An Introduction to TASER®
Electronic Control Devices,
History, Electricity, Electrical Stimulation,
Electrical Measurements, and the Human Body
TABLE OF CONTENTS
INTRODUCTION .................................................................................................. 1 Early Medical Considerations of Electricity ........................................................ 1 WHAT IS ELECTRICITY? ..................................................................................... 3 Hoover Dam Water Analogy .............................................................................. 4 Water Hose Analogy ......................................................................................... 4 Joule (J) – Water Analogy ................................................................................. 5 BASIC ELECTRICAL PRINCIPLES (HIGH SCHOOL PHYSICS 101) .................. 6 Power Supply Limitation .................................................................................... 6 50 kilovolt (kV) from A Battery of Small Cells? .................................................. 6 WHY TASER DEVICES ARE HIGH VOLTAGE .................................................... 7 50,000 V DO NOT ENTER THE BODY ................................................................ 7 IT’S NOT THE VOLTS, IT’S THE DELIVERD CHARGE THAT MATTER THE
MOST ................................................................................................................... 8 TASER CURRENT (AMPERES) DOES NOT LAST LONG ENOUGH TO
FORESEEABLY AFFECT THE HUMAN HEART ............................................... 10 Limited by the Very Limited Battery Power Supply .......................................... 11 Power Limited by Wire Conductors ................................................................. 11 Power Limited by Delivery ............................................................................... 11 In Summary ..................................................................................................... 13 Average Current vs. Root Mean Square (RMS): ............................................. 13 Average Current .............................................................................................. 13 For TASER ECDs RMS Calculations Do Not Provide an Accurate Picture ..... 13 Average Current Relevant to TASER Devices ................................................ 14 2002: TASER Tried Using RMS Calculations (Learning from Experience) ..... 14 BASIC TASER DEVICE OPERATING PRINCIPLES.......................................... 15 Telephone Network Communication Analogy ................................................. 17 Effects of Repeated Pulses on Muscle Tension .............................................. 18 HISTORY OF TASER DEVICE TECHNOLOGIES ............................................. 19 1967 – NASA Scientist Jack Cover’s TASER TF-76 ....................................... 19 Tasertron Emerged ......................................................................................... 19 1980s: Studies and Risk Utility Comparisons .................................................. 19 Early 1990s: The Need for Non-Firearm Self-Defense .................................... 19 ICER Corporation Formed ............................................................................... 20 TASER 34000 – 2nd Generation TASER Device ............................................. 20 1994: TASER 34000 Limited to Non-Law Enforcement .................................. 20 Nov. 1995: The Czech Experience: Original TASER Devices Did Not Get the
Job Done! ........................................................................................................ 21 1996: ADVANCED TASER M26 Is Born ......................................................... 21 Stratbucker Testing ......................................................................................... 21 TASER M26 Developed .................................................................................. 22 TASER M26 Emerges – 3rd Generation TASER Device ................................. 22 Medical and Scientific Research ..................................................................... 22 Late 1999: ADVANCED TASER M26.............................................................. 23 May 2003 – TASER X26 Debuted – 4th Generation TASER Device ............... 23 Rev: E
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2007 – TASER eXtended Range Electronic Projectile (XREP™) – 5th
Generation TASER Device .............................................................................. 23 TASER C2™ ECD........................................................................................... 23 BASIC TASER DEVICE OPERATIONS ............................................................. 24 Transformers: Analogy: An Electrical Lever .................................................... 24 THE TASER DEVICE CIRCUIT: AN ILLUSTRATIVE LOOK .............................. 25 Basics of Nerve and Muscle Stimulation ......................................................... 26 The Neuromuscular Junction .......................................................................... 27 Tetanus ........................................................................................................... 27 How the TASER Device Does What It Does to the Body ................................ 28 TASER Device Outputs and Comparisons ...................................................... 29 TASER Risk Benefits ...................................................................................... 33 DEGREE OF CERTAINTY ................................................................................. 33 Rev: E
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TABLE OF FIGURES
Figure 1 Electrotherapy 1785. From Adams (1785). ............................................. 1 Figure 2 Galvani (1790) From Beard & Rockwell 1878. ........................................ 2 Figure 3 Let-go testing. From Dalziel, 1972. ......................................................... 2 Figure 4 Electricity is the Flow of Electrons through a Conductor ......................... 5 Figure 5 Mother and Daughter Experience up to 20 Million V from a Van de Graff
Generator .............................................................................................................. 8 Figure 6 Common U.S. Wall Outlet and TASER ECD Waterfall Analogy
Comparison .......................................................................................................... 9 Figure 7 Current Comparison ............................................................................. 10 Figure 8 Maximum Power Battery of (8 AA) Alkaline Cells ................................. 12 Figure 9 M26 Battery: Alkaline vs. NiMH Cells 10/16/06..................................... 13 Figure 10 Neurons. Fig. 3.1 of Reilly, 1998. ........................................................ 15 Figure 11 Sensory Receptors. Fig. 3.16 of Reilly (1998). ................................... 16 Figure 12 TASER Devices Stimulate the Motor and Peripheral Nervous Systems
with Pulses Similar to Those Used by Nerves to Communicate ......................... 17 Figure 13 Fig. 3.22 from Reilly, 1998. ................................................................. 18 Figure 14 Understanding Transformers Analogy ................................................ 24 Figure 15 An Illustrative Representation of the TASER M26 Circuit ................... 25 Figure 16 Air Force Research Lab Tests Show TASER M26 Muscle Contractions
at 40% or less of Maximum Contraction Force ................................................... 29 Figure 17 Comparison of Current Output of AIR TASER 34000 and TASER M26
............................................................................................................................ 30 Figure 18 Comparison of Current Output of ADVANCED TASER M26 and
TASER X26 ........................................................................................................ 32 Figure 19 Examples of TASER Risk Benefits ..................................................... 33 TABLE OF TABLES
Table 1 Electricity/Water Analogy ......................................................................... 5 Rev: E
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INTRODUCTION
The purpose of this appendix is to provide a basic partial overview of the
fundamental operating principles and concepts of how TASER1®-brand Electronic
Control Devices (ECDs, or devices) work. To many people, electricity sounds
dangerous. Indeed, it can be. However, many people do not realize that life
cannot exist without electricity. We are not talking about life being difficult without
television, cell phones, and electric light bulbs. Literally, the life process cannot
happen without electricity. Without electricity, Earth would be nothing but a
barren rock in the cosmos.
