The Benefits of Bulk Emulsion Explosives in UndergroundDevelopment Mining

S Parsons1 and N Bennett2

ABSTRACTThis paper examines the practical and economic benefits of using bulkemulsion explosives in underground development mining; compared toANFO, ANFO derivatives and packaged explosives. The key economicbenefit of bulk emulsion is the replacement of relatively high costpackaged explosives with a bulk product. Key practical benefits includewater resistance, improved coupling of explosive, reduced toxic gasproduction, increased shock energy and improved manual handlingthrough the use of bulk products.

Each of the benefits is proven using a variety of measurements andfield results in order to quantify them. Where possible, dollar values aredetermined so that the benefits can be shown to translate into savings forthe mine operator. The results show that, despite the difference in pricebetween ANFO and bulk emulsions, bulk emulsions are most capable ofdelivering the lowest total cost of blasting.

The savings potential of the introduction of bulk emulsion systems canresult in an improvement in drill and blast costs for a mine operator, or asignificant increase in profit margin for a contract mining company.

INTRODUCTION

Packaged emulsion is traditionally used for charging wet holes,with operators manually loading each cartridge into the hole,then tamping in place. The effective coupling using thistechnique is generally in the range of 60 - 70 per cent. Byloading with a water resistant bulk emulsion, 100 per centcoupling is achieved, providing much greater energy forbreakage. The manual handing of boxes and cartridges isremoved, with the hose simply inserted to the toe of the hole andthe pumped emulsion slowly filling the hole to the desired collar.

Perimeter products vary from low-density bulk products topackaged decoupled charges or high strength detonating cord.String loaded bulk emulsion achieves results comparable topackaged decoupled charges whilst maintaining the manualhandling and cost benefits of a bulk product. Charge rates as lowas 0.35 kg/m in a 45 mm blasthole are achievable using bulkemulsions; with the string size controlled by simply changinghose retract speed.

Bulk emulsion explosives detonate with a higher velocity ofdetonation (VoD) than ANFO. The shock energy component istherefore higher in bulk emulsions than ANFO, providing moreenergy for breaking the rock rather than moving it. With in situblock size generally much larger than that required fordevelopment mining, it is preferable to have as much energyavailable for breakage as possible, creating smaller blocks moresuited to the breakage and clearing methods used in developmentrounds.

PRACTICAL BENEFITS

Water resistance

Bulk emulsions have excellent water resistance properties and, assuch, all wet holes including those drilled below horizontal can

be charged successfully without dewatering. Charging of wetholes is essentially the same as a dry hole. The emulsion ispumped, via the hose, to the back of the hole, completely fillingit. As the hose is withdrawn, the water is displaced from the holeas the emulsion is pumped in.

Coupling

Completely filling the hole is of particular significance wherebulk emulsion replaces packaged products. Adamson et al (2000)found using plastic packaged 32 mm diameter emulsioncartridges and best practice tamping techniques yielded acoupling ratio of only 60 per cent of the hole volume. This is theequivalent of a 35 mm diameter cartridge in a 45 mm diameterhole. This decoupled charge results in a breakage radius of halfof the blow-loaded ANFO equivalent charge.

Plastic tube charges fare even worse, with cartridge diametersaround 30 mm, resulting in even greater decoupling and reducedbreakage radius.

Lifter and knee hole performance is excellent with theimproved coupling of bulk emulsion compared to packagedproducts. This can result in the opportunity to remove knee holesand expand the burden between holes at the bottom of the face.Ground vibration monitoring has indicated that increasedburdens on lifter and knee holes did not affect the blastperformance.

With bulk emulsion, around two-thirds of the holes drilled inthe face can be drilled below horizontal, providing a more evencharge distribution throughout the face. The burn, box anddiamond, a total of 17 holes, are the only holes in the face drilledabove horizontal. Further trials are required to investigate theperformance of burns drilled below horizontal, with particularemphasis on the performance of water-filled relief holes.

