Unit 12 explosion Dynamics

Question 1

For fire and explosion investigations, an explosion
is the sudden conversion of potential energy
(chemical or mechanical) into kinetic energy with
the production and release of gas(es) under
pressure. These gases then do mechanical work,
such as defeating their confining vessel or moving,
changing, or shattering nearby materials.

Answer 1

Explosion

Question 2

Explosion Pentagon

Answer 2

Fuel
Oxidant
Ignition Source (heat)
Confinement
Mixture

Question 3

– A chemical reaction given by an explosive
substance, which produces a shock wave.
– High temperature and pressure gradients are
generated in the wave front, so that the
chemical reaction is initiated instantaneously.

Answer 3

Detonation

Question 4

– The decomposition (burning) of a substance at
a rate below the speed of sound (explosives
powders burn particle to particle).

Answer 4

Deflagration

Question 5

• Two factors that determine your survival

when a device detonates:

Answer 5

– Distance.
– How far you are from the device.
– Separation.
– What is between you and the device.

Question 6

•   The sudden and violent escape of gases 
from a central point accompanied by 
high temperatures violent shock and a 
loud noise.
• What are the three general types:

Answer 6

Nuclear

Mechanical

Chemical

Question 7

Nuclear Explosion

High pressure created by enormous quantities
of heat produced by:

Answer 7

Fission
— the splitting of the nuclei of 
atoms.
•
Fusion
— the joining of 
the nuclei of atoms.

Question 8

•   Explosions caused when a high-pressure 
gas produces a purely physical reaction.
•   No change in the basic 
chemical nature of the substance.
•   Steam boiler or water 
heater.

Answer 8

Mechanical Explosion

Question 9

• The rapid conversion of a substance, solid
or liquid, into a gas.
• Generation of high pressure gas is the
result of exothermic (formed with heat)
reactions wherein the fundamental chemical
nature of the fuel is changed.

Answer 9

Chemical Explosion

Question 10

What are the four basic effects of an explosion:

Answer 10

• Blast pressure.
• Incendiary/Thermal.
• Fragmentation.
• Shrapnel.

Question 11

– Portion of the blast pressure front in which the
expanding gases are moving
away from the point of origin.

Answer 11

Positive Pressure

Question 12

– When the positive pressure phase dissipates, air
rushes back to the seat of explosion to equilibrate
the low air pressure condition.

– Can cause secondary damage and move physical
evidence toward the blast seat. Negative pressure
lasts three times longer than the positive pressure.

Answer 12

Negative Pressure

Question 13

Usually seen as the bright flash or fireball at
the instant of detonation, and is measured in
fractions of a second.

Answer 13

INCENDIARY OR THERMAL

EFFECTS

Question 14

Occurs when the force of the explosion breaks
material, that was part of the casing or device into
small pieces, and propels them in the direction of the
blast pressure wave.

Answer 14

Fragmentation

Question 15

Objects such as nails, ball bearings, glass, etc., that are added to the casing of an explosive device to enhance its ability to cause damage or injury.

Propelled at high velocities.

Anti-personnel effect.

The distance fragments or shrapnel can travel outward
depends on their initial direction, weight and aerodynamic characteristics.

Answer 15

Shrapnel

Question 16

• Walls bulged out or laid down virtually
intact.
• Roofs may be lifted slightly, appearing to
be in their original position.
• Windows may be dislodged with or
without broken glass.
• Debris is generally large and is moved
short distances.

Answer 16

Low Order explosion

Question 17

• Shattering of structure, producing small
debris pieces.
• Walls, roofs and structural members are
typically splintered or shattered with
complete destruction of the building.
• Debris is a considerable distance from
the blast event.

Answer 17

High order explosion Damage

Question 18

STRUCTURAL FAILURE
Myth:
Natural Gas explosions cause damage to 
the upper portion of the wall, and propane 
explosions blow out lower portions of the wall.
•
Fact:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 18

Fact

During a fuel/air explosion, the structure
will fail at its weak point.

• The type of gas (heavier or lighter than air) will
not directly impact the height of the failure.

Question 19

• Rupture of a closed container, cylinder,
tank, or similar vessel resulting in the
release of pressurized gas or vapor.

Not a chemical reaction.

Answer 19

Mechanical Explosion

Question 20

Form of mechanical explosion most often
encountered by fire investigators involving vessels
that contain liquids under pressure at temperatures
above their atmospheric boiling points.

Answer 20

BLEVE

Question 21

BLEVE

Answer 21

BOILING LIQUID EXPANDING

VAPOR EXPLOSION

Question 22

The result of overpressure created by an
exothermic reaction wherein the fundamental
and chemical nature of the
fuel is changed.

Answer 22

Chemical Explosion

Question 23

•   Most common of the chemical explosions caused 
by the burning of hydrocarbon fuels.
•   Fuel/Air, backdraft and dust.
•   Overpressures are caused 
by the rapid volume 
production of heated 
combustion products as 
the fuel burns.

Answer 23

combustion Explosion

Question 24

Ignition of Gases (notes)

Answer 24

• Gases require the least amount of energy to ignite
(< 1 megajoule (mJ)).
• Strong static shock is on the order of 1 joule (J) or
1,000 mJ.
• Must be within flammable range (upper explosive
limit (UEL) and lower explosive limit (LEL))
to start the reaction.

Question 25

EXPLOSION INVESTIGATIONS
• Initial assessment. Check for secondary devices.
• Establish perimeter (1.5 times farthest debris
found).
• Document damage; debris field diagram.
• Identify type of explosion, seated or nonseated.
• Identify fuel.
• Establish origin.
• Establish ignition source.

Answer 25

Explosion Investigations

Question 26

When establishing a perimeter of an explosion investigation, what distance should you establish your perimeter?

Answer 26

1.5 times the farthest debris found

Question 27

CSST

CORRUGATED STAINLESS
STEEL TUBING

Answer 27

• Unique threaded couplings.
• Termination plates with coupling.
• Specialized manifolds.
• Separate bonding jumper to electrical system.
• Polyethylene covering (20 mils).

Controversial because it’s thinner than the black steel pipes.

Lightening has caused failure in the tubing.