Frequently Asked Questions

Rock blasting generates very low-level ground vibrations and air blast (or air pressure) that may travel away from the blast site to the surrounding structures. Structures may pick up some of these vibrations. Depending on certain structural characteristics along with ambient interior noise levels, inhabitants may feel or sense some structure motion. Blasters understand off-site blasting impacts and know how to design each blast to minimize air blast and ground vibrations, keeping levels as low as practically possible. Blasters load each blast hole with carefully measured explosives, accurately place correct amounts of “stemming” material at the top of each hole to prevent air blast, and precisely time each blast hole detonation with millisecond delays. 

The use of explosives in Washington is regulated by the Department of Labor and Industries and local fire marshals as it relates to transportation and storage. Regulations place limits on blasting to prevent damage to property outside any controlled blasting site area.

These regulations require pre-blast notifications to property owners, limitations on blasting times, use of blasting seismographs and place limits on ground vibrations and air blast to control adverse effects. Limits placed on vibrations and air blast were adopted from the U.S. Bureau of Mines (USBM) safe blasting standards. These standards were published in 1981 based on over 60 years of crack observations correlated with blast vibrations and are applied throughout the U.S. to ensure blasting does not cause cracking of structures. 

The reaction to blasting vibrations depends on personal levels of tolerance and activity at the time of blasting. If inhabitants are busy at home and reside in a well-insulated structure that does not easily respond to vibrations, they may feel or sense very little. Noise may be “heard” while vibrations may not readily be perceived. However, if a resident is in a quiet environment or in a lightly-loaded structure, vibrations may be readily perceived. 

The question has been carefully researched by the USBM in a two-year blasting study. The USBM determined as long as blasting takes place within the safe criteria, structure wall strains are far below the “elastic” or recoverable limit and do not accumulate over time within structures. There has never been any observed damage from repeated effects and researchers continue to study the topic.

When vibrations are felt, it is human nature to start looking for structure cracking. Many homeowners subsequently will find a number of cracks, noted for the first time, and associate them with blasting. Typically, these cracks were already present but not noticed before blasting began. By adhering to safe vibration standards and regulated blasting limits, no cracking will occur in structures due to blasting operations. Cracking in structures is normal and should be expected over time. Cracks readily form in new construction for many reasons including subtle, differential soil deflections, natural aging of new construction materials, and changes in weather. Soil deflections up to 0.5 inches are normal. Larger deflections may be a sign of foundation problems. Shrinkage of new construction materials such as concrete mortar, and wood framing is the largest contributor to structure cracking. Post-construction natural atmospheric humidity fluctuations create differential expansion and contraction of materials, resulting in potential wall and joint stresses, separations and cracking. Thermal stresses from daily temperature fluctuations also cause material expansion and contractions of stucco and drywall that may result in hairline cracks. Other common causes of cracking are poor soil conditions, lack of drainage control, high wind forces during storms, and simply the everyday wear and tear we, as homeowners, impose on structures. 

The survey is an inspection, usually photographed and/or videotaped, of the structures to document conditions prior to blasting. This is a standard procedure that we employ prior to blasting commencement. An independent third party will survey structures located close to the blast area. If damage is suspected, the pre-blast survey company will check for discrepancies.

Yes, vibration and noise are inherent by-products of a blast, all of which can be controlled to minimize human perception. All blasts are carefully designed by professionals and results are predetermined.

We contact any local law enforcement, fire departments, and emergency response prior to blasting operations. In addition, we contact anyone within a 300 foot radius from a blasting operation. This is done verbally and/or by letter. This is standard for any project we do. Permits for blasting are also handled by McCallum Rock Drilling.

Rock hammering is slow, inefficient, costly, and has the same inherent properties of blasting on a smaller scale. Blasting can actually be quieter than rock hammering, and takes much less time. A typical blast duration is usually 1 to 3 seconds, while rock hammering can take over two weeks to displace the same amount of volume incurred by a single blast.

By definition, flyrock is debris that is propelled outside of the blast zone. Shot design, powder factor, stemming material, delay sequence, and blasting mats are all factors considered to control flyrock. Every blast we design and shoot uses proper principals for all applications to control flyrock.

Blasting seismographs will be used to measure and control ground vibrations and noise generated during blasting. Seismographs help to ensure safety and compliance with regulated intensity levels. Seismograph reports are generated and reviewed after each blast. The reports are retained by the blaster for future reference. The use of blasting seismographs is very important in understanding and controlling the off-site effects of each blast.