Explosives and explosive residue

Question 1

What is an explosion?

Answer 1

Sudden increase in volume and release of energy in a violent manner, usually with the generation of high temperatures and the release of gases. Instantaneous release of energy from chemical residue

Question 2

How are explosions categorised?

Answer 2

Based on velocity of pressure waves produced giving deflagrations and detonations

Question 3

What is a deflagrations?

Answer 3

Waves travel at speed less than speed of sound (subsonic). Confined can progress to explosion

Question 4

What are detonations?

Answer 4

Wave travels at speed faster than sound (supersonic). High pressures and more destructive

Question 5

What is the speed for propagation?

Answer 5

Range of 1500-9000ms-1

Question 6

What are the 3 primary effects of explosion?

Answer 6

Blast pressure (causes significant initial damage with damage decreasing with distance as wave loses power), fragmentation and thermal or heat effects

Question 7

What is negative pressure?

Answer 7

As initial wave dissipates, compressed air and gases rush back towards the bomb seat. Blast goes one way but gas moves in opposite direction

Question 8

What is the principle of explosion?

Answer 8

Combustion requires fuel and oxidant. Atmospheric oxygen can supply at fast rate enough for reaction. This is why use molecules with O2

Question 9

What is Oxygen balance?

Answer 9

Mass of oxygen release or consumed/ mass of explosive. When OB is +ve, explosive supplied required oxygen. When OB is -ve requires O2 from atmosphere.

Question 10

What are the 3 types of explosives?

Answer 10

Low explosives, High explosives (primary and secondary) and Improvised explosives

Question 11

What are low explosives?

Answer 11

Explode with velocity of explosion <1000, slow burning rate, throwing/propelling action. Eg propellants, black powder and pyrotechnics mixtures. Dangerous when confined. Sample fuel and oxidisers are potassium chlorate or perchlorate and sugar. Will only occur between UEL and LEL. Significant structural damage can occur

Question 12

What are high explosives?

Answer 12

Explode with velocity of detonation > 1000ms-1. Detonate almost instantaneously, smashing/shattering effect. Eg military explosives (TNT, PETN, RDX), commercial/ industrial explosives (dynamite, emulsions and slurries)

Question 13

What are primary explosives?

Answer 13

Ultrasensitive to heat, shock or friction, will detonate violently rather than burn, used as ‘primers to detonate other explosives. Major ingredient in blasting caps (detonators) and ammunition primers include lead styphnate, tetrazene

Question 14

What are secondary explosives?

Answer 14

Insensitive to heat, shock or friction, will tend to burn if ignited. Generally requires a primary explosive before it will detonate (very safe). Majority of commercial and military blasts (TNT, PETN, RDX)

Question 15

What are improvised explosives?

Answer 15

Criminal/terrorist use, may be high or low explosives, numerous formulations. Typically, fuel/oxidisder mixtures eg ANFO, AN + sugar or explosive compounds eg toluene or urea nitrate

Question 16

What is black powder made of and its ratio?

Answer 16

Potassium nitrate (oxidiser), charcoal (fuel) and sulphur (fuel ) at 75:15:10

Question 17

What is smokeless powder?

Answer 17

Plasticised nitrocellulose as principle component. Burn vigorously, used for photographic film, nail polish and lacquer. Have single base propellent (only nitrocellulose as energy source), double base propellent (Nitrocellulose and nitroglycerine) and triple base (nitrocellulose, nitroglycerine and nitroguanidine)

Question 18

What are the components of explosives?

Answer 18

Explosive train called initiation sequence or firing train. Progresses from low levels of energy to initiate final or main charge. Have low or high explosive train

Question 19

What is a low explosive train?

Answer 19

Simple as a firearm cartridge including primer and propellant charge

Question 20

What is a high explosive train?

Answer 20

Complex, either 2 step (detonator and cartridge explosive) or 3 steps (detonator, booster of secondary explosive and main charge of secondary explosive)