HOW TO HANDLE BLASTING MISFIRE

MISFIRE DEFINITION

 An explosive charge in a drill hole that has partly or completely failed to explode as planned. Causes include unskilled charging; defective explosive, detonator, or fuse; broken electric circuit or--most dangerous--cutting off of part or all of the charge through lateral rock movement as other holes in the vicinity are fired. Stringent safety precautions cover procedure in minimizing these risks and in dealing with known or suspected misfires. A smoldering fuse may delay explosion, causing a hangfire, so return to workings after a suspected failure is necessary. Another main cause of accident is drilling into or dangerously near a socket--an apparently empty drill hole.

Rules for misfires ( MMMR-2002)

A.When a misfire occurs in a mine, indicated by the counting of exploded shots in case of fuse blasting, or observed by the blaster from other indications in case of electrical or detonating cord blasting, no person shall enter the place of blasting until 30 minutes in case of fuse blasting and 5 minutes in case of electrical or detonating cord blasting after the firing of shots. The place of the misfire shall be marked by a red flag to indicate it as a danger zone.

B. In the event of a misfire, the following procedure shall be followed:

1.The tamping may be sludged out with compressed air or water under pressure and the hole may be reprimed and fired.

2. When the misfire is due to a faulty cable, or is due to a faulty connection in case of electrical firing, the shot may be fired again after the defect has been rectified.

3. Where the steps in Sections 1 and 2 have not been successful, another shot may be fired in a relieving hole where practicable. The relieving hole shall be drilled at least 30 cm away from and parallel to the misfire hole.

4.After the relieving hole has been fired, a careful search shall be made for cartridges and detonators amongst the material brought down by the shot.

5.Before leaving the mine, the blaster shall inform the foreman and the manager of the misfire that has occurred; when a misfired shot has not been relieved or re-blasted, he shall also inform the officer of the next shift before he leaves the mine.

6. The blaster shall record every incident of misfire in a bound-paged book kept for that purpose.

C. The manager shall ensure that utmost care is exercised when working is carried out in the mine in an area where the presence of a misfired hole has been reported and the hole has not been relieved.

HOW TO AVOID MISFIRE

To avoid misfire, the condition of the hole in check for water before loading must be done, proper selection of Explosive and avoid using deteriorated Explosive, careful loading and tamping during stemming to avoid detonating cord damage, proper priming to ensure good placing of the cap into the prime Explosive cartridge.

Defining misfire as

In the case of accidental detonation of Explosive

Precautions include:

1. Proper handling of Explosive during storage and transportation

2. Avoid using low current exploder

3. Stop all Blasting operation under heavy thunderstorms

How to handle misfire when it happens

1. Detect misfire from blast sound and fume observation

2. Give clearance time 15-30mins before visiting the blast area

3. Carryout post Blasting inspection after blasting

4. Demarcate or barricade blast zone with signs after observing misfire

5. Never try to pull out the detonation cord with force from the charge hole

6. Check if the Explosive charge and cord can still be detonated, if yes reblast the charges. If no redrill and recharge the formation with all eye Care. Reblast drill holes should be drill vertically and Abit far from the undetonated hole.

7. Remove any budged or undetonated Explosive and accessories from rock socket to avoid damage to loading , transporting or processing equipments.

Note all undetonated Explosive left over in misfire are unstable, they must be handle with Care.

Life and property must be secured.

Misfire can be classified into three base on cause and source.

 Misfire  resulting from

1. Manufacturer factor

2. Design factor

3. Human factor.

HOW TO DEAL WITH MISFIRE

1. identify type and position of misfire

2. Take remedial action with misfire

3. Recover Explosive material or refire.

STEPS TO DEAL WITH MISFIRE

1.REMOVING STEMMING AND REPRIMING: In doing this, "No use of force".  For electric detonator, do not use high velocity air as it can generate static charge sufficient to initiate the Explosive primer.

For top priming do not forcefully remove Stemming with metal or iron bar. In case of decking, remove inert material from each deck gradually and continuous with care.

For bulk/slurry Explosive, wash off with pressurized water, but for cartridge Explosive, care should be use to avoid unwanted initiation.

Use large quantity of water to desensitize Explosive.

2.DRILLING AND FIRING RELIEVING HOLES

in case of stocked in Explosive charge which I unremovable, instead of using force and create static charge, drilling relieve hole at a define distance from the load Explosive to release the holes is done with precaution.

