Unit 12 explosion Dynamics Flashcards
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.
Explosion
Explosion Pentagon
Fuel Oxidant Ignition Source (heat) Confinement Mixture
– 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.
Detonation
– The decomposition (burning) of a substance at
a rate below the speed of sound (explosives
powders burn particle to particle).
Deflagration
• Two factors that determine your survival
when a device detonates:
– Distance.
– How far you are from the device.
– Separation.
– What is between you and the device.
• 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:
Nuclear
Mechanical
Chemical
Nuclear Explosion
High pressure created by enormous quantities
of heat produced by:
Fission — the splitting of the nuclei of atoms. • Fusion — the joining of the nuclei of atoms.
• 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.
Mechanical Explosion
• 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.
Chemical Explosion
What are the four basic effects of an explosion:
- Blast pressure.
- Incendiary/Thermal.
- Fragmentation.
- Shrapnel.
– Portion of the blast pressure front in which the
expanding gases are moving
away from the point of origin.
Positive Pressure
– 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.
Negative Pressure
Usually seen as the bright flash or fireball at
the instant of detonation, and is measured in
fractions of a second.
INCENDIARY OR THERMAL
EFFECTS
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.
Fragmentation
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.
Shrapnel
• 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.
Low Order explosion
• 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.
High order explosion Damage
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: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
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.
• Rupture of a closed container, cylinder,
tank, or similar vessel resulting in the
release of pressurized gas or vapor.
Not a chemical reaction.
Mechanical Explosion
Form of mechanical explosion most often
encountered by fire investigators involving vessels
that contain liquids under pressure at temperatures
above their atmospheric boiling points.
BLEVE
BLEVE
BOILING LIQUID EXPANDING
VAPOR EXPLOSION
The result of overpressure created by an
exothermic reaction wherein the fundamental
and chemical nature of the
fuel is changed.
Chemical Explosion
• 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.
combustion Explosion
Ignition of Gases (notes)
• 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.
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.
Explosion Investigations
When establishing a perimeter of an explosion investigation, what distance should you establish your perimeter?
1.5 times the farthest debris found
CSST
CORRUGATED STAINLESS
STEEL TUBING
- 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.
