What are Explosions?

busyicicleMechanics

Feb 22, 2014 (3 years and 5 months ago)

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What are Explosions?


A sudden conversion of potential energy
(chemical or mechanical) into kinetic
energy with a production and release of
gases under pressure.


Caused
by a chemical reaction
³
either by



Explaining Explosions


Kinetic molecular theory explains the
properties of gases



Combined
Gas Law






Explaining Explosions

If the temperature of the
enclosed gas increases and
volume is held constant,
the
pressure _________

Explaining Explosions


Wave
³




Longitudinal
wave

a pressure
wave



Shrapnel


Low
Explsoives


Tend to react more slowly






Deflagration
³
the resulting combustion reaction


Rapid, intense burning


Pressure waves at less than 340 meters / sec
.



Explosives

Low Explosives


Black powder


Smokeless
gunpowder
(nitrocellulose)


High Explosives


Materials that


Detonates easily


Produces pressure waves to 8500
meters / sec.


Shock wave moves faster than
speed of sound


Detonation
³


DETONATION

VAPOR CLOUD DEFLAGRATION

TIME

OVERPRESSURE

Pressure
vs

Time Characteristics

Detonation


Highly turbulent combustion


Very high flame speeds


Extremely high pressures >10 bars

Explosion Investigation


Primary

High Explosives


Extremely sensitive to heat,
pressure, and movement


Usually too volatile for most
uses



Secondary

High Explosives


Less sensitive


Often used for military and
commercial purposes


TNT
(trinitrotoluene
)


dynamite


PETN
(
pentaerythritol

tetranitrate
) for grenades


RDX
(
cyclotrimethlylenetrinitramine
) this is
often found in moldable C
4

explosives



Examples of Primary High Explosives

C
H
2
O
H
C
H
O
H
C
H
2
O
H
C
H
2
O
N
O
2
C
H
O
N
O
2
C
H
2
O
N
O
2
H
N
O
3
H
2
S
O
4
G
l
y
c
e
r
i
n
e
N
i
t
r
o
g
l
y
c
e
r
i
n
e
H
O
H
2
C
C
C
H
2
O
H
C
H
2
O
H
C
H
2
O
H
H
N
O
3
H
2
S
O
4
O
2
N
O
H
2
C
C
C
H
2
O
N
O
2
C
H
2
O
N
O
2
C
H
2
O
N
O
2
P
e
n
t
a
e
r
y
t
h
r
i
t
o
l
P
e
n
t
a
e
r
y
t
h
r
i
t
o
l
t
e
t
r
a
n
i
t
r
a
t
e
(
P
E
T
N
)
Nitroglycerine


Pure Nitroglycerine is way too “sensitive” to be a useful
explosive. It was the invention of dynamite by Alfred Nobel
that converted nitroglycerine into a useful commercial and
military explosive by mixing nitroglycerine with clay
(diatomaceous earth) and forming the mixture into dynamite
sticks
.



nitroglycerin
-
based
dynamite has all but disappeared from
the industrial explosive market and has been replaced by
ammonium nitrate
-
based
explosives





C
H
2
O
N
O
2
C
H
O
N
O
2
C
H
2
O
N
O
2
1
2

C
O
2
+
1
0

H
2
O
+
6

N
2
+
O
2
D
e
t
o
n
a
t
i
o
n
4
Types of explosives

Amatols

= mixtures of ammonium nitrate and
TNT

ANFO

= mixtures of ammonium nitrate and
fuel oil

Organic Peroxides


A very different and less predictable class
of potentially explosive compounds.

H
3
C
O
O
O
H
H
O
O
O
H
O
O
O
O
O
O
O
O
O
H
O
O
O
H
P
e
r
x
y
a
c
e
t
i
c

A
c
i
d
P
e
r
o
x
y
f
o
r
m
i
c

A
c
i
d
D
i
b
e
n
z
o
y
l
p
e
r
o
x
i
d
e
D
i
e
t
h
y
l
p
e
r
o
x
i
d
e
n
-
o
c
t
y
l
d
i
p
e
r
o
x
y
s
u
c
c
i
n
i
c

a
c
i
d
Types of explosives

Acetone Peroxide


Formed from acid catalyzed reaction
of acetone with hydrogen peroxide.