The relieving hole distance from the undetonated hole depend on the following factors:

a. Diameter of the undetonated hole

b. Inclination of the undetonated hole and that of the Drilling machine

c. Sensitivity of the Explosive in the undetonated hole

All relieving hole must be;

a. Parallel to the undetonated (misfire) hole

b. Be of thesame length with the undetonated hole.

c. Must be lightly charged.

3.DISCOVERY AND RETRIEVAL OF EXPLOSIVE

Most misfire leave Explosive in Muckpile, boulder socket and on bench wall.

Unretrieve Explosive can led to unexpected detonation during loading, haulage or crushing. Therefore, to avoid any unwanted initiation, retrieving all undetonated Explosive cartridge from muckpile help to avoid accident in both mine and milling factory.

Above all steps, post Blasting inspection and blast risk assessment should be done and any evidence of misfire must be handled by expert and competent person.

Misfire zone should be barricade and *All clear* signal should not be given until misfire location is clear.

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DRILLING PRE-PLANNING IMPORTANT

Drilling is the creation of Artificial cavity into rock for the placement of Explosive.

Drilling can be done for different purpose ranging from:

1. Rock Blasting

2. Oil and gas production

3.rock stability and Safety purpose

4. Exploration purpose 

5. Water and borehole drilling

6. Among others.

Drilling for rock Blasting is done for the loading of Explosive into the rock formation so as to generate the shock and gas energy require to fragment the rock mass.

Planning for an event makes the event or operation more perfect and productive.

The condition of the drill holes and arrangements in place of pattern design of the hole drilled for Blasting has great impact on the effectiveness of the blasting.

Some of the parameters that explains the status of blast holes are:

1. Burden: the perpendicular distance between the first drill holes row to the nearest free face. Or in others way, the distance between two adjacent 

Hole rows.this affect distribution of energy within the holes during initiation.

2. Spacing: the distance between two adjacent holes on thesame row.

3. Hole diameter: the circumferential size of the Drilling bit

4. Hole depth: the vertical depth of the drill hole.

5. Hole drill angle, and others

The accuracy of all this drill parameters have great effect on the functionality of the Explosive energy.

To avoid any form of deviation in drill hole angle, error in spacing, burden and other possible mistake we must ensure all planing is perfected, drilling team are aware of the drill plan and purpose, the rock properties and location conditions are studied and account for.

During drilling, the supervisor should ensure drilled holes are checked, count and measured to avoid any form of oversight in depth, design.

Some effect of oversight during drilling:

1. Hole closure with drill cuttings resulting into depth shortage. Depth shortage directly result into reduction in tonnage. The volume of material blasted is a function of hole depth, decrease in hole depth result into decrease in tonnage.

2. Unexpected site Accident: drilling in an unknown geographical so or unknown rock mass formation may result into unexpected accident during drilling. Just as the condition of each rock layers are study during oil and gas drilling to understand the bottom pressure and fluid static condition. Thesame during drilling operation for Blasting, rock been a heterogeneity material it varies in strength and characteristics with depth. Pre-planning before drilling operation proceed will help to avoid any form of drilling Accident. It will also give sufficient information to Blasting team on the required energy needed to fragment the rock mass productively.

3. Poor Blasting output: poor drilling plan (PDP) and poor drilling supervision (PDS) makes blasting team to be stranded of information about the rock formation. Detailed information about the rock mass can best be optained from drill cuttings. Proper supervision of drilling makes the blasting teams to have sufficient information to plan for the blasting operation. The availability of enough information about the rock mass help the blasting team to plan for the charge distribution and density needed to fragment the needed rock mass. It also help blast team to account for possible blast accident. Having understanding of the rock strength, variation in composition, rock structure (dyke,sill among others) help to control charge distribution within the holes column to prevent improper use of charge energy which can result into flyrock, ground vibration among other blasting impact.

In general, drilling operation should be well planed and supervise to avoid any oversight and ensure enough information is provided on the drill log  for blasting team to rely on.

Let Blasting been done safely in accordance to National, global and state laws and regulations.

Say no to illegal mining and use of Explosive and Blasting material as it deadly and bad.

Let Blast safe and relate safely with the ecosystem and earth lithosphere, this is our home.....

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INDUSTRIAL MINERAL MINING: MARBLE

Marble is a white colour calcitic lime stone.

It a stone with  glaring and decorative texture.

