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Page 1: Ventilation strategies to meet future needs of the South ... · VENTILATION STRATEGIES TO MEET FUTURE NEEDS 277 Introduction The provision of ventilation systems for modern mines

VENTILATION STRATEGIES TO MEET FUTURE NEEDS 277

IntroductionThe provision of ventilation systems for modern mines is anintegral part of the mine’s technical design. The art of mineventilation consists in finding a balance between what is asafe and healthy environment while providing a costefficient infrastructure in terms of both capital andoperational expenditure.

The definition of a safe and healthy working environmentis derived from baseline risk assessments aimed atidentifying the hazards and quantifying the risks relating tothe working environment. This process leads to theapplication of what are termed ‘reasonable’ protectivemeasures aimed at eliminating or in the least mitigating thedetrimental impact of the hazard on workers. The outcomeof this process is the ventilation engineered design criteriaagainst which the performance of the system can bemeasured objectively.

It is against this background that all the various facets ofmodern ventilation systems are structured. Althoughingenuity is a primary requirement of any engineeringdesign process to ensure effectiveness at an acceptable cost,the strategy on which ventilation systems are based mustremain focused on the mining and engineering requirementswhile attaining the design criteria generated in the riskassessment process. Ultimately a functional ventilationsystem must not become an impediment to miningoperations. On the other hand, the adaptation of the systemdesign to meet mining and engineering requirements shouldnot lead to the transgression of boundaries beyond whichthe resilience of any ventilation system will fail.

It is for these reasons that the challenges presented bymodern platinum mining operations to the ventilationengineer have to be addressed in a logically structured andmethodical manner. The design process to which a modernventilation system has to be subjected must interactiteratively within the parameters posed by the mining andengineering requirements of the project so as to providesolutions that reflect the dynamic nature of a mining project

and that cater for different system performancerequirements at different stages in the life of the project.

BackgroundThe range of platinum mining operations currentlyundertaken in Southern Africa varies greatly from newoperations where the reef outcrops or is very close tosurface to operations currently approaching a third phase intheir lifespan at depths approaching and sometimes beyond2 000 m below surface. The challenges presented by thelatter type are obvious in terms of the need for cooling andthe provision of more extensive and sophisticated airconditioning systems. In addition, the extent of theseoperations on strike can be as much as 6 000 mnecessitating relatively high electrical power demand tocirculate the required air quantities

Mining methods are also varied and affect the ventilationsystem requirements significantly. Modern platinum miningoperations are characterized by a higher degree ofmechanization. Machinery is employed primarily for safetypurposes where the worker is removed from the dangerzone. In addition, mechanization can accelerate andstreamline production and enhance flexibility of miningmethods. For example, the introduction of ultra low profilevehicles designed for hard rock mines has been stimulatedprimarily by the needs of this sector of the mining industry.Even in narrow channel width mining operations, it is notuncommon to encounter conveyor belts in strike gullies thatare developed by low profile LHDs. The ore is dumped on acomprehensive conveyor belt network that leads to verticalor inclined shaft systems for hoisting or that is extended allthe way to surface surge bins directly. The use of conveyorbelts is further justified in terms of the extent of theseoperations on strike where the advantages of this mode oftransport become apparent and also where the life of theproject is relatively long.

It is also typical that a trackless equipment fleet should bepowered by diesel combustion engines that offer greater

BIFFI, M., STANTON, D., ROSE, H. and PIENAAR, D. Ventilation strategies to meet future needs of the South African Platinum Industry. InternationalPlatinum Conference ‘Platinum Surges Ahead’, The Southern African Institute of Mining and Metallurgy, 2006.

Ventilation strategies to meet future needs of the SouthAfrican platinum industry

M. BIFFI*, D. STANTON†, H. ROSE* and D. PIENAAR†

*Prysm Resources (Pty) Ltd†Anglo Platinum

This paper provides an overview of possible approaches for structuring the ventilation systems formines that will become operational within the next decade. Features addressed in the paperinclude: aspects of airway design and layout in the absence of centralized vertical return shafts,the impact of using diesel-powered trackless equipment in conjunction with conveyor belts in thedevelopment and production phases of the project, and the need to balance increasing electricalpower costs against the requirement for reduced capital expenditure.