Perimeter charging

Perimeter holes are charged using Dyno Nobel’s patented stringloading process. The charge hose is retracted from the back ofthe hole using a motor driving a set of wheels. This allows theemulsion to be loaded at a set rate per metre, according to thespeed at which the hose is retracted. String charging has beensuccessfully used to load charge densities of 0.35 kg/m intunnelling applications and down to 0.70 kg/m for miningapplications. Breakage radii for common perimeter productswere calculated using the Holmberg-Persson method andJKSimblast software and are listed in Table 1.

Qualitative results are difficult to compare between perimeterproducts in most mining operations at present, due to popularityof in-cycle fibrecrete as the surface support. This prevents visualinspection of the backs and walls and hides any potentialdeterioration in the rock mass following mining. Inspectionscarried out immediately following blasting reveal an increase inthe number of half-barrels evident in the backs and upper wallswhen using emulsion.

Advance rates

Face advance per round has improved with the introduction ofbulk emulsions. For example, a mine in the North-EasternGoldfields of Western Australia had experienced very good

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1. Technical Consultant, Dyno Nobel Asia Pacific, Level 6, 553 HayStreet, Perth WA 6000. Email: stuart.parsons@ap.dynonobel.com

2. Business Manager Underground West, Dyno Nobel Asia Pacific,Level 6, 553 Hay Street, Perth WA 6000.Email: nigel.bennett@ap.dynonobel.com

results when firing 5.8 m long rounds using ANFO andANFO-derived products. The historical advance per round was inthe order of 5.3 - 5.5 m per round, which is between 93 per centand 95 per cent of a full round. Following the introduction ofbulk emulsion, the advance improved to the point where, uponscaling, the advance achieved would be between 100 per centand 102 per cent. The faces quickly scaled to a solid base givingthe operator a strong indication of when to stop scaling.

Improved re-entry timesThe instantaneous gas levels resulting from five blasts monitoredbetween 4 and 6 July 2006 were recorded at a mine in theNorth-Eastern Goldfields of Western Australia using anOdalog 6000 multigas logger. Gases monitored included carbonmonoxide (CO), oxygen (O2), hydrogen sulfide (H2S), nitricoxide (NO) and nitrogen dioxide (NO2). The first three blastsused Titan 7000 in short rounds, 4.2 m hole length. The final twoblasts used ANFO and Titan 7000 respectively, in long roundswith 5.8 m hole length. A graph displaying the results of themonitoring for the 5.8 m rounds is illustrated in Figure 1.

The CO gas levels took the greatest amount of time to bediluted to below short-term exposure limit (STEL) for bothANFO and Titan 7000. The time taken for fumes to clear the facefor a round charged with ANFO or Titan 7000 is not significantlydifferent. Fumes took between 20 and 25 minutes to reach theportal 1.1 km from the face after firing.

Peak CO levels were above 500 ppm (maximum recordablelevel) for both ANFO and Titan 7000 but were not at these levels

for a significant amount of time. Peak NO and NO2 levels aresignificantly greater for ANFO blasts. Bakke et al (2001) show arelationship between high peak exposures to NO2 from blastingfumes and a temporary decrease in lung function. Lung functionreturns to normal after approximately ten days without exposure.It should also be noted that NOx gas is toxic and can lead topulmonary oedema and death if inhaled at sufficiently highquantities.

Velocity of detonation (VoD)

Bulk emulsion explosives detonate with a higher VoD thanANFO under the same conditions. The energy partition diagram(Figure 2) illustrates the effect that VoD has on the amount ofenergy converted into shock and heave energy during detonation.The shock energy component is higher in bulk emulsions thanANFO, providing more energy for breaking the rock rather thanmoving it. The higher VoD produces higher detonation pressure,which results in more intense fracturing of the rock. With thein situ block size generally much larger than that required fordevelopment mining, it is preferable to have as much energyavailable for breakage as possible.

