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Wednesday, 21 September 2016

Blasting awareness session


Blasting awareness session





Objective



What is blasting


Definition

Definition

Blasting parameters

Principle of Rock Blasting

Explosives
  
Classes of Explosives


Types of Explosives


Different Initiation Techniques


Ordinary Detonator


Electric  Detonator


Electric Delay  Detonator


Electronic  Detonator


Mechanism of Rock Blasting


Drilling by Jack hammer


Mechanism of Rock Blasting


Classification of Rock Blasting


Drilling pattern in Trenching


Contour Blasting


Pre - splitting


Alignment of Blast-holes in Pre-splitting



Controlled Blasting


Control of Fly-Rock


Control of Fly-Rock


Control of Fly-Rock


Control of Fly-Rock



Muffling by Sand bag & Steel plate


Rubber mat placing


Muffling completed


Control of Vibration


Quarrying


Layout of a Quarry


Code of ethics for shot-firer


Code of ethics for shot-firer


Storage & Transportation of Explosives


Storage & Transportation of Explosives


Explosive Container


Storage & Transportation of Explosives


Storage & Transportation of Explosives


Explosive van


Licensing for establishing a Magazine


MisFire


Charging  of Explosive


Handling of misfire


Some useful tips


Some useful tips


Some useful tips


Thank you.





Welcome to
Blasting awareness session


What is Blasting

Blasting is the process in which, the high pressure to which the rock is exposed ,shatters the area and exposes the space beyond that to vast tangential stresses and strains.

The phenomena takes place under the influence of outgoing shock waves which travel in the rock at velocity of 3000-5000 meters per second.

DEFINITION

After inserting ED into the cartridge is called prime cartridge & the process is called priming.
For priming sharp edge wooden stick should be used
Don’t use ferrous metallic tools.
.Don’t prime directly, first puncture it with wooden stick & then insert detonators
STEMMING: material used for confining a charge of explosive in a hole.
MAGJINE:-Explosive storage building
CARTRIDGE: Explosive containing cover 

Blasting Parameters

Principle of Rock Blasting
A Blasting operation is constituted of three stages:
ØCompression: High velocity pressure waves create micro-fractures.
ØReflection: Waves bounce back from the free face & convert into tensile & shear waves causing more fracture growth.
ØGas Pressure: Large volume of high pressure gas expand the cracks
Explosives
An Explosive is a solid or liquid substance or mixture of substances which change themselves instantaneously into a large volume of gases of high temperature or pressure when a flame, heat or sudden shock is applied to it.
The amount of energy developed per unit of time is of the magnitude of 25000 MW -  i.e it exceeds the power of most of world’s present largest power station
Classes of Explosives
Low Explosives
High  Explosives
Low Explosives  Example  Gun powder
High  Explosives Example  Nitroglycerine
  Dynamite
Types of Explosives

Different Initiation Techniques

Detonators - To initiate the explosives.
A Detonator is a small copper or aluminium tube containing essentially a small auxiliary charge of special explosive.
Detonators - Mainly of four types:
ØOrdinary Detonator
ØElectric Detonator
ØElectric Delay Detonator
ØElectronic Detonator
    

1. Ordinary Detonator

§Used with a safety fuse.
§Contains a base charge of PETN (Pentaerithritol Tetranitrate) and a priming charge of ASA (Lead Azide, Lead Stiphnate & Aluminium Powder).
§Base charge ignited by Fuse.

2. Electric Detonator

Base charge of PETN and priming charge of ASA.
Fired by (exploder)electric current through leg wires.
Converts electrical energy into heat energy igniting  initiating charge, which in turn fires base charge.
3. Electric Delay Detonator

Modified form of Plain Electric Detonator with a Delay Element (Antimony Powder) inserted between Priming Charge and Electric fuse-head.
Gives reduced vibrations, air-blasts, over-break & fly-rocks.
Increases Fragmentation
Delay depends on the length of sleeve.

4. Electronic Detonator

Electronic Detonator based on Microchip Technology.
Stores electrical energy for a while & delivers  as sharp pulse at precise time.

Mechanism of Rock Blasting

Explosion pressure greatly exceeds the dynamic compressive strength of the rock immediately around the hole.
Crushed Zone is created in the immediate vicinity of the hole.
Extent of Crushed Zone, probably does not exceed two or four hole radii.

DRILLING By Jack hammer

Mechanism of Rock Blasting
Intensity of the explosion pulse decreases with the increase in distance from the drill hole.
Cracks / fissures developed in the Fractured Area, extent of which averages 20-40 borehole radii.
Blast-influenced area, where no cracks are visible, called Seismic Zone which extends 50 borehole radii.
Classification of Rock Blasting

Drilling Pattern in Trenching

Contour Blasting

Specialized Blasting Technique practiced so that:
ü Rock wall after the blast is of good quality
ü Rock-falls & Rock-slides avoided or minimized.
Two methods used to produce stable & smooth rock contours:
1.Smooth Blasting
2.Pre-splitting
Pre-splitting

Row of holes drilled along the final excavation line & hole to hole distance should be 3-4 times of hole dia.
Hole depth should be 20% more than main blasting area.
Holes loaded with light charge prior to the main blast causes a fracture.
Fracture generates a discontinuity which minimize the Over-break & produces a smooth finished wall.

