For a majority of the blasting we do at MRD, we are either using ANFO (ammonium nitrate and fuel oil) or a bulk emulsion blasting agent. Both of these blasting agents have been in use for a long time and are used around the world every day. MRD is not unique in the fact that these are our two main blasting agents.
Ammonium nitrate is a chemical commonly used as fertilizer. However, when properly mixed with diesel fuel oil, it becomes a potent explosive that is extremely effective when placed in a borehole and used to fracture rock. ANFO, as this mix is commonly known in the industry, has been in use since the 1950s. Since then, ANFO has been a huge tool for the blasting industry, allowing many new ventures that were once thought to be uneconomical to now thrive. The mix has lasted over 60 years, without much change to the original formula of about 94% ammonium nitrate prills and 6% diesel fuel oil.
The mix we use is either placed in 50 lb. bags or 2000 lb. totes that are then moved around the job site via skid steer loader. MRD has blasted millions of pounds of ANFO over the years, relying on its consistency and reliability for fracturing rock. For all of its positives however, ANFO does has some major limitations.
As many of you know, the Pacific Northwest is one of the most beautiful regions in the United States. One reason why our region is known for being so lush and green is due to the fact that west of the Cascade Mountains we get a significant amount of rainfall each year. If you are not familiar with blasting in wet conditions, this moisture can wreak havoc on the drilling and blasting process. When dealing with ANFO, we must realize it is highly sensitive to moisture, which means it absorbs water, whether from the air or from the ground. All of the great properties ANFO offers only work when conditions are dry. Some years are better than others but for MRD, this is a daily element of planning and executing blasting projects throughout the region.
We do have some options when it rains or if we run into an area with significant groundwater (which happens all the time). One option is to suck the water out of the boreholes after they are drilled. Once the blast is drilled and we can check each hole to see whether it contains water, we can determine if we want to attempt to dewater. Dewatering a blast consists of using an air pump with a long hose connected to it to attempt to suck the water out of the boreholes. We use the word “attempt” on purpose when discussing dewatering because this process is not always successful. If the water is groundwater running into the holes, as opposed to surface water, we will have a tough time displacing the water. Once we suck some water out, more water will more than likely replace it from wherever in the ground the moisture is coming from. This is a major issue with ANFO because even the smallest bit of water can cause the product to become ineffective.
There are other ways to use ANFO in wet conditions, but it is definitely not as efficient or reliable as using it in completely dry conditions. When dealing with ANFO in our region, we must be very mindful of the weather as well as underground water sources, as these can negatively impact any drilling and blasting project.
Check back soon to learn about the emulsion blend blasting product we use and how it differs from ANFO.