Risk assessment and management in mining

Category Mine
Group GSI.IR
Location 20th WORLD MINING CONGRESS 2005
Author Mohammad Shahriari*
Holding Date 04 January 2006
Safety issues are usually of primary importance in the mining activities as accidents can have extremely severe consequences for the human. To provide a safe and efficient operation of a mine, some demands should be fulfilled. These are: 1. Hazards and incident scenarios should be identified and eliminated, 2. Protective tools should be designed to minimise the effect of the accident, 3. Operators and personnel should be trained, and 4. A more effective rescue organisation should be provided. This study is focused on the first demands. In this paper a safety model is presented to assess the risks in mines and minimise them to an acceptable level by applying an analytical procedure. The model has a tool box to carryout the necessary analysis in different steps of the study. In the frame of the risk assessment model a “Risk Ranking Index” has been proposed to assess the level of risk semi-quantitatively. In order to apply the model of risk assessment and the risk ranking matrix, a case is presented and analysed. It was found that analytical method accompanied by risk ranking matrix could be capable to identify the incident scenarios and level of risk in relation with each scenario. Further research found that the reduction of the risk level could be achieved by providing appropriate safeguards. As far as the case is concerned, safeguards include the increase of the knowledge of human resources, providing an appropriate control procedure e.g., checklist and regular inspection and maintenance.
Key words: Mining, Safety, risk assessment, risk management, accident prevention, risk ranking matrices

Every year, many people lose their life in mining accidents. Among these, coal mine accidents are responsible for most of the casualties. Statistics given by BLS (Bureau of Labour Statistics, U.S. Department of Labour) show that in the United States the fatality rate in coal mine accidents are higher than the other mine activities and even private industries (Figure 1).
Considering work location, the rate of fatality in underground mines of America are more than twice comparing with surface mines.(Figure 2).
The work that coal miners try to accomplish in their everyday work is extremely dangerous. The history of coal mining accidents in the United state has tallied over 13,793 deaths from 1839-2001. (1)
In 2004 a total of 6,027 people were killed in China's coal mines. (2). China produced 35 percent of the world's coal in 2004, but reported 80 percent of the total deaths in coal mine accidents, (3).  The accidents that can befall a coal miner include: explosion, cave-in, fire, cage-fall (shaft), smoke, suffocation, in-rush of water, dam failure, and many other dangers pose fatal consequences. Mine accidents may occur due to:
1.        Pressure on mining operator for increasing the production without considering the capabilities and appropriate facilities.
2.        Poor control due to poor management and system complexity. Mines are considered as complex systems. Complexity is a cause for losing the control on system operation ending to some kind of losses. The more complex a system, the more difficult it is likely to be to control and to prevent errors by those who operate and maintain it.(4). Mine closure plans include complex natural and engineering systems involving geology, geotechnics, tectonics, hydrogeology, hydrology, ecology, mineralogy, and social systems. Failure modes and risks exist for each of these systems and as a result of interaction between these systems. (5).
3.        Poor knowledge about the sources of risk.
Risk is the probability that a hazard as an energy with the potential of producing an accident could be released and cause damage to human, environment and properties. It can be expressed as Risk = f (P,C); where P is the probability that an event occurs and C is the consequences of that event. Safety could be achieved by minimising the risk in the system. It might be expressed as: Safety = f (1/Risk)
On the basis of deviation theory (Kjellén, 1984), and the definition of risk a simple model was developed called “the process of damage”. The model describes system behaviour and represents the relationship between different actions and critical situations which will lead to some kind of damage (Figure 3). In the process of damage two main types of risk might be characterized as: primary risk (risk for occurring accident) and secondary risk (risk in relation with losses during the dissipation or release of energy in accident chain events). Furthermore, another risk system connected with human casualty as a result of the function of the rescue groups in the phase of post-crash can be added to the previous risk systems /tertiary risks).  Concerning the risk systems, safety might be described in three different concepts: 1. Active safety (prevention of accident), 2. Passive safety (Protection of miners when an accident occurs) and 3. Post-accident safety (providing an effective rescue operation). The total safety in the whole system is the product of safety in the different phases of the process.
Figure 1
In order to increase the safety in mining, the risks should be eliminated or reduced in all phases of “the process of damage”. To achieve this goal, the following demands should be fulfilled (see Figure 3):
·          Demands for finding and eliminating the sources of risk and possible accident scenarios during the mine design and operation,
·          Demands on designing protective tools to minimise the effect of the accident,
·          Demands for a more effective emergency actions and,