The VoD of the first fired hole was measured using aShotTrack time-domain reflectometer (TDR) over a series ofblasts at a mine in the North Eastern Goldfields of WesternAustralia. The ShotTrack works by measuring the length of a

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ANFO versus Titan 7000 Fumes

-100

0

100

200

300

400

500

600

-5.00 0.00 5.00 10.00 15.00 20.00 25.00 30.00

Time (minutes)

PP

M

T7000 CO

T7000 H2S

T7000 NO2

T7000 NO

ANFO CO

ANFO H2S

ANFO NO2

ANFO NO

FIG 1 - Gas levels from 5.8 m round.

# Charge type Breakage radius

1 Packaged tube type charge, 19 mm diameter 0.1 m

2 Packaged tube type charge, 29 mm diameter 0.4 m

3 70 g/m detonating cord 0.05 m

4 String charge with 1.5 kg toe charge,0.35 kg/m string

0.2 m

5 ANFO/polystyrene blend, 50% ANFO,blow loaded

0.6 m

6 Blow loaded ANFO 1.0 m

7 Bulk emulsion, 1.0 g/cc density 1.4 m

TABLE 1Energy distribution distances of various perimeter charges.

Heave EnergyHeave Energy

Shock EnergyShock Energy

Increasing Velocity of Detonation

100%100%

0%0%

Heave Energy

Shock Energy

Heave EnergyHeave Energy

Shock EnergyShock Energy

Heave Energy

Shock Energy

Increasing Velocity of Detonation

Ex

plo

siv

eE

ner

gy

Ex

plo

siv

eE

ner

gy

FIG 2 - Energy partition diagram.

coaxial cable installed in the hole 100 000 times per second. Asthe detonation front travels along the explosive column, the cableis consumed. The slope of the resulting graph of cable lengthversus time is the VoD of the explosive. A typical VoD trace isillustrated in Figure 3. The VoD ranged from 3600 to 3800 m/s,which agrees with theoretical calculations for Titan 7000 at adensity of 0.90 g/cm3, calculated using the Vixen idealdetonation code developed by African Explosives Limited(Cunningham, Braithwaite and Parker, 2006). As a comparison,VoD values for ANFO are typically 3000 m/s.

Face pattern optimisationA standard ANFO pattern will generally be modified to takeadvantage of the characteristics and benefits of bulk emulsions inthe following ways:

• the burden on all fully charged holes can be increased as thebreakage radius for emulsion is greater than ANFO;

• the central knee holes are shifted upwards, increasing theburden on the lifters;

• the offset of the shoulder and knee holes with respect to theback and lifter holes can be increased; and

• a number of stripping holes can be removed and the burdenon the remaining holes adjusted.

As the string loading method achieves similar results topackaged decoupled charges, burdens and spacings for perimeterholes should remain the same.

Metered hole loading and explosive consumption

The liquid form of bulk emulsions, combined with the pumpingsystems commonly used, allow for accurate metering ofquantities of emulsion and trace chemicals using commerciallyavailable programmable logic controllers (PLCs). For standardholes, this results in an accurate, repeatable amount of emulsion,delivered at the correct density to each hole. For string loading,PLCs also allow for control of hose retract speed, whichdetermines the size of the emulsion string. Metered hole loadingalso prevents much of the spillage typical of a face charged withblow loaded ANFO.

The application of longer standard collar lengths can beachieved due to the loading accuracy achieved with the PLCs. Atypical uncharged collar length for a face charged with bulkemulsion is around 0.7 to 1.0 m. This will reduce the amount ofexplosives required to charge the face, with a 1.0 m collar in a64 hole face saving around 56 kg of equivalent ANFO.

Charging timeReducing the time required to charge a face provides a number ofbenefits to the operation. The most obvious is the ability tocharge more headings in a given shift. However, the mostsignificant benefit is a reduction in the overall exposure ofoperators to the hazards associated with charging a face.

