Blasting safely with proper techniques

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Blasting safely with proper techniques

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Module one

• The most important responsibility of the blaster
  in charge is to prepare and fire safely. They
  are to practice safety in transportation,
  storage, handling, and the proper use of
  explosives.

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Module TwoPreparing and using blast design.

• (a) Identify characteristics of
  overburden-material which lies above the deposit
  of material desired. Rock quarry may identify
  this as waste.
• (b) Hard to break rock looks regular in shape
  and easy to break rock looks shattered and
  broken. Drill penetration is a good indication
  of hardness. If drill penetrates 4 to 5 feet per
  minute the rock is soft. If drill vibrates and
  is noisy rock is hard.
• (c) Determine the size and drill pattern of the
  blast. Three common patterns are square,
  rectangle, and staggered. Keep blasting rate up
  with the production rate. When choosing patterns
  know faces and cuts, and know order of shot.

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• (d) Choose the type of blasting agent or
  explosives. Most important is if hole is wet or
  dry. Bulk ANFO is most common.
• (e) Benching - the process of excavating where
  terraces or ledges are worked in step patterns.
• (f) Burden 2.5xHole diameter, or, B30xd/12
  can be 24,30,36
• (g) spacing1.5x burden, or, sbx1.2 to 1.8
• (h) stemming.7xburden, or, st.7 to 1.x burden
• (i) powder factorpounds of powder/cubic yards
  of rock.
• (j) compute scaled distance factor- w(d/ds)2
  wweight of explosives. Ddistance in feet.
  Dsscaled distance on chart. 0-301 feet is 50.
  301-5000 feet is 55. 5001 feet and beyond is 65.

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• (k) Cubic yards per hole burden x spacing x
  face height / 27
• (l) pounds of explosives per hole is cubic
  yards per hole times selected powder factor
  pounds per hole.
• (m) Loading density (lb./ft..34 x density x
  diameter squared.
• (n) Total lbs. of powder/delay(distance to
  nearest dwelling/60 squared.)
• (o) A well designed delay patterns can affect
  the direction that the overburden moves,
  fragmentation, flyrock, noise, vibration,
  explosives used, how well the toe is pulled, the
  condition of the new face.
• (p) deck charges may be used to reduce ground
  vibrations. If using deck charges, fire the
  bottom first.
• (q) The four types of firing systems are
  electric, detonating, nonel, and hercudet.
  Hercudet is hardly any longer used.

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Federal Law Requirements

• Pre blast survey regulation. Federal law
  requires that a mine operator conduct a pre
  blast survey on any home within one-half mile of
  the permit area, if the owner requests. A report
  must be submitted to the regulatory authority and
  to the person making the request.
• Blasting schedule publication. The mine operator
  must publish a blasting schedule before beginning
  a blasting program. The blasting schedule must
  be published in a local newspaper of general
  distribution. The schedule
• must be distributed to all property owners and
  utilities within one-half mile of permit area.
  Copies of the blasting schedules that are sent to
  residents must be accompanied by information
  advising the owner of how to request a pre blast
  survey. The schedule must be republished and
  redistributed at least every twelve months, or
  whenever there is a change in the schedule.
• Blasting schedule contents should identify the
  location of the blasting site and the time
  periods when blasting will occur. It should also
  include the methods to be used to control access
  to the blast site.

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• Public protection. All blasting should be
  conducted between sunrise and sunset. You may
  have to blast between sunset and sunrise under
  the following conditions If a blast that has
  been prepared in the daytime has to be prolonged
  and can not wait until the next day. A complete
  report should be prepared including a reason why
  the blast had to be shot at night and could not
  wait until the next day, when the blast actually
  occurred, and the warning notices that were
  given, and a copy of the usual blasting record.
  Access must be controlled to protect all the
  public and livestock.

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Minimum Distance for blasting.

• According to federal law even if you are granted
  a waiver, 300 feet is the absolute minimum
  distance you can mine from structures that are
  not operator-owned. If you blast closer than 300
  feet to a structure or pipeline of the types
  mentioned in the regulations, you are violating
  federal law.

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List of information that Federal law requires you
to have on the blasting record.

