Four basic surface firing patterns

The firing pattern is a tool to break and fragment a mass of rock in the most effective way for further handling andtreatment in the mining or quarrying process. Although there are a lot of different patterns used in the industry, most of them are derived from the following four basic designs:1. Row by Row -This firing pattern can be applied in a pure Row-by-Row initiation sequence with delay times only between rows or in a pattern with short delay times between holes and long delay times between rows so there is no interaction between the rows. This design requires at least one free face.2. Chevron -In a Chevron firing pattern the delays between holes and rows are chosen so that the firing sequence results in aV-formation. By using different delays, the angle of the V-formation can be modified. The Chevron design requires at least one free face.3. Echelon -The Echelon firing pattern is simply one half of a Chevron pattern. Echelon pattern requires at least two free faces.4. Diamond -Diamond firing pattern is used for box cuts, sump blasts and other applications where there are no free faces parallel to the blast holes. The broken rock will be displaced upwards, with an increased risk of fly-rock.*********************************************************************************************************

************************************************************************************************************FLYROCK ISSUES IN BLASTING:Analysis indicates that lack of blast area security, flyrock, premature blasts, and misfires are the four major causes of blasting-related injuries in surface mining operations. Flyrock and lack of blast area security issues continue to pose problems for blasters.Generally, flyrock is caused by a mismatch of the explosive energy with the geomechanical strength of the rock mass surrounding the explosive charge. Factors responsible for this mismatch include:* Abrupt decrease in rock resistance due to joint systems, bedding layers, fracture planes, geological faults, mud seams, voids, localized weakness of rock mass, etc.* High explosive concentration leading to localized high energy density,* Inadequate delay between the holes in the same row, or between the rows,* Inappropriate blast design,* Deviation of blast holes from its intended directions,* Improper loading and firing practice, including secondary blasting of boulders and toe holes.a) BURDEN:Insufficient burden is a primary cause of flyrock from a highwall face. Blasters need to visually examine or laser profile the highwall face and search for zones of weakness, backbreak, concavity, unusual jointing and overhang.b) BLAST HOLE LAYOUT AND LOADING:Any deviation in the direction of a blast hole can reduce or increase the burden. While loading a hole, blasters must frequently check the rise of the explosives column to prevent overloading due to the loss of powder in voids, cracks, or other unknown reservoirs. Such overloading will generate excessive release of energy.c) GEOLOGY AND ROCK STRUCTURE:Sudden change in geology or rock structure can cause a mismatch between the explosive energy and the resistance of the rock. It is prudent to try to detect such changes in advance and adjust accordingly.d) STEMMING:Stemming provides confinement and prevents the escape of high-pressure gases from the borehole. The stemming should provide resistance to the escape of high-pressure gases comparable for that of the burden. Improper or inadequate stemming can result in stemming ejections. Insufficient stemming also causes violent fragmentation of the collar zone resulting in flyrock and airblast.e) DETONATOR FIRING DELAY:Critical elements of any blast design are firing delays between adjacent holes in a row and also those between successive rows. The firing delay is a function of the burden, spacing, hole depth, rock type, and the quantity of charge fired per delay. Proper firing delay helps to achieve good fragmentation of the blasted material. It also reduces ground vibration, air blast, and flyrock.f) LACK OF BLAST AREA SECURITY:An analysis of blasting injuries indicates that several factors are involved in causing injuries due to lack of blast area security. These factors are: (i) failure to evacuate the blast area by employees and visitors; (ii) failure to understand the instructions of the blaster or supervisors; (iii) inadequate guarding of the access roads leading to the blast area, or the secured area; (iv) taking shelter at an unsafe location, or inside a weak structure. Blast area security issues could be addressed by providing adequate training and refresher courses to the blaster and other involved employees.********************************************************************************************************Influence of geology on OC blast performanceIt is well known fact that, geology plays a very important role deciding performance in OC blasting. OC blasting performance and its adverse effects, to a great extent depend on various geological parameters such as, strata condition, dip, jointing, compressive strength, presence of disturbances etc., of the site. Geology of the blasting site is one of the most important uncontrollable factors to be considered for blast-design purpose. For deciding optimum fragmentation, geological information of the site is needed. Geologic information also needed during mine planning stage, before selection of drilling equipments as well. However, rock mass information is utilized by explosive engineer most to improve blasting efficiency.Blasting performance in relation to geology of blast site For every successful blast, explosive energy level and explosive distribution must be matched with geologic condition of the strata to be blasted. Designing of initiation timing sequence must be done in relation