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  • 1. SURFACE SHOTFIRER Name: Module S1 Version 03 February 2010 Copyright © BTI 2010 BLASTTRAININGINTERNATIONAL Leaders in Explosives Training and Applications
  • 2. 18 BTI SUPPORT SHOTFIRER Storage life The storage life (shelf life) of an explosive is the manufacturers recommended time that the explosive can be stored in normal magazine conditions (cool and dry). If conditions are other than cool and dry, storage times can shorten dramatically particularly for hydroscopic products such as prilled AN which may only last a few weeks in a very humid, warm climate. The quoted storage life is conservative and will vary from supplier to supplier but will generally lie within the following guidelines. Product Maximum shelf life Effect of aging ANFO 3 months Absorbs moisture, becomes blocky and may break down Packaged emulsion 2 years Emulsion crystallises. Critical diameter may increase beyond product diameter Non-electric detonators 12 months after opening, 4 years in unopened packages Delay compositions age through moisture absorption and oxidisation. Delay times show increased scatter Detonating cord 5 years Very little Pentolite boosters 5 years Very little Gassing agents Refer specific MSDS* Evaporation and crystallisation Bulk Emulsion Precursor Refer specific MSDS* Product separation, crystallisation, loss of viscosity *The material safety data sheet (MSDS) will detail storage issues. Temperature effects AS2187.1 10.6.1 defines ‘hot’ material where the temperature is greater than 55 degrees Celsius but less than 100 degrees Celsius. There are specific requirements for blasting in hot ground and these must be followed. In particular specific recommendations must be obtained from the manufacturer before loading any product into ‘hot’ ground. It is not possible to make firm recommendations about safe exposure times for explosives at various temperatures because of the wide range of operating conditions and products available. Emulsions are generally safe to use up to 100 degrees Celsius, but in most cases the limiting factor will be the initiating system, which contains the most sensitive components.
  • 3. MODULE A5 19 For explosives inside blastholes at constant elevated temperatures, maximum safe temperatures for exposure are summarised below: Product Maximum temperature o C ANFO 100 Packaged emulsion 100 Non-electric detonators 70 PETN based detonating cord 70 Cast Pentolite boosters 70 Hot and reactive ground Blast crew must always be aware of the potential for the presence of hot and reactive ground. Where any of the the following are observed they must be immediately reported to the shotfirer. Reactive ground • The presence of black sulphide bearing sediments • Sulphides within mineralised rock • Sulphides often appear as glittery or shiny bands in the rock • Presence of white or yellow salts on rock. This is an indication that oxidation is taking place • Acidic conditions (generally resulting from oxidation) as indicated by the colour of run off water, usually yellow-red brown in colour • The spontaneous combustion of overburden or waste rock / ore either in dumps or in the pit, especially as it is exposed to the air • The acrid smell of sulphur dioxide caused by the naturally occurring sulphide oxidation reaction • The rock type occurring in the transition zone just below the limit of the oxidation line (ie where light coloured bleached rock ends and darker coloured rocks begin) Hot ground • Steam rising from the blast hole • Heat felt at the collar • Melted dip rope • Heat shimmer coming from hole PROPERTIES OF EXPLOSIVES Incandescent reactive ground in the 500 Orebody, Mount Isa Mines c.1960s. (Mount Isa Mines, n.d.) Sulphide mineral (pyrite) in bedded formation
  • 4. MODULE A5 25 ANFO In 1947 in Texas City USA two ships loaded with wax coated AN caught fire and subsequently exploded. The investigation into the accident, which killed 576 persons, identified the liquid wax ‒ AN mixture as being responsible for the powerful explosion. This led to further investigations into ANFO type mixtures. Although any number of carbonaceous materials can be used with ammonium nitrate (AN) to produce a satisfactory explosive distillate has been the fuel of choice since the late 1950s. Distillate is an ideal fuel for mixing with AN to form explosives. It is readily available, relatively inexpensive and easily blended with AN to produce a uniform mix, commonly called ANFO (Ammonium Nitrate Fuel Oil). ANFO is more sensitive and, therefore, more reliable than mixtures of AN and powdered fuels. More volatile fuels (e.g. petrol, kerosene) give greater sensitivity but offer no significant advantage in effective energy; they also exhibit lower flash points, thereby introducing the risk of a vapour explosion during mixing and charging operations. For this reason, legislation prohibits the use of liquid fuels with flash points lower than 61 0 C. Mixing of ANFO AN is usually mixed with distillate (diesel / FO) on site for use as an explosive. Correctly proportioned and mixed ANFO can be charged most efficiently and rapidly by means of Mobile Processing Units. Mixing unit must be regularly calibrated. This is commonly done by disconnecting the oil line and operating the mixer while catching the separate oil and AN. These can then be weighed to check the % mix of each. Good mixing is needed as it is possible to have the correct % of fuel overall but not consistent throughout the mixture. Any machine used for mixing must be designed to avoid the possibility of frictional heating and any bearings or gears must be protected from spillage of AN or ANFO. A petrol engine must not be used for power-operated mixers. Approved electric – powered motors can be used. To provide an immediate visual indication of the distribution of distillate in the mix and to distinguish between a mixed product and straight AN, it is standard practice to colour the distillate with a vivid oil soluble dye before the distillate is added to the AN. Mixing of AN and distillate constitutes manufacture of an explosive. For this reason, a licence or permit to mix ANFO must be obtained from the appropriate statutory authority. BULK EXPLOSIVES