While much of what follows could come right out of high school physics 101 and
biology 101, many of these concepts may be outside the existing knowledge and
understanding of most people who do not study and/or keep abreast of these
areas. Additionally, due to early life experiences many people are electricaphobic
in that they have an unreasonable fear (or phobia) of electricity.
It is important to keep in mind that all electricity is not the same. Just as all “balls”
are not the same – a nerf ball, whiffle ball, beach ball, ping-pong ball, golf ball,
racquet ball, tennis ball, dodge ball, softball, baseball, basketball, soccer ball,
football, medicine ball, bowling ball, and wrecking ball are different – the same is
true for electrical discharge or delivered electrical charge or energy. A lightning
bolt or a high-current power line would be equivalent to a wrecking ball, a bowling
ball to a 110 V AC outlet, and a handheld, battery-powered ECD would be
approximately equivalent to a tennis ball.
Early Medical Considerations of Electricity
Figure 1 Electrotherapy 1785. From Adams (1785).
1
AIR TASER, M26, and X26 are trademarks of TASER International, Inc. TASER® and
ADVANCED TASER® are registered trademarks of TASER International, Inc.
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Figure 2 Galvani (1790) From Beard & Rockwell 1878.
Figure 3 Let-go testing. From Dalziel, 1972.
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WHAT IS ELECTRICITY?
Electricity is the flow of electrons through a conductor (a physical material that
allows an electric current to flow through it). Electrons are the negatively charged
subatomic particles that orbit around the positively charged nucleus of every
atom.
Since a flow of electrons through a conductor, such as a metal wire, cannot
physically be seen, it is helpful to think of the analogy of water flowing through a
pipe, a fire hose, a garden hose, or a drinking straw. This analogy may help to
visualize and understand some of the basic principles of electricity that many
students learn about in high school science classes.
Basically, there are five (5) key elements to characterize electricity: Voltage,
Current, Power, Energy, and Charge.
VOLTAGE2 (measured in “volts” and symbolized by “V”): Also called
electromotive force, voltage is the pressure behind the flow of electrons. As will
be more fully explained later, it is important to note that high voltage in and of
itself is not necessarily dangerous. A strong static electricity shock can be in
excess of 30,000 volts (V) and a Van de Graff generator that many children have
experienced in science classes or museums can generate up to 25,000,000 V.
In the water analogy, voltage would be the pressure measured in pounds per
square inch. Voltage can also be analogized to height – from how high does the
water fall? The higher a waterfall or rain from the sky, the greater the pressure
with which the water hits the ground. Voltage is measured in volts (one volt is the
amount of force required to send one ampere (A) of current through a resistance
of one ohm [Ω]).
CURRENT (measured in “amperes” and symbolized by “A” or “I”): Current,
measured in amperes (A), measures the flow rate, how many electrons flow each
second. The ampere (A) is the International System of Units (SI) base unit of
electric current or amount of electric charge per second.
CHARGE (measured in “coulombs” and symbolized by “C”): Is the total
number of electrons moved over a given period of time. A coulomb (C) is the SI
base unit of electric charge. One coulomb is equal to 6.24150962915265 × 1018,
or approximately 6.24 quintillion, electrons or elementary charges. One C is the
amount of electric charge transported by a current of 1 A in 1 second (s).
2
Voltage, expressed in volts (V), (often also referred to as electric or electrical tension)
is the difference of electrical potential between two points of an electrical or electronic
circuit. Voltage measures the potential energy of an electric field to cause an electric
current in an electrical conductor. Depending on the difference of electrical potential the
voltage may be called extra low voltage, low voltage, high voltage, or extra high voltage.
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The water analogy would be the water flow rate measured in gallons per second.
Current is measured in amperes (A). One ampere (A) is equal to a flow rate of 1
C (approximately 6,240,000,000,000,000,000 electrons) per second. While this is
a very large number, it is approximately equivalent to the number of water
molecules in two (2) drops of water. In the water analogy, charge, measured in
C, would be the total amount of water that has flowed, measured in gallons.
POWER (measured in “watts” and symbolized by “W” or “P”): The watt (W)
is the SI derived unit of power, equal to one joule (J) of energy per second. One
W is a small amount of power. A person climbing a flight of stairs is doing work at
a rate of approximately 200 W. Power is thus the measure of the amount of
energy generated by an electric current in one second. Power is a function of the
voltage and the current [P = V x A].
Hoover Dam Water Analogy
Consider the water analogy that the Hoover Dam generates power from a flow of
water. The amount of power is determined by how much water pushes through
the generator, and how much pressure is behind the water. In fact, in electrical
terms there is a very simple relationship between power, current, and voltage.
Power is measured in watts.
