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Modern professional blasting, when conducted within the vicinity of susceptible structures (homes, buildings, utilities, etc.), is planned and designed to facilitate rock excavation without causing damage to nearby structures. Blasts are carefully designed to impart only the amount of energy necessary to achieve the blast’s objectives. Conservative safe vibration standards have been established based on years of study by the United States Bureau of Mines (USBM) and decades of experience in the professional blasting industry. Safe vibration standards are applied as limits to be met in the design and execution of a blast. The recommended limits provide a safety factor, or cushion, in that vibrations can exceed these limits without causing damage. If blasting damage were to take place, damage will occur in the weakest elements first, therefore, vibration standards were developed to protect the weakest elements of a structure: lath, drywall, and plaster. Multiple factors are taken into account in the design of a blast to assure that ground vibration and airwave energies are safely limited at nearby homes and structures. Blasting seismographs are used to monitor ground and air waves, documenting blast energies at the location they are monitoring. Seismographs will be deployed at various locations to monitor blast energies. The data are used to evaluate the intensity of the vibrations and determine compliance with vibration standards.
Homeowners may be concerned about possible blasting damage. With modern blasting practices, the occurrence of blasting damage is infrequent. Blasting damage can only occur at the moment blast vibrations excite the structure. There is no residual effect from blasting. Blasting cannot cause damage that develops in the following weeks or months. When damage is cited, it occurs first in the weakest materials resulting in cosmetic damage that can typically be easily repaired. The strongest elements of a home, the structural elements, will not experience damage with a well-designed blast. Foundations, concrete driveways, framing, roofing, and other strong elements cannot be damaged without extensive damage to the weakest elements.
Most of the energy from a blast is used to break rock, but some energy will travel from the blast site in the form of ground and air waves. These waves spread out from the blast much like waves from a pebble dropped in a pond, dissipating with distance. Both the ground and air waves can cause your house to vibrate or shake. Humans are very sensitive to such vibrations and sounds. The likelihood of blasting damage cannot be estimated by the perceptions of occupants inside during the event. When inside a house, you feel, sense, and hear the structure and objects around you responding to the vibrations. You may hear windows and dishes rattling, hanging objects may swing, and other phenomena may occur. These responses can occur even though the vibrations are well below levels that cause damage. A well-designed blast will result in vibrations which are below the threshold that causes damage even to the weakest elements of the home. Blasts are designed to limit ground motion, or ground displacement, to an amount that’s no greater than the width of a single sheet of paper, yet these minor movements can be strongly felt. Blasts will be covered to limit dust and fly rock.
For public safety, the blast site will be strictly monitored during blasting activities. Notifications of the blasting schedule will be displayed at the project site. Be aware that roads adjacent to the site will be closed at the time of a blast.
Many answers to common blasting-related questions can be found at www.explosives.org under FAQ.
A video explaining the effects of blasting vibrations can be viewed on www.youtube.com. Search for “Understanding Vibrations from Blasting” by ISEE, the International Society of Explosives Engineers.