The paper provides brief descriptions of the strategies employed in real-life situations andpresents an overview of various operational parameters affecting the design of ventilation systemsthat will be used as ‘platforms’ for much deeper mines in the future.

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PLATINUM SURGES AHEAD278

flexibility and better all-round performance in terms ofproduction per unit power output. The use of tracklessequipment is maximized during the primary development ofthe orebody’s infrastructure in order to reduce productionlead times and anticipate creation of revenue.

For the purpose of this paper it might be useful tocategorize different mine types into three groupings:

• Category A consists of mines that operate from surfacedown to a depth of 700 m below surface. Theseoperations tend to be relatively new and in many casesrepresent the first stage of mines that will expand to agreater depth in this century. These operations arecharacterized by direct access from surface by means ofadits and vehicle and conveyor belt declines. Chairliftsmay be provided for the transport of workers. Hoisting shafts are not used and will form part of thenext phase of the project. Typically the infrastructure islimited — not only due to restrictions imposed by thestrategy of a ‘pay as you go’ strategy — but also due torestrictions posed by limitations in infrastructureavailability such as electrical power and process watersupply. Being the latest generation mines, occupationalenvironmental impacts are of primary importance.These also affect the location and number of accesspoints into the mine for ventilation purposes.

• Category B operations typically extend from about 700m to a depth of about 1 200 m below surface. Theseoperations are beyond the initial phase and are well intotheir production target zone. The infrastructure is moredeveloped than that of category A mines and typicallyinclined or vertical shafts are in use forming platformsfor production as well as for the next phase ofexpansion. The use of air cooling to varying degrees ofcomplexity through the use of mechanical refrigerationis a reality for these operations. Aspects related to theavailability of electrical power and water supply aremanaged, although future expansion will entail super-linear increases in power demand for hoisting,pumping, ventilation and cooling. The surfaceinfrastructure in terms of ventilation shafts is in placeand further expansion at depth will maximize the use ofthe existing and older infrastructure in terms of intakeand return airways. For this category air cooling is inthe form of primary surface bulk air coolers thatprocess various proportions of the downcast airquantity.

• Category C comprises mines that can be termed ‘ultra-deep’ from a ventilation system design perspective. Insome cases these mines operate at depths approachingand in excess of 2 000 m below surface where the rocktemperature is in well in excess of 60°C. Mines in thiscategory are in the third stage of development typicallyemploying deep vertical shafts or sub-decline clustersthat extend on dip the reach of the current surfacevertical shafts. In future, this category of mines will seethe sinking of sub-vertical shafts. These systems are anextension of the surface intake shaft infrastructure andplay an essential role in conveying fresh air to theworkings. At this stage of the development of thesemines, primary surface air cooling is supplemented bysecondary underground air cooling as well as by in-stope cooling in some instances. In this category ofmines underground chilled water reticulation systemsare employed and electrical power requirements areaffected significantly by higher water pumping andrefrigeration capacity.

In all cases return air is conveyed through the reefhorizon to main horizontal return airways that are linked tothe various upcast shaft systems. The dependence ofventilation systems on the worked-out reef horizon andabandoned levels as return airways present challenges andrisks — particularly for deeper mines where the risk ofincreased airflow resistance and airway failure isheightened by stress-induced deterioration and eventualfailure of excavations and by the effects of seismic activity.

Primary ventilationPerhaps the most dreaded question asked of a ventilationplanner is: ‘What size airway (shaft or decline) do yourequire?’ This is not an easy question to answer at the timeit is usually asked — usually at the very start of the project.The size of the main intake airways may only bedetermined once the mine layout (both in terms ofproduction levels and methods), extent of miningoperations served by the airway and production schedulingare established with a degree of finality.

The mine layout determines quantitatively the air flowrequirements at different stages of the life of the project.This is dictated by the tonnage produced and themethodology adopted (usually degree of mechanization).The size of ventilation systems is also determined by thedegree of scatter of mining operations. The creation of anumber of stopes in a regular array will require less air perton than that consisting of clusters scattered both on dip andon strike.

The primary requirement in both a breast stoping or roomand pillar arrangement is the provision of adequate airvelocities at the face (for breast mining) or in the lastthrough road (room and pillar). Consideration for airleakage completes the air quantity requirements per stope.The air requirements for each stope together with the airrequirements for development activities determine the airquantity for each half level. Table I summarizes a set of airvelocity criteria in stoping sections.