Water Hose Analogy
In the water analogy, power is the rate at which energy is applied. Think of a fire
or garden hose, or a drinking straw, with a certain amount of water being ejected
at a certain amount of pressure. The power you would feel is a function of both
the amount of water and the pressure behind it.
A good analogy is a waterwheel mill. If the current is low (trickling flow) but the
voltage (pressure) is high because the water is falling 100 feet, there will not be
much power. Conversely, if the flow is rapid (high current) but the stream is level
(no potential or voltage or pressure) then the power will also be low. Only when
there is a heavy current and a high potential (large fall in water height) is high
power produced. So, in a water wheel, power = current times pressure (or
height). In an electrical device, power (W) = current (A) times voltage (V). One
horsepower is equal to 746 watts. So, a high performance, 300-horsepower (hp)
car engine produces 223,800 watts.
ENERGY (symbolized by “E”): Energy is the total energy from a given amount
of power applied for a given period of time. The relationship between Energy (E)
and Power (P or watt [W]) is like the relationship between Current (A) and
Charge (C). Current is the flow rate of Charge (C). Power (W) is the Flow Rate of
Energy. Energy is measured in joules (J). The J is the SI unit of electrical,
mechanical, and thermal energy. A J is the unit of electrical energy equal to the
work done when a current of one ampere (A) is passed through a resistance of
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one ohm (Ω) for one second (s). Hence, 1 watt (W) of Power = 1 (J) joule of
Energy per second (s).
One J is a very small amount of energy. One J is approximately the amount of
energy:
•
required to lift a small apple 1 meter (m) straight up;
•
released when that same apple falls 1 m to the ground;
•
the amount of energy, as heat, a quiet person produces every 1/100th of a
second;
•
the energy required to heat one gram (g) of dry, cool air by 1.39 degrees
Celsius; or
•
1/100th of the energy a person can get by drinking a single drop of Pepsi®
soft drink.
Joule (J) – Water Analogy
In the water analogy, think of a joule as a packet of energy. It could be the total
energy from being hit with a garden water hose for twenty minutes, adding up all
the power over that time (this would equate to a constant current delivered over a
period of time). Or, it could be like getting hit with a single discrete pulse, such as
a small water balloon (this would correspond to brief pulses of electric charge –
similar to what a TASER device delivers). One joule is also 0.2388 calorie3 (as a
measurement of heat, or thermal energy, created).
Figure 4 Electricity is the Flow of Electrons through a Conductor
Table 1 Electricity/Water Analogy
UNIT
Voltage (in volts [V])
Current (SI base unit – A)
Charge (SI base unit – C)
“WATER ANALOGY”
Volt (V)
Ampere (A)
Coulomb (C)
Pressure
Water Flow Rate
Total Water Volume
“WATER UNIT”
lbs / in2 or PSI
Gal / Second
Gallons
3
A “calorie” is a very small amount of thermal energy. Often confused with kilocalorie
(1,000 calories), the kilocalorie (kcal), often simply referred to as “calorie,” is the
common measure for the amount of food energy. As an example, one drop of Pepsi soft
drink has 21.14 calories or 0.02114 kcal.
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UNIT
Power (V)
Voltage (V) x Current (A)
Energy (J)
Power (W) x Time (s)
Resistance
ECD Current Pulses
“WATER ANALOGY”
Watt (W)
“WATER UNIT”
Flow Rate x Pressure
Joule (J)
Water Balloon
Ohms (Ω)
PPS
Diameter of Water Hose
Bursts of Water
Flow Rate x Pressure
x Time
Centimeters (cm)
Water Balloon
BASIC ELECTRICAL PRINCIPLES (HIGH SCHOOL PHYSICS 101)
A very important aspect to understand about electricity as used by an ECD is that
in order for the ECD to be effective, the electricity must flow in a complete circuit.
In an ECD, an electric current starts at a battery power source, flows through a
circuit, and must return to the power source. In this respect, electricity seems
different than the flow of water – which simply flows downhill due to gravity or
through a pipe, hose, or straw due to pressure. But eventually it ends up in the
ocean and is recycled through evaporation and rain back into the water supply. In
ECD electricity, the flow must return to the source. In some cases, such as the
TASER device, the source is the energy cells, or multiple cells in a battery (of
cells). In other circuits, such as your home, the source of electricity is the local
power station that generates the power.
Power Supply Limitation
In any given electric circuit, the total power is limited by the power supply. In the
case of the TASER device, the power supply is the very limited power battery of
cells. Hence, the power delivered by the TASER device cannot exceed the power
supplied by the battery of eight AA penlight cells (AA cells are used in the
TASER M26 – the power level is even smaller in the TASER X26™ (X26), with
its two three-volt digital camera-type cells).
50 kilovolt (kV) from A Battery of Small Cells?
A common question often asked is, “How can the TASER device generate up to
50,000 peak arcing volts output from the very limited power of eight AA cells or
two 3 V cells?” The answer is, the TASER device uses transformers and the
principles of physics that define the relationship between power, current, and
voltage to generate the high voltage output from the very minimal power supply
input. As will be explained later, the 50,000 V do not enter (are not delivered into)
a person’s body.
•
4
From an ADVANCED TASER® M26™ (M26) device only 5,000 V peak,
3400 V average over the duration of the pulse, enter the body, or 1.44 V
average (one-second baseline)4.
All numbers are calculated based upon a 400 Ω resistance.
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•
From the TASER X26 only 1,200 V peak, 400 V average over the duration
of the pulse, enter the body, or 0.84 V average (one-second baseline).