Extremely
dangerous and
unpredictable in it’s detonation
behavior
.


Has been used by terrorists.


-

easily prepared from common
chemicals which
are not regulated.



-

not detected by bomb
-
sniffing dogs.




Diesel
and Jet fuel tanks have a higher risk of explosion
than automobile fuel tanks
.


TWA Flight 800 exploded in mid air in 1996, probably due
to a vapor phase fuel tank explosion.

Types of explosives



“The July 17, 1996, crash of TWA flight 800, a Boeing 747
airplane, was blamed on a fuel
-
air explosion within the center wing
tank, with the ignition source still unidentified. As a consequence of the
accident, the Federal Aviation Administration (FAA) is evaluating
improved safety requirements for the fuel tanks on commercial aircraft.
One technique, recommended by the National Transportation Safety
Board (NTSB), is to maintain sufficient fuel in the center wing tanks of
transport aircraft to limit the liquid fuel temperature rise and
evaporation, thus keeping the vapor fuel/air ratio below the explosive
limit. Initial attempts to determine the benefit of additional fuel in the
center tank were frustrated by the lack of an acceptable method for
determining the explosive hazard in the tank under varying conditions.”




-

FAA final report, TWA Flight 800 crash investigation.




The
result of a vessel failure in a fire and release of a
pressurized liquid rapidly into the fire


A pressure wave, a fire ball, vessel fragments and burning
liquid droplets are usually the result

B

L

E

V

O

I

L

I

N

G

I

Q

U

I

D

X

P

A

N

D

I

N

G

X

P

L

O

S

I

O

N

S

E

A

P

O

R

FUEL

SOURCE

Types of explosives


An overpressure caused when a gas
cloud detonates or deflagrates in
open air rather than simply burns.

V

C

E

U

N

C

O

N

F

I

N

E

D

A

P

O

R

L

O

U

D

X

P

L

O

S

I

O

N

S

Types of explosives


Cloud will spread from too rich,
through flammable range to too lean.


Edges start to burn through
deflagration (steady state
combustion). Cloud will disperse
through natural convection.


Flame velocity will increase with
containment and turbulence.


If velocity is high enough cloud will
detonate. If cloud is small enough
with little confinement it cannot
explode.




113

257

467


756

1078


1513

1

2

5

10

15

20

30

35

50

65

Peak

Overpressure

psi

Equivalent

Wind Velocity

km
/
h



Knock personnel down


Rupture eardrums


Damage lungs



Threshold fatalities

50% fatalities

99% fatalities

Effects

Impact of Explosions on People

Explosion Impacts

0.5
-
to
-
1

1
-
to
-
2





2
-
to
-
3

3
-
to
-
4



5

7

7
-
8

Peak

Overpressure

psi



Glass windows break

Common siding types fail:


-

corrugated asbestos shatters


-

corrugated steel panel joints fail


-

wood siding blows in

Unreinforced concrete, cinder block walls fail

Self
-
framed steel panel buildings collapse

Oil storage tanks rupture

Utility poles snap

Loaded rail cars overturn

Unreinforced brick walls fail

Typical Damage

Impact of Explosions on Facilities

Explosion Impacts


Origin and Cause Analysis

Collection and analysis

Categorizations of Explosion Causes:


Accidental, unintentional and explainable


Undetermined, cause unknown or unable to be identified


Incendiary, intentional act for profit or revenge


Terrorism



One approach for screening objects for the presence of explosive
residues in the field or laboratory is the ion mobility spectrometer
(IMS).



All materials collected for the examination by the laboratory must be
placed in sealed air
-
tight containers and labeled with all pertinent
information.



Debris and articles collected from different areas are to be packaged in
separate air
-
tight containers.



It has been demonstrated that some explosives can diffuse through
plastic and contaminate nearby containers.


Collection and analysis

Back at the Lab


Typically, in the laboratory, debris collected at explosion scenes will be
examined microscopically for unconsumed explosive particles
.



Recovered debris may also be thoroughly rinsed with organic solvents
and analyzed by testing procedures that include color spot tests, thin
-
layer chromatography, high
-
performance liquid chromatography, and
gas chromatography
-
mass spectrometry
.



Confirmatory identification tests may be performed on unexploded
materials by either infrared spectrophotometry or X
-
ray diffraction.