Welcome back to the surface mining model. In the previous topic, we learned about different types of surface mining operations, about equipment, about different methods that are commonly used to extract coal or different ore deposits. It’s not difficult to understand that mining is one of the most dangerous working environments in the world and in this topic, we will go through some of the main safety issues that we are facing when we work in this environment.
The International Labour organisations is a United Nations agency that sets guidelines of minimum safety requirements for working in a mining environment. The objectives of the safety measures are: the protection of workers from safety and health hazards and the minimisations of risks in their working area, the prevention and reduction of incidents and severity of illness or injury, the training and implementation of safe operating procedures to improve safety and health. The ultimate goal is always to eliminate the risk. As this is not always possible, the safety measures should assist controlling right at its source and minimizing the risk.
Personal protective equipment should always be used in conjunction with other measure to increase the safety of the workers but should never be the only protective measure in place. As we said before, mining is one of the most dangerous working environments and a multitude of different hazards can emerge. This can be classified as surface hazards like rock falls at the bottom of the bench, bench failures at the top of the high walls, or shift firing during blasting. Hazards by mining equipment, like the movement of large mining equipment, such as draglines, or heavy mobile equipment like haul trucks and excavator, light vehicles such as four wheel drives, or stationery machinery with rotating equipment, such as crashers and conveyors.
Incidents with moving mining equipment are often triggered by a lack of adequate visibility, insufficient job site communication, and operator’s fatigue. Therefore, clear rules for traffic management and job site communication are required. Hazards created by works conditions, like working at heights, working in confined spaces, lifting and mechanical handling. Hazards created by the work environment include airborne contaminants, fumes, noise and toxic substances.
There are several causes of injuries in a mining environment. This is why the mine operator has to ensure that all of the working personnel is going under strict safety induction and sit-specific training. The minimum requirements are as follows: the introduction to health and safety aspects of the task to be assigned, hazard recognition and avoidance, hazards relating to explosives, ground control and working areas of high walls, hazards of machinery and equipment, basic knowledge of first aid procedures in case of an emergency. In addition, there are strict controls to ensure that workers are not entering the mine site under the influence of drugs or alcohol. personal protective equipment is designed to protect workers from working hazards that could cause injuries or illness. Basic personal protective equipment consists of safety helmets where falling objects might create a hazard; protective gloves, when handling material or performing work which might cause injuries to hands; protective footwear, where there is no danger of slipping, or of injuries to the feet; eye protections, like safety glasses, goggles, face shields; hearing protection like ear plugs or muffs; respiratory protections, like dust mask and respirators, and highly visible closing to enhance the visibility of personnel.
In this topic, we saw some of the main safety issues that we can face in a surface mining environment. In the next topic, we will go through which are the main protective measures against some of the most important geotechnical hazards in surface mining.
From what we learned so far, we can say that mining is a very high risk business, from both the safety and economic point of view. Slope stability is one of the major sources of risk, and hazards arise in several ways, from an incomplete knowledge of geological conditions, and an incomplete knowledge of damage caused by mining processes, or an inadequate execution of work procedures. The main task is the definition and the assessment of the acceptable risk in terms of safety and economics.
There are two main classes of geotechnical hazards: unplanned rock slope movements and rock falls. Consequences of these geotechnical hazards include: potential fatalities. And the likelihood of these consequences should be carefully assessed. Rock falls pose a significant risk in both underground and open pit mines. They could be responsible for a substantial number of fatalities, and serious injuries, infrastructure damage, and financial loss, meaning the production should be stopped for safety issues.
Rock fall safety hazards need to be seriously managed in surface mining in order to reduce the risk for personnel and equipment. Rock fall means the rock fragment, or a block, that detaches from a vertical or sub vertical cliff and falls along it. Rock fall range from cobbles to big boulders of several hundreds of cubic metres and they travel with speeds that are ranging from a few to tens of metres per seconds. Rock fall protection systems can be classified in two main categories: active systems and passive systems. Next, we will define passive and active protection systems.
Active protection systems are designed to prevent instability from occurring. They are usually installed directly on the surface itself and they prevent the detachment of the block from the rock surface. Active protection systems include anchors, rock bolts, grouted bars, rock scaling, berms and excavations, blasting machines modification of the slope, rock mass hydraulics conditions or operations that aim to protect from superficial alterations. Where these artificial measures cannot be installed directly on the rock surface, other protective measures can be taken into account in order to control the motion of the blocks, and to intercept their movement along the fall. In this case, we refer to the passive protective measure against rock fall.
Passive protective measures include catch ditches, mesh drapery systems, flexible rock fall barriers, like catch fences and reinforced and also not reinforced embankments. The first three methods are commonly used in surface mining operations. Catch ditches are one of the most cost effective rock fall protection measures used in open pit. The ditch, placed along ramps and at the top of the high walls, should be covered by a layer of gravel in order to absorb the energy of falling rocks and it should have an adequate dimension determined by field tests and American modelling. Ditches are usually in place at the bottom of the high walls, together with berms constructed with waste material placed at a designed distance from the top. Draperies directly act on the stability of the blocks, but also control their fall should failure occur. Such systems are common practice within Australia open pit mines. In surface mining, draperies are used to prevent rock from impacting directly onto the concrete covers used as portal structures for underground access.
Depending on the application, two categories of mesh facing could be designed. The first is the simple mesh facing where the draper is anchored at least at the top of the slope. The second type is the cortical strengthening where the mesh is associated with a pattern of nails on the rock surface. In these images, we can see the final installation of a drapery system on top of a wall surface. The mesh has been anchored at the top of the wall and then unrolled along the slope. Catch fences are becoming more and more popular in the surface mining acclivities. This is due to their relatively low cost and their easy and fast installation. Net fences should be able to intercept the motion of blocks along the slope and to stop it without breaking. In surface mining, these types of fences can be used to provide protection for slope with no berms at the bottom of the wall or protection for highway road and ramps. With this topic, we conclude the third module of this mining engineering course.
In the next module, we will bring you through the world of the underground mining and we will be able to see the main differences with what we have learned in this module.