  • 5. 26 BTI SUPPORT SHOTFIRER Maximum explosive energy is obtained with 5.8% by weight of distillate. The addition of 5.8% distillate to AN almost trebles the energy yield. With too much or too little distillate, energy yield falls off. As one would expect, the VOD is also greatest at 5.8%. The density of diesel is 0.83 kg per litre. If litres is used to calibrate the mixing of ANFO (rather than weight) the correct proportion is 7 litres fuel oil to 100 kg AN. ANFO (kg) AN (kg) Diesel (kg) Diesel (litres) 10.6 10 0.62 0.74 53.1 50 3.1 3.7 265 250 15 18.5 10 9.42 0.58 0.7 50 47.1 2.9 3.5 250 235.5 14.5 17.5 The advantage of having a uniform mix of AN and distillate is obvious. Even when the correct amount of distillate is added unless it is evenly distributed explosives performance will suffer. For example where 75 litres of distillate is added to one tonne of AN but half receives 60 litres while the other half tonne receives only 15 litres, then the energy generated by this tonne of ANFO will be about 23% lower than that from a completely uniform mix. The appearance of distinctly orange – coloured nitrogen dioxide fumes after an ANFO blast may indicate too little distillate in at least some of the ANFO. (However this is usually an indicator ANFO that has been attacked by blasthole water or has been inadequately primed.) Correct ratios for mixing small quantities of ANFO Amonium Nitrate (kg) Diesel 5.8% (litres) 10 0.75 25 1.9 50 3.75 ANFO properties by weight % of FO Mixing ratios for ANFO.
  • 6. MODULE A5 31 Emulsion / AN blends – Doped Emulsion Emulsion explosives may blended with AN prill and diesel to improve energy and reduce cost. By blending varying proportions of AN and EP it is possible to manufacture a range of products. Where emulsion is the major component, greater than 50%, they are called doped emulsion explosives; where AN is the major component, they are called Heavy ANFOs. Doped emulsion explosives Doped Emulsion explosives consist of particles or prills of ANFO or AN (dry phase) within an emulsion matrix, the percentage of emulsion usually lying in the 55 to 90% (weight basis) range. Provided the emulsion phase content is maintained above about 45% (weight basis), there is sufficient emulsion to completely cover the AN and the product is considered waterproof. The high proportion of emulsion gives doped emulsion explosives excellent water resistance. They are specifically designed for use in blastholes, withstanding water and are often described as “waterproof”. Doped Emulsion must be pumped into blastholes through flexible hoses that deliver the product to blasthole toes, displacing the water upwards. It is normal for emulsion explosives to be chemically “gassed” for sensitivity and to produce a range of densities as required. A doped emulsion explosive will compress under load and lose sensitivity with increasing column height. For this reason the manufacturer’s guidelines for maximum depth and diameter must always be observed. As greater percentages of a dry phase are added to an emulsion, both the reaction rate and detonation velocity decreases. The initial reaction proceeds through and takes place within the emulsion matrix; the reaction in the (coarser) dry phase is initiated by the emulsion’s reaction and extends over an appreciably longer period. Therefore, by adding dry phase, the overall duration of the reaction is extended, thereby increasing heave energy and muckpile looseness at the expense of strain wave (or shattering type) energy. In relatively weak rocks, the presence of a dry phrase has the beneficial effect of reducing energy losses associated with excessive fragmentation and plastic deformation close to the charge. Where the dry phase is totally enveloped by highly reactive emulsion, its reaction commences with great vigour and proceeds to completion more easily and efficiently than in the case of ANFO where prills are surrounded essentially by air. Therefore, it seems reasonable to believe that the actual energy produced from an emulsion / dry phase blend is appreciable greater than that for ANFO. This is perhaps the most important factor to explain the observation that such products perform better than their theoretical energies suggest. BULK EXPLOSIVES
  • 7. 32 BTI SUPPORT SHOTFIRER The importance of fragmentation seems to have been over emphasised at the expense of muckpile looseness. Whilst fragmentation is usually the most influential feature of a muckpile, looseness has a very considerable effect on the ease, speed and cost of digging and hauling. The desired amount of muckpile looseness depends very largely on the explosives heave energy. By adding a dry phase to an emulsion, the heave energy and, hence, muckpile looseness are increased. The inclusion of up to 40% dry phase has the beneficial effect of increasing muckpile looseness usually without detracting from effective fragmentation.
