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INTRODUCTION
1.1 General
In this section the literature relegating to the understanding and definition of various types of risk, risk assessment methodologies and measures undertaken to assess them and certain examples has been collected and studied.
It involves: Risk Nomenclature, Basic Definition of risk, exposure level, quantitative and qualitative risk assessment, hazard etc.
Environmental Risk Assessment: Involves study of environmental factors and hazards due to mining, such as Acid mine drainage, Mine fires, Slope Instability etc. Risk Management: Incorporates study of risk evaluation, emission and exposure control, and risk monitoring.
The literature has been collected from various mining publications and journals and has been referenced at the end of the report.
(i)As per Oxford dictionary: Risk is ―the chance of or probable danger, and loss, injury or other adverse consequences to human life‖.
(ii) Risk is defined as ―the probability of injury, disease, or death under specific circumstances.
(iii) The chances of something happening that will have an impact on objectives. It is measured in consequence and likelihood.
Therefore
Risk = Consequence * Probability * Exposure
Where,
Consequence = degree of harm that could be caused to people exposed to the hazard
Exposure = How often and how long people are exposed to the hazard
Probability = Chance that a person will be harmed when they are exposed to the risk
Environmental Risk
Environmental risk is the risk associated with the likelihood or probability that a given chemical exposure or series of exposures may damage human health. Environmental risk takes two factors into account: the amount of a chemical present and its relation to the amount the exposed person can tolerate.
1.1.1 Environmental Risk Assessment
Environmental risk assessment (ERA) involves the examination of risks resulting from natural events (flooding, extreme weather events, etc.), technology, practices, processes, products, agents (chemical, biological, radiological, etc.) and industrial activities that may pose threats to ecosystems, animals and people. Environmental health risk assessment addresses human health concerns and ecological risk assessment addresses environmental media and organisms. ERA is predominantly a scientific activity and involves a critical review of available data for the purpose of identifying and possibly quantifying the risks associated with a potential threat.
1.1.2 Acceptable risk
This is a risk management term. The acceptability of the risk depends on scientific data, social, economic, and political factors, and the perceived benefits arising from exposure to an agent.
1.1.3 Adverse effect
Change in the morphology, physiology, growth, development, reproduction, or life span of an organism, system, or (sub) population that results in an impairment of functional capacity, an impairment of the capacity to compensate for additional stress, or an increase in susceptibility to other influences.
1.1.4 Analysis
Detailed examination of anything complex, made in order to understand its nature or to determine its essential features.
1.1.5 Assessment
Evaluation or appraisal of an analysis of facts and the inference of possible consequencesconcerning a particular object or process.
1.1.6 Assessment end-point
Quantitative/qualitative expression of a specific factor with which a risk may be associated as determined through an appropriate risk assessment.
1.1.7 Assessment factor
Numerical adjustment used to extrapolate from experimentally determined (dose–response) relationships to estimate the agent exposure below which an adverse effect is not likely to occur.
1.1.8 Effect assessment
Combination of analysis and inference of possible consequences of the exposure to a particular agent based on knowledge of the dose–effect relationship associated with that agent in a specific target organism, system, or (sub)population.
1.1.9 Exposure Concentration or amount of a particular agent that reaches a target organism, system, or (sub) population in a specific frequency for a defined duration.
1.1.10 Exposure assessment
Evaluation of the exposure of an organism, system, or (sub) population to an agent (and its derivatives). Exposure assessment is the third step in the process of risk assessment.
1.1.11 Exposure scenario
A set of conditions or assumptions about sources, exposure pathways, amounts or concentrations of agent(s)involved, and exposed organism, system, or (sub)population (i.e., numbers, characteristics, habits) used to aid in the evaluation and quantification of exposure(s) in a given situation.
Inherent property of an agent or situation having the potential to cause adverse effects when an organism, system, or (sub)population is exposed to that agent.
1.2 Hazard assessment
A process designed to determine the possible adverse effects of an agent or situation to which an organism, system, or (sub)population could be exposed. The process includes hazard identification and hazard characterization. The process focuses on the hazard, in contrast to risk assessment, where exposure assessment is a distinct additional step.
1.2.1 Hazard characterization
The qualitative and, wherever possible, quantitative description of the inherent property of an agent or situation having the potential to cause adverse effects.
