Question 1

Can I dig and remove the dirt overlying the rock?

Accepted Answer

We prefer to leave native overburden in place on the majority of any construction type blasting projects.

Removing the overlying dirt may end up costing your project more expense and time.  The overlying dirt creates a natural cover for the blast that reduces the risk of flyrock.  If you remove the dirt, we may need to bring in blasting mats and the uneven surface is more difficult to work.  We may have to use a series of smaller blasts.  This takes more time and is more expensive for your project. Not all projects present this concern, on some occasions pre-excavation ahead of the blasting may be needed.

Question 2

What licenses are required to perform blasting?

Accepted Answer

Both federal and state explosives licenses are required to blast.  In addition, a commercial driver’s license with a hazardous materials endorsement is required.

Question 3

How much vibration will be felt in a home or other structure near the blast site?

Accepted Answer

We use seismographs to monitor blasting operations when structures are close to the blast. The amount of ground vibration  we are allowed to produce when near a structure is defined by state and federal rules. Normal household activity like heavy footsteps, running children, a nearby thunder clap,  or a slamming door will generally produce vibrations in your home that can be felt. During a nearby controlled blasting operation you may feel vibration from the blast and hear some noise similar to these. Its not uncommon for us to safely blast within a few feet of existing structure, utilities, wells, etc.

Question 4

What is a pre-blast survey?

Accepted Answer

A survey that may be conducted by a construction professional prior to drilling and blasting.  The pre-blast survey documents existing defects in a structure such as cracks in a foundation or retaining wall. These may be suggested depending on the number of nearby homes and the size of the blasting operation.

Question 5

How do you blast close to a structure without damaging the structure?

Accepted Answer

We use a combination of techniques to minimize ground vibration and air-blasts and direct vibration away from the structure. These techniques include the spacing and depth of the holes, the amount of explosives placed in each hole, and the timing sequence used to delay the detonators.  These techniques are combined with covering the blast site with blasting mats and/or soil.

Question 6

Can you use explosives in holes that fill with water?

Accepted Answer

Yes.  Special explosives material is used that will successfully function when wet.

Question 7

How are explosives stored?

Accepted Answer

Explosives are required by state and federal laws to be stored in magazines that are constructed according to specific requirements.  These requirements include a heavy wooden interior, a thick metal exterior and tamper resistant locking mechanisms.  On the job site, the explosives storage magazine may be built into a truck bed or a portable freestanding magazine.

Question 8

What happens if a thunderstorm occurs while a site is being prepared for a blast?

Accepted Answer

This unfortunately happens fairly commonly in the Rocky Mountain west during the summer.  A lightning strike that occurs while holes are being loaded is potentially dangerous.  Depending on the weather forecast and local site factors, we may reschedule the work or time the loading and blasting to be before or after a storm or do smaller blasts so no explosives are exposed to lightning strikes.

Question 9

What is the white stuff?

Accepted Answer

We get asked this frequently by customers when they are observing the explosives placement. A typical blast hole has 3 main components: A detonator which is the colored  plastic line that  is seen on the surface of blasts, a high explosive, which can generically be called dynamite or booster and will only  weigh  1/2 to a couple of pounds, these are placed in the hole first with the detonator secured to it.  Then comes the blasting agent which produces the majority of the blasts energy; this on most projects is known as ANFO (ammonium nitrate / fuel oil) which looks white but actually has a pink tinge due to the diesel fuel. On most construction type blasting projects the amount of blasting agent is 10 to 15 lbs or less. On bigger projects the amount of blasting agent in each hole can be several times that, all generally detonated  by the small amount of high explosive.

Question 10

There are some technical terms used that I don't know... What do they mean?

Accepted Answer

Technical terms are often used in our industry. Here are some of the most common ones you'll encounter:

Blasting.  Controlled use of explosives to fragment rock, concrete or similar materials into sizes that can be moved by heavy equipment.

Drills.  Drills range in size from hand drills (also called sinker drills) that weigh 55 pounds and are operated by one person, to hydraulic drills on tracs that weight up to 12 tons.  Hand drills are capable of boring holes generally rangin from 1 – ½ to 2 inches in diameter.  Hydraulic trac drills bore holes ranging from 2 – ½ to 4 – ½ inches in diameter.

Blasting mats. Blasting mats are used to cover a blast, particularly in close proximity to a structure.  Blast mats can be constructed of automotive treads and sidewalls, cables or manila rope. Our mats are 8’ x 10’ and weigh approximately 2,800 pounds each.

Blast Pattern. The overall design of the blast, includes hole diameter and  distance between holes.

Native Overburden: The material above hardrock that can be dug.

Ground Vibration: The amount of vibration produced from a blasting operation measured in “inches per second” on a seismograph.

Air blast or air over pressure: Produced from the blast noise and rock displacement. Also measured on the seismograph, this would be similar to a sonic boom. Our controlled blasting operations are designed to avoid measurable air over pressures.

Flyrock: Any material produced from the blast that lands outside the blasters defined blast area.

Magazines and Dayboxes: What explosives are stored in. Lockable and  have non sparking interiors.

Stemming: Explosives are only loaded in a portion of the blast hole, stemming is typically gravel used in the top portion of the hole to prevent the explosives energy  from venting vertically. Our average depth of stemming in a common 3” diameter hole is 4 to 5 feet.

FAQ

FREQUENTLY ASKED QUESTIONS