demands on training of the operators and personnel
In this paper, the study is focused on the first demands. The main purpose of the study is to develop methods capable of identifying measures to increase safety in mining to prevent the accidents with serious consequences.
Figure 2
In order to fulfil the demands, for identifying and eliminating the sources of risk in mining, a general model is presented. (Figure 4).Risk assessment is an effective means of identifying the sources of risk in any system and determining the most cost-effective means to reduce risk. It is an elaborate exercise involving several steps, starting from hazard identification through development of accident scenarios to preparation of strategy for risk reduction and control of damage. (6). The first step in risk assessment is system description. In the second step, hazard identification should be performed. In order to identify the sources of risk and incident scenarios/top events in mining operation the best technique could be the historical incident survey, interview with the experts, what-if analysis and FMEA (Failure Mode Event Analysis). What-if analysis as a brain storming method could provide answers in terms of consequences, safeguards and recommendation topics to the generic question “what-if”.(6).

Figure 3: The process of damage
FMEA evaluates the ways components or equipments can fail and the effects these failures can have on the system. These failure descriptions provide analysts with a basis for determining where changes can be made to improve a system design. (7)

Based on the hazard identification, list of hazardous events/ incident scenarios will be identified and subsequently the risk estimation is being carried out.
Figure 4: General model of risk assessment
Risk assessment can be applied to a complex system such as mining or can be used for a single piece of equipment. Risk in mining can be assessed at different levels depending on the depth of information and the user requirements. Sometimes the only hazard identification maybe sufficient for making the decision. It may be called as “qualitative risk assessment”. In case incident scenarios to be ranked and judged by means of a risk matrix to reach a risk reduction decision, the process may call as “Semi-Quantitative Risk Assessment”. (8). Quantitative Risk Assessment (QRA) involves with calculation of risk estimate when incident scenarios probability/frequency and the magnitude of consequences are available. In fact, mining accidents are rare events and estimation of accident frequencies is rather difficult. Therefore, for mining operation the first approach is recommended that is a qualitative or semi quantitative risk assessment. Semi quantitative risk assessment could be performed by means of a risk ranking matrix presented as a relation between “severity categories” for both frequency and consequences and assessing the risk category of each particular hazard in terms of these factors. (6). This method can provide a relatively rapid understanding of the risk profile of the mine.
Risk assessment matrices have been used for many years in industry and by the US military to rank different risks in order of importance. This allows priorities to be set for the implementation of control measures. The two variables, probability and consequences may be classified by qualitative terms or quantitative values. (9).
Figure 5: Risk ranking matrix
Although many companies have developed and published their own forms of semi quantitative risk assessment which present their own challenges, but the most common approach is a risk ranking matrix which assesses individual incidents. One limitation with applying risk matrices is that at mines where a large number of mining hazard exist, risk matrix cannot be used easily to assess cumulative hazards. More detailed methods are likely to be required to assess such issues as required by safety regulations. (10).
Construction of a risk matrix starts by first establishing how the matrix is intended to be used. Some typical uses for risk ranking are process and mining hazard analyses, facility sitting studies, and safety audits. A key initial decision that has to be made is to define the risk acceptability or tolerability criteria for the organization using the matrix. Without adequate consideration of risk tolerability, a risk matrix can be developed that implies a level of risk tolerability much higher than the organization actually desires. Another key aspect of risk matrix design is having the capability to evaluate the effectiveness of risk mitigation measures. The risk matrix should always allow the risk ranking for a scenario to move to a risk tolerable level after implementation of mitigating measures. Otherwise it may be difficult to determine the effectiveness of mitigation measures. (8).
The likelihood and consequences or severity could be defined differently depending on which definition of the incident used. Hence the mine operator should decide how incidents will be defined, and use the same approach for all incidents.
Is expected to occur in mine life
Has occurred in our company
Has occurred in other companies or the industry sector of  the country
Has occurred in mining or industry worldwide
Not known to have occurred
Table1: Ranges of Probability
On the basis of a literature survey (5,8,10,11) a risk ranking matrix could be proposed for mining activities as Figure 5. The likelihood and severity ranges of the matrix are defined in Tables 1 and 2. The likelihood coordinate is divided into five categories ranging from “Expected” to “Practically impassable.” The consequence coordinate includes scales of consequence for harm to people, production loss, environmental damage, and equipment losses. These scales are divided into five categories from “Negligible” to “Catastrophic.” Given the likelihood and severity, a risk rating can be determined and displayed on the matrix. The resulting significance rating has got three risk categories: High, Medium and Low representing risk indexes 1-25 as described in Table 3.
Table 2: Ranges of Consequence

