MNG 331 - Explosives and Blasting Final

Match the following event to its cause in the fragmentation process.

• Fractures extend to free face → Gas Pressure
• Crushing and grinding in moving of muckpile → Secondary Fragmentation
• Crushing around the hole → Shock Wave
• Rotation of fragments → Momentum

Who invented the blasting cap?

Alfred Nobel

Who invented dynamite?

Alfred Nobel

The purpose of explosives is to break rock so we can easily:

Load, crush, haul, dig it

What is the most efficient way to use explosives?

Minimize energy expended on making air blast, ground vibrations, and flyrock; maximize energy used to break rock to requirements.

On average, how much explosives does the United States use every year?

3.5 billion pounds

The goals of the course include:

To be knowledgeable in the subject and be confident and able to design blasting shots.

The course objectives include:

Obtain an understanding of explosives and explosive products, and the ability to apply this to the breakage of rock in an environmentally acceptable and safe manner.

Are explosives affected by freezing temperatures?

True

Water gels and slurries contain:

Ammonium Nitrate (AN), Fuels

The difference between detonation and deflagration is dictated primarily by which explosive property?

Sonic velocity of the explosive mixture.

In wet holes, explosive density should be?

Greater than 1, the hole should be dewatered, and a water-resistant explosive should be used.

Does propagating ground reduce misfires?

No, it does not.

Is it possible to get a blend density that is higher than the density of 100% emulsion?

Yes, it is.

A moderate variation of the amount of fuel oil in ANFO will affect?

Energy, production of fumes, sensitivity, and velocity.

The relative bulk strength of an explosive is relative to?

ANFO

Which of the following is not an advantage of Gassed Emulsion?

Does not require special equipment to load.

Permissible explosives are?

Low flame, classified for use in coal mines, and used in underground operations that are classified "gassy."

Black Powder is a?

Deflagrating explosive product.

Which is the highest density explosives product?

Cast booster

When considering fuel content in ANFO?

It is typically preferred to be overfueled rather than underfueled.

Which explosive has the least water resistance?

ANFO

Detonation velocity is dependent on:

Explosive type, confinement, charge diameter, and priming.

Which of the following statements is incorrect regarding propagating ground?

Reduces misfires

Which type of initiation system lingers as a player in the market due to permissibility?

Electric

If 10 blasting caps are wired in parallel and each blasting cap is 3 Ohms, the total resistance of the circuit will be?

0.3 Ohms

Are electronic detonators accurate to 1 microsecond?

No, they are not.

Non-electric systems are safe to use in the presence of which of the following?

Stray electricity

Which initiation system is traditionally known to have cap scatter of at least +/- 5%?

None!

Which type of initiation system is used most effectively for vibration control?

Programmable Electronic

If 20 electric blasting caps are wired in series and the resistance of each cap is 2.5 Ohms, the total resistance is?

50 Ohms

The ALL FIRE current of a standard electric cap is?

250 milliamps

The NO FIRE current of a standard electric cap is?

50 milliamps

None! can be cut and spliced where?

Only on the lead line.

Commercial detonating cord contains which of the following explosives?

PETN

What primary explosive is typically used in commercial detonators currently being produced?

Lead Azide

What is the safety factor of a blaster’s multimeter when checking an electric blasting cap?

10

Which of the following are correct about a safety fuse?

It is designed to burn at 40 seconds per foot, its burning rate varies with moisture content and age, and its burning rate varies with altitude.

None! comprises a hollow tube with?

Dusting of HMX and Aluminum.

For bench blasting a 4-inch hole loaded with ANFO, the burden and spacing should be?

8 x 12 ft

If a large void is encountered during drilling, the hole should be loaded as follows?

Deck through the void with stemming, reprime above decking, and continue loading.

Hard toe is caused by?

Too high a burden at the toe, insufficient energy at the bottom of the hole, bad drilling, misfires.

The most effective way to produce smaller rock is to?

Increase powder factor.

The most complete fragmentation occurs?

Around the powder.

Oversize found in the middle of a muckpile is most likely a potential sign of?

A misfire.

The column density of a 3.5-inch hole loaded with bag ANFO is how many pounds per foot of hole?

3.5

The jointing and bedding in a limestone ledge will?

Determine the suitability for jetty stone, control face profile, determine the best blasting direction.

Primers should only be assembled?

At the time of use, not be tamped, not have cartridges above 4" in diameter be dropped on them in the blast holes.

A good starting place for powder factor in bench blasting is?

0.5 lb/ton or 1 lb/yd³

Oversize will be a problem if the blast hole spacing is?

2 to 3 times the joint spacing.

For blasting massive rock, which is the most important rock strength?

Tensile

Having a face height too low normally results in?

Poor breakage, too small of powder factor, flyrock, stemming ejection.

Which post-blast phenomenon is the key indicator of insufficient delay on the back row of a bench blast?

Rock from the blast on the bench behind.

Having too high of a face height can result in?

Drilling inaccuracies, flyrock, and toe.

For the use of delays in a blast, which of the following are correct?

Using delays reduces ground vibrations, there are optimum delay periods for minimum vibration, there are optimum delays for fragmentation.

The fragmentation process includes?

Dynamic shock wave fracturing the rock, tensile reflection at the free face, gas pressure-induced radial fracturing, crushing and grinding caused by movement.

Increasing degrees of freedom in blasting results in?

Increased fragmentation.

The rules of thumb for minimum delay period are?

1 ms per foot of burden hole to hole (on same row), 3 ms per foot of burden row to row, and 3 ms per meter of burden hole to hole (on same row).