It has coarse texture with dominantly calcite Mineral. Marble has white streak but varies in colour from pure white, off white, Ash depending on it formation.It color also depends on the following:

Primary rock from which it formed, composition, degree of weathering process it has undergone, type of metamorphism it undergone (contact or regional) among others. Marble is a monomineralitic rock..

Marble is a carbonate rock, it has hardness of 3 on mohr's scale of hardness.

"Marble More of Formation" 

Marble bus formed through metamorphosim process. When Argillaceous grain limestone undergone metamorphosim under high temperature, it undergone recrystallization which led to the formation of Marble. As existing limestone formation is heat up by intrusive magma it grains undergo Reformation.. Marble is an industrial  rock as it a useful industrial material.

Marble as one of the useful industrial raw material can be mined as aggregate and also can be extracted as dimension block. Marble as a competent rock of compressive strength greater than 35Mpa can be mine by Quarry Mining method, Open pit and other applicable methods depending on the formation orientation, dimension (size&shape), overburden thickness.

Marble aggregate is mine using drilling and blasting to break the marble deposit into handable sizes. 

This method involved the following operation sequentially:

Development operation, Drilling, Blasting, loading and hauling, Processing.

The following documents are required to apply for a Mineral title; Exploration Report, Minimum work program report (MWP) Environmental impact Assessment (EIA), Community Agreement signed by necessary community leaders, evidence of compensation to the land owner and previous land users. Have once explain each of this documents once. In case you want to write or learn how to write you can reach me, I will put you through @Giant Miner training stope.

After acquiring the deposit, development operation start by road creation and land clearing to give a work space allowance where mining can start proper. Development operation: The first thing before any mining operation can commence is to acquire the deposit both as mandated by Mining Act and Regulations. After exploring the deposit, necessary mapping operation to understand formation orientation and dimension is carryout. This is operation is follow by core drilling operation to know both quantity and quality of the formation. All this operation is done under Exploration License (EL). This license is renewable and  can be extend on additional Mineral. After exploration process, Exploration Report is submitted to the ministry of mine office along side with other documents for Mining license processing. After successful Blasting, marble aggregate is load and haul for milling.

Uses of marble aggregate includes; for animal feed production, paint production, cement production, iron ore pyrometallurgical processing in blast furnace, tooth paste and pharmaceutical industrial use, construction purpose, uso as drilling mud addictive among other uses. The marble Run-off-mine is milled into fine product or hammer milled.

After drilling operation which is assumed to be as planned and design in alignment with the mine design.

Blasting operation is done by loading the drill holes with specified quantity of explosive. In open pit the deposit is work in benches, why in Quarry it's worked in a single bench. For the first Blasting operation, box cut Blasting design is use for the creation of additional free face. In the box cut design, inner holes are initiated first then preceeded by the following ones. Th inner hole create a crater which create horizontal Free face. The crater geometry depends on the depth of burial of Explosive and other parameters in place.

Drilling and Blasting operation commence after the deposit has been developed. For both open pit and Quarrying, the overburden material removed from the deposit is stockpile in a remote area where it's kept for reclamation. All operation on this marble deposit must be done as proposed in the minimum work program report (MWP). Drilling as we all know is the creation of cavity into the marble formation for the placement of Explosive. The development operation can b done using Excavator machine, payloader and other mine machineries. Most time when the area to dump marble overburden is far, dump trucks and other haul trucks can be used  Reason why Marble is as useful as it's

Marble compose of calcite (CaCO3). Calcite is a Mineral of high cementric property and it's rich in calcium. Calcite find it use in cement company due to it cementing property and ability to glue. During Diagenesis process of sedimentary rock formations, calcite play the role of cementing sediments together after lithification and dewatering process. This calcite of plane cleavage and two dimensional cleavage plane is said to be formation from the remain of past sea creatures. High calcium content in marble makes it useful for pharmaceutical industry. Marble dimension block Extraction:

Apart from mining marble as aggregate it can be cut into slabs and polish into chair, table and tiles among other things. Marble as a source of calcium is also use for animal feed (pig meal and poultry meal). Marble is use for iron ore process as a reactant to remove hematite (Fe2O3)  oxygen as CaCO3 need more oxide to burn off its carbonate so as to produce quick lime.

When calcite is heated at high temperature, the carbonate content combust and burn off to produce quick lime. When hydrated produce hydrated lime which is a raw material for water purification and other uses. Marble aggregate is useful as an industrial material. 