Similarly, during the development phases of a verticalshaft or a decline cluster, criteria are used to provide therequired air quantity. Typically, these are based onproviding a minimum flow rate per unit area of theexcavation — for example 0.20 m3/s/m2 for developmentends and 0.30 m3/s/m2 for sinking shafts — that will allowand adequate number of air changes during the re-entryperiod. Usually, however, the development of a declinecluster may need to handle air volumes well in excess of thevalues thus obtained and this may affect the dimensions ofthe decline itself. The additional air flow requirements cater

Minimum face Notesair velocity

(m/s)

Breast miningDepth to 650 m below surface 0.40 For VRT < 37,5°C only;

else use next value

Between 650 m and 1 500 m 0.60

Depth in excess of 1 500 m 1.00

Room and pillar Last through road 1.50

Adjacent road 1.00

Table IStoping air velocity criteria

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VENTILATION STRATEGIES TO MEET FUTURE NEEDS 279

for any development operations that originate from theseprimary structures.

The use of diesel-powered vehicles in the development ofdecline cluster on minor gradients is favoured as it providesgreater flexibility and has the potential of faster rates ofadvance. Figure 1 shows schematically a typical twindevelopment arrangement. The dimensions of the ends are4.0 m wide and 3.5 m high for a total area of 14 m2. Aprimary flow of 50 m3/s is induced by fans at the head ofthe return airway. In accordance with the criterionventilation rate of 0.2 m3/s/m2, each end will require aminimum of 4.2 m3/s. However, mining operations requirethe use of diesel powered LHDs and trucks. The applicationof an exhaust diesel fume factor of 0.06 m3/s/kW (as will bediscussed later) increases the fresh air flow requirements atthe face to 13.0 m3/s, for, say, a total rated power of 210kW.

Figure 1 (not to scale) also indicates the use of rigidexhaust ducting. These are usually sized to handle therequired air quantities and are likely to interfere withloading, transport and construction operations. In verticalshaft systems development operations will be setoff oncethe shaft is completed and a permanent up-cast facility is inplace. For decline systems, as considered presently,development of levels may be setoff as soon as the levelelevation is reached and therefore the system has to handleenough fresh and return air for operations until through-ventilation is established on each level. A cursory analysisof Figure 1 highlights the fact that the number of levels thatmay operate from such a primary system is limited by thecapacity of the primary air mover at the top of the returnairway and the number of diesel-powered vehiclesoperating simultaneously.

In some instances the need to integrate mining andengineering requirements to the maximum create verycomplex arrangements, as shown schematically in Figure 2.The figure represents a layout that was proposed for anoperating platinum mine and although this is not anengineering drawing, the relative proportions of theequipment are consistent with the size of the excavation.The mining team proposed in this case to combine twoexcavations into a single larger entity. On paper the layoutis feasible but in reality it presents a number of issues thatare too detailed for the purpose of this discussion. Suffice tosay that the capacity of this arrangement to support furtherdevelopment is very limited and that therefore the netadvance rates were affected accordingly. It is also to benoted how the relatively small ducts (maximum totalcapacity of about 40 m3/s of air for significant distances)

limits the size of vehicles that may effectively operate inthis decline.

As part of the longer-term use of shafts and declineclusters as airways, the following should be noted:

• Although equipped shafts inherently present a higherfrictional resistance to airflow, they are designed forhigher air velocities. Air velocities in equipped shaftsmay be as high as 12 m/s whereas in access declinesthe velocity is limited to 8 m/s due to worker andvehicular access.

• Air velocities of up to 22 m/s may be tolerated inunequipped shafts — particularly in instances wherethey have been raise-bored.

• Vertical shafts are shorter than inclined airways andtherefore for equivalent frictional losses, they are moreaerodynamically efficient.

• Use of declines for equipment such as conveyor beltsand chairlifts limit the capacity of the excavations. Forconveyor belts a maximum velocity of between 3.0 m/sand 5.0 m/s is recommended (for an air flow contraryto the conveyor’s operational direction) while the airvelocity in chairlift excavations is limited to 6.0 m/s.Furthermore, due to the fire risk posed by conveyorbelts, there an increasing reluctance to use excavationscontaining this equipment as a main intake airway.

