- Choose a situation with which you are familiar, preferably work-related. Following the guidance given in the notes, establish a comprehensive risk register for that situation including both energy and non-energy Threats. Explain your overall thinking. A table is a good way to list entries. Provide a brief description or explanation of the entries.
- In the notes some examples are given of possible qualities of individual risk register entries. Consider these, or others you may feel more relevant to the entries you have and add at least two of them to your risk register and show how they are relevant to each of the entries.
- Read the case study appended. In the context of Module 3 notes, consider how you would go about justifying the expenditure of $600,000 on the provision of intrinsically safe electrical equipment in the mine.
Part B Relative significance of Risks
- Decide on a set of parameters you will use to enable you to distinguish the relative significance of the entries in your risk register. Justify your selection. Establish a Nominal and a related Ordinal scale suited to each of these parameters. A good Nominal scale is one that is not ambiguous – each item in the scale is clearly different from the others. Use these on each entry in your risk register. Decide on a suitable algorithm to enable a single Ordinal number to be determined for each register entry and list the Risks in ranked number order.
- Select the most significant risk derived as above and develop a set of risk factors for it. Justify your choice of factors. For each of the factors, develop both a Nominal and an associated Ordinal scale.
Part C Risk Analysis
The purpose of this task is to give you some introductory experience in identifying Mechanisms and Outcomes and drawing risk analysis diagrams as a model of the risk in question. The forms these logic diagrams take is important as they are used and understood in this way around the world, so don’t invent your own.
Note that Mechanisms are neither “causes” not failed control measures. They are physical possibilities. Outcomes are also physical possibilities.
- Define the appropriate Event and draw, with a brief written explanation, a Mechanism analysis logic diagram for the coal mine case study below.
- If you were to draw an Outcome Analysis (aka Event Analysis) for this case, what would the questions be on which the analysis diagram was based?
- Draw an Outcome Analysis diagram for the case based on those questions.
Case Study: Gas explosion in a coal mine
This case study has been created from the investigation reports of explosions in two mines. The explosion frequency figures are from one of these reports and the number of people killed from another. The circumstances referred to existed at the end of the 1990s in a first world economy.
Mining is often carried out in an area known for the presence of various organic gases, including methane, ethane, propane and butane, as well as hydrogen, helium and nitrogen.
A routine practice is to “cover drill” ahead of the development face. The development face is the name given to the face of the rock at the end or side of an existing tunnel that is about to be removed by drilling and blasting either to remove ore or to extend the tunnel being used to reach the ore body. The purpose of cover drilling is to explore the rock in the direction of development as well as to discover any sources of gas. Typically, cover drilling uses a coring diamond drill. That is, the rock from the hole is drilled out as a cylinder (core) with the core barrel. When the drill rods are retracted the core is removed and the drill rods are re-inserted to continue the process.
If drilling penetrates a gas pocket, the gas is released through the drill hole into the mine. There are no methods immediately available to the cover drilling crew to plug a gas emission if it occurs. The gas will escape into the tunnels and eventually be diluted and extracted by the ventilation system. Due to the complexity of the tunnel layouts, ventilation routes and controls etc., it is difficult to accurately predict where gas concentrations in the explosive range might occur.
Because of the known presence of gases in the mine workings (these gases after seeping through cracks in the rock), gas detection instruments are supplied to supervisors of work teams. However, the use of these is not reinforced and it is common for workgroups not to carry gas detectors with them wherever they go.
A common practice is to test for pockets of gas at high points in the workings, using probes attached to the gas detectors. However, the gas contained in the probe pipe needs to be periodically flushed, using an aspirator bulb. This detail is commonly overlooked so that these probes typically are not measuring the gas currently in these high points. As some of the gases are heavier than air, it is also possible for gases to accumulate from the floor upwards. It is not practised to test for concentrations in low points.
There are numerous electrically powered items of equipment in the mine, including ventilation fans and lights. None of these is of explosion–proof design standard. Smoking is not permitted because of the presence of flammable gas; however, this rule is not effective in preventing minors from smoking.
If an explosion occurs, shock and heat waves travel through the tunnels and maybe at injurious intensities even at some distance from the ignition source, where crews could be working in otherwise uncontaminated air, i.e. not warned by their detectors.
In this case, during cover drilling, a significant pocket of gas under pressure was intersected, with gas leaving the cover drill hole at such a speed that it could be felt up to 3m away. Approximately 20 minutes later a large explosion occurred, killing 19 people and creating widespread damage up to 500m from the centre of the explosion.
Numerous previous explosions have occurred in the mine. In the most recent 6-year period there have been 12 cases in which a total of 23 people have died.
Cover drilling is done for one week every two months in each of the four development sites in the mine. Gas is discovered during this drilling in half of all cases.
None of the electrical equipment in the mine is intrinsically safe. After the most recent fatality, the recommendation was made to replace all electrical equipment in areas that do not have through ventilation with intrinsically safe equipment. This is estimated to cost $600,000.
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