To say that 50,000 V is delivered to a person from a handheld battery-powered
TASER ECD is sensationalistic and very misleading.
WHY TASER DEVICES ARE HIGH VOLTAGE
Short Answer: TASER ECDs are high voltage to avoid the necessity of having
to embed TASER probes into a person’s body to deliver the electrical energy. To
be able to jump up to approximately 50 millimeters (mm), or 2 inches, combined
air gap. This allows for minimizing the discharge velocity of the probes from the
TASER cartridge.
A TASER device needs to generate the high voltage to jump the air gap to avoid
the necessity of embedded probes. Consider a garden hose; the higher the water
pressure, the farther the water will eject from the end of the hose. The same
holds true for a drinking straw. Similarly, the TASER device uses high pressure
(high voltage) to eject electrons from the tips of the darts (probes) across a gap
of up to approximately 2 inches of accumulated air and clothing and into a
conductor such as the human body. Because of the high voltage generated, the
darts (probes) from the TASER device do not have to penetrate, or even touch
the skin, to deliver electrical energy. The high voltage allows the TASER device
electrical output to jump through up to 2 inches cumulative of air or clothing to
complete the circuit with the target’s body. Electricity flows easily through metal
wires. However, it cannot flow through the air very easily. It takes about 1,000 V
of “pressure” to cause an electric arc to jump across a roughly 1 millimeter (mm)
air gap. Accordingly, the TASER device must generate a peak of up to 50,000 V
to jump across a 50 mm (roughly 2-inch) air gap.
Without the high peak arcing voltage, the TASER device would need to have
much longer probe-tip needles coupled with far stronger probe propulsion to
ensure penetration through various types of clothing a subject may wear and to
ensure skin penetration and continuous attachment to have any effect. This
would make the TASER device far more intrusive and more likely to penetrate
deeper into the body. In this respect, the usage of high voltage allows TASER to
make the device a safer, less intrusive tool.
50,000 V DO NOT ENTER THE BODY
Even though the M26, ADVANCED TASER M18 and M18L, TASER X26, and
TASER C2™ Personal Protector have a 50,000 peak open circuit voltage to jump
the air gap, none of these TASER devices delivers 50,000 V to a person’s body.
The M26 has an average (one-second baseline) voltage of 1.44 V, with a peak
loaded voltage of 5,000 V, and a 3,400 V average over the duration of the pulse.
The X26 has an average (one-second baseline) voltage of 0.84 V, with a peak
loaded voltage of 1,200 V, and a 400 V average over the duration of the pulse.
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IT’S NOT THE VOLTS, IT’S THE DELIVERD CHARGE THAT MATTER THE
MOST
Many people ask how safe a TASER device can be since it generates a high
(peak open circuit) voltage. In fact, voltage is not generally a key measure of
electrical safety. While voltage indicates the pressure behind a flow of electrons
and how far that electric current will arc through the air, voltage is generally not a
key indicator of safety or effectiveness when it comes to stimulating the human
body. The key indicator for safety and effectiveness is the number of electrons
delivered into the body – i.e. the current (A) over time, or the total electric charge
(C) in very short duration discrete pulses, and not the high open circuit peak
voltage.
Figure 5 Mother and Daughter Experience up to 20 Million V from a Van de Graff Generator
To demonstrate this principle, note the above, a picture of a mother and daughter
happily experiencing millions of volts from a Van de Graff Generator at a science
museum. This Van de Graff generator creates very high voltage, but nearly zero
current. Accordingly, while the static forces associated with the high voltage
cause their hair to stand on end, they feel no sensation or ill effects because
virtually no current flows.
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Wall Outlet
TASER ECD
Med Voltage: 110V
High Voltage: 5,000+ V
Continuous Current
Pulsed Current
High Current
Low Current
Danger: High
Danger: Low
Figure 6 Common U.S. Wall Outlet and TASER ECD Waterfall Analogy Comparison
Another way to look at this is the difference between rainfall and a very large
waterfall (such as Niagara Falls). Although rainfall travels thousands of feet it
does not cause injury, while a very large waterfall travels a much lesser distance
but has much more force, and thus can cause injury/damage. Another example is
a fire hose versus a garden hose, or a common beverage drinking straw.
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TASER CURRENT (AMPERES) DOES NOT LAST LONG ENOUGH TO
FORESEEABLY AFFECT THE HUMAN HEART
Consider static electricity. Everyone has received at least one strong static
electricity shock in their lifetime. The typical current pathway is from a doorknob
through a fingertip and then through the chest and down through the legs to the
floor. The shock can be painful and cause a significant muscle twitch, but it has
never caused a cardiac arrhythmia, much less a death. A search of over a
century of medical, scientific, and electrical literature shows only one case of a
static shock possibly affecting the heart – and that individual claimed he was
cured of atrial fibrillation (a fairly benign chronic arrhythmia) after a static shock.5
The current of a strong static shock would easily kill someone if it was
continuous. But, it typically lasts less than a millionth [.0000001] of a second and
is thus much too short to affect the heart.
Also, there is an international standard that sets out the electrical characteristics
of a “strong static electricity” shock. This standard is necessary for many of the
electrical devices we use today. Meaning, if a cell phone, a pager, a pace maker,
etc. could not withstand a “strong static electricity” shock, then each of those
electrical devices would soon be damaged. Thus, the International
Electrotechnical Commission (IEC) has defined a “strong static electricity” shock
as having electrical characteristics of 15,000 V and 30 A peak. (International
Standard IEC-61000-4-2).
The maximum current output from a wall outlet is approximately 4,000 times
higher current potential than that of a handheld, battery-powered TASER ECD.