  • 8. MODULE A5 41 Non-electric detonators The development of shock tubing in the early 1970’s revolutionised initiation system design. Thirty years later the majority of surface and underground blasting is still based on this product. It is only the development of simple and reliable electronic initiation systems that are now starting to challenge the dominance of shock tube systems. Usage Non-electric detonators are widely used as in-hole delay downlines to initiate cast and packaged primers in blastholes. Other applications include providing a delay in a detonating cord trunkline, hookup in a surface ‘daisy chain’ network to provide hole by hole initiation in surface blasts and initiating detonating cord. Construction Non-electric detonators typically consist of a length of shock tubing with one end sealed and the other crimped into a detonator. Variations to the base unit include the addition of plastic connector blocks and different spooling and coiling configurations. In the next sections we look at the shock tube and detonator construction. Shock tube Shock (or signal) tubing is the basis of all non-electric initiation systems. Shock tubing consists of a 3 mm outer diameter plastic tube with a 1 mm hollow core. The core is lined with a coating of reactive powder (HMX and Aluminium) at around 16 grams per kilometre. INITIATION SYSTEMS
  • 9. 42 BTI SUPPORT SHOTFIRER Functioning Shock tube When the tubing functions the shock wave travelling in front of the reaction lifts the powder from the walls of the tube. The reaction then progresses through the tube in the form of a ‘dust explosion’ unlike detonating cord which ‘detonates’. The velocity of detonation of tubing is only 2000 metres per second compared to 9100 m/sec for HMX explosive. Hazards and failure modes Shock tube sensitivity Shock tubing is relatively insensitive to accidental initiation from impact and heat although there have been regular occurrences of initiation by the ‘snap, slap and shoot’ mechanism. This occurs when machinery becomes entangled in shock tube and when moved stretches and snaps it. Initiation is possible and around one incident per annum is reported from somewhere around the world. The consequences of an accidental initiation of a downline when there are persons and equipment in the vicinity is often catastrophic. Shock tubing is relatively insensitive to accidental initiation from radio frequency (RF) energy, static and stray currents. Tests with static discharges over 10 kV have failed to initiate tubing. However shock tube is not immune to initiation from direct lightning strike and normal evacuation procedures in the event of electrical storm must be followed. Failure modes Shock tube may also fail when exposed to the oil phase of explosives for extended periods of time. Standard tubing should last for at least two weeks sleeping in a blasthole. For longer periods most manufacturers produce a ‘heavy duty’ tubing. This is formulated from a plastic more resistant to oil penetration. High temperatures reduce the amount of time to unit failures occur. Shock tubing will also fail should a small quantity of moisture enter the tubing. To prevent this the end seal should never be removed.
  • 10. MODULE A5 71 Geotechnical assessment When assessing a work area for risk rock slope stability must be assessed on a continual basis. Blasted faces exposed to weather and mining activity may deteriorate further during the mining cycle meaning that what was safe last week may not be now. Rock slope stability is dependent on many factors, the key ones for blast crew are: 1. Characteristics of the rock mass 2. Geometry of the exposure 3. Common failure mechanisms These will be briefly identified in the following sections. Characteristics of the rock mass Rock masses vary enormously in strength and structure. At one extreme there is completely intact rock masses with no joints At the other there is highly jointed weak rock with weathered and slippery joints. These rock masses will behave very differently when exposed by mining activity. BLAST PREPARATION
  • 11. 72 BTI SUPPORT SHOTFIRER Geometry of the exposure The exposure geometry in relation to stability is defined by three key parameters: Height The higher the exposure the more load on the toe and the more likely that failures will occur on existing planes of weakness. Moreover failures on high faces generally involve more rock moving faster. Angle The steeper the face the more likely a failure. Steep faces are more prone to all failure mechanisms including ravelling, sliding and toppling.