Marble Dimension block Extraction

Dimension stone Quarrying is another aspect of mining that involves the cutting of rock mass into block which is to be polish into different ornamenal finish goods including chair, table, stool, tiles among other. 

Slab cutting techniques of marble extraction involve creating face for dimension block and detachment of the cut block from the insitu rock. This extraction begins from site mapping to check the formation competency. For a marble formation to be competent for dimension block cutting it must be of; discontinuity and crack free, low water absorption, low porosity, moderate strength among other characteristics. Availability of fracture in rock mass render the formation useless as dimension block material. Existing fractures in marble rock mass (joint, fault, and others fissures) makes it difficult to extract block as they tends to break into chippings and undimensional boulders. High strengtharble formation containing metallic minerals and hard grains affect the cutting tools and it cutting efficiency. Therefore before establishing a dimension block cutting Quarry, the following properties of the formation must be justify with the international Rock Mechanics standard.

Properties to be test for includes but not limited to:

1. Rock Uniaxial compressive strength UCs

2. Porosity

3. Water absorption rate

4. Durability

5. Discontinuity mapping

6. Petrographic check for aesthetic appearance.

7. And others

Marble Dimension stone cutting can be done using cutting machine, drilling and blasting, usebof soundless demolition Chemical Agent and presplitting.

Principle of Control Blasting 1: Presplitting blast Techniques Theory

Open pit mining is one of the surface mining method use in exploiting less overburden material. Open pit method is one of the special mining method use to extract competent ore with flat shape.

This method is unique with it's step wise approach use to mine the deposit in benches.

The safety requirements for the success of this type of mine is not restricted to 

Open pit blasting at first may require box cut approach to create additional free face at the horizontal direction for successful throw.

Mostly if the blasting is carried out at the last bench floor or as the first blasting for face opening.

In such case where:

1. Environmental Impact has to be controlled,

2. Safety of workers, equipment and nearby things have to be presented,

3. Blast economy in place of cost of blasting material effect on overall blasting cost have to be minimize,

4. Success optimum fragmentation size with less than 5% oversize and undersize, and

5. Dilution, overbreak and back break needs to be prevented for high safety and low downstream operation cost sake...

The use of control blasting tends to be very crucial and must be practice in all mine site.

Control blasting is a special Blasting approach that involves strategic control of Explosive energy to avoid damaging intert rock wall and to avoid environmental impact of blasting.

Control blasting techniques include;

1.Presplitting technique, 

2.smooth blasting, 

3.cushion blasting,

4. line drill hole, 

5.post splitting,

 6.Air decking among many others. All control blasting techniques try to achieve the same aim but through different objective.

To control the rate of shock energy, gas energy, radial cracks, flyrock, ground vibration, airblast released during blasting.

But optimizing powder factor, drill and blast design parameters.Thou rock heterogeneity and anisotropic nature makes control blasting design varies from formation to formation.Most civil engineering construction blast involved control blasting to avoid overbreak of wall and floor. Some of the reasons why control blasting is needed:

1. To avoid overbreak: this is creation of discontinuity by the shock energy beyond the bench width during charge detonation.

2. To avoid reduction in support wall strength and competency: fracturing of support wall and toe reduce the stability of slope which prompt rock to easily fall under load redistribution during excavation.

3. To prevent high ground vibration, flyrock, airblast and other environmental Impact 

 4. To control blasting cost through charge weight reduction and still achieve optimum fragmentation

5. To control dilution rate in grade variation formation.

For civil engineering works, control blasting techniques are use to fragment road obstructing rocks (outcrops) during tunneling, building foundation laying and road construction.

This idea is to ensure the hindring rock is break down with competent and smooth face at LHS AND RHS.

Now to presplitting blasting technique after understanding reason why we need control blasting in mining and petroleum (casing perforation at production zone) in civil engineering.

Presplitting is one of the control Blasting techniques use to ensure good Explosive-rock interaction during Blasting. It involves splitting the production zone from the supporting rock block (unblast rock wall). This techniques is differ from post-splitting by the initiation timing as the one detonate production hole first why another detonate perimeter hole First. Presplitting had been practice earlier before the use of Explosive in construction.

In Egypt and other countries, the use of wedge wood and fire heat had be ultilize to split rock mass, likewise in Northern locations spallation effect of freezer water is used. Drill holes are filled with water, as the water frozen it expand and split rock mass.

