EXPLOSIVES

An explosive is a solid or liquid substance or a mixture of substances which changes themselves instantaneously into a large volume of gases at high temperature and pressure when a flame, heat or sudden shock (detonation) is applied to it.

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The high pressure that is built up is capable of doing the work of breaking rocks.

Detonation: is a process of giving sufficiently violent shock to the explosive to bring about an almost instantaneous re-arrangement of atoms.

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The chemical energy in an explosive is released and converted suddenly into heat and mechanical energy when heat, flame or detonation is applied and this conversion is due to a chemical reaction which is essentially a process of oxidation.

An explosive, by virtue of its Constituents, contains enough oxygen necessary for complete oxidation. A commercial explosive contains, apart from the explosive substance or explosive mixture, the following materials :-

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1. Combustible matter: such as wood meal, fibre, sulphur, charcoal etc.
2. Oxidising Agents: such as Sodium Nitrate, ammonium nitrate, potassium nitrate etc.
3. Stabilizers: such as magnesium & calcium carbonates
4. Antisettling agents: to prevent caking of salts
5. Sensitisers like metallic powder

Properties of an explosive

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1. Strength: - weight strength (as known in IEL) as compound to Blasting Gelatine
2. Velocity of Detonation: - shock energy
3. Density:- energy of shot concentration
4. Water resistance:- resistance to water & moisture penetration
5. Sensitivity:- insensitive to normal handling but sensitive to satisfactory detonation
6. Fume Characteristics :- minimum harmless gas produced, Slurry and ANFO is preferable to Nitro Glycerin bondage
7. Legal Permission: - Only permitted explosives are used in U/g

Types

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• Low explosive e.g. Gunpowder
• High Explosive e.g. ANFO, Slurry, Nitro Glycerin, Special Gelatine

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Low

Gunpowder: 15% Charcoal, 10% Sulphur, 75% Potassium Nitrate, None of the constituent by itself is explosive. Produces flame, and not used U/g + wet places.

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High

Nitroglycerin : Oily fluid with sp. gr. of 1.6 & freezing point at 13^OC.

Insoluble in water & very sensitive to explosion by shock of any nature. NG have high shattering effect & NG based explosives are available in 3 consistencies –

1. Gelatinous, 2. Semi-gelatinous 3. Powdery

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Produce fumes after blasting & freeze at 8^OC or less.

Ammonium Nitrate (NH₄NO₃) - It is white hygroscopic salt, very soluble in water & comparatively very safe to handle, Ammonia Gas with Nitric Acid & on detonation, decomposes to :

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2 NH₄NO₃ = 4 H₂O + O₂ + 2 N₂ + 346 Kcal/gm

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Collodian Cotton – Reaction between cellulose compound and nitric acid yields Collodian Cotton – a high explosive.

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TNT (TriNitroTolune) – Reaction between Nitric Acid & Benzene or Tolune compound – Highly explosive

Detonation of High Explosive:

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Is cap sensitive

Inserted with explosive or kept in intimate contact.

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Advantages of ANFO

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• It is cheap
• It is easy and safe to manufacture
• It may be handled in bulk to save costs

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Disadvantages of ANFO

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• It is not water resistant
• Its density is low
• It is non-ideal reacting
• It is not Cap sensitive and must be initiated with a primer

Boosters

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For effective detonation of some slurry explosives and ANFO mixture such as GN-1, Use of High detonation velocity booster is necessary.

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e.g. PRIMEX – which is mixture of PETN (Penta Erythritol Tetra-Nitrate) & TNT (TriNitroTolune)

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Velocity of Detonation of 7000 m / sec; Wt. Strength of 82

Permitted Explosives

P₁ – Unsheathed Explosives – e.g. AjaxG, VikingG, Slurry Explosives like Godyne

P₂ – Sheathed Explosives

P₃ – Equivalent sheathed explosives (Eq. S) e.g. Unisax - G, Permadyne

P₄ – Explosive approval for special purposes, such as delayed firing, firing in ripping, etc. hitherto known as ultra safe explosives. These are not produced in India. British example – Carribel, Nobel’s Explosive 1235.

P₅ – Off the Solid Explosive (for solid blasting) e.g. SOLIGEX, Slurry explosives – Pentadyne.