Alignment of Blast-holes in Pre-splitting

Controlled Blasting

Control of Fly-Rock

FLY ROCK
Two type rock movement occurs in bench blasting
Forward movement of entire rock mass which is horizontal – Rarely represents any hazard in blasting operation.
Fly rock which scatters from the rock surface and in front of the blast – Tend to travel long distance and main cause of on side fatalities and damage to equipment.
CAUSES OF FLY ROCK
Excessive Explosives in the blasting
Improper burden
Inappropriate firing pattern
Too short or Too long delay time
How to avoid Fly rock
Proper stemming
Proper drilling pattern
Design of firing pattern so that each blast hole has free breakage
Use of right amount of explosives

Fly Rock control
Blast to be covered by energy absorbing covering -
  Commonly used covering (muffling)
-  Use of 3 / 6 mm steel plates & few layers of sand bags
-  Use of heavy rubber blasting mats made of scrap tyres which are cut into section & twined with steel rods 
Fly Rock Control

MUFFLING by sand bag & steel plate

Rubber mat Placing

Muffling completed

Control of Vibration

When an explosive charge detonated in the blast-hole propagates in form of seismic waves generating Ground Vibrations.
To control vibrations, a row of holes drilled along the periphery of the block, which are left uncharged to provide a plane of weakness to which final row of blast-holes can break.
To minimize vibrations, every hole should be given an individual delay to avoid superposition of waves.


Bottom initiation should be avoided.
Quarrying

Quarry is a factory that converts solid bedrock into crushed stones which are crushed & screened in various sizes for subsequent sale and use.
Quarries can be either of the common pit type, or in mountainous terrain, the hillside type.
The excavation is often split into several benches, depending on the depth of operation.
The width of bench should be sufficient both to accommodate the spread of rock, and to provide space for the equipments.

Layout of a Quarry

Code of Ethics for Shot-firer

While working with explosives, don’t use matches, naked light or mobile phone, walky-talkies.
Don’t keep or transport, explosives & detonators in the same container / magazine.
Don’t try to soften the hardened cartridges by heating them over fire.
Don’t force a detonator into the cartridge.
Post guard with red flags around the site to prevent persons approaching the danger area.


Before firing, make sure that all men, equipments, & surplus explosives have been removed.
Don’t use a burning explosive cartridge for lighting fuses.
The shots must be counted with utmost care to ensure that there are no misfires.
Soon after the blast, Shot-firer should take into his possession,the key of the exploder.
All misfires should be treated with highest precaution & care and all operations dealing with them should be entrusted to experienced & careful men or the shot-firer himself.

Storage & Transportation of Explosives

As per The Explosive Rules,1983, all explosives should be stored in a specially constructed magazine.
Explosives & detonated should never be stored or transported in the same container.
Men entering the magazine, should be searched for cigarettes, matches etc.
Area surrounding the magazine should be kept free of inflammable material.
Magazine should be well-ventilated. It should be kept open for at least half an hour every day.
Explosive containers up to 5kg should be made of                       Finished wood-50mm thick
Plastic—6mmthick
Over container –
Manufacturers name or trade mark
Name of explosive
Lot number
Date of manufacture
Expiry date
Explosive handle with care
Explosive Container

Storage & Transportation of Explosives

The design of magazine should be such that there is an internal volume of not less than 0.4 cubic meter per 100 kg of explosives.
A magazine, irrespective of its size, must be provided with a lightening conductor.
The quantity of the explosive transported shall not exceed-
Ø 4500kg or half the carrying capacity of railway wagon, whichever is less.
Ø3600kg or 75% carrying capacity of a licensed road van, whichever is less.

Speed of the explosive van should not more than 25 Km/hr
Not more than 200detonetors should be transported at a time
Tyre pressure should be maintained and vehicle inspection should be in every 24hours
Warning-write “EXPLOSIVE” both sides,word size should not less than 100mm. With white paint over RED base
Two Co2-fire extinguishers not less than 3Kg                                  
Explosive Van

Licensing for Establishing a Magazine

Form 21, 22 & 24 govern the licensing for, storage & supply of explosives.
An application in form 4 or form 5, as the case may be, is sent to the Licensing Authority (Controller of Explosives), who, after approval, refers it to the District Collector for NOC.
The license is granted if the NOC is issued.
Following documents shall be attached with the application form:
ØSite plan and drawings of premises.
ØStatement showing the safety distances in form 17.

MISFIRES

When a detonator fails to explode ,or after exploding fails to blast the charge of the main explosive cartridge,it is known as “misfire”.
Reasons 
          1. defective firing exploder.
          2. defective detonator.
          3. bad quality explosives.


          4.due to bad connections.
Charging of explosive

Handling of misfire

If shots are fired with safety fuse no person should enter the site of blasting for 30minutes after firing but incase of ED blasting it is 5minutes.
Red Flag should be fixed at the area of misfire.
The stemming should be sludged out with compressed air or water under pressure
No second use of misfire detonator.
Second Charge should not be placed in the same hole & it is 600mm away from the old bore and depth should be less than 300mm

Some useful tips

Ohm meter & Exploder should be tested by DGMS
Explosive Cartridge should be at least 3mm smaller in diameter than shot holes.
Detonators are inserted into a primary cartridge should not be taken out.
Every shot hole should be stemmed with sufficient and suitable non-inflammable stemming to avoid blow out.
No. explosive shall be placed forcibly .

No person should remove any stemming or pull out any detonator lead or remove any explosive from shot holes either before firing or after misfire.
Cable for exploder should not less than18m in length.
Check Strata & overburden with a view to avoiding land-slides after blasting.
Loading and drilling should not be allowed in same area.
A bore hole should not be loaded with explosive immediately after drilling.

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