Figure 7 Current Comparison
5
Screnock T. “Static Electricity Stops a Recalcitrant Arrhythmia.” Ann Intern Med. 130,
no. 1 (January 5, 1999):78.
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To appreciate TASER technology, one needs to only imagine a similar, very
short shock (actually involving less peak current) but delivered repeatedly 15 to
25 times per second. This can immobilize a violent or resisting subject, but
without significant risk of affecting the heart.
The TASER X26 is programmed to deliver a very short electrical pulse of
approximately 100 microseconds (µs) duration with about 100 microcoulombs
(µC) of charge at 19 pulses per second (PPS) for 5 seconds (s)6. The peak
voltage delivered to the body is about 1,200 volts during the shock. The peak
current of about 3 amperes is far less than that of a strong static electricity shock,
which can be as high as 37.5 amperes.7 The average current from the TASER
X26 is approximately 2 milliamperes (0.002 amperes).
Now, put together and consider as previously discussed: power, voltage, and
current.
Limited by the Very Limited Battery Power Supply
First, the power in a circuit is limited to the power output of a power supply (in the
case of a TASER device, this is the battery of cells). TASER makes a
sophisticated device, but there is no perpetual motion machine; nor is the product
nuclear powered.
Power Limited by Wire Conductors
This power is further limited by the wire conductors between the TASER device
and the target. The TASER device wires are very small, and are not capable of
delivering large currents that would require much larger wires such as automobile
jumper cables or home electrical extension cords.
Power Limited by Delivery
Further, there is a mathematical relationship between power, voltage, and
current:
P (power or watts [W]) = I (current or “A”) * V (voltage)
The next section will discuss how transformers work to convert a given amount of
power into different currents and voltages. But the big picture is simple – for a
fixed amount of power, the HIGHER the voltage, the LOWER the current must be
(not including power loss due to circuit inefficiencies, or failure of any circuit to
perfectly move power without loss due to circuit inefficiencies).
6
This initial 5-second TASER X26/M26 discharge can be interrupted at any time simply
by the X26/M26 operator activating the TASER device’s safety.
7
http://www.web-ee.com/primers/files/ESD_Tutorial.pdf
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For example, if the battery of cells in a TASER device could output a maximum of
50 W (which it cannot), the table below would illustrate the maximum voltage and
current it could generate:
Power
50 W
50 W
50 W
50 W
=
=
=
=
Voltage
5V
50 V
500 V
50,000 V
x
x
x
x
Current
10 A
1A
0.1 A
0.001 A
These numbers are for illustration purposes, but the point is important: With a
fixed power source and limitations such as limiting capacitors, the higher the
voltage, the lower the output current must be! And, again, delivered current, or
energy, is the key measurement for how electricity affects the body.
Actually, a TASER M26 with a battery of eight (8) AA [1.2 V or 1.5 V per cell]
cells has a peak power in watts as seen in this graph:
Figure 8 Maximum Power Battery of (8 AA) Alkaline Cells
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M26 Battery Alkaline Vs NiMH
10/16/2006
18.00
16.00
14.00
Pulse Rate
12.00
10.00
8.00
6.00
4.00
2.00
00
:0
5
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:2
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0.00
-2.00
Elapsed Time (mm:ss)
Duracell Ultra Alkaline
Pulse Rate
Energizer NiMH 1700maH
Pulse Rate
Figure 9 M26 Battery: Alkaline vs. NiMH Cells 10/16/06
In Summary
•
•
Voltage is the pressure that determines how far an electric arc can jump.
Delivered current or energy determines how intensely the human body will
react.
Average Current vs. Root Mean Square (RMS):
Average Current
Average current is the true flow of the amount of charge per second. Average
current is calculated by adding the amount of charge in each pulse, add all of the
pulses per second, and this total provides the electrical charge per second that is
actually delivered.
For TASER ECDs RMS Calculations Do Not Provide an Accurate Picture
RMS current is calculated as an approximation for the current used when
analyzing continuous alternating currents (AC), as opposed to pulsed current
(e.g. the short duration pulses produced by TASER devices). Since an
alternating current switches between positive and negative current flows if an
average was calculated then the total would always average to zero – because
the positive and negative elements cancel each other out. In order to measure
currents in AC systems, engineers frequently use RMS for two reasons.
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1.
RMS eliminates the negative numbers. When a negative number is
squared the number then becomes positive. When calculating RMS
currents
a. first square all the values;
b. then average; and
c. then take the square root of the result.
2.
RMS is very helpful to understand the amount of electrical power being
consumed – power is a function of the square of the current (power =
I2R). As an example, power can measure how much thermal energy or
heat an electric current can generate, or how much light a light bulb
can emit. Also, since electrical utility companies sell electricity based
on power consumed (watt-hours [Wh]), RMS current is proportional to
power and is hence a good measure for electricians and the utility
company when dealing with continuous AC power.
Average Current Relevant to TASER Devices
The average current is more relevant to measuring TASER device outputs and
far more relevant to neural stimulation, rather than heating (or continuous
output), because it looks at the actual amount of electrical charge delivered.
Because of the squaring effects used in RMS, the result is not an actual measure
of the charge delivered. When using RMS with pulsed currents (where there are
high peak currents for very short durations of time with relatively long pauses
between pulses, the RMS calculations artificially significantly overstate the
delivered current because the high peaks are squared before averaging).
