Fires And Explosions

Question 1

What are 4 techniques used to analyse explosives?

Answer 1

1. TLC
2. HPLC
3. Capillary electrophoresis
4. Infrared spectrophotometery

Question 2

Explain low and high explosives

Answer 2

LOW - oxygen and fuel physically mixed giving slow detonation = effect is push rather than shatter

HIGH - requires severe shock for detonation = used of initiating explosives

Question 3

Define the terms ‘blast pressure’, ‘fragmentation’ and ‘thermal’ effect

Answer 3

BLAST PRESSURE - A) | B) / C) \ D) |

FRAGMENTATION EFFECTS

1. Bomb casing shatters and pieces propelled away
2. Shrapnel wrapped around bomb being propelled
3. Bomb blast may shatter other objects

THERMAL EFFECTS

• upon detonation = great flash
  - > high explosives = quick and hot
  - > low explosives = long and cooler

Question 4

Define the terms ‘high’ and ‘low’ explosives

Answer 4

HIGH - velocity of explosion is powerful and combustion is instantaneous

LOW - velocity of explosion isn’t powerful

Question 5

Describe the 2 absorption methods for collecting accelerant residue

Answer 5

PASSIVE ABSORPTION - charcoal in container to absorb quantities of hydrocarbons from accelerant present

ACTIVE ABSORPTION - pumping air through charcoal tubes causing accelerant to evaporate and pass through tube to be collected in a vacuum

Question 6

Why are airtight containers used to collect evidence?

Answer 6

• accelerants are highly volatile = readily evaporate

- evaporation removes evidence = tampering with quantity and quality

Question 7

What are 4 indications of a fire being arson?

Answer 7

1. Presence of accelerant
2. Eliminating natural/accidental causes
3. Fire trails
4. Multiple points of origin

Question 8

What are 4 ways to locate the point of origin of a fire?

Answer 8

1. Low burning
   
   • generally start at low point = burn upwards
   • arson fires start high = easy exit for offender
2. V patterns
   
   • near wall or corner = smoke damage in V shape
3. Wood charring
   - origin has greater charring depth
4. Soot and smoke stains
   - soot first deposited in surface and then burnt = point of origin

Question 9

What are the 3 types of fires?

Answer 9

1. Natural
2. Accidental
3. Deliberate

Question 10

Define the terms ‘flash’ and ‘flame’ point

Answer 10

FLASH - lowest temp that allows a liquid to produce a flammable vapour

FLAME - highest temp that allows combustion to occur

Question 11

Describe the conditions needed for a fire to occur

Answer 11

1. Oxygen
2. Heat
3. Fuel
4. Chain reaction