Risk Index

Actions required

Risk Level


Requires priority actions

High (H)


Must be reduced based on ALARP* (As Low As Reasonably Possible)

Medium (M)


No action required

Low (L)

  *: ( 12  )

Table 3: definition of risk ratings and levels
In order to apply the model of risk assessment and the risk ranking matrix, proposed in this paper, a case is presented and analysed. This case which is concerned with Risk assessment on Hydrabolt Pre-Stressed Rock Anchor has been selected from the literature (13).
The main purpose of the study is to identify the hazards and assessing the risks related to handling and installing the Hydrabolt Pre-Stressed Rock Anchor in underground mines. Furthermore, to see how risk levels could be changed by using the recommended safeguards. The goal is to minimise the risks concerning human safety during the handling and operation.
The result is presented in a risk ranking matrix showing prioritised actions where applicable. In order to reach the goal, risk assessment will be carried out based on the logical steps of the general risk assessment model (figure 4). These are: 1. System function 2. Hazard and incident scenario identification 3. Estimation of probability and severity in the ranges given in tables 2 and 3. 4. Indication of the level of the risks. 5. Identification of the safeguards to minimize the risk. The results will be given in a matrix consisting risk rates before and after the safeguard implementation.
System Function: System function consists of different activities as : 1. delivering and reception. 2. Storage on surface. 3. Handling to underground and into the slopes. 4. Site-preparation for installation of Hydrabolts. 5. Unit installation. 6. Pre-stressed to required load.
Hazard Identification: In order to identify the hazards and incident scenarios both What-If or FMEA could be applied properly. However, in this study What-If study is used. The analysis resulted in identification of hazards, top events, and possible incident scenarios.
The most important hazards identified in this study are:
·          Human- Hydrabolt interaction
·          Hanging and side-wall rocks
·          Geological and tectonic characteristics of the site and the area
·          Hydrabolts for being sub-standard, complicate to work with, non-flexibility, etc
·          Instructions and work procedures
·          Work conditions
The most important top event in this study is Rock fall. The major incident scenarios found in this study are listed as follows:
Rock fall during installation followed by injury and fatality. This may occur due to:
·          Hanging rock conditions and lack of appropriate temporary support
·          Holes drilled are too short
·          Holes drilled at the angle lower than 70 degrees
·          Incorrect length Hydrabolt used for conditions
·          Using Hydrabolts for a long time without sufficient control and regular maintenance
·          Using sub-standard, damaged, or defective Hydrabolts
·          Hydrabolt is not pre-loaded to the correct pressure while load indicator is not visible
Determination of the level of risk: Risk associated with each scenario could be achieved by considering event/incident probability and the consequences based on tables 1 and 2 validated by the relevant experts. The results related to pre-controlled situation is shown in Table 4. The new estimation of risk level with the application of the recommended safeguards is also shown in Table 4.
Table 4
According to the study the highest level of risk in Hydrabolt handling and installation could be caused by scenarios 3-6. However, the risks could be minimised to at least moderate level by supplying standard bolts, training, improvement of the control procedures and regular maintenance. On the basis of this study a logic instruction might be suggested as follows to improve the safety in this field of activity:
·          Describe the rock and geological/tectonic character of the working area and the site as well.
·          Describe/define the working conditions.
·          Identify the most important criteria needed for the conditions for supplying appropriate Bolts.
·          Prepare an instruction and check-list for handling and installation of the Bolts.
·          Test the validity of the instruction by using hazard identification techniques.
·          Design a control procedure and an effective regular maintenance.
·          Make an effective planning for the training
One of the most important factors in mining sustainability is safety. In fact safety is the number one priority in mining operations. In this paper the nature of hazards within the mining activities and possible elimination or minimisation of risks has been highlighted. Semi quantitative risk assessment in terms of risk ranking matrix has been used to identify the level of the risks in mining activities. A case concerning Hydrabolt handling and installation has been selected from the literature and studied to evaluate the validity of the proposed assessment method. It was found that analytical method accompanied by risk ranking matrix could be capable to identify the incident scenarios and level of risk in relation with each scenario. Further research found that the reduction of the risk level could be achieved by providing appropriate safeguards. Those include the increase of the knowledge of human resources, providing an appropriate control procedure e.g., checklist and regular inspection and maintenance.
I would like to express my gratitude to Neyriz White Marble Quarries Co. especially Mr. Farashbashi director manager of the company for supporting this study.

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