CASE STUDY: REDUCING FLYROCK BY IMPROVING ENERGY RETENTION
The purpose of the Varistem® stemming plug trial conducted at Coal Mine X was to reduce flyrock, noise, and airblast by retaining blast energy. The
When your blast outcomes are inconsistent, the problem is often not the explosive. It may be based on blast design, and whether the energy is being directed where you need it. Varistem stemming plugs and AMS ROO gasbags both improve control in the blast hole, but selecting the right product for your specific site is key. We break down cost, diameter coverage, explosive compatibility, mechanism, and real-world results, so you can choose the right option for your hole sizes, production goals and more.
Varistem plug pricing scales with hole diameter, typically starting around US$1 per plug on smaller sizes and reaching about US$16.13 on larger sizes. In this way, you can match the plug to the actual hole diameter and keep the cost per hole predictable across mixed hole patterns.
AMS ROO gasbags are priced on a quote basis. That pricing scales by hole diameter and is sold in cartons of 25 to 30 units, depending on size. Public online pricing is not available for these gasbags.
Varistem offers transparent unit pricing, making cost-per-hole planning predictable. AMS ROO gasbags are quoted per carton, so budgeting requires a supplier quote. Online list pricing is not publicly available for AMS ROO gasbags.
Varistem stemming plugs cover blasthole diameters from 1.75″ to 10″ (45 to 251 mm) across the BP size range. You can pick a plug that matches the as-drilled hole diameter rather than forcing one size across a mixed pattern.
AMS ROO gasbags cover blasthole diameters from 76 mm up to 311 mm, with different ROO size codes mapped to specific diameter bands. These size codes range from ROO76 to 115, from ROO115 to 127, and end at ROO311.
Varistem covers 45 to 251 mm holes with a straightforward BP size range that’s easy to match to as-drilled diameters. AMS ROO gasbags extend coverage up to 311 mm through banded ROO size codes, making them the better fit when you’re running larger production diameters or need coverage for bigger holes.
In terms of explosive compatibility, Varistem is commonly used with ANFO, emulsions, water gels, and heavy ANFO. Selection still follows hole conditions, including ANFO for dry holes and more water-resistant products for damp/flooded holes, as well as your site’s blasting procedures.
AMS ROO gasbags are typically used as decking plugs alongside the same common bulk products you’d load in production holes, including ANFO, heavy ANFO, emulsions, and water gels. The practical “compatibility” decision is driven less by the explosive type and more by hole conditions.
Both Varistem plugs and AMS ROO gasbags are generally compatible across the same mainstream bulk explosives. Although this is important, it is not an important factor to consider when choosing a stemming plug.
Varistem is installed point-down and pushed onto a loading pole to sit directly on top of the explosive column. Subsequently, normal stemming is placed above it. On firing, the initial shockwave forces the plug upward into the stemming, where its flexible, tear-resistant body “locks” the stemming in place and forms a short-term pressure seal in the blasthole. This brief seal drives more explosive energy into the surrounding rockmass before the burning front reaches and destroys the plug.
AMS ROO gasbags are 2-speed, aerosol-inflated blast-hole plugs used for decking. Each unit contains a non-flammable gas inflator aerosol, a 2-speed “total release” actuator, a gas-impervious inner bladder, and a robust woven outer bag. To deploy, you attach a lowering cord to the breakout tag, then actuate the canister. Activation starts immediately and cannot be stopped, with a brief window to lower and position the gasbag before it fully expands.
Varistem is a shock-activated stemming plug: it sits on top of the explosive and, at initiation, is driven into the stemming to create a short-term pressure seal that reduces early venting and improves confinement. The AMS ROO gasbag’s mechanism provides in-column control with decking or air-decking and deck separation. It should be noted that as a result of the AMS ROO gasbag’s deployment mechanism, a risk exists of deploying the gasbag in the incorrect portion of the hole column, necessitating destruction of the incorrectly deployed gasbag and re-deployment of a new one.
Varistem plug results are reported independently across three areas: safer blasts, improved fragmentation, and downstream productivity gains. At one underground platinum mine, Varistem was credited with an average 11% improvement in advance per blast, increasing advance per blast from 2.46 m to 2.82 m, and was associated with an estimated R1.19 billion in annual net benefit linked to improved ore recovery.
Across other sites, reports describe flyrock reductions of up to 80%, an 87% improvement in cast, crusher throughput gains exceeding 14%, more than US$10 million per year in added value, roughly US$1.45 million in savings from reduced waste, and loading rate improvements of up to 8%.
AMS markets ROO gasbags as a “proven” blasting accessory, yet does not publish public KPI tables. They claim that the product saves on explosives and provides stemming enhancement, lower vibration and overpressure levels, improved fragmentation, and an inflatable design that assures a perfect seal-off.
Varistem has site-level, quantified results showing improvements in advance, fragmentation, flyrock control, cast, and crusher throughput, alongside documented productivity and cost gains across multiple operations. AMS ROO positions their gasbags as a performance-enhancing decking/air-decking tool, with manufacturer claims focused on explosive savings, improved stemming/seal-off, lower vibration and overpressure, and improved fragmentation. AMS does not publish public KPI tables for ROO gasbags specifically.
Choose Varistem for an everyday stemming solution that improves collar confinement without inflating consumable costs. With sizes from 1.75″ to 10″, it suits small- to mid-diameter production holes and helps crews deliver more consistent collar performance from blast to blast.
It’s the right fit when your main goal is to keep energy in the rock at the collar, rather than solving wet-hole conditions, voids, or other issues deeper in the column.
Choose the AMS ROO gasbag when you need a decking or sealing solution inside the column, not just tighter collar confinement. It’s a strong fit for larger diameter holes and mixed patterns where you want to create a reliable air deck, separate explosive decks, or manage voids and irregular ground that make energy distribution unpredictable.
Varistem and AMS ROO gasbags are both proven tools for improving blast performance, but they do it in different ways and belong in different parts of the hole. Varistem is the practical choice when you need a consistent, everyday stem upgrade that strengthens collar confinement in small- to mid-diameter holes, with transparent unit pricing that keeps the cost per hole predictable.
AMS ROO gasbags are better suited to situations where the blast design requires in-column control through decking or air-decking, especially in larger-diameter holes or variable ground, where separating decks and creating air gaps can reduce explosive consumption while maintaining fragmentation targets.
Contact us for a quote to see how your blasting team can benefit from Varistem.
The purpose of the Varistem® stemming plug trial conducted at Coal Mine X was to reduce flyrock, noise, and airblast by retaining blast energy. The
In our business, we are in a unique position where we get to spend time at countless sites, working with drillers and blasters during the planning,
Introduction Pre-split blasting is a vital controlled blasting technique used in surface mining, quarrying and construction operations to preserve the stability of final pit walls,