Flyrock can damage equipment and property, shut down operations, and even kill. When you're blasting, especially near open faces or poor geology, one bad shot can end your project or someone's career.

Most sites know what causes it—poor burden, insufficient stemming, overloading, but knowing the problem and fixing it are two different things.

Blasting Near a Free Face

If blasting along a free face, start by verifying you have sufficient burden. The general rule of thumb is, Burden = 25 to 40 x Hole Diameter. This can vary based on rock hardness, but it is a great place to start.

Poor Ground Conditions 

Where you have poor ground conditions in the top of the bench, here's a solution that works well. This allows you to reduce the amount of explosives in the "top zone" and create an air deck. Gases expand into the air gap, fracturing the rock, but with less energy than explosives.

Stemming

Crushed rock or competent drill cuttings work great in good ground. But if you're dealing with fractured or broken ground that won't hold stemming, you need something that confines the charge better.

BLASTBAGS™ lock into the hole and create a seal that will easily support stemming. BLASTBAGS™ combined with stemming can help confine gas pressure in the hole where it breaks the rock, instead of venting out the top.

We've seen sites reduced flyrock by 60-70% by introducing an air deck then stemming with crushed stone in problem areas. The case study results showed dramatic reduction in ejections when introducing a top hole air deck.

Which BLASTBAG to Use

Pick based on your hole sizes, how deep you're going, and whether you're dealing with wet conditions.

Use Air Decks

A gold mine in West Africa ran test blasts comparing standard stemming to air-decked columns with BLASTBAGS™. Here's what they changed:

That's 15kg (33 lbs) less explosive per hole with better fragmentation and dramatically less flyrock.

The air deck reduced upward pressure on the stemming and stopped stemming contamination. The BLASTBAGS™ locked into place and held the stemming where it needed to be instead of letting it blow out.

Mark Your Blast Zone

Flyrock travels. Even when you do everything right, you need people to stay clear. You should NEVER be closer than 500' (152m), but the general rule of thumb is 1.5 times the distance the furthest rock has flown in the past.

MTI offers Barricades, Road Cones, Barricade Tape, Signs, Warning Sirens, and Flashing Solar Lights to help safely barricade your blasting zone.

What Worked in the Field

The mine had been dealing with excessive flyrock near housing and infrastructure. They'd tried changing blast designs and using blast mats. Nothing worked. After a tragic incident, they shut down all boundary blasting until they could fix it.

MTi's blasting experts reviewed the site conditions, designed three test blasts, and worked on-site with the crew.

Blast 1 – Split test comparing standard stemming on one side to BLASTBAGS™ on the other. The BLASTBAG™ side showed better confinement and fewer ejections.

Blast 2 – Full optimization: 2.5m(8.2 ft) stemming, 1.5m(4.9 ft) air deck, BLASTBAGS™ throughout. Excellent confinement, dramatic flyrock reduction, and good fragmentation.

Blast 3 – Refinement of Blast 2 design. Continued strong performance.

The optimized design used 11% less powder per hole and cut flyrock risk significantly. After seeing the results, they switched to this method for all boundary blasts.

Operations resumed along the property line. Community relations improved.

The Bottom Line

Flyrock isn't one thing. It's insufficient burden, poor stemming, bad charge placement, poor ground conditions, or a combination of these.

Verify you have sufficient burden based on the hardness of your rock. Fix confinement by using competent drill cuttings or crushed stone. Use BLASTBAGS™ combined with stemming in broken collars. Air deck your charges where it makes sense. Clearly mark your blast zones so people stay clear.

That's how you keep rock in the blast area and off someone's truck.