Therefore, although the concept of surface or sub-surfacedecline systems may offer a number of opportunities, thepotential limitations that these might impose on theventilation system capacity must be recognized andconsidered accordingly. At present the capacity of surfacedecline cluster is increased by positioning vertical raise-bored holes that can ‘inject’ high velocity fresh air fromsurface to strategically advantageous positions in the mine’sintake airway system.

A last remark in terms of ventilation requirements isneeded at this point. Although the criteria and parametersdiscussed previously give adequate indications of the airflow requirements, the sequential use of air will assist inlimiting the air flow. This ‘optimization’ may be possibleparticularly in breast stoping environments where there isvery limited or no use of diesel-powered vehicles. In well-ventilated room-and-pillar sections where the relativevehicle power to tons to air ratio is low, re-use of air maybe possible as long as the air quality entering the lastworking place in the series is within acceptable standards.Breast stopes may also be ventilated sequentially if theseFigure 1. Schematic twin development end layout

Figure 2. Schematic layout of decline development

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are developed in regular grid pattern. The ability of ventilating working places sequentially

maximizes the utilization of fresh air but has its limitations.In fact the limiting factor in many instances proves to behigh wet bulb temperature increase experienced as the airabsorbs heat energy in working places further downstream.

Considerations relating to heat loadsAnother question that the ventilation engineer is oftenasked is, ‘When will refrigeration be required?’ The answerdepends on a number of variables that include the meanrock breaking depth, production rate, strike distance overwhich operations take place (linked to the ambient rocktemperature), the equipment operating in the mine and thecriterion used to determine the acceptability of theenvironment, to name the more significant ones.

Currently the air wet bulb temperature is the thermalproperty that is used to define the acceptability criterion forambient conditions in the occupational environment.However, there is a growing support to use the concept ofair cooling power as a more adequate indication of theworking environment’s ability to provide the necessarycooling capacity. Presently there are two shortcomingspreventing the wide-scale use of the air cooling powerconcept as a criterion:

• air cooling power is not readily measurable at theworking place and, more importantly,

• scientific verification of a data-set that would validatethe acceptability of such a criterion has not beenperformed.

It is for these reasons that a wet bulb temperature varyingbetween 26.5°C and 28.5°C (depending on the operation)and termed ‘reject wet-bulb temperature’ is used as thedesign criterion. Figure 3 demonstrates the versatility of theair cooling power concept in defining ‘equivalentenvironments’.

The figure shows that an air stream at a wet bulbtemperature of 29.0°C and an air velocity of 1.2 m/s has anair cooling power of 300 W/m2. This is equivalent toanother air stream at 27.4°C wet bulb temperature at an airspeed of 0.6 m/s. The concept forms the basis of thedifferentiated face air velocity criteria demonstrated earlierin Table I above and allows greater latitude for theintroduction of air cooling — particularly in borderlinesituations

The geophysical properties of formations constituting theBushveld Igneous Complex (BIC) are such that thetemperature gradient increase with depth is twice as severeas in the West Wits Basin. This is depicted in broad termsby Figure 4. The graph indicates the variation of virgin rock

temperature with depth and also shows that ‘milestone’rock temperatures in the BIC are reached at much shallowerdepths than in the West Wits Basin. Therefore, in the BIC avirgin rock temperature of 40.0°C will be reached at anapproximate depth of 650 m as compared to a depth ofabout 1 800 m in the West Wits Basin.

Another observation in relation to Figure 4 is that thetrends shown are generic and that actual profiles will varyfrom site to site in relation to geophysical properties ofoverlying rock structures. In addition, the presence of hillsand mountains close to the surface will increase theeffective temperature gradient as a function of ‘depth belowsurface’ irrespective of wherever surface might be. Thiseffective increase is not directly proportional to the heightof the hill or mountain but effectively decreasessignificantly with the depth below collar at which‘milestone’ temperatures are encountered.

The virgin rock temperature and the geophysicalproperties of the host rock in the design of a ventilationsystem determines the surface temperature of the rockexposed to the airflow. This in turn establishes the heatenergy flux form the rock into the cooler air and results inthe increase of the air temperature of the air stream.

Computerized modelling of the mine using softwarepackages such as VUMA and ENVIRON 2.5 are tools usedto assist designers in determining the aerodynamic and the‘thermodynamic’ performance of the system.

