What is an explosives?

Read more a bout Explosives and Blasting in Mines
An explosive material, also called an explosive, is a substance that contains a great amount of stored energy that can produce an explosion, a sudden expansion of the material after initiation, usually accompanied by the production of light, heat,sound, and pressure. An explosive charge is a measured quantity of explosive material.

The energy stored in an explosive material may be
chemical energy, such as nitroglycerine or grain dust
pressurized compressed gas, such as a gas cylinder or aerosol can
nuclear, such as fissile isotopes of uranium-235 and plutonium-239

Explosive materials may be categorized by the speed at which they expand. Materials that detonate (explode faster than thespeed of sound) are said to be high explosives and materials that deflagrate are said to be low explosives. Explosives may also be categorized by their sensitivity. Sensitive materials that can be initiated by a relatively small amount of heat or pressure are primary explosives and materials that are relatively insensitive are secondary explosives.
Blasting Agents 
The most commonly used is Ammonium Nitrate Fuel Oil – 
ANFO. It can be bought ready mixed or more usually mixed 
onsite. This is used at Staffs last underground mine at Fauld 
where it’s initiated with 100g sticks of Gelignite.

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An Introduction 
What is an explosive? 
• A substance which contains a fuel & a source of oxygen 
either intimately mixed or in the same molecule. It is 
able to very rapidly change state(burn!) to produce a 
volume of gas much larger than the volume of the 
original substance This change should preferably be 
“on demand” & NOT at random! 
Low & High Explosives 
• Low explosives burn more slowly than the speed of 
sound, from around 40m/s – 1500m/s. This is called 
deflagration. Eg. Black Powder burns at 500m/s 
• When detonated high explosives “burn” faster than the 
speed of sound, from around 1500 – 9000m/s. Eg. TNT 
“burns” at 6900m/s or 15,523mph! 
Low explosives can set off by; 
• A fuse 
• An electric detonator 
• An electric ignitor or “squib” 
• In addition black powder can be set off by static 
electricity, sparks, heat, shock & friction – don’t be 
deceived by the term low explosive. All explosives 
should be treated with the greatest respect, the first 
time you make a mistake will probably be your last! 
Low Explosives 
These must be confined to do useful work or they just 
produce a genie like puff of smoke & flames! 
If they are confined in a hole drilled in rock or coal (the 
burden) & the hole is sealed with clay for instance (the 
stemming or rommin!) then the large volume of gas released 
in the explosion blasts the burden apart. 
High Explosives 
• These do not necessarily need to be confined to do 
useful work – they will explode when unconfined. 
• This is because they burn supersonically – the gas 
already produced cannot get out of the way of gas 
being produced quickly enough. 
• This also produces a supersonic “shock wave” that 
shatters whatever the explosive is in contact with. 
There are three broad categories of 
High Explosives 
• Primary – these are very sensitive to shock, flame 
etc so are only “safe” in very small amounts. 
• Secondary – these are much less sensitive & 
usually require the supersonic shock wave from a 
detonator to initiate them (set them off). 
• Blasting Agents – these are very insensitive & 
usually need a small (“primer” or “booster”) charge of 
secondary explosive to initiate them.
Primary Explosive 
Such as Lead Azide are used in very small ( 10’s of mgs.) 
amounts as the primary charge in detonators. When lit they 
very rapidly go from sub to supersonic combustion - they 
detonate! Detonators initiate explosives.

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