This traditional approach was used before 1950's. The first presplitting blast wast done in Lewiston power plant as part of Niagera powder project. This was a project involve the blast of dolomite & limestone formation with shale bed.  Many Presplitting method was applied including line hole drilling with three hole step charging, cushion blasting before presplitting was use with dynamite cartridge. The are various type of presplitting:

Traditional, precision and many others but all still in the optimize of Explosive load, stemming and spacing parameters.

From different scholars (Joseph Konya, cook, beckee-kietiakowsky) point of view, Explosive released energy theory were studied to ensure good control during presplitting blast. For the shock wave release, various theory like; Livingston cratering theory, Bureau of mines catering theory, shockwave spallation theory and strain wave theory among others were propanded and infused to ensure the control of micro-fracturing rate during presplitting.

And for the gas energy study for precision splitting, the following equation of state was propanded to calculate the explosion pressure released from charge at detonation; Beckee-kistiakowsky-wilson (BKW) equation of state, Cook's equation of state, Taylor's equation of state, Outoyne-Skidmore-Konya (OSK) equation of state and many more. Learning on the shock and gas energy generation rate during detonation gives the scholar great confidence to give precise and accurate approach to presplitting blast and other Control blasting techniques. If the capacity and energetic strength of each Explosive charge is understand, to control it damage rate becomes easy and accurate.

Presplitting Blast design Parameters

Presplitting make use of the following approach in order to ensure proper Explosive energy;

1. Explosive load weight: blast energy both shock and gas energy increases with exolosive load. During presplitting blast charge, decoupling of peripheral (control holes )to reduce the charge density. Decoupling is the use of small diameter Explosive cartridge in large diameter hole. The decoupling ratio is the ratio of the the Explosive cartridge diameter to the drill hole diameter. Decoupling reduce Explosive energy by creating air allowance between Explosive cartridge and rock wall, therefore the release wave interact with air (having low Sonic velocity) before interacting with the rock mass. In a bit to contain the Explosive energy within the cut line, Explosive load weight is calculated using various design rule of thumb formula including;

Dcc=(Dh^2)/28

Where;

DCC is the charge weight in pounds,

She is the Explosive cartridge diameter.

Also Joseph Konya propose presplitting Konya constant to model Explosive load weight,

K=(40579/E)^0.625

EL=7000*(S/K)^2

Where;

K is the Konya presplitting constant,

E is the rock Young modulus,

EL is the Explosive load weight.

S is the spacing

2. Spacing: spacing is the distance between two adjacent holes in thesame row. Providing wide and optimum space between hole controls the volume of rock block to be fragment by each energy release from each kilogram of edplosive. Increase in spacing reduce the efficiency of hoop stress distribution amongs the holes detonated. The spacing between presplitting holes increase the resistance offer by the rock mass against the release Explosive energy.

Some rule of thumb formula use for spacing during presplitting blast include;

S=10Dh

3. Stemming length: stemming according to konya have no effect on Explosive shock wave but affect the explosion pressure. Well confined holes generate high explosion energy, this will avoid flyrock and also support good throw and backbreak.

4. Initiation timing sequence: Initiation timing of blast charge simple explains the detonation pattern follow by each of the hole during firing. In order for presplitting blast to prevent overbreak at the design boundary between the production block and the supporting rock wall,the peripheral holes (The hole at the production and support wall boundary) are decoupled and initiated first ahead of the production holes. This is where the name Presplitting comes from. The peripheral holes split apart the production section of the ore deposit, creating a free face between the two rock block. This split point avoid further fracturing during production hole Blasting.

Summarize Theory of presplitting blast

The whole idea is to divide the drill hole into two sections.

1. Production holes: holes to be blasted for Run-off- mine crude production Or the holes place in the rich grade zone during dilution control or the hole arranged on the rock mass to be broken away from highway.

2. Peripheral holes or the control holes: These are hole placed at the boundary of the blast rock and supporting wall.

The hole powder factor or load weight is controlled base on the rock strength and the Explosive strength.

Also the hole design is done using specified rule of thumb formula.

The initiation system use in presplitting is design such that the initiating signal reach the peripheral holes first before the production holes. This is achieve through the use of delay detonators (which can be surface delay or down-The-Hole delay). In this case, the charge in peripheral holes are detonated before the production holes charge. The peripheral holes charge is light and decoupled, this ensure perfect splitting and detachment of production block from the insitu rock with smooth face. As soon as the energy from the production hole gets to the split point it's escape to the surface vertically.

Some of the special blasting accessories use for presplitting blast include: delay detonator, decoupling sleeves among others.

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