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Options for mine ventilation


This case describes a fast, high-level review of mine ventilation options. It used Kepner Tregoe analysis to focus on the ability of the options to achieve project goals, providing clarity and a sound rationale for management decisions. If straightforward approaches are sufficient, then there is no need to over-complicate the process or invest effort in greater detail.

Background and approach

Operational requirement

An underground coal mine was implementing a longwall expansion project, but the current gas extraction system would not have sufficient capacity. A new gas extraction capability was required, to ultimately supply a new gas handling plant. The reason for extracting gas was to draw to reduce the concentration of methane from the coal seam to safe levels, and to draw fresh air into the mine working area; extracted methane was to be used for generating power.

Three shortlisted gas extraction options were being considered, with design and engineering progressed to concept level. Time pressures required that a preferred option be selected quickly.

The three options were:

  • Surface bore: drill from the surface into an unmined area in the seam and then mine into the borehole to create the connection; all material is removed at the surface with minimal or no disruption underground
  • Raise bore: a small diameter hole is drilled into the workings and the full sized hole is reamed back vertically to the surface; all muck and material falls into the underground area of the mine and then has to be removed to the surface or placed in an underground dump
  • Existing shaft: install a ventilation pipe in an existing shaft.

All three options had significant drawbacks. In particular, there had been only limited success with both surface and raised boring in the area.

Objectives and scope

The objective of the work described here was to help the mine manager decide on the preferred ventilation option within the expansion project precinct. (Keeping it within the project precinct meant that a new project approval would not be required.)

The project timeframe required an early decision, which therefore had to be based on currently available information. A decision analysis workshop was facilitated by Broadleaf to help identify the preferred option and allow the project to progress.


A Kepner Tregoe (KT) decision analysis process was followed, outlined in Figure 1. The situation appraisal and the problem definition steps were largely performed ahead of the workshop. In the workshop the criteria and weightings were agreed and the decision analysis and outcome assessment steps were performed.

Figure 1: Decision analysis process

Situation appraisal


Situation appraisal starts with the overall goals of the project, establishes what is important and determines the criteria that will be used to support the decision (Figure 2).

Figure 2: Situation appraisal

Goals and objectives

The goal of the gas extraction project was to provide the most cost effective solution in the timeframe available. It must enable the mine plan and not expose the company to any significant negative community, health and safety, financial or operational impacts.

The performance objective was to provide the required gas extraction capacity. Operability and maintainability, including the life of the asset and its operating costs, were also performance objectives.

Underground gas extraction would link to the proposed gas drainage plant. The concept schedule indicated that all three options could be completed before the gas drainage plant was completed. The schedule objective was to minimise the chance of significant schedule extension and to avoid impacting production forecasts.

Minimal impact on production during the construction period was an objective, as was minimising the total cost.

The construction objective was to implement the selected option reliably, with minimal adverse impacts on health and safety, the community, the environment, the company’s image and reputation, and its relationship with regulatory authorities and Government.


Prior to the workshop, participants were asked by email for their opinion on the criteria that could be used to differentiate between the three options. A draft set of criteria was developed for review in the workshop.

Three mandatory criteria were agreed. The solution must:

  • Be able to be installed and operated within tolerable safety bounds
  • Have sufficient ventilation capacity
  • Be located within the approved project precinct.

All three options satisfied these ‘must have’ criteria.

There were eight agreed ‘want to have’ criteria that could differentiate between the options.

Construction safety and constructability: This criterion considered the safety and reliability of the technique required to implement each option.

  • Shaft boring options were likely to need complex, new, difficult and potentially dangerous construction involving substantial effort to implement and manage
  • In contrast, using an existing shaft was likely to involve simple, proven, reliable, low risk and low effort construction.

Direct production impacts: This criterion was used to differentiate planned schedule impacts on production. The reduction in net present value from a three-month slowdown (to 50% capacity) on one longwall was estimated, to provide a means of measuring production impact.

Indirect production impacts underground: This criterion considered the impact on underground infrastructure such as conveyors, production support, maintenance, development activities and other production-related activities.

Indirect production impacts on the surface: This criterion considered logistical and management effort to deal with the size and impact of the surface works and possible interfaces with other critical activities.

Capital cost: This criterion was relatively simple. To help evaluate the importance of cost differentials an approximate estimate was developed.

Operability, maintainability and asset life: This criterion considered the cost of monitoring and maintaining the new ventilation asset throughout its life and its impact on mine operating costs.

Licence to operate, image and reputation: This criterion considered the likelihood that an option could – through noise, visual intrusion, environmental concerns or other impacts – damage the image and reputation of the company and potentially disrupt the project. It included the reputation with regulatory authorities, and local and state governments, both during construction and in operation.

Schedule delay: This criterion was used to differentiate options that had different chances of significant schedule overruns and associated impacts on operations and production.


Weights were developed iteratively:

  • Initial weights were estimated before the workshop, as integers between one and ten
  • In the first part of the analysis, a simple paired comparison technique was used to structure the discussion, asking the question ‘Is this criterion more important than that criterion, and by how much?’
  • As the analysis evolved a percentage scale was used to support finer distinctions, but increments below 5 percentage points were strongly resisted
  • The agreed relative weights are shown in Table 1.

