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Alright, I've missed the football completely for this, so here goes and I haven't had
a beer yet. I think all police should be aware of the information below.
Hi Johnsy
Since you are a policeman (or have been a policeman), Let me explain why in
my opinion, shooting criminal perpetrators with a taser is more likely to result in
death than incapacitating them with a bullet to the leg. I wouldn't submit this to
the institution of engineers or the AMA just yet, but it should serve as an adequate
lay explanation. This is not like the "law" in the way a lawyer would understand.
The laws of physics don't change, and they simply are what they are.
How to electrocute somebody
There is long established empirical evidence that 100 - 200mA through the heart
causes electrocution resulting in death. This has been confirmed by measurement
over more than the last 100 years. The human body is a fantastic conductor, current
flows via electrolytes in the blood and fluids (as opposed to free valence electrons
in a traditional conductor like copper). The only relevant resistance is the skin contact
resistance, which is a function of moisture (wet skin is a good conductor, dry skin is a poor
conductor). The level of humidity is an important factor in many electrocutions.
What does the above mean? It means that if the taser darts breach the skin and place the
electrode in contract with the flesh (as distinct from the skin), the resistance is now very low.
So at 5000V you will have very low resistance at very high currents which generally don't
cause electrocution (which is what tasers rely upon), but if sustained for to long
will cause the burning of internal organs.
The function of a taser (from an engineering perspective) is to cause convulsions. The
convulsions caused by a taser are caused by the electrical current disrupting the nervous
system which controls muscular action. Electrocution arises when the electrical current
disrupts the nervous system controlling the heartbeat. It is a small step from disrupting
the nervous system to cause convulsions to disrupting a heart beat.
How electrocution is possible at 5000V
Electricity flow in the human body is best not understood as a single current
flow of so many amps, but as a three dimensionally distributed current flow
of varying current densities. The totality of which will add to the single amount.
Additionally the resistivity of the human body (resistivity is what limits current
flow) is not homogenous and some paths will have higher resistance than other
paths. In all circumstances the longer the path the greater the resistivity,
and the lower the current density. It is thus conceivable that what seems
to amount to a high total current flow will produce low current densities in remote
body parts and particularly if the current path is a high resistivity path.
For example, a high current flow from one leg to the other will result in high current
densities through the groin, and progressively lower and lower current densities
higher up the body. It is the current density through the heart that matters,
not the total current flow.
This means that depending upon where the contact is made the current distribution
may be such that even though the total current may be several amps, in fringe locations
it may still be as little as 100-200mA.
The best way to understand this, is to think in two dimensions and extrapolate to three.
If you take a copper sheet (a traditional conductor), and pass a current through it like so:
|--------------------|
| *( +9V) *(-9V) |
|--------------------|
The current will flow via the path of least resistance, but it flows in two dimensions
, ie. it takes multiple paths of least resistance. What is significant here, is that the
current diminishes the further away you get from most direct path (linear point to
point). This is roughly an inverse square law. What does he mean? You can put
5000V across your leg and still have 200mA go through your heart.
What else may occur if you are subjected to 5000V
Whilst the intention of a taser is to deliver a high current payload which will not
electrocute, the high current payload does have the potential to cause burning of
internal organs.
E (energy) = IxIxRxt (E is energy, I is current, R is resistance and t is time).
To summarise what that means, the burning potential is proportional to the square of the
current and the duration of the current, which is why taser currents must be limited to very
short duration. (In public power systems (eg an 11kV transformer) when instances of
high voltage electrical contact occurs usually internal organs aren't burnt (although sometimes
they do) because the protection systems interrupt within a ~ 150ms. In an ideal
world this would all occur in a few milliseconds, but the mechanical switching used
just simply takes longer.)
A taser is akin to an electronic interruptor (presumably a capacitor being
discharged in no more than a burst of few milii seconds (I would hope). However, if multiple
applications are applied, the heating affect is cumulative and it is possible that perhaps
internal burning will occur.
I don't know how a taser works, but I would suggest that on a single fire, it is delivering
successive bursts. The heating effect of these bursts is cumulative, and if there is too
many of them then internal burning is possible. This is what sets it apart from an
electric fence. A cow isn't silly enough to come back for another go, but the poor
bastard on the ground has no means to get away.
Death by Electric shock.
A taser delivers you a serious electric shock (even if all goes well). The moment you
receive a significant electric shock (be it from a 240V outlet, a 5000V taser or an 11kV
transformer) you should go to hospital for a heart check immediately. I assume
this is standard police procedure. These kinds of shocks have the potential to cause
arrhythmias, even in a healthy person.
The physics behind killing someone with a taser by dropping them on concrette
Tasering people of different heights is not equivalent when you are dropping them
on concrete. You need to look at a persons centre of gravity. The centre of gravity
of a tall person is higher than the centre of gravity of a average height person. This
means that when they hit the ground they have greater energy to dissipate and
higher velocity of impact. potential energy is converted to kinetic energy which
is disappaited on impact.
1/2m(v)(v) = mgh.
The above equation means that energy dissipation is proportional to the height and
mass of the victim. This means that dropping a person of the same height has more
energy to dissipate, than the person of lower mass.
taking a volunteer policeman and hitting them with 5000V
In my view it is both unethical and disingenuous of the police to publiclty promote
the safety of tasering using fit healthy volunteers in controlled idealised circumstances
backed with a raft of risk mitigation backup. In the real world, the physical condition
of the victim is unknown, and given the mobility of the victim, the accuracy of the
target taser is highly unreliable. As a consequence there is a real risk that tasering
will result in fatality. The police promotion of taser use is disingenuous.
The safety guide lines of Tasers are wrong.
Conventional wisdom would suggest that it is safer to taser away from
the heart and this is in the taser user guide lines (please correct me if I
am wrong). Tasering directly across the heart will deliver a current well
above the 100-200mA, tasering other parts of the body could well result in
lethal current densities across the heart. having said this, the safest way to
taser someone is from the shin to the thigh (lower leg).
CONCLUSION
No matter how you look at it, tasering involves significant risk of death. The
use of a fire arm at least has a deterrent effect that a taser may not have,
because people don't understand it (or they are on drugs etc). I would suggesst
being shot in the leg is a safer means of incapacitating the perpetrator than
shooting them with a taser.
Take a look at the aboriginal bloke the WA police tasered 13 times whilst on the ground.
The
So what about the bit about tasers, police brutality and Tony Abbott? Are his lawyers doing anything about that?
Spot on.
