Blasting safely with proper techniques

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.

Module Two Preparing 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.

(d) Choose the type of blasting agent or explosives (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, B=30xd/12 can be 24,30,36 (g) spacing=1.5x burden, or, s=bx1.2 to 1.8 (h) stemming=.7xburden, or, st=.7 to 1.x burden (i) powder factor=pounds of powder/cubic yards of rock. (j) compute scaled distance factor- w=(d/ds)2 w=weight of explosives. D=distance in feet. Ds=scaled distance on chart. 0-301 feet is 50. 301-5000 feet is 55. 5001 feet and beyond is 65.

(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.

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.

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.

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.

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.

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.

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 manufacturer’s recommended multimeter and follow manufacturer’s recommendations for replacing the cell or battery.

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.

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

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

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

Hercudet firing system Hercudet is no longer in use.

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.

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 hasn’t 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.

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.