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www.rockproducts.com ROCK products • March 2017 • 61 Heavy ANFO A Heavy ANFO is similar to a blend, yet it contains more ANFO than emulsion; the case that will be presented is a 30 percent emulsion and 70 percent ANFO. A Heavy ANFO will have more energy per pound than a blend or normal ANFO. It should always be made from a properly oiled ANFO mixed with an emulsion and is augured into the borehole. A Heavy ANFO is distinguishable from a 50/50 blend because it begins to look like prills with an emulsion coating. A Heavy ANFO should also have the emulsion sensitized to decrease the amount of fumes generated from the blasting. While chemical gassing can be used, microspheres will give a more reliable and consistent detonation. In some parts of the world, companies are charged for a sensitized emulsion and given an un-sensitized emulsion in a Heavy ANFO. For example, let's assume that an un-sensitized emulsion sells for $0.40 per lb. and a sensitized emulsion sells for $0.65 per lb. In a 30/70 Heavy ANFO this would be an overcharge of $0.075 per lb. This can equate to more than $300,000 at larger aggregate operations and more than $1,500,000 at metal mines. When ammonium nitrate prills are added to emulsions, the prills should not contain large quantities of crushed prill or fine prill dust. Water resistance decreases as prill size decreases. Large quantities of AN dust can also change the characteristics of the explosive and also result in rapid aging and breakdown of the emulsion. Conclusion Blends and Heavy ANFOs are fantastic options for many mining operations looking to optimize their blasting or reduce their blasting costs. However, many of the costs asso- ciated with blends are not accurately identified and go hidden in feasibility studies including the large increase of blasting fumes and critical diameter of the product. With stringent EPA regulations, many mines can face problems with large increases to blasting fumes produced exceeding permit models. In addition, "visible NO x " can cause concerns of neighbors and damage to the reputation of the mine in the local community. Finally, this increase in critical diameter of the product can result in an increasing number of misfires. These blends and heavy ANFO can also have confusing termi- nology that can lead to a mine operator being overcharged on product, costing hundreds of thousands per year. In order to avoid this and other problems a general knowledge of blends, ANFO and emulsion is necessary. It is best practice to have an experienced explosive engineer help in the development of blend usage at a mine. Dr. Calvin Konya is the president of Precision Blasting Services, and Anthony Konya is a project engineer for the company. They can be reached at 440-823-2263, or Anthony@idc-pbs.com. Figure 4 – 50 percent emulsion and 50 percent ANFO blend. Figure 5 – 30 percent emulsion 70 percent ANFO Heavy ANFO.