These tools are used to:• Generate a balanced airflow model of the mine to

ensure that airflow patterns meet the distributiondetermined by the application of the design criteria

• Determine the fan performance characteristics to verifyfan operating points, and the need for main booster fans

• Optimize the location and dimensions of main airways.• Determine heat load and temperature variations

throughout the mine to verify compliance with designcriteria (be these in terms of reject wet bulbtemperature or air cooling power)

• Determine the capacity and position of primary,secondary and tertiary air coolers

• Provide an indication of the overall cooling systemextent, capacity and performance

All the data gathered from these simulations are collatedinto a set of performance specifications that are used in theselection of equipment, optimization of the chilled waterdistribution system and the positioning and selection of therefrigeration plants. Other software packages such asCoolflow may be used in conjunction with these to assist inthis process.

All this software simulates steady-state conditions and is

Figure 3. Equivalence of air cooling power Figure 4. Virgin rock temperature variation

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VENTILATION STRATEGIES TO MEET FUTURE NEEDS 281

deemed to be adequate for the purpose of definingperformance parameters. However, in hot environments theeffect of transient conditions has to be considered as afunction of the geophysical properties of the host rock.

The thermodynamic properties of the BIC rock massbeing mined (mostly norite) are such that the rock will coolmore rapidly than quartzite (representative of the West WitsBasin) and will find equilibrium at a sensibly lower surfacetemperature. This will result in a lower energy flux per unittunnel length for the same virgin rock temperature and thesame air temperature, as shown in Figure 5. The figureshows the theoretical heat flux variation over a period ofninety days after exposing a section of the tunnel to anairstream having a constant dry bulb temperature of 30.0°C.It is stressed that the results shown here are approximateand indicative but that they point to the fact that the heatflux in norites is considerably lower. The figure alsoindicates the limited effect that tunnel insulation (100 mmthick and with a conductivity of 0.1 W/m2/K) would have inreducing the heat flux and that indeed norites are better offthan the best insulated tunnel excavated in quartzite.

The following points are noted from the above and Figure 5:• The heat flux in the first three to four hours after the

blast is extremely high, resulting in high temperaturesduring re-entry and at the beginning of the cleaningshift.

• Although in terms of ‘average conditions’,temperatures may appear to be acceptable, on re-entryand during cleaning operations conditions at the faceare likely to exceed acceptability criteria.

• The use of diesel-powered vehicles during cleaningoperations will aggravate the situation further.

• The use of tertiary cooling (at the face) together withextensive use of chilled service water (water jetting)will assist in cooling the excavation, the ambient airand the blasted rock relatively quickly and reduce theheat flux at a rate greater than that induced by the airflow alone.

• Design of the cooling system in terms of equipmentand capacity must cater for high demand peaks tohandle this additional load profile.

The foregoing comments briefly highlight the challengespresented both in terms of design and operational issuesthat will arise with deeper operations. The findings alsopoint out the usefulness of software currently available inarriving at these conclusions. It is stressed that the resultsare very site specific and that, as with many other types ofmodelling, the validity of the results is dependent on thequality of the input data. Also it is noted that the resultsobtained from a steady-state analysis of the system are

suitable for system design purposes but that transientconditions may differ significantly from the average.Designers must be aware of these pitfalls and adapt systemsto cater for transient demands.

The usefulness of software simulations is highlighted interms of the speed with which alternative designs may beevaluated and the data that may be obtained detailed as wellas from ‘first order’ analyses. Figure 6 shows the variationof cooling load as a function of virgin rock temperature(VRT) for a number of reject wet bulb temperatures. Thisanalysis is typically performed at pre-feasibility andfeasibility level to assess the extent of the coolingrequirements. The results shown in Figure 6 are for a deeplevel platinum project in the BIC. The results are once morevery site specific and depend on the production rate, strikeextent and mine methods, among the most relevantparameters.

Figure 7 demonstrates further how software simulationsmay be used in the analysis of different mining methods.The graph shows the variation of heat load as a function ofdepth below surface for a set of different mining methods.The heat load is ‘normalized’ by the tonnage produced atdifferent depths — which in this case would represent meanrock breaking depth. The mining methods analysed as partof this work were variations of breast stoping operationswith different ore transport and access strategies anddifferent cooling system applications. The noteworthyaspect of this analysis is the comparison of the two ‘I seriesalternatives’. These options are identical except that the ‘D’option utilizes diesel powered vehicles while the ‘E’ optionhas a corresponding fleet of electrically powered vehicles.

