Ch. 3 Chemical Fires and Explosions Flashcards
Define explosion.
Sudden conversion of potential, chemical, or mechanical energy into kinetic energy resulting in the release of gases under pressure
What are the 3 main types of explosions covered in class?
1) Chemical
2) Mechanical
3) Electrical
Fire and explosions frequently accompany each other. With this knowledge, what is the fire investigator tasked with figuring out?
If the fire or the explosion came first
What type of explosions are diffuse-phase and condensed-phase explosions?
Chemical
Define diffuse-phase explosion.
Rapid combustion of fuel (gas, vapor, dust) premixed with air or oxygen and then ignited
Define condensed-phase explosion.
Explosion not dependent on oxygen from the air.
What 3 types of fuels can be found with diffuse-phase explosions?
Gases, vapor, and dust
What is the most common type of fuel involved in a diffuse-phase explosion?
Natural gas
Define deflagration.
Propagation of the combustion zone at a velocity less than the speed of sound in an unreacted medium
How are deflagrations different than detonations?
Deflagrations are slower than the speed of sound while detonations are greater than the speed of sound
Define backdraft.
Deflagration resulting from the sudden introduction of air into a confined space containing oxygen-deficient products of incomplete combustion
Why do condensed-phase explosions not require oxygen from the air (HINT: 2 reasons)?
1) Fuel and oxidizer are mixed together
2) Monomolecular material itself is combustible
How long does it take for a detonation to occur?
Microseconds
How long does it take for a deflagration to occur?
Milliseconds to seconds
Describe the relationship between the speed of an explosion and the force produced by it.
Greater explosion speed = greater explosive force
A propellant is another term for a…
Low explosive
Define low explosive.
Combustible materials that carry both fuel and necessary oxygen for their combustion
What are two examples of low explosives?
Gun powder and flash powder
Will a low explosive produce a deflagration or a detonation?
Deflagration
Define high explosive (HINT: by the speed at which it moves).
Material capable of sustaining a reaction front that moves through material greater than or equal to the speed of sound
Seeing that high explosives are capable of producing a supersonic reaction, do they function by detonation or deflagration?
Detonation
What does IED stand for?
Improvised Explosive Device
Name 2 types of high explosives.
Straight dynamite and TNT
Define mechanical explosion.
Explosion where a container, vessel, or pipe bursts when internal gas or liquid pressures exceed the tensile strength of the container
Do mechanical explosions involve chemical reactions?
No. They’re purely physical changes
What does the acronym BLEVE stand for?
Boiling Liquid Expanding Vapor Explosion
What is the cause of a BLEVE.
Mechanical failure resulting in the sudden release of contents
Do the contents of a BLEVE have to be flammable to explode?
No
The contents of a BLEVE may not have to be flammable, but they are well above their… (HINT: chemical property).
Boiling point
Define electrical explosion.
Passage of high currents through air, insulating oil, or undersized conductors that cause very rapid heating and, in turn, an explosion
