ANFO - the diversified blasting agent for the future

摘要

ANFO is the most used industrial blasting agent in the world, and is often used as a reference for comparison of other explosives. It is known to work very well under dry conditions in large borehole diameters, whilst in small bore hole diameters the formation of high amounts of toxic fumes (CO, NO and NO_2) can result. In underground blasting, problems can also occur with reduced visibility caused by uncombusted ammonium nitrate. ANFO is made by mixing ammonium nitrate porous prills (AN-PP) and fuel oil. Norsk Hydro has measured velocity of detonation (VOD), toxic fumes and visibility after blasting with ANFO in 54×2 mm steel tube based on several grades of AN-PP. The differences are remarkable: By using an AN-PP grade developed for underground blasting and small diameters, the following can be obtained: - VOD increases from 1500 to more than 3000 m/s. - The amount of CO can be reduced by more than 30%. - The amount of NO and NO_2 can be reduced by more than 50% and 80%, respectively. - The visibility can be improved by more than 90%. The results show that it is important to chose the correct AN-PP grade for the different applications. A good "surface AN-PP" is not necessarily a good "tunnel AN-PP", and vice versa. It is also pointless to use ANFO as a reference blasting agent for VOD and toxic fumes without referring to the AN-PP characteristics. The results in this paper are based mainly on tests in steel tubes. Norsk Hydro will follow up this work with full scale tests, and will continue to develop different AN-PP grades, tailor made for different applications.