Explosions 5 Flashcards
What are the two main ways explosives can be detonated?
Direct and Indirect
What are direct ways of detonating explosives?
- Electrical
- Mechanical (percussion)
- Deflagration/detonation
What are indirect ways to detonate explosives?
- Magnetism
- Acoustic
- Radar
Where is an example of a percussion detonation and how does it work?
In blasting caps
* Pulling the trigger moves a hammer which hits a cartridge case
* The percussion sets off a low explosive
* This compresses the anvil that sets off the powder explosive in the powder chamber
* The flash hole allows gas to escape
What causes percussion and why can the detonation be problematic?
Caused by localised heating upon decreased volume
* Hammer compresses the voids of air - gas gets hot and initiates explosion
* Can compress air so much to generate sufficient heat to cause cracks in he explosive material
* Detonation can be non-uniform (wont be controlled)
* Can be easily detonated accidentally from dropping it
What are stabbing based detonation systems?
- Needle is stabbed into explosive material
- Causes hotspots through high localised friction
- Needle can get bent causing a misfire (have a blunt end to decrease chances of bending)
- Friction and percussion can combine in a stabbing detonator
- Some materials are more sensitive to stab and others to percussion
Electrical detonators
- Uses an electrical current to heat up the explosive causing it to detonate
- Low power (not a lot of current passing through) devices often use lead styphnate to start detonation sequence as it is highly sensitive
- High power detonators use higher currents
- More controlled
What is an explosive train?
Where one explosive sets off another, which then sets off another
* Deceases in sensitivity
What is a slapper detonator?
- Indirect electrical detonator
- Uses high electrical current to indirectly detonate an explosive
- Electrical current vapourises a thin piece of metal (slapper plate) that is then propelled into the explosive material
- Initiates an explosive shock with a percussive force
- More controlled - easy to set up but hard to accidentally go off
- Can have multiple slappers from different directions to compress
What are blasting caps and what are different types?
A small explosive device used to detonate a more powerful explosive
* Pyrotechnic Fuse Type
* Solid pack electric type
* Match or fusehead electric type
* Exploding bridgewire type
How does a pyrotechnic fuse type blasting cap work?
Light a fuse that burns away and causes the next explosive to start burning (explosive train)
* Crimping point to stop fuse falling out
How does a solid pack electric type blasting cap work?
Wire heats up and detonates primary explosive
* electrical type
How does a match or fusehead electric type blasting cap work?
Wire heats up and pyrotechnic burns which allows for a time delay
* Can have a controlled time delay to have explosives go off at different times
How does a exploading bridgewire type blasting cap work?
Wire heats up rapidly and vapourises the material to cause initiation
What are the three chemical compositions in blasting caps?
- Pyrotechnic ignition mix - metal with a salt (metal makes it very tracible so need to use metals that arent commonly found in the background environment) - Ti/Zr/B + KClO4/KNO3
- Primary explosive - lead styphnate + lead azide + Al (ASA)
- Output explosive - small amount of high explosive - TNT, PETN