Most operators have reported a 20 - 30 per cent reduction inthe time to complete charging. Time savings are achieved by:

• not having to individually load and tamp packaged product,

• not having to switch products to charge perimeter holes, and

• loading the holes at a faster rate through faster pumping rates.

Safer delivery system

Underground ANFO delivery systems are based on using highpressure air to deliver the product to the end of the charge hose.This is achieved using either a venturi style loader or apressurised kettle, or a mixture of both. The operating pressure ofthe systems can be up to 650 kPa. Working with high pressuresystems exposes operators to a number of hazards, including:

• the discharge of the ANFO from the end of the charge hose –it can travel at over 200 km/h, and

• issues associated with use of the pressurised ANFO kettle.

Development-specific emulsion loading systems are able tooperate at much lower delivery pressures whilst maintainingloading rates of up to 100 kg per minute. The back pressure onthe charge hose is just enough to gently push the hose from thehole whilst charging.

Transport, storage and handling

The transport and storage of bulk emulsions is generally easierthan ANFO due to the classification of unsensitised bulkemulsions as an oxidising agent, rather than an explosive. Liquidemulsions are easily transported by road as a dangerous goodsload in either road tankers or Isotainers. On-site storage isgenerally in vertical tanks or, for temporary sites, in Isotainers.

Storage as a dangerous good is particularly useful on remotesites subject to seasonal rainfall, as the licensing and storagerequirements for ANFO can restrict the quantities permitted onsite.

As a bulk liquid, emulsions can easily be pumped from the sitestorage facility into the underground unit using a simple, airpowered ‘Wilden’ type diaphragm pump. In comparison, ANFOhandling systems vary from simply loading 20 kg bags directlyinto the kettle, loading kettles with bulkabags and an IT with jib,

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THE BENEFITS OF BULK EMULSION EXPLOSIVES IN UNDERGROUND DEVELOPMENT MINING

0 1 2 3 40

1

2

3

4

Length (m)

VoD (km/s)

Average VoD 3660 m/s

FIG 3 - Velocity of detonation (VoD) trace.

through to overhead rail systems in underground magazines.These systems have various drawbacks, including being labourintensive or requiring expensive equipment.

Scorpion® direct priming

Dyno Nobel’s Titan 7000 emulsion can be reliably initiated witha #12 detonator in a 45 mm diameter blasthole. Blow loadedANFO can also be reliably detonated with a #12 detonator;however, the conventional loading technique coupled with waterin the blasthole and the deleterious effect of water on ANFO canlead to misfires. The emulsion loading technique allows forreliable full encapsulation of the detonator with a water resistantexplosive and displacement of all water from the blasthole.

As a result, conventional packaged emulsion primers can bereplaced with a simple device to centralise and protect thedetonators in the blasthole. The Scorpion is an example of such adevice, constructed from extruded plastic. It is illustrated inFigure 4 and comprises four fins attached to a central spine andfacilitates direct priming of blastholes with detonators.

As the Scorpion is not an explosive, the ‘primer’ can beassembled in the detonator magazine prior to charging, and betransported to the face fully assembled.

ECONOMIC BENEFITS

Table 2 is a generic summary of the savings available whenreplacing ANFO with bulk emulsion in a development heading.The savings are described both as a theoretical dollar value, andas a percentage of the cost of explosives required for a typicalANFO round.

The parameters used for the calculations are:

• 64 hole pattern, 4.2 m round;

• knee holes and lifters considered wet; and

• perimeter products used grade line to grade line.

Replacement of packaged products

The major economic benefit associated with the use of bulkexplosives in development blasting is gained by replacingpackaged emulsion products or tube products used in lifter, kneeand perimeter holes. These products are very expensivecompared to bulk products, with bulk emulsion 40 per cent to60 per cent cheaper than the packaged products. It is also timeconsuming to load packaged products, particularly plastic filmpackaged emulsions, as each cartridge needs to be tamped.Combined with the higher loading rates of bulk emulsionsystems, the time saved in charging a face can be around threeper cent of the overall drill and blast costs for each round. Thereis also the lost opportunity cost that comes with the extra timerequired for each face.