This should, where possible, include a dose–response assessment and its attendant uncertainties. Hazard characterization is the second stage in the process of hazard assessment and the second of four steps in risk assessment.
1.2.2Hazard identification
The identification of the type and nature of adverse effects that an agent has an inherent capacity to cause in an organism, system, or (sub) population. Hazard identification is the first stage in hazard assessment and the first of four steps in risk assessment.
1.2.3 Margin of exposure
Ratio of the no-observed-adverse-effect level (NOAEL) for the critical effect to the theoretical, predicted, or estimated exposure dose or concentration.
1.2.4 Margin of safety
For some experts, margin of safety has the same meaning as margin of exposure, while for others; margin of safety means the margin between the reference dose and the actual exposure.
1.2.5 Measurement end-point
Measurable (ecological) characteristic that is related to the valued characteristic chosen as an assessment point.
1.2.6 Risk analysis
A process for controlling situations where an organism, system or population could be exposed to a hazard. The risk analysis process consists of three components: risk assessment, risk management, and risk communication.
1.2.7 Risk assessment
A process intended to calculate or estimate the risk to a given target organism, system, or (sub)population, including the identification of attendant uncertainties, following exposure to a particular agent, taking into account the inherent characteristics of the agent of concern as well as the characteristics of the specific target system. The risk assessment process includes four steps: hazard identification, hazard Characterization, exposure assessment, and risk characterization. It is the first component in a risk analysis process.
1.2.8 Risk characterization
The qualitative and, wherever possible, quantitative determination, including attendant uncertainties, of the probability of occurrence of known and potential adverse effects of an agent in a given organism, system, or (sub) population, under defined exposure conditions. Risk characterization is the fourth step in the risk assessment process.
1.2.9Risk communication
Interactive exchange of information about (health or environmental) risks among risk assessors, managers, news media, interested groups, and the general public.
1.2.10 Risk estimation
Quantification of the probability, including attendant uncertainties, that specific adverse effect will occur in an organism, system, or (sub) population due to actual or predicted exposure.
1.3.1 Risk evaluation
Establishment of a qualitative or quantitative relationship between risks and benefits of exposure to an agent, involving the complex process of determining the significance of the identified hazards and estimated risks to the system concerned or affected by the exposure, as well as the significance of the benefits brought about by the agent. Risk evaluation is an element of risk management. Risk evaluation is synonymous with risk–benefit evaluation.
1.3.2 Risk management
Decision-making process involving considerations of political, social, economic, and technical factors with relevant risk assessment information relating to a hazard so as to develop, analyse, and compare regulatory and non-regulatory options and to select and implement appropriate regulatory response to that hazard. Risk management comprises three elements: risk evaluation; emission and exposure control; and risk monitoring.
1.3.3 Risk monitoring
Process of following up the decisions and actions within risk management in order to ascertain that risk containment or reduction with respect to a particular hazard is assured. Risk monitoring is an element of risk management.
1.3.4 Safety
Practical certainty that adverse effects will not result from exposure to an agent under defined circumstances. It is the reciprocal of risk.
1.3.5 Safety factor
Composite (reductive) factor by which an observed or estimated no-observed adverse-effect level (NOAEL) is divided to arrive at a criterion or standard that is considered safe or without appreciable risk.
1.3.6 Uncertainty
Imperfect knowledge concerning the present or future state of an organism, system, or (sub) population under consideration.
1.3.7 Uncertainty factor
Reductive factor by which an observed or estimated no-observed-adverse effect level (NOAEL) is divided to arrive at a criterion or standard that is considered safe or without appreciable risk.
1.4 Quantitative Risk Analysis
The assessment of risk can be qualitative or quantitative. The latter requires significant specialist effort, and therefore, the qualitative assessment is often used as being the simpler of the two. However, the Quantitative Risk Analysis (QRA) provides significant benefits as it not only helps to identify and rank the risk contributors, but also assists in setting priorities for directing the risk reduction efforts to achieve optimal outcome.
The QRA integrates all the individual technical studies of the Safety Assessment and evaluates the risk from operations to personnel. The risk levels calculated are then evaluated against performance standards to ensure ALARP levels are reached.
The main limitation of QRA is the lack of adequate frequency data for initiating event for the MAE (e.g. fire or drilling into misfired hole), and dependency on human error failure probability, which is not available for the mining industry.