2002: TASER Tried Using RMS Calculations (Learning from Experience)
Back in 2002, TASER had tried using RMS to attempt to measure TASER
discharge. This was similar to trying to put a large square peg into a very small
round hole. Because many of the U.S. and international electrical safety
standards are based on alternating currents, and because those standards
include mathematical adjustments for comparing pulsed currents, TASER
fruitlessly attempted to measure the RMS current of the TASER device for
comparison to those electrical safety standards that used RMS currents.
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BASIC TASER DEVICE OPERATING PRINCIPLES
A TASER-brand device is an Electronic Control Device (ECD). Its intended
purpose is to assist with capturing, controlling, and (when necessary) restraining
a person with minimized risk (compared to most similar force tools) of serious
injury. Prior less-lethal weapons function by merely causing pain or destructive
injury. The intention with these other force tools and techniques are that the pain
or the bodily injury will dissuade the subject from continuing an unwanted
behavior and elicit cooperation. However, for a myriad of reasons people who are
focused, under the influence of drugs, or who are pain insensitive may not feel
pain, or may be sufficiently motivated to attack or fight through pain or even
destructive injury (e.g., the Philadelphia barber shop incident). The proprietary
Neuromuscular Incapacitation (NMI) technology in TASER devices does not
solely rely on pain or on intended destructive injury for its incapacitating effect(s).
Rather, the TASER device, in probe deployment mode, is designed to use shortduration, pulsed, low-energy electrical stimuli to interfere with the signals sent by
the command and control systems of the body, at the peripheral and motor
nervous system levels, to impair the subject’s ability to temporarily voluntarily
control his own body.
Figure 10 Neurons. Fig. 3.1 of
Reilly, 1998.
(a) Motor (muscle) and (b)
sensory
neurons
are
responsible for movement and
sensation. They operate by
propagating electrical signals.
The human nervous system is
the command and control
system of the human body. It
has three primary elements:
•
•
•
The central nervous
system
The motor nervous
system
The sensory nervous
system
The central nervous system includes the brain and spinal cord. This is the
command center, where all decision-making processes occur. The central
nervous system can be thought of like the computer that controls the body,
including all memory and conscious thought. Out from this central computer is a
Rev: F
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Page 15
network of “wiring” that carries signals to and from the brain. This “wiring” is
composed of nerve cells, or “neurons” that function very similarly to the wiring of
a computer network. In fact, neurons carry information in the form of electrical
impulses to and from the brain.
The motor nervous system includes the nerves that carry commands from the
brain out to the body. These nerves are primarily involved in muscular control.
Commands from the brain are transmitted as patterns of electrical impulses
through the motor nerves into the muscles, causing the muscles to move in
certain patterns caused by the pattern of stimulation from the brain.
The sensory nervous system includes the nerves that carry information to the
brain about the state of the body and its environment. Sensory nerves in the skin
communicate heat, cold, touch, pressure, pain, and other sensations. Similarly,
nerves carry visual data from the eyes, auditory data from the ears, and olfactory
data from the nose. All of this data is transmitted in the form of electrical impulses
along the neurons into the brain.
Figure 11 Sensory Receptors.
Fig. 3.16 of Reilly (1998).
Section
of
the
skin
showing several types of
sensory
receptors.
Sensory receptors can
include sensors for touch,
heat, feel, pressure, cold,
etc.
Figure 12 is a conceptual representation illustrating the concept of operation of
TASER devices. TASER devices use very short duration low energy electrical
pulses that are somewhat similar to the pulses used by neurons to communicate.
If you think of the nervous system as an electrical communications network,
TASER devices are like remote controls that plug into that network, and
temporarily take control of, or interfere with, the communication patterns between
the brain and the body.
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Figure 12 TASER Devices Stimulate the Motor and Peripheral Nervous Systems with
Pulses Similar to Those Used by Nerves to Communicate8
Telephone Network Communication Analogy
One analogy helpful in understanding TASER technology is a telephone network.
If person A is talking on the telephone with person B, and suddenly person C
picks up another telephone handset and begins yelling into the phone, persons A
and B can no longer effectively communicate – their conversation has been
interfered with by person C’s intervening disturbance. However, when person C
ceases yelling and disconnects, the normal conversation between A and B can
resume again. The telephone hardware is not damaged by the yelling, it is just
that the temporary over-stimulation of, or interference with the communication,
the network prevented communication on a transient and temporary basis.
Similarly, TASER devices cause stimulation of the nerves that is designed to be
temporary in nature with minimal risk of causing serious damage to the hardware
of the communication network by the interference.
8
This illustration is for illustrative conceptual purposes only. These are not intended to be scientific
measurements of actual pulse characteristics, but to illustrate the basic concept for lay persons that the
electrical discharge from the TASER device is a brief pulse which causes stimulation of neuron membrane
mechanisms in a fashion similar to the capacitor-discharge type depolarization mechanism used by neurons
in normal communications within the nervous system.
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Effects of Repeated Pulses on Muscle Tension
Figure 13 Fig. 3.22 from
Reilly, 1998.
Single muscle twitches
will fuse together with
sufficient
repeated
stimulus pulses producing
increased muscle tension.
TASER devices have a
pulse rate of up to
approximately twenty (20
± 25%) pulses per second
(pps).
