Blasting

PROCESS

Blasting involves the use of explosives to loosen up rock and soil.  Once it is loosened from the explosion, it is much easier to remove and haul away.  This is typically implemented when the usual means of removing rock through drilling, hammering and excavating aren’t effective or fast enough.  In this example video, the construction site encountered a subsurface rock pinnacle that would have taken months to drill and hammer through to excavate.  Upon finding the rock pinnacle, the contractor made the request to the owner to pursue blasting.

In order to be allowed to blast on the site, the contractor is required within the state of Pennsylvania to acquire a blasting permit through the DEP and local fire department’s separate approvals.  The permit process will require the contractor to perform a pre-blast survey of the area around the blasting.  Nearby residents and businesses within a prescribed distance to the blasting area must be notified of the upcoming blasting, and inspections of the existing structural conditions of the buildings will be offered.  If anything occurs to the buildings as a result of the blasting, the pre-blast survey will be useful in determining what has been damaged.  The local fire marshal must also give their approval to the blasting permit and will assist with determining temporary traffic closures and public safety.  The fire marshal or his personnel will be welcome to observe the blasting process.

A seismograph will be set up on the site to monitor underground vibrations for unsafe levels during the blasting. If a blast creates too large of vibrations, the contractor will be required to coordinate more with the DEP for subsequent blasts.

Before the day of the blasting, a drilling unit will bore holes to the prescribed depths and areas marked on the blasting plan.  On the day of the blasting, the contractor will use a specialized truck to bring the explosives.  They will set the charges in the pre-drilled holes, set the fuses, and maintain a safe zone that nobody besides the contractor may enter.  Large mats made of used tires and steel cables will be draped over the blast area and will absorb a majority of the upward forces.  A site meeting is held with all personnel present to ensures that everyone knows the various horn signals, schedule, safe locations to stay, and any other applicable rules.

The nearby roads will be temporarily shut down 8 minutes prior to the blast and will only be reopened upon the “all clear” horn signal.  As you can see from the video, the blast itself only lasts for a few seconds.  The contractor will inspect the blast area before giving the “all clear.”  At that time, the crew will disassemble the blasting mats and uncover the results of the blast.  Based on its performance, the contractor may adjust any subsequent blasts.

Here are a few final tips for the blasting process:

  • Ensure that the permits and pre-blast survey are complete prior to proceeding with any blasting.
  • Always be aware of any potential risks including nearby historical buildings, underground gas lines, or other fragile infrastructure that could be damaged.
  • Establish a relationship with the local fire marshal – it’s likely that they will be returning to your site for future inspections.
  • Receive weekly drilling and blasting logs from the contractor to document their progress and understand any issues encountered.