Reduced number of holes

Along with the savings in explosives costs outlined in Table 2, itstands to reason that there are savings to be made in not havingto drill the holes to begin with. Removing five holes from a facecould save 15 minutes of drilling time along with savings inconsumables. This would save a typical operation $156.53 perface in drill and blast costs, or around six per cent of the cost todrill and blast a face.

Reduced explosive requirements

With improved metering, longer collars and reduced spillage,savings of around $57 per face, or 6.4 per cent of explosive costsare easily achievable. It is assumed that around 10 kg of ANFOis lost on the ground during charging operations, not includingprime up.

Improved advance per round

Using the example detailed in the practical benefits section, aseven per cent improvement in advance will result in a costbenefit due to the extra metres advance achieved withoutincreasing drill and blast costs. Using the parameters detailedabove, a seven per cent increase is an extra advance of 0.29 mper round. If the operation achieves an average of four rounds pershift, this will result in an extra 72.9 m per month.

The additional drill and blast costs that would normally berequired to achieve these metres would be $42 666 per month.

Primer costs

A plastic detonator centraliser and protector such as the Scorpionis a much cheaper priming system than packaged emulsions orcast primers. Replacing packaged emulsion primers withScorpion primer can save $53 per face, or around eight per centof explosives costs.

CONCLUSIONS

Bulk ANFO is cheaper to manufacture than bulk emulsions.Delivered to site, ANFO is generally about 40 per cent cheaperthan bulk emulsions. Incorporating the savings outlined above,the lowest total cost of charging and blasting a face is, however,not achievable using the cheapest bulk explosive (ANFO). Bulkemulsions instead in development mining have the potential toreduce explosives costs by 25 per cent and reduce overall drilland blast costs by 14 per cent. For a typical underground

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FIG 4 - Detonator centraliser.

Savings perround (A$)

Reduction inexplosives costs (%)

Replacement of packagedemulsions in wet holes

212.52 24

Replacement of tube chargesin perimeter holes

178.90 20

Replacement of tube chargesin wet holes (eg lifters)

100.73 11

Reduced number of easer holesin face

62.84 7.1

Replacement of packagedemulsion primers with Scorpion

52.78 7.9

Improved metering with longeruncharged collar lengths

48.63 5.5

TABLE 2Savings in explosives costs per face charged.

operation charging four faces a shift, this would save over$54 000 a month, or $650 000 a year in explosive costs andalmost $92 000 a month or $1 103 000 a year in drill and blastcosts.

The combination of these savings, and the practical benefitsoutlined previously, has led numerous underground miningoperations to change from ANFO based development mining tobulk emulsions. These include mining contractors and owner-operators, with annual development rates between 3.6 and15.6 km. The acceptance of bulk emulsion systems by theoperators has been exceptionally high, with very few wishing toreturn to ANFO once familiar with the bulk emulsion systems.

REFERENCESAdamson, W, McKern, E J, Pearce, D O and Duke, D D, 2000. The

influence of cartridge length and tamping practices on the efficiencyof packaged emulsion explosives in development blasting, inProceedings First World Conference on Explosives and BlastingTechnique (ed: R Holmberg), pp 259-264 (Balkema: Rotterdam).

Bakke, B, Ulvestad, B, Stewart, P, Lund, M B and Eduard, W, 2001.Effects of blasting fumes on exposure and short-term lung functionchanges in tunnel construction workers, Scand J Work EnvironHealth, 27(4):250-257.

Cunningham, C, Braithwaite, M and Parker, I, 2006. Vixen detonationcodes: Energy input for the HSBM, in Proceedings EighthInternational Symposium on Rock Fragmentation by Blasting:FragBlast 8, Santiago, pp 169-174

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