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HISTORY OF TASER DEVICE TECHNOLOGIES
1967 – NASA Scientist Jack Cover’s TASER TF-76
The original TASER device (the TF-76) was launched in the mid 1970s by
National Aeronautics and Space Administration (NASA) scientist Jack Cover, the
TASER device inventor. The TASER TF-76 fired two darts up to a distance of 15
feet. These darts remained attached to the handheld device by small, thin,
insulated wires. The original TASER TF-76 used a gunpowder propellant to
launch the darts. Because of the explosive (gun powder dart) propellant, the TF76 was classified by the United States Treasury Department’s Bureau of Alcohol,
Tobacco and Firearms, and also now Explosives, as a firearm. However, the TF76 looked like a flashlight, not a firearm. Because it did not fit the specifications
for either a pistol or a long gun, the TF-76 was classified as a Title 2 weapon –
the same as a “sawed-off” shotgun. This classification meant that the TASER TF76 could only be sold with special permits that were expensive and difficult to
obtain (just as it would be for a “sawed-off” shotgun). Accordingly, the TF-76
could only effectively be sold to law enforcement agencies. While the Title 2
weapon classification did not adversely affect law enforcement agencies
acquisition and use of the early TASER devices, it did prevent most civilians from
acquiring, possessing, and using the devices. Shortly after the TF-76 was
classified as a Title 2 weapon, TASER Systems (the company that made the TF76) collapsed.
Tasertron Emerged
This early company eventually raised funding, re-emerging as a company called
Tasertron, but struggled over the next decades and sold only a limited number of
devices into the law enforcement marketplace. The Tasertron devices were
originally offered in seven-watt versions and then later in eleven-watt models that
had a 15-foot range and still used gunpowder propellant and were still classified
as special class firearms.
1980s: Studies and Risk Utility Comparisons
In the 1980s there were numerous studies and risk utility analyses performed on
ECDs. These included the Greg Meyer Los Angeles Police Department use of
less-lethal force study and the Ordog mortality and morbidity study.
Early 1990s: The Need for Non-Firearm Self-Defense
In the early 1990s, two friends of Rick Smith’s (Corey and Todd) were shot and
killed in a traffic altercation in Scottsdale, Arizona. This tragic event caused Rick
Smith to start thinking about violent crime, and wondering why the state of the art
in self-defense weapons required killlng, or at least reliably seriously injuring,
other human beings – just as it had been for centuries. Mr. Smith came to believe
that, if advances in technology could provide truly effective non-lethal
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alternatives, many people would choose less-lethal weapons instead of lethal
weapons – and many lives could be saved.
ICER Corporation Formed
In September of 1993, brothers Rick and Tom Smith formed ICER Corporation –
a company whose mission would be to develop future less-lethal electronic
weapons. As part of their early research, Rick contacted Jack Cover, the original
TASER inventor. Jack Cover shared with Rick the history of the TASER
technology, and he proposed a business model whereby they could develop a
new, non-firearm version of the TASER device using a compressed air (or
nitrogen), as opposed to gunpowder explosive, dart (probe) propulsion system.
On October 15, 1993 they signed an agreement whereby Mr. Cover licensed his
technology to ICER Corporation and joined the corporation as a full-time
employee, infusing all of his knowledge and years of experience into the
company, to help develop the next generation of TASER devices. Shortly
thereafter, they then changed the name of the company to AIR TASER, Inc.
TASER 34000 – 2nd Generation TASER Device
In December of 1994, this work culminated with the launch of the AIR TASER
model 34000. The design intention of the AIR TASER 34000 was to use the
same electrical output as the original TASER TF-76, but with a compressed air
propulsion system that would comply with federal firearm statutes and allow for
private citizen sales.
The AIR TASER 34000 implemented an innovative new user accountability
technology called Anti-Felon Identification (AFID), which used serialized confetti
tags dispersed from every cartridge at the time of firing. These AFID tags would
enable law enforcement to trace persons who misused a TASER device. This
was another first for weapons’ use accountability – a self-defense device that left
a tracer at the scene of the incident back to the purchaser. Also, the AFIDs are
made in both paper and clear Mylar – making it more difficult for a criminal to pick
up the AFID evidence of his crime. Also, some of the AFIDs are made to literally
glow under a black light, thus making them very easy for law enforcement
investigators to locate and recover.
1994: TASER 34000 Limited to Non-Law Enforcement
Shortly after the launch of the AIR TASER 34000 in 1994, AIR TASER Inc. was
sued by Tasertron, the remainder of the original TASER systems company from
the 1970s. Tasertron asserted that it had exclusive rights to the underlying
technology for use in the law enforcement and military markets in North America.
To avoid a costly legal battle, AIR TASER Inc. signed a non-compete agreement
that recognized Tasertron’s exclusivity and precluded AIR TASER Inc. from
selling to law enforcement or military agencies in North America until the patent
in question expired in 1998.
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Nov. 1995: The Czech Experience: Original TASER Devices Did Not Get the
Job Done!
Around November of 1995, the company received an inquiry from the Czech
police seeking a product demonstration in Prague. The AIR TASER’s noncompete agreement with Tasertron did not preclude foreign police or military
sales. Accordingly, the company agreed to make, and was very eager to give, a
presentation of the AIR TASER 34000.
Around December of 1995, Rick Smith flew to Prague with the company’s head
of sales. After a brief technology demonstration, the Czech police asked for a
volunteer demonstration. Prior to being hit with the AIR TASER 34000, the
volunteer was strongly instructed – ordered – by his superior officer to fight
through the (pain compliance) effects of the 34000 device and get to the shooter
– Mr. Smith. In fact, several focused and highly motivated volunteers that day
were all able to overcome the (pain compliance) effects of the AIR TASER
34000.
1996: ADVANCED TASER M26 Is Born
Following this highly embarrassing Czech debacle, the company set out to
develop a more effective device – a device that would not only involve
discomfort, but also interfere with voluntary muscle control. The result of this
development was the TASER M26. Earlier generations of TASER devices such
as the TF-76 and the AIR TASER 34000 caused a strong peripheral-nerve shock
sensation. However, focused or pain-insensitive subjects, such as the police
volunteers in Prague, could fight through these effects. Accordingly, these
earlier-generation devices can be considered stun devices. Their effects may
psychologically stun the subject, but they did not cause involuntary
incapacitation.