• 1. Location
• 2. Number of holes
• 3. Diameter and depths of holes
• 4. Total weight of explosives
• 5. Maximum weight detonated in an 8-ms period.
• 6. Maximum number of holes detonated within any
  8-ms period.
• 7.Sketch of the delay pattern.

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Handling, transporting, and storage

• (a) As blaster-in-charge make sure all the
  explosives you need are at the blast site.
• (b) As blaster-in-charge you will be in charge
  of the magazines.
• (c) Taking deliveries, storing, records,
  cleanliness of magazines.
• (d) Stack boxes correctly, MSHA says 8 ft. high,
  ODM says 6 ft. high.
• (e) The ATF says to check magazines every three
  days.

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Using electric firing system

• (a) using a blasting galvanometer, the amount of
  electricity that can flow through material
  depends on the resistance of the electric
  blasting caps and cap circuits. Make sure to
  zero the galvanometer .
• (b) using blasting machines- there are 2 types
  of blasting machines, generator type and
  capacitor discharge.
• (c) using a blasters multimeter- This is a test
  instrument that can measure resistance and
  voltage in electric blasting system. Never let a
  cell or battery come into contact with electric
  blasting caps. Use only a manufacturers
  recommended multimeter and follow manufacturers
  recommendations for replacing the cell or
  battery.

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Loading bore holes

• (a) check bore holes for depth, obstructions,
  water, open holes, and hot holes.
• (b) Load primers- Lower the primers into the
  holes by using the detonating cord or tubing.
  Clip the detonating cord or hercudet tubing so
  that about 24 inches will be left outside the
  holes. Tie the cord off to something stationary
  to keep from slipping into the hole.
• (c) Load explosives- choose the proper
  explosives for the job. For wet holes load an
  explosives that is water resistance. If using
  ANFO line holes with plastic bags. For holes
  with voids, cartridged or packaged explosives.
• (d) Load and tamp stemming materials. Damp
  sand, crushed rock, and drill cuttings are all
  good for stemming. When tamping holes make sure
  to not hit directly on cap.

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Detonating cord firing system

• (a) Choose detonating cord for down lines and
  trunk lines.
• (b) Choose delay devices
• (c) Choose primers
• (d) Make up primers
• (e) Hook up system
• (f) Fire shot

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Using an electric firing system

• (a) Specifying type
• (b) Choosing primers
• (c) Making up primers
• (d) Computing the resistance
• (e) Connecting leg wires
• (f) Connecting firing circuit
• (g) Test the complete circuit
• (h) Fire the shot

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Using Nonel firing system

• (a) Nonel is a non-electric initiation system
  made up of plastic tubing coated internally with
  a light dusting of explosive powder.
• (b) Choose delay devices
• (c) Choose detonating cord for down lines
• (d) Choose primer
• (e) Make up primers
• (f) Hook up system
• (g) Fire shot

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Hercudet firing system

• Hercudet is no longer in use.

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Detecting and handling misfires

• (a) Burning explosives- If you see a steady
  rise of smoke you probably have a misfired hole.
• (b) Poor fragmentation- If overburden does not
  move like it should this could be a misfire.
  MSHA regulations state that if using electric
  caps keep the area clear for 15 minutes. If you
  used safety fuse keep the area clear for 30
  minutes.
• (c) Detonating cord- If you find detonating
  cord that goes into the ground, the hole has
  misfired.

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Re-firing misfired holes

• (a) If a misfire occurs the first thing that you
  have to determine is whether or not you can use
  the existing caps and primers. If so re-connect
  the line and fire, making sure that the burden
  hasnt been reduced enough to cause excessive fly
  rock.
• (b) If you decide that you cannot re-fire the
  existing caps and primer cord, you may remove the
  stemming material from the blast hole with an air
  compressor. Move the blow tube up and down until
  all stemming material is gone. If using bulk
  ANFO, this will not work. Put new primer in and
  shoot.

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Secondary blasting

• (a) Identify the need for a secondary blast
• (b) Find and mark the spot for holes to be
  drilled. Choose the explosives you wish to use.
  Load hole and blast using the proper procedures
  of which type of blasting that you choose.