Necessary
We think past production and see our impact on the world.
An essential part of our civilization is the wide availability and distribution of inexpensive, high-quality stone. The most economical way to extract Wisconsin’s famously hard limestone is with explosives. This keeps costs down for every builder and supports our state’s infrastructure. If there were a more economical way to extract stone, the industry would immediately switch to that.
Safe
We take risks on new ideas, but not on safety.
Blasts in our quarries are designed by highly trained and skilled blasters who are certified by both the Mine Safety and Health Administration and the Wisconsin Department of Safety and Professional Services. The heavily regulated explosives used are generally safe to handle, and components are delivered separately to ensure safety over the road. Blasters place multiple seismographs and audio sensors near the closest residences and businesses to ensure that the ground vibrations and “airblast” are well below state limits.
Getting better
Mining is our craft and our passion.
In the early days of quarrying, explosive placement was not done scientifically, although attempts were made to minimize cost and maximize output. High explosives were detonated instantaneously, causing ground vibration and “airblast” often felt by the whole neighboring community.
Today, instead of instantaneous detonation, explosives in each drill hole are initiated in a predetermined sequence so that there are delays of a few milliseconds between each activation. The shock waves generated direct much more energy into breaking the stone effectively (making the blast more economical) and less into air and ground vibration (making blasting less alarming for our neighbors).
Blasters create a detailed record of each blast, including the results of seismographic monitoring, and we maintain those blast records for years. The most important use of the records is to continually make blasting outcomes more predictable.
We work with, appreciate and learn from all people. New blasting research and techniques are coming out constantly. We attend industry conferences several times a year to learn about improving blast results from the experts. We love trying new approaches and are constantly experimenting to see if other methods used around the world may improve blasting outcomes for our miners and neighbors.
We appreciate feedback from our neighbors because we need more information about blast performance to continue improving our program. Blasters can often optimize the layout and timing of a blast to manage the impact that’s perceived by the community around the quarry, so every bit of feedback helps.
Blasting FAQs
What causes ground vibration and how is it measured?
When a blast detonates, energy radiates in all directions as wave motion, like a ripple created in a lake when a stone hits the water. This wave travels mainly along the surface at 5,000 to 20,000 feet per second. Its energy level falls off rapidly with distance and is normally undetectable by most people beyond several thousand feet. Because explosives are expensive and vibration represents wasted energy, it is to the blaster’s advantage to minimize ground vibration.
How is ground vibration controlled?
Blasters control ground vibration by limiting the weight of explosives detonated within any 8-millisecond period of time. They use millisecond-delay detonators (blasting caps) to separate the firing time of each hole. A typical 50-hole blast, therefore, is actually 50 smaller, separate explosions.
What is “airblast” and how is it measured?
When a blast is detonated, some energy is lost to the atmosphere as noise or concussion. This is caused by gases venting through cracks and the motion of rock on top and in front of blastholes. The resulting sudden increase in air pressure is called airblast. Like ground vibrations, airblast levels decrease rapidly with distance. However, airblast travels only at the speed of sound, about 1,100 feet per second, depending on air temperature, and can be greatly influenced by wind direction and speed. Atmospheric temperature inversions can also influence airblast by bending it back towards the earth and focusing its energy several miles away. Airblast is measured with a special microphone connected to a seismograph. The most common units of airblast measurement are pounds per square inch (PSI) and decibels (dB).
How is airblast controlled?
Airblast is controlled by placing stemming material (drill cuttings or crushed stone) above the explosives in the blasthole and by not loading explosives into parts of holes with cracks, voids or mud seams.
What are the legal limits for ground vibration and airblast?
The United States Bureau of Mines conducted extensive research over a 35-year period and has published recommendations that limit blast-induced ground vibration and airblast to protect homes and other structures from damage. The Division of Mineral Resources has incorporated these recommendations into mining permits as special permit conditions for mines across the state.
Per Wisconsin Code SPS 307.44, an airblast may not exceed 133 peak dB at the location of any dwelling, public building or place of employment outside the controlled blasting site area. The blaster shall use the ground vibration limits specified below to determine the maximum allowable ground vibration.
Seismographs measure ground vibration in terms of particle velocity, which is the speed, in inches per second, at which ground particles oscillate as the wave passes. Beyond several thousand feet, ground movement is only a small fraction of an inch.
Who do I call with blasting questions?
To give us feedback directly, or for a tour of operations, call our main office (262) 251-1520 and ask for Nate Swinton. Contact Charlene Vogt with the Wisconsin Department of Safety and Professional Services at Charlene.Vogt@wisconsin.gov for regulatory questions.