DETONATORS

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A detonator is a small copper or aluminium tube containing essentially a small auxiliary charge of special explosive.

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High explosives are initiated by detonators or detonating fuse.

A chemical reaction initiated by a flame or electrical current in the special explosive can build up very rapidly into an explosion of sufficient intensity to project a detonation wave throughout a high explosive enclosing the detonator.

Types of Detonators:

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1. Plain detonators – These are fired by safety fuses, the spark or “spit” from the fuse causing the detonator to explode. These are called ‘ordinary’explosion.

2.Ordinary electric detonators – These are fired by passage of electric current through the detonator.

They are sub-divided by:

a. Low tension detonators, and

b. High tension detonators (not generally used in mining)

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These are instantaneous i.e. without any delay element. They are of copper or aluminium tubes.

3. Delay Detonators: These are essentially low tension electric detonators with a delay element, the object in their using being to phase the firing of shots, so that time and effort are saved in charging and firing several successive rounds of shots.

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They are sub-divided as:

(a) Half second or long delay detonators, and

(b) Milli-second delay detonators (also known as short delay detonators)

Delay Detonators

Ordinary i.e. Non-delay type electric detonators

1. Instantaneous type i.e. non-delay
2. Long Delay Detonators- available in delay numbers 0 to 10 delays with aluminium tube. Interval 300 milliseconds, Lead wire – one yellow other one green. Not used in Underground mines. Primarily used for Quarries, Drifting and Shaft Sinking.
3. Short Delay Detonators – Average delay in nos. 0 to 10 in aluminium tubes. Delay interval between successive delays is 25 milliseconds. Both wires are green.
4. Carrick short delay detonators (non - incendive): Available in delay numbers 0 to 6 with copper tube only. Delay interval between successive delays is 25 milliseconds. Both leading wires orange. These are used with P5 explosives.

PETN (Penta – Erythritol Tetra – Nitrate)

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ASA – A – Lead Azide, S – Lead Styphnate, A – a little aluminium powder

Advantages of Delay Detonation:

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• Reduced Consumption of explosive because of availability of free face for each row or round of shots.
• Increased fragmentation and ease of loading the rock or coal. Broken rocks from successive shots collide in air, thereby increasing fragmentation.
• Considerable time is saved – whole round of shots are fired in fraction of a second. This is the Chief Advantage. (for U/g otherwise, time taken to clear fumes, inspect etc.)
• Millisecond Delay (short delay) produce, less ground vibration than the half second delay. This is useful in large dia. Holes in OCP’s with heavy charges – not to effect buildings, foundations of important engines, structures etc.

EXPLODERS:

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Electric shotfiring is safer, quicker, and more convenient than ordinary fuse firing by flame or ignition as it provides safety to the shotfirer and helpers. Tapping of electric power from lightning or signalling lines is not permitted by the regulations.

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Portable apparatus which provides the current necessary for firing electric detonators is called an exploder.

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(no stored electric energy but generate the necessary electrical power by means of a dynamo or magneto).

1. Little Demon & Schaffler – 750 exploders – also known as Magneto or dynamo exploders.
2. Rhino (capacitor, charged by batteries or dynamos) – also known as battery condenser type if battery is used and dynamo condenser type if a built-in dynamo provides the current.
3. Sophisticated exploders – are exploders with transistorized circuits where output and current are controlled both in magnitude and duration by electronic means. For example, ME-12, TZK-100G (Polish make) exploders.

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Low tension exploder gives a voltage of 15 Volts

High tension exploder gives a voltage of about 125 Volts

25 holes with Rhino – 25.

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Different Types of Blasting Patterns:

Wedge Cut

Drag Cut

Pyramid Cut

Burn Cut

Fan Cut

Cone Cut

Coromant Cut

Underground

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Stemming Material:

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• Test of gas within 18 m of holes
• Holes less than 150 mm
• Primed cartridge at end
• Spray water or sprinkle stone dust within 18 m
• Remove people – Take Shelter – Warn with Audio Visual Alarms
• Fire the shots

OPENCAST BLASTING

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1. Rectangular Pattern
2. Triangular Pattern
3. V- Pattern
4. Zig – Zag Pattern

Burden & Spacing

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CAST Blasting: Use of blasting to move overburden directly to the spoil site without re-handling