The difference in the heat loads between the two optionsis appreciable and it is shown in relation with the overallheat load that comprises the effect of the rock masstemperature, depth, extent and auto-compression of the airin circulation. Although the use of electrically poweredmachinery offers distinct advantages in that it will translateinto lower cooling plant costs, these have to be offsetagainst the higher cost of the electrical vehicles, higherinfrastructure costs and ease of operation (trailing cables,battery re-charging).

This example demonstrates that trade-off studiesinvolving aspects relating to the underground environmentmay be undertaken with relative ease and will yield resultswithin the required degree of confidence in order toenhance the validity of the comparison.

Figure 5. Comparison of heat flux variation as a function of timeFigure 6. Air cooling variation as a function of VRT and design

reject wet bulb temperature

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PLATINUM SURGES AHEAD282

Aspects of health and safety As stated previously, the objective of any ventilationsystem is the provision of safe and healthy conditionswithin the working environment. In this section certainaspects relating to environmental health and safety relatingto modern platinum mining requirements will behighlighted.

Choice of power plantThe comparison outlined above highlights one aspect of themany dilemmas facing modern mine designers: diesel orelectric mining equipment? Part of the answer was givenand, in terms of the ‘bigger picture’, the choice of diesel-powered equipment for the options described by Figure 7may be the correct one.

However, it is a fact that, excluding the case wherethermodynamic work is done (as for example where aloaded truck hauls ore up a ramp) diesel-powered vehicleswill produce three times more energy as heat energydischarges to the surroundings as is drawn mechanically bythe engine. In the case of an electrically powered unit, theheat energy emission is equal to the energy drawn by themotor.

Another aspect that has to be considered is the fresh airdilution that must be provided to minimize the adverseeffect of diesel exhaust fumes. The dilution factors willdictate primarily the air quantity required in sections wherediesel-powered vehicles are operated — as was mentionedearlier in this paper. In the case of highly mechanizedoperations, vehicle operation may be seriously hampered bylimited fresh air quantity availability. In addition, the natureof operations is such that maximum dilution will berequired in ends being mucked where poor ventilationconditions and accumulation of exhaust fumes, particulateand hot air are more likely.

The dilution factors are selected in terms of best practiceand are in general not regulated in terms of the MinesHealth and Safety Act. The dilution factor mostly applied is0.06 m3/s of fresh air arriving at the point of application forevery kilowatt of rated diesel power operational in theworking place. In general, this represents a minimumapplied by the industry and assumes that a number of otherprotective measures are in place:

• Latest generation (at least Euro IV) engines are in use.• Catalytic converters are installed as part of the

vehicles’ exhaust systems.• Particulate filters are used and maintained properly and

regularly.

• Low emission diesel fuel is used.• All vehicles are maintained regularly by suitably

qualified and equipped staff.Without these ‘additional’ measures, the required dilution

factor would increase to 0.08 m3/s/kW and up to 0.12m3/s/kW thus requiring more extensive ventilation systems,which will complicate mining operations as demonstratedpreviously.

Underground firesThe danger posed by fire is another aspect of large-scalemechanization in mining operations. Fire is a constanthazard wherever large sources of energy are stored andused, as is the case in mining machinery. The outbreak of asudden, highly intense fire underground has the potentialfor catastrophic outcomes and must be avoided at all costs.

The combination of combustible materials such ashydraulic oils and rubber tyres in the vicinity of hotsurfaces has to be managed continuously and safelywherever vehicles operate. The fire risk posed by diesel-powered machinery is further intensified by the presence ofdiesel fuel, which may participate in the combustionprocess and increase the intensity of the heat, smoke andgas emissions in the event of a fire.

A further dimension to the risk in terms of using dieselpower underground is found in the large-scale transport anddistribution of the fuel as part of routine operations. Thestorage of fuel underground requires awareness in terms ofa thorough risk assessment and the adoption of protectiveand preventative measures to limit the fire risk.