  • 12. MODULE A5 81 Validate drill pattern After checking for risk the next step is to validate the drill pattern. The objective here is to confirm that the drill design has been properly executed and that holes are in the correct position and properly identified. An accurate drill plan is required for reference. The plan should be scaled and show all holes, hole ID’s and relevant local features to enable the blast crew to locate themselves. Drill pattern detail. Where a drill monitoring system has been used the drill plan should be based on this data. Plans that show redrills and true positions are a more reliable check of the as-built. Redrills should be shown on the plan and identified on the ground. Drilled holes are to be checked against the provided drill plans. As a minimum the end hole in each row should be identified and confirmed. Where holes are missing these should be recorded on the drill plans. BLAST PREPARATION
  • 13. MODULE A5 123 Preparation When blastholes are being primed and loaded, ensure security of the blast area. Minimise other work in the area and allow no other work to be done within a safe distance of charged holes. Working with load standards Each site should develop a general load standard to communicate to shotfirers the site requirements of the blast design and the allowable tolerances. Load standards, typically expressed in a site data sheet, will reflect site equipment, available products and design standards and should define design parameters and details such as backfill requirements, stemming tolerances and product selection criteria. An example of a load standard is shown adjacent. Load standards provide general information in regards to a site or an area or bench on a site. They are an appropriate means of managing loading where there is little variation in the blast designs and the bench height and faces are relatively constant. A limitation with using load standards / site data sheets as the design communication to the shotfirer is that changes to bench geometry may not be picked up and may lead to poor blast performance and increased risks. The diagram below (taken from an actual flyrock incident) demonstrates the problem with using a site data sheet without consideration of actual / changing bench conditions. Owing to situations like this many operations choose to go to the next level and implement load sheets to manage blasting on a daily basis. LOADING
  • 14. 124 BTI SUPPORT SHOTFIRER Working with load sheets Load sheets are produced on a shot-by-shot basis and provide detailed information for each hole in the pattern. Whilst the use of load sheets provides a higher level of control it requires a drill and blast office to develop the sheets from survey and mine plans and process the drill and dip data to calculate the design hole loading. Even with accurate load sheets, the individual load heights must be controlled by the shotfirer owing to variations in column rise due to holes drilled by worn bits and variation in explosives density from design. Whilst load sheets cannot be used without shotfirer supervision they still provide the best level of control. Accurate blasthole depths and water levels are key to designing loads for individual holes, particularly on sites where multiple products are used. An example of a load sheet identifying the key parts is shown to the right. Whilst the blast design and load sheets will provide sufficient information to correctly load holes that are correct to design it is up to the shotfirer in charge to determine when holes are sufficiently‘out-of-spec’ to justify a change in explosive loading or stemming. “On-bench” decisions on loading typically involve holes where burden or bench conditions present potential overcharging and generation of flyrock or environmental excursions. Any change from either a load standard or a load sheet specification should be recorded for later reference. Example: A 150 mm hole has a design load of 17.7 kg/m at density 1.0. A 15 m hole with 5 m stemming would therefore have a design load of 177 kg. However if the bit is worn to 142mm the hole will load at 15.8 kg/m. The column loaded is then 177 / 15.8 = 11.2 m and the resulting stemming height is 3.8 m. This may be insufficient to contain the explosives resulting in rifling and potential flyrock. LOAD SHEET Shot NR-3204- West Toe Super-Slurry density 1.25 Location Centre pit - Bench 26 Column ANFO @ 0.8 Date 22/11/2009 Hole diameter (mm) 165 Design Stemming (m) 4 Hole ID Dipped Target Backfill Water Toe Column Toe Column Comments A26 24.7 25.5 3 150 250 160 240 A27 26.4 25.5 4 200 200 400 Fully wet A28 26.2 25.5 3 150 250 160 240 A29 26.8 25.5 1.3 3 150 250 