Bill Hamlin-Boxley’s Vice President-Aggregate Operations
We find that many of our neighbors’ concerns come from misconceptions about modern blasting. They have notions that we light sticks of dynamite and drop them down the hole. None of our pay ranges come close to what it would take to pay someone to do that!
These days quarry blasting is a precise and highly engineered activity that uses a series of smaller blasts which actually work against the following blast to significantly reduce noise and vibration. It is stringently regulated and should be. All of our quarry blasts are designed, loaded and overseen by a professional blaster, certified by the State of Virginia.
So how are shots measured and monitored to ensure compliance? The energy released from a blast generates ground vibration and air overpressure. Ground vibration is measured in inches per second. This is the speed at which the vibrations move through the ground not displacement of the ground. Overpressure is measured in decibels which can also be converted to pounds per square inch. Seismographs are placed at the nearest off site occupied dwelling per state law to measure the vibration and overpressure generated by each of our blasts to ensure compliance.
If you live within a half mile or sometimes even a little further from a quarry shot you will know when the blast is initiated. The fact that you can feel or are aware of the shot does not mean that your house has been or will be damaged.
The United States Bureau of Mines has issued guidelines to ensure homes are not damaged by quarry blasting. These guidelines are based on 50 years of data from scientific studies to determine exactly what levels of vibration or air overpressure can cause damage to residential structures. These standards are based on science, physics and engineering and have been proven to be factual and have never been successfully challenged in a court of law. Vibrations and decibel levels from Boxley’s blasting operations are well below the allowable limits dictated by Virginia law.
Virginia law allows vibrations up to one (1.0) inch per second which is twice as stringent as the U.S. Bureau of Mines guidelines. Virginia laws are based on the U.S. Bureau of Mines extensive testing on what level of vibration or overpressure can cause even cosmetic damage to residential structures. Vibration levels from blasts at Boxley’s operations are 70%- 80% below the state allowable levels.
The U.S. Bureau of Mines has also completed several studies on wells and underground pipelines to determine if blasting will cause damage to these underground structures. Virginia’s vibration limit of 1.0 inch per second is 4% of what these underground structures can safely tolerate.
Most people are surprised to learn that common household activities exert many times the stress and strain on a home than a quarry blast. Slamming a door produces 25% more stress on a residential structure than Virginia’s vibration limits allow.
While normal human activities in a home produce a lot of stress on a house, the real culprit in routine cosmetic cracking and minor damage in residential structures is weather. Changes in temperature and humidity and wind have been proven to cause the overwhelming amount of normal and routine cosmetic damage that occur in residential structures. An outside change in temperature of 27 degrees causes stress on a home 8 times what the state laws allow from a quarry shot. A change in humidity of 35% is equivalent of a quarry blast over 5 times allowable state limits. Winds of 23 miles per hour stress a home more than two times what the state allows a quarry blast to produce.
To give further perspective to the amount of disturbance a typical blast causes, here is a chart with information provided by Sauls Seismic and the US Bureau of Mines:
Facts about blasting at Boxley:
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Blast records are open to state regulatory inspection.
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Each shot is designed and overseen by a professional licensed blaster.
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No explosives are stored on site.
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The bulk explosives are delivered to the quarry in a safe and inert form. Only after their arrival are the explosives activated prior to being placed in the rock formation.
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Blasting would occur about once a week at the Flat Creek operation.
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A blast last about 1-2 seconds.
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Dust from a blast settles in a couple minutes.
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Unprecedented large buffer (distance from neighbors) at the Flat Creek site will allow dust from the shots to settle on site.
Safety is the paramount concern of our blasting program. Your safety, your home’s safety and the safety of our people are the highest priority when each and every shot is designed and detonated.