Bench blasting is the most common form of blasting because?

It's easy to drill vertical holes, free face to blast allows easy breakage, low-cost blasting.

Under MSHA regulations, a vehicle carrying explosives must be?

Maintained in good condition, equipped with sides higher than the explosive transported, equipped with a non-sparking cargo space, have dry chemical fire extinguishers, and be secured while parked with the brakes set, wheels chocked off, and the engine shut off.

The person most likely to be injured during a blast is?

Blaster

If a blast is delayed more than 72 hours, then?

The operator shall notify the appropriate MSHA district office.

Flyrock is caused by?

Insufficient burden, mud seams and cavities, improper timing, stemming that doesn't hold well (all of the above).

Which of the following causes the most fatalities in blasting?

Failure to clear the blasting area.

The principal hazard associated with initiation system is?

Lightning

Under MSHA regulations, "the area where explosive material is handled during loading included…" is defined as the?

Blast Site

Under combined MSHA and OSHA regulations, the drilling of holes next to holes being loaded or already loaded is only allowed at a distance farther than?

50 ft, 30 ft if a barrier is used.

It is important to select blast guards that are?

Trustworthy

Persons assigned to securing a blast site during blasting operations should be?

Trained, properly equipped, and have knowledge of procedures.

Static electricity is a problem for initiation systems and is most prevalent in?

Dry conditions

It is important as a blaster to be confident in blast designs and make sure that all conditions on the blast match those that the blast was designed for.

TRUE

You should NOT fire blasts from the same place?

No matter what the orientation or location of the blast is at a particular mine site.

If a misfire is suspected, the blaster should first?

Wait for 15 minutes unless safety fuse is being used.

What is the minimum distance permitted for smoking or open flame from explosives?

50 ft

When setting up a seismograph, the geophone should be placed?

Buried in the ground or weighted down by sandbags to insure proper coupling with the soil.

If a house is 500 feet from a blast, the air blast will arrive how many seconds after the first ground vibrations?

0.5 seconds

Under OSM guidelines, what is the scaled distance that should be used when blasting between 301 and 5000 feet from a structure (without seismic monitoring)?

55

Most people can easily tell the difference between ground vibrations and airblast.

FALSE

When filling out a blasting record, the following should be completed?

Date with the time of blast, signed by blaster, have a sketch of the blast with its exact position, have number of holes, max pounds per delay, and delay sequencing, and all lines filled with none left blank.

Type 5 magazines are?

Drop trailers or bulk product bins.

How much explosives can you detonate per delay to maintain a scaled distance of 50 with the closest structure 400 feet away?

64 lbs

DOT regulates?

Transportation of explosives on public roads and assignment of explosives 1.1, 1.4, and 1.5 labeling.

For the storage of explosives and blasting agents, which of the following is correct?

Explosive magazines should not display explosives signs, with the exception of type 5 magazines. All explosives storage areas should have perimeter signs displayed in such a way that a bullet passing through a sign does not have a clear line of sight to a magazine.

To transport explosives on a public road in a vehicle that requires DOT placards, the driver is required to have a?

Shipping manifest, fire extinguishers, a written route plan, and a commercial driving license with hazardous materials endorsement.

ATF regulates?

The storage of explosives and sale of explosives.

Which of the following can be stored in an explosives magazine with class "1.1" explosives?

Non-sparking tools necessary for magazine operation.

Pre-blast surveys are useful for new operations, but are a double-edged sword with regard to?

New housing and existing blasting operations.

Ways to reduce airblast include?

Good explosives confinement, elimination of detonating cord, and avoiding blasting during temperature inversions.

According to ATF regulations, how much explosives could be stored in a "barricaded magazine" that is 850 feet from an inhabited building?

500 lbs

You are required to maintain a scaled distance of 50 and you have 100 lb. per delay in your regular blast pattern. You can come up to how many feet from the neighboring houses before you have to modify your blast pattern?

500 ft

The ploys you are likely to experience in a court case are?

Your blaster is incompetent, your blaster was negligent, your blaster has no respect for other people's property.

Pre blast surveys are?

Only mandatory by federal law for the permitting of new mining operations under OSM control, useful to establish the condition of nearby building before blasting, and best performed by a qualified, experienced vibration or engineering consultant of company.

To best protect yourself and your company from unwarranted damage claims you need?

Accurate blasting records and seismograph records of your blasts.

If you are blasting within 1500 ft of the closest structure and your maximum charge weight per delay is 225 lbs, your scaled distance is?

100 ft.

Blast vibration studies have shown that residential structures are sensitive to?

A combination of PPV and Frequency.

What is optimum fragmentation?

It varies from operation to operation.

Why is the use of explosives important to our economy?

If it’s hard rock, you have to use explosives to break it so you can economically mine it. If we didn’t have explosives, many raw materials would be very expensive. Drilling and blasting is the least expensive way to break solid rock.

Pick the best explosive product for the scenario with a brief explanation: Underground coal mine. Holes are 2" in diameter and dry conditions.

Permissible dynamite - because it is an underground coal mine.

Pick the best explosive product for the scenario with a brief explanation: Very large surface quarry operation using 7-7/8" holes. Rock is intact limestone.

Water gels or emulsions - preferred because the loading is much easier and the explosive performance is high.

Pick the best explosive product for the scenario with a brief explanation: Limestone quarry using 6" holes. A heavy thunderstorm moved through the area last night.

Water gels or emulsions - water resistant and good in holes larger than 4" because loading is easier and explosive performance is high.