chapter 23 - fire and explosions

fire

a combustion reaction with a fuel, oxygen, and sufficient temperature

incendiary fire

arson; deliberately set

where are arson fires more likely?

50% occur outdoors

poor neighborhoods

where are arsons less likely?

20% in vehicles

rich neighborhoods

how is fire investigated?

done by fire investigator

search for point(s) of origin

electricity often turned off or destroyed by fire

structure may be weakened, unsound, or collapsed

hazardous chemicals or fumes from burned materials often present

point of origin might be burned under upper stories

types of fires

natural, accidental, deliberate

point of origin of a fire/accelerants

crucial piece of evidence in determining type of fire

often most intense location of burning

usually at low point in the building - may be buried under tons of rubble

smoke or damage often shows a “V” pattern

how is fire evidence analyzed?

labs examine debris to determine if an accelerant may be present

isolates and identifies accelerants

this may support the fire scene investigator in determination of arson

deflagration

oxygen is physically mixed with the fuel in a way to lower the heat necessary to make it explode

called low explosives: more energetic than fires, less energetic than high explosives

detonation

instantaneous explosives, high explosives: escaping gases travel higher than the speed of sound, oxygen is incorporated into the fuel molecules

initiating explosives

sensitive to detonation, nitroglycerine

non-initiating explosives

require a booster charge to detonate, plastique explosives (dynamite), popular in demolitions (where debris scattering is kept at a minimum)

accelerant

a fuel that is used to start a fire that wouldn’t start on its own or speed up a fire

black powder

a low explosive made from potassium nitrate, sulfur, and carbon

bomb seat

the point of origin of a bombing

combustion

a type of chemical reaction whereby a fuel reacts with oxygen to release energy

dynamite

an explosive containing nitroglycerine that is impregnated in paper and other absorbent materials

exothermic

a chemical reaction that gives off heat

fire trail

when an accelerant is poured on a floor from room to room and then it is ignited

griess test

a chemical test used in the analysis of explosive. gives a positive reaction to all substances that contain nitrate or nitrite

headspace

the airspace above a closed container that contains debris from a fire

low explosive

explosions that produce escaping gases of velocities less than the speed of sound

point of origin

the location where a fire started

spalling

blistering of concrete by exposure to extreme heat