Explosion
- the sudden and rapid escape of gases from a confined space accompanied by high temperatures, violent shock and a loud noise
What are the types of explosions? (3)
- mechanical
- chemical
- atomic
Mechanical Explosion
- the release of high pressure gases as the result of the failure of a containment vessel
ex) bursting of a boiler
Chemical Explosion
- the rapid conversion of solid or liquid explosive compounds into hot, expanding gases
Atomic Explosion
- the use of nuclear fission or fusion to produce energy
- caused by breaking apart the nuclei of atoms
What is the difference between the “burning of a log and the “detonation” of a stick of dynamite?
- the TIME duration of the combustion process
What is Ordinary Combustion?
- 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
What is an Explosion?
- rapid combustion
- a rapid form of ordinary combustion
ex) internal combustion of automobile engine
What is Detonation?
- “instantaneous combustion”
- in reality, it’s just a very fast chain reaction of combustion happening
Detonation Velocity
- the speed of an explosive
- this has been measured for most explosives
Accidental Explosion
- 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
What are the effects of explosions? (6)
1) primary blast pressure wave
2) earth and water shock
3) structural fires
4) fragmentation effects
5) thermal effects
6) reflection, focusing and shielding
Positive Pressure Phase
- 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
Negative Pressure Phase
- 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
Earth & Water Shock
- produced when an explosion occurs in earth or water; the shock wave may damage buildings or other structures
Structural Fires
- caused by breaking of electrical conduits or rupture of gas mains or fuel oil lines
Fragmentation Effects
- 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
Thermal Effects
- 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
Reflection, Focusing or Shielding of Blast Pressure Waves
- 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
How are chemical explosives classified?
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
What is a Streak Camera?
What is it used for?
- 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
What is the Rate Stick Method?
slide 38
schematic
What is the detonation Velocity of Black Powder?
1312 ft/s
What is the detonation Velocity of Dynamite?
9,000 ft/s
