
- Attached witness strings to the BLASTBAGS™ to confirm Blastbags and stemming did not slip
- Took VOD measurements in every test blast to confirm explosive performance
- Compared dig rates from the shovel in the baseline area to dig rates in the test area
The Results
All test blasts hit the expected VOD. The bulk explosive performed the way it was supposed to.
But the numbers that matter are these — from Test Blast 3 (with a reduced powder factor of 0.64 lbs/CYD):
| Metric | Baseline | Air Deck | Change |
|---|---|---|---|
| Digability Index | 160.96 | 163.86 | -1.8% (slightly better) |
| Payload (tons/bucket) | 106.57 | 109.15 | +2.4% |
| Cycle Time (sec) | 44.10 | 43.70 | -0.8% |
Read that again. Fragmentation didn't suffer. Payload actually went up slightly. And cycle time stayed the same.
Test Blast 4 confirmed the same results.
So What Does This Mean?
By replacing a portion of the explosive column with an air deck, this mine reduced their powder factor without compromising dig performance, fragmentation, or cycle time.
The mine estimates they can reduce explosive consumption by up to 5,800 tons per year. That's approximately USD $1.6 million saved annually on bulk explosive costs alone.
The extra time to deploy the BLASTBAGS™ in each hole? The study called it negligible. Non-consequential. The cost-benefit was clear.
What Happened Next
The mine adopted air decking in all their overburden shots. They're planning to trial it in their coal shots as well.
Two other miners in the region ran similar tests — both for overburden and coal. Both produced successful results. One has fully adopted air decking in their blasting procedures. The other is in advanced trials.
This case study was conducted by Respec, an independent consulting firm, at a coal mine in the Powder River Basin, USA.