to rockmass response to explosive used. Information and understanding of geology of the blast site and its strata condition needed to carryout these adjustments made by blast designer for achieving better result. Experienced blasting engineers are aware of geologic conditions that affect the blast results.It has been recognised that,fragmentationis the most significant problem encountered by blasting engineers. Generation of over-size is the universal problem in blasting. Sources of generation of over-sizes are as given below, and their possible control measures:(a) Hard massive boulder in the stemming zone:This problem can be addressed in several ways, such as, placing small explosive decks in the stemming zone which help to overcome this problem by proper distribution of explosive energy closer to the massive layers at the top, satellite holes placed between the production holes also have the same effect of proper distribution of explosive energy near hard strata, and reducing spacing and burden in some case.(b) Bedding plane slabs from within the blast:This problem causes when blast dimension, hole burden and spacing are much larger than joint spacing. Explosive energy is dissipated within the rockmass through weak bedding planes, so that areas between holes are not effectively fragmented. This problem can be checked by reducing blast dimensions and substituting a higher energy explosive product. This problem may also be aggravated because of insufficient stemming, as the explosive gasses are not confined for a sufficient time they cannot produce the expected breakage within the rockmass.(c) Hard rock at / near intrusive dykes:Softer dyke rock absorbs the explosive energy. Explosive energy is also being lost along the dyke contact, where open weathered fractures are common. By reducing the blast dimensions or by substituting a higher energy explosive product this problem can be minimized.(d) Rock isolated from explosive energy by excessive over-break:Measures to reduce back-break include, allowing more time before the last row of holes fires by proper delay timing sequence, design blasts for more movement resulting in less confinement, or cushion blasting the last row of holes.For more info refer:Characteristics of Rock and Geology influence Surface, UG and Tunnel Rock BlastingResults********************************************************************************************************Problem of unintentional and premature detonator firing in MinesFrequently accidents in mines are caused by the unintentional premature firing of explosives caused by extraneous electricity stray current or voltage, static electricity or high-frequency irradiation. Ideally, a detonator should be immune to any type of extraneous electricity but unfortunately, this is not possible with conventional electric detonators.Electronics safer than electrics:Now Electronic Detonator system has taken a huge step forward to creating a safe environment with a solution that provides protection against all kinds of extraneous electricity. Unlike conventional electric detonators, Electronic digital-coded detonator system uses a built-in capacitor to fire the fuse head. Charging and firing are controlled via an electronic system integrated into the microprocessor of each detonator. Only when this chip receives a digital-coded signal can the capacitor be charged to the required firing voltage. After charging the capacitor, an additional specific digital code must be delivered to the detonator to release an electronic switch, allowing the capacitor to discharge and initiate the fuse head.Immune to inadvertent ignitions:Electronic detonator provides protection against accidents caused by extraneous electricity:* Safe against Radio Frequency (RF): unparalleled safety against high-frequency irradiation* Safe against stray current and voltage: far superior to electric detonators* Safe against static electricity: unaffected by electrostatic discharges, e.g. in the human body* Safe against induced power caused by lightning: immune to stray current from a lightning strike when the gun system is in the hole*********************************************************************************************************Autonomous Haulage System(also known as Robotic or informally as Driverless Trucks)Autonomous Haulage System (AHS) is a comprehensive fleet management system for mines. The dump trucks, which are equipped with vehicle controllers, a high-precision global positioning system (GPS), an obstacle detection system and a wireless network system are operated and controlled via a supervisory computer, enabling them to be unmanned. Information on target course and speed is sent wirelessly from the supervisory computer to the driverless dump trucks, while the GPS is used to ascertain their position. When loading, the dump trucks are automatically guided to the loading spot after computing the position of the bucket of the GPS-fitted hydraulic excavator or wheel loader. The supervisory computer also sends information on a specific course to the dumping spot.From a safety perspective, the fleet control system prevents collisions with other dump trucks, service vehicles or other equipment at the mining site. In case an obstacle detection system detects another vehicle or person inside the hauling course under AHS operation, the vehicles will reduce speed or stop immediately, making the system extremely safe and reliable.In addition, AHS enables stable operation under gruelling conditions such as at high altitudes or in sparsely populated, arid desert areas. At the same time, by optimizing operations, the system contributes to reducing maintenance costs, conserving energy and curbing CO2emissions.******************************************************************************************************************