Explosives

Question 1

Explosion

Answer 1

• the sudden and rapid escape of gases from a confined space accompanied by high temperatures, violent shock and a loud noise

Question 2

What are the types of explosions? (3)

Answer 2

• mechanical
• chemical
• atomic

Question 3

Mechanical Explosion

Answer 3

• the release of high pressure gases as the result of the failure of a containment vessel
  ex) bursting of a boiler

Question 4

Chemical Explosion

Answer 4

• the rapid conversion of solid or liquid explosive compounds into hot, expanding gases

Question 5

Atomic Explosion

Answer 5

• the use of nuclear fission or fusion to produce energy

- caused by breaking apart the nuclei of atoms

Question 6

What is the difference between the “burning of a log and the “detonation” of a stick of dynamite?

Answer 6

• the TIME duration of the combustion process

Question 7

What is Ordinary Combustion?

Answer 7

• slow combustion
• a combustible material (something that can be burned) and supporter of combustion (something that will simulate burning) must be brought together and the temperature raised to the point of ignition

Question 8

What is an Explosion?

Answer 8

• rapid combustion
• a rapid form of ordinary combustion
  ex) internal combustion of automobile engine

Question 9

What is Detonation?

Answer 9

• “instantaneous combustion”

- in reality, it’s just a very fast chain reaction of combustion happening

Question 10

Detonation Velocity

Answer 10

• the speed of an explosive

- this has been measured for most explosives

Question 11

Accidental Explosion

Answer 11

• most common ones involve gas or dust explosions in enclosures
• the violence depends on the shape of the enclosure
  Cubical Build = pressure builds until window or doors blow out
  Elevator shaft shape = explosion can result in devastating damage

Question 12

What are the effects of explosions? (6)

Answer 12

1) primary blast pressure wave
2) earth and water shock
3) structural fires
4) fragmentation effects
5) thermal effects
6) reflection, focusing and shielding

Question 13

Positive Pressure Phase

Answer 13

• when the blast pressure wave is formed at the instant of detonation, the pressures actually compress the surrounding atmosphere (blow out)
• becomes a visible rapidly expanding circle SHOCK FRONT
• Shock Front applies a sudden, hammering blow to any object in its path
• outward compressing and pushing of air forms a partial vacuum
• last only a fraction of a second

Question 14

Negative Pressure Phase

Answer 14

• negative or suction phase
• the partial vacuum causes he reverse movement of the air inward to fill the void
• not as fast or powerful as positive pressure but still very dangerous

Question 15

Earth & Water Shock

Answer 15

• produced when an explosion occurs in earth or water; the shock wave may damage buildings or other structures

Question 16

Structural Fires

Answer 16

• caused by breaking of electrical conduits or rupture of gas mains or fuel oil lines

Question 17

Fragmentation Effects

Answer 17

• encased explosives or explosives with random pieces around it can cause damage and injury by fragmentation as well as by blast

High Explosives = stretched, torn & thinned fragments

Low Explosives = larger fragments without the thinning

Question 18

Thermal Effects

Answer 18

• think of an extreme sun burn
• exposed skin can suffer flash burns
• other than skin exposure, they are most likely to be insignificant unless highly flammable materials are present
• materials in shock wave are exposed to them for only a short time

Question 19

Reflection, Focusing or Shielding of Blast Pressure Waves

Answer 19

• blast pressure waves will bounce off reflective surfaces; this reflection can cause the blast pressure wave be scattered (dissipated) or focused
• the shaping of the explosive charge can also focus the blast pressure waves
• the shaped charge effect depends on the fact that blast pressure waves propagate perpendicular to the surface of the explosive

Question 20

How are chemical explosives classified?

Answer 20

1) by detonation velocity
- low explosives (dv<1,000 m/s)
- high explosives (dv>1,000 m/s)

2) by composition
- chemical explosives undergo combustion; they must contain a fuel and oxidizer
- explosive mixtures (separate fuel and oxidizer)
- explosive compound (fuel and oxidizer in same molecule)

2) sensitivity
- primary explosives = explode easily; can be detonated by shock, passage of electric current, heat
- secondary explosives = TNT/RDX; require a detonation to initiate
- Tertiary Explosives = ammonium nitrate/ fuel oil

explosive compounds may be either high or low explosives; mixtures are low explosives

Question 21

What is a Streak Camera?

What is it used for?

Answer 21

• A streak camera is an instrument for measuring the variation in a pulse of light’s intensity with time
• They are used to measure the pulse duration of some ultrafast laser systems and for applications such as time-resolved spectroscopy and LIDAR

slide 36

Question 22

What is the Rate Stick Method?

Answer 22

slide 38

schematic

Question 23

What is the detonation Velocity of Black Powder?

Answer 23

1312 ft/s

Question 24

What is the detonation Velocity of Dynamite?

Answer 24

9,000 ft/s

Question 25

What is the detonation Velocity of RDX?

Answer 25

27,500 ft/s

Question 26

What are some Explosive Compounds? (4)

Answer 26

• organic nitrates
• nitro compounds
• nitroaromatic compounds
• nitramines

Question 27

Slurry & Water Gel Explosives

Answer 27

• these were introduced as substitutes for dynamite

Question 28

What is a Firing Train?

Answer 28

• convert a low-energy input into an explosion

ex) firing pin–>primer–>propellant

Question 29

How is evidence collected in bombing cases?

Answer 29

• more dangerous than other CS
• expanding spiral search
• grid search
• in both search methods, each area of the scene is searched twice to reduce the probability of a critical piece of evidence being overlooked

Question 30

What are some types of physical evidence in bombing cases?

Answer 30

• items that were near the bomb; objects, explosive vapors on materials, fragments
• bomb components; container, shrapnel, batteries, timing devices, blasting caps, fuses, explosive residues

Question 31

What goes into the examination of non-electric blasting caps?

Answer 31

• note size and shape
• note color of tube and markings
• identify primer
• note colors of leg wire insulation
• identify polymer in leg wire insulation
• note characteristics of plastic plug
• make brand identification

Question 32

What goes into the examination of batteries?

Answer 32

• collect fragments of casing

compare with collection of batteries

Question 33

What goes into the examination of debris?

Answer 33

slide 74

Question 34

What are the types of Smokeless Powder?

Answer 34

1) Single Base (SB)
- nitrocellulose (NC) is the only energetic ingredient
2) Double Base (DB)
- DB powder contains both NC and nitroglycerin
3) Triple Base (TB)
- TB powder contains NC, NG and nitroguanidine (NQ)
- TB is produced for military use (artillery propellant)