Explosives used in surface mine blasting

More than 90% of the domestic explosive and blasting agent formulations generally used are ammonium nitrate (AN) based (USGS, 2000). A mixture of ammonium nitrate and fuel oil, commonly known as ANFO, gained acceptance for blasting at surface mines. The major advantages of ANFO are related to safety, economy, and ease of handling when compared to nitroglycerine (NG)-based high explosives. Various forms of NG-based high explosives were used in surface blasting before the introduction of ANFO. During the past two decades, ANFO formulations have undergone numerous innovations to improve performance, shelf life, density, porosity, specific energy, and water resistance. Since its introduction, ANFO has replaced many grades of dynamites and other high explosives. Hundreds of patents related to improvements of ANFO and its loading procedures have been filed at the U.S. Patents Office. ANFO-based explosives are now available in various sizes, styles, and consistencies. Because of the diverse mechanical and geological properties of rock and the unique conditions at each blast site, a wide variety of products are available. Free-flowing dry blasting agents, with the addition of finely divided, flaked, or even granular aluminum, can be mechanically loaded in dry holes for improved performance. A variety of emulsified and gelled products are specifically designed for wet blastholes. Ingredients have been developed to improve density, rheology, sensitivity, water resistance, and detonation velocity of packaged and bulk products. Between 1990 and 1999, roughly 22.3 billion kg of explosives were used by the mining, quarrying, construction, and other industries in the United States (USBM, 1991; USBM, 1992; USBM, 1993; USBM, 1994; USGS 1995; USGS, 1996; USGS, 1997; USGS, 1998; USGS, 1999; USGS, 2000). Out of this, coal mining used 66.4%, nonmetal mining and quarrying 13.5%, metal mining 10.4%, construction 7.1%, and all other users 2.6%.

By T. S. Bajpayee, T. R. Rehak, G. L. Mowrey, and D. K. Ingram