The large-scale use of conveyor belts also presents asignificant risk for the rapid development of undergroundfires. The flow of fresh air over conveyor belts provides acontinuous source of oxygen that may cause the fire tobecome self-sustaining under certain circumstances. Inaddition, the location of conveyor belts in intake airwaysprovides the potential for large-scale contamination of themine’s atmosphere.

These hazards are managed effectively by the analysis ofvarious risk scenarios and the implementation of protectiveand preventative measures devised in accordance with suchanalyses:

• Issue-based risk assessments are essential to identifypractices and situations that require specificintervention.

• The prevention of fires through the adoption ofadequate design, equipment, procedures, maintenanceand inspections is an essential aspect of this process.

• Routing of fresh air away from high risk areas(conveyor belts, underground rubber tyre, fuel and oilstorage areas, etc.) will limit air contamination during afire.

• The identification of high risk areas by managementand workers will highlight the presence of the hazardand provide the necessary awareness.

• The provision of early detection systems, actionprotocols and firefighting procedures is essential inlimiting the spread of a fire. This includes the remotemonitoring of the air flowing through high risk areas,the provision of adequate and back-up communicationsystems and protocols, the provision of effective fire-fighting equipment (e.g. on-board automatic andmanual fire suppression systems; fire hoses at strategicposition within the high risk areas; automaticsprinkler/water deluge systems; etc.) In addition and

Figure 7. Heat load variation as a function of VRT for differentmining methods

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VENTILATION STRATEGIES TO MEET FUTURE NEEDS 283

more importantly, adequate training of key personnelsuch as operators, supervisors, etc. in fighting firessafely using the equipment at their disposal is essentialin preventing the degeneration of a small fire into amajor catastrophe.

• The timely provision of protective measures and thetraining of workers in the use of protective equipmentis the last component of the strategy. Of particularimportance are systems designed to provide respirableatmosphere to workers who are affected by the smokeand gases emanating from the fire and who may not beable to reach a point in fresh air. These measurestypically include the provision of self-contained self-rescuers and the location of adequately equipped refugebays at strategic positions that may be reached byworkers using self-rescue devices.

• Adequate awareness and training are essential inproviding adequate and timely response as soon as thefire is detected.

ConclusionsThis paper has provided a brief overview of the ‘ventilationperspective’ on future challenges facing the expansion ofplatinum mining operations. The space and time at one’sdisposal make it difficult to provide a justly extensivecoverage of the many facets of this subject. The authorshave provided an insight on the more important aspects.

The most significant aspect is that the solutions to thesechallenges are well within reach of technologies currentlyat the disposal of designers. Having said this, theimportance of integrating the ventilation system design as afully fledged component of the overall mine design isemphasized.

Maximizing the use of the infrastructure to convey air tothe various working places at different stages of the life ofthe mine is likely to reduce costs. The integration ofventilation requirements in the planning of primary

development and production methods has been highlightedin the paper. Ventilation systems designed as‘afterthoughts’ are likely to provide the required outcomebut at a considerable additional cost — both measured interms of time and money. The impact of inefficiencies onoperational costs seen against the backdrop of everincreasing power costs is going to hamper futureprofitability considerably. In shallow operations where themetallurgical process is off the mine site, the cost ofelectrical power for ventilation systems is likely to ranksecond only to that of ore transport.

The ‘modular’ design approach to new operations and toextensions of existing ones provides opportunities to devisea ventilation infrastructure to a large extent also modular innature. It is important, however, not to lose sight of the‘final’ picture so that adequate capacity is incorporated toavoid delays or becoming an excessive burden on thefinancial viability of the project.

The paper has also shown the value of using computermodelling for the generation of comparative tools that areessential for the preliminary as well as for the detailedphases of the project. The software provides a basis formore sophisticated analysis of costs and facilitates thecompletion of trade-off studies.

Cooling strategies pioneered in the gold mining sectorserve as a useful basis for aspects of future ventilationplanning. However, the adaptation and expansion of thisknowledge to meet requirements particular to platinummine operations has already been undertaken by designersand equipment manufacturers alike.

The challenge remains the provision of a healthy and safeworking environment that is effective and cost-efficient andthat is adequate for all facets of mining operations from theinitial establishment to closure of operations.

The authors acknowledge the management of AngloPlatinum for permission to publish this paper.

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