The workshop time devoted to developing and refining the weights was reduced by the initial preparation, and holding to the coarser 5% increments for the weights helped to draw discussion to a close.

Table 1: Criteria and weights




Construction safety and constructability


Very important, above average weight

Direct production impacts


The most important criterion

Indirect production impacts underground


Slightly less than average weight

Indirect production impacts on the surface


Minor criterion, low weight

Capital cost


High, above average weight

Operability, maintainability and asset life


This is the legacy of the project and the second most important criterion

Licence to operate, image and reputation


High, above average weight

Schedule delay


Important negative impact, but less than average weight

Note: the schedule delay criterion has a negative weight. The participants found it easier to evaluate a large delay as a high score on this criterion rather than a low score, although larger delays were not desired. Flexibility in this aspect did not hinder the process, and it helped the participants.

Problem definition

In this case the problem was well defined: the need to decide between three ventilation options, based on the available information, to enable the project to proceed.

Briefing material was prepared to inform participants in the decision analysis workshop about the process and the options. As well as an outline of the criteria noted above, substantial material about each option was included:

  • A detailed presentation from senior managers describing the background and the particulars of the option, with diagrams, concept layouts and initial cost and schedule estimates
  • A summary of the main points relating to each criterion, in a form like Figure 3.

Figure 3: Information summary for the raise bore

Decision analysis

The decision analysis workshop was held at the colliery, with senior production and project managers and engineers. The first section of the workshop focused on reviewing, adjusting and agreeing the criteria, the relative weights, the description of the problem and the options being considered. A scoring guide was developed; a sample is shown in Table 2.

Table 2: Scoring guide (sample)

The participants then reviewed each option against each criterion, and agreed raw scores in the range from zero to ten. Raw scores were multiplied by the criterion weights and a total weighted score was calculated for each option. The outcomes of the analysis are shown in Table 3. The rationale for each score was recorded; a sample is provided in Table 4.

Table 3: Weighted analysis outcomes



Surface bore

Raise bore

Existing shaft

Construction safety and constructability





Direct production impacts





Indirect production impacts underground





Indirect production impacts on the surface





Capital cost





Operability, maintainability and asset life





Licence to operate, image and reputation





Schedule delay










Table 4: Rationale for individual scores (sample)

Outcome assessment

No option was without flaws. However, the existing shaft option had severe drawbacks and was clearly the least favoured in the analysis, with particularly low scores on three criteria:

  • Direct production impacts
  • Operability, maintainability and asset life
  • Licence to operate, image and reputation.

The surface bore was slightly favoured over the raise bore option. The two options were scored similarly for most of the criteria. However, the key differences were in terms of:

  • The construction safety and constructability criterion, where the raise bore was penalised due to the potential for slumping during construction, and materials handling and conveyor difficulties associated with removing excavated spoil
  • The indirect impact on production criterion, where demands on constrained underground resources are significant for the raise bore, particularly as the current mine plan, new longwall starts and other activities would require large numbers of personnel underground at the same time as shaft construction was in progress.

The participants agreed that the surface bore was favoured, but not by a significant margin. The surface bore did have drawbacks:

  • A higher capital cost and a later finish date than the raise bore, limiting the opportunity to bring forward other activities
  • Potential contractual difficulties if the current project contractor were selected
  • Capability concerns if a new borehole contractor were selected.

The agreed recommendations from the decision analysis were:

  • Prioritise and proceed with the surface bore option
  • Progress the raise bore option in parallel, so long as this does not impose significant additional costs or delays
  • Stop work on the existing shaft option.


Kepner Tregoe analysis

Kepner Tregoe (KT) analysis is a simple, structured approach to support simple decisions, using a form of multi-criteria decision analysis. The detailed evidence and descriptions of the rationale involved in each step of the process serves to justify the decisions that are made.

If straightforward approaches are sufficient, then there is no need to over-complicate the process.

Supporting decisions

The project required a decision quickly. KT analysis allowed a fast, high-level review of the options, focussed specifically on their ability to achieve the project goals.

The outcomes indicated clearly that using an existing shaft was not preferred, and by a substantial margin. However, it was not sufficient for clear differentiation between the other two options; the surface bore was preferred to the raised bore, but not by much. It was decided that work would proceed on both options as resources permitted, although with a focus on the surface bore.

While the outcomes from KT analysis generate a preference order for the options, this should not over-ride sound managerial judgement and common sense.


The structured process with definition and relative weighting of objectives provided some much needed clarity for the project team. Before this the individual options had champions who could make reasoned arguments about why their preferred option was superior, but not sufficient to persuade others with differing priorities. Understanding the mandatory criteria was straightforward, but defining and weighting the desirable criteria was key to obtaining agreement.

Agreeing the weights in the workshop did take some time, but it was worthwhile. As the initial weightings were refined it forced the participants to set aside their personal preferences and reach agreement on the relative priorities of the objectives from the perspective of the company. Once the relative priorities were agreed, the pathway to reaching a decision was relatively straightforward.

The ratings were based on what was known at the concept design stage, and they may change as more information is developed. On the other hand, the objectives and the weightings should remain fairly constant. The same weighted criterion approach can be used as the project progresses to decide between the surface bore and raise bore options. Importantly, the project’s priorities were now clear to all involved.

Coal mining company
Mining and minerals processing
Services included:
Technical risk analysis and hazard studies