1.4.1 Risk Evaluation
There are no formally established regulatory criteria for risk to personnel in the mining industry. Individual organisations have developed criteria for employee risk, the concepts originally arising from the chemical process industries and oil and gas industries.
Because of the uncertainties associated with probabilistic risk analysis, used for quantification of risk levels, the general guiding principle is that the risk be reduced to a level considered As Low.
As Reasonably Practicable (ALARP). It is not easy to define what ALARP is, where we stop the risk reduction process.
Figure illustrates the risk criteria. It has three tiers:
a. A ―Tolerable‖ region where the risk has been shown to be negligible, and comparable with everyday risks such as travel to work.
b. A middle tier, where it is shown the risk has been reduced to As Low As Reasonably Practicable level and that further risk reduction is either impracticable or the cost is grossly disproportionate to the improvement gained. This is referred as the ―ALARP‖ region.
c. An ―Intolerable‖ region where the risk cannot be justified on any grounds. The ―ALARP region is kept sufficiently broad to allow for flexibility in decision making and allow for positive management initiatives, which may not be quantifiable in terms of risk reduction. Some organisations in the process industries and oil and gas industries have set numerical criteria for risk as demarcation between the tiers. It is not appropriate to apply the criteria from one industry to another, as the nature of the operations and types of risks are entirely different. For a well managed mine site, the risk values for underground mining are expected to fall within the ALARP range. Therefore a demonstration of adequacy of control measures as part of overall ALARP demonstration is crucial.
1.5 Qualitative Risk Assessment
Qualitative Risk Analysis consists of performing a qualitative analysis of the risks identified during risk identification to prioritize their effects on project objectives. The risks are analyzed in terms of existing controls, likelihood of occurrence, severity of impact, precision with which the risk is understood, intervention difficulty, and risk level.
Qualitative techniques are applicable when it is not feasible to quantify risk. Common qualitative techniques include the risk assessment matrix, hazardous event severity matrix, and the risk graph. These techniques vary in terms of the type and detail of available information. The risk assessment matrix is the simplest. Risk is determined by using severity and frequency. The hazardous event severity matrix is similar to the risk matrix, but it also takes independent layers of protection into account. The risk graph uses severity and frequency, but it takes two additional parameters into account. The risk matrix is quite similar to the hazardous event severity matrix. This qualitative method enables the determination of a risk index. The safety integrity level (SIL) can be determined by using the risk index. For each hazard, this basic process is used:
• Determine severity category
• Determine frequency category
• Determine the risk level
• Relate the risk to the SIL
1.6 Study Area
1.6.1 About Neyveli Lignite Mines
Neyveli Lignite Mines play a major role in generating the energy needs of the states of South India. Lignite mining at Neyveli commenced about half a century ago by Neyveli Lignite Corporation Ltd (NLC), a Government of India Enterprise. Continuous mining technology using Bucket Wheel Excavators (BWE), Belt conveyors and Spreaders was adopted. The transfer and adoption of Bucket Wheel Excavator technology at Neyveli was a landmark event, and it has helped the company to reap profits during its life. The successful deployment of BWEs was made possible by adopting suitable modifications in the design of the buckets, teeth and structural parts to tackle the hard and abrasive nature of overburden strata. The lignite mining is also faced with adverse hydrological conditions caused by confined aquifer occurring below lignite seam, with an upward thrust of 5 to 8 Kg/cm2.
The challenges posed by nature on lignite mining were aptly handled in the Neyveli mines by continuous improvement in coherence with the technological development and up-scaling capacity of BWEs and by continuously optimizing the Ground water pumping pattern. Initially smaller capacity 350 litre BWEs with 1000 mm fabric belt conveyors deployed were upgraded to 1400 litre Bridge type BWEs and 2400 mm steel cord belt conveyors, to augment the lignite production from 3.5 MT/Annum to 24 MT/Annum. The paper traces the history of the developments introduced in lignite mining at Neyveli mines during the past five decades.
1.6.2. Lignite Resources of India
Unlike coal, lignite is a low calorific fossil fuel for producing electricity. About
38.93 billion Tones (BT) of lignite reserves of various categories have been identified in India, (Table. 1) mostly in the states of Tamil Nadu, Puducherry, Rajasthan, Gujarat, Jammu & Kashmir and Kerala. Tamil Nadu and Puducherry possess 31.74 BT of lignite.