170 230 A30 24.5 25.5 5 200 200 230 170 A31 24.1 25.5 5 200 200 230 170 A32 23.7 26 5 200 200 220 180 A33 24.6 26 6 250 150 270 130 A34 25.4 26 6 250 200 260 190 A35 24.3 26 4 200 200 Blocked at 5m A36 25.7 26 4 200 200 220 180 A37 26.1 26 5 200 200 210 190 B1 23.5 24.5 2 150 200 180 170 B2 23.7 24.5 100 250 110 240 B3 26.3 24.5 1.8 100 250 130 220 B4 26.7 24.5 2.2 100 250 130 220 B5 25.7 24.5 1.2 100 250 140 210 B6 24.1 24.5 100 250 130 220 B7 25.0 24.5 100 250 120 230 B8 25.9 24.5 1.4 2 150 250 180 180 Inc stem to 6m weak collar B9 26.5 24.5 2.0 3 150 250 180 220 B10 23.7 24.5 3 150 200 160 190 B11 27.2 24.5 2.7 3 150 250 160 240 B12 25.4 25 4 200 200 220 180 B13 24.5 25 4 200 200 210 190 B14 24.3 25 4 200 200 240 160 Design Charge (kg) Actual Charge (kg)
  • 15. MODULE A5 151 Using a “reel off” LIL kit A “reel off” LIL kit provides a spool of shock tube with splices and end caps to allow more flexible use and user control of tube consumption, commonly with remote firing systems. Part spools may be retained for later use. A surface detonator unit is used as the initiating detonator. Be aware that any ingress of water or dirt into an open signal tube may result in shutdowns. Use a reel off, field assembly, LIL system only where shutdowns can be tolerated. A typical application is illustrated above; note the use of a reel off LIL to the initiating point. To ensure that the splices do not become separated, it is good practice to double the tubes and tie a loose overhand knot. Again the last connection should be at the initiation point. HOOK-UP
  • 16. 192 BTI SUPPORT SHOTFIRER Types of explosives Explosives are classified in a number of different ways. For example a shotfirer might refer to cast boosters as HE or High Explosives whereas these will be “Composite Molecular Explosives” to the chemist and ‘Class 1.1D’ to the shipper. For the purpose of storing explosives it is the Class of explosive that defines compatibility. All explosives are Class 1. This is denoted by the ‘1’ at the bottom of the orange diamond as shown here. The Class is then further defined by the Hazard Division and the Compatibility Group, these being the number and letter after the 1 on the diamond shown. Hazard Divisions 1.1 those ‘substances and articles which have a mass explosion hazard’ i.e. if any part detonates the entire load is likely to detonate. 1.4 means that there is no significant hazard in that a part may detonate but this will not set off the remainder of the load. 1.5 comprises substances which may explode but are so insensitive there is little probability of initiation or transition from burning to detonation. After the Hazard Division, the letter denotes the Compatibility Group. This tells us what explosives can be stored and transported with which other explosives. The two main Compatibility Groups are D, for secondary explosives and B for articles containing primary explosives. As a support shotfirer you will generally only deal with Compatibility Group D and Group B explosives. Group D (secondary explosives) contains articles such as boosters, detonating cord, packaged explosives, shaped charges and ANFO. Group B (Primary explosives) contains articles with a primary explosive such as detonators (both in-hole and surface) and detonating relay connectors. The golden rule for storage and transport is: Never mix Compatibility Group D and Group B products together.
  • 17. MODULE A5 193CLASSIFICATION and STORAGE of EXPLOSIVES In summary the classes of explosives you will likely come across as a support shotfirer are as follows: Class General description Examples 1.1D Secondary explosives with a mass explosion hazard. Boosters, packaged explosives, ANFO. 1.1B Primary explosives with a mass explosion hazard. MS detonators, Millisecond connectors. 1.4B Primary explosives with no mass explosion hazard. Some detonators packed with protective sleeves around the base charge 1.4S Article packed such that the packaging contains any hazardous effect from accidental functioning Shot shell primers for lead in line starters 1.5D Very insensitive substances which have a mass explosion hazard Some emulsions, slurries and watergels. The class of a particular explosive is shown on the: • Technical Data Sheet (TDS) available from the manufacturer. • Material Safety Data Sheet (MSDS) also from the manufacturer. • The Australian Explosives Code (AEC) lists all explosives, their properties and the classification. • The orange diamond printed on the box or other packaging. More information on the various classifications, hazard divisions and compatibility groups is provided in the Australian Explosives Code (AEC) particularly to Appendix 2 on pages 127–183.