Stratbucker Testing
In late 1995, TASER contacted Dr. Robert Stratbucker, M.D., Ph.D. (the leading
medical and scientific expert on electrical weapons at the time), and retained him
to conduct a complete relevant electrical, medical, and scientific literature review
and to conduct safety studies of the impulse generator module of the TASER
device. The goal of the study was to perform an analysis to establish a margin of
safety for the AIR TASER 34000 by testing significant increases in relevant
electrical characteristics and evaluating the physiological response.
Dr. Stratbucker was chosen to test the devices because he had over a decade of
experience in researching and testing a number of similar devices both physically
and physiologically in his laboratory and had become quite familiar with the
necessary procedures to accurately accommodate such testing. Dr. Stratbucker
had even demonstrated electronic weapons by using a stun gun on a U.S.
Attorney General.
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Dr. Stratbucker conducted the tests in January 1996. The studies included
skeletal muscle response and assessment of any possible affect on cardiac
rhythm. For the cardiac rhythm testing a three-channel, battery-powered
cardiograph unit was continuously employed to accomplish orthogonal lead axes.
As a realistic necessity, the tests also included physiologic and biomarker
monitoring to assure physiologic stability.
Dr. Stratbucker’s experiments corroborated earlier findings in consulting reports
and peer review journals9 that the electrical emission from stun-type pulse
generators, delivered to the body surface in the recommended manner did not
cause serious cardiac rhythm abnormalities in the otherwise healthy adult swine
heart. As the study investigated outputs equivalent to 400% the capacitance and
300% the battery voltage of the standard AIR TASER 34000, an adequate
margin of safety appeared to exist.
Due to Dr. Stratbucker’s qualifications and extensive knowledge and history with
electronic devices he later became TASER’s Medical Director.
TASER M26 Developed
Mr. Smith was proud to have led the development team, designed the test
methodology used to develop the TASER M26, and was the listed inventor on
the patent for the electrical waveform of the M26.
TASER M26 Emerges – 3rd Generation TASER Device
Because the earlier stun devices did cause a strong overwhelming discomfort
(pain) sensation, they clearly caused some degree of stimulation of the sensory
nervous system. However, there was little or no interference with or impairment
of volitional muscular control with these early devices. In contrast, the new
TASER M26 was designed to cause significant, uncontrollable muscle
contractions capable of incapacitating even the most focused and aggressive
combatants. Accordingly, this new technology was termed Electro-Muscular
Disruption (EMD). More recently, a new term was adopted that was more
accurately descriptive terminology: Neuromuscular Incapacitation (NMI).
Medical and Scientific Research
During the development of the TASER M26 medical, scientific, and engineering
literature was extensively researched with regard to electrical energy, charge,
9
O.Z. Roy and A.S. Podgorski, Tests on a Shocking Device - the Stun Gun. Med. & Biol.
Eng. & Comput, 1989, 27, 445-448. Robert A. Stratbucker and Matthew G. Marsh. IEEE.
The Relative Immunity of the Skin and Cardiovascular System to the Direct Effects of
High Voltage - High Frequency Component Electrical Pulses. Proc. IEEE Engineering in
Medicine & Biology Conference, October 1993, San Diego, CA. Pearce, J.A., et. al:
Myocardial Stimulation with Ultrashort Duration Current Pulses. PACE, Vol. 5, JanuaryFebruary 1982.
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safety of electrical devices, similar forms of electrical devices, etc. This research
has been continuously ongoing since the mid-1990s.
Late 1999: ADVANCED TASER M26
The ADVANCED TASER M26 was launched in late 1999, with an initial shipment
of thirty (30) M26 devices to the New York City Police Department, with
significant shipments starting in early 2000. By this time, the company had
changed its name to TASER International, Inc. to signify the company had more
than just the one AIR TASER product. The TASER M26 was adopted by
thousands of law enforcement agencies, and was hailed as a state-of-the-art
breakthrough – as the first less-lethal weapon capable of stopping aggressive,
focused, or drug-impaired persons. In addition to the AFID system, the TASER
M26 implemented a new accountability control technology – the dataport. The
dataport is a function wherein the M26 would record the time and date of every
five (5) second discharge trigger pull10 in order to allow law enforcement
agencies to monitor use of the device – another use-of-force accountability break
through.
May 2003 – TASER X26 Debuted – 4th Generation TASER Device
In 2003, TASER introduced the TASER X26. The X26 implemented a newer,
more efficient electrical stimulation pulse called “Shaped-Pulse Technology.” This
“Shaped Pulse Technology” pulse allowed for a more efficient power supply that
enabled the X26 to be packaged in a form factor that was approximately 60%
smaller and 60% lighter than the M26. However, the X26 design was tuned in
laboratory testing to deliver an incapacitating effect that caused muscular
contractions approximately 5% stronger than those of the M26.
The TASER X26 has been very well received and as of early 2006 accounts for
the majority of the company’s law enforcement ECD shipments.
2007 – TASER eXtended Range Electronic Projectile (XREP™) – 5th
Generation TASER Device
The XREP projectile is self-contained, wireless, and fires from a 12-gauge
shotgun. It delivers similar Neuro Muscular Incapacitation (NMI) bio-effect as the
handheld TASER X26 ECD, but can be delivered to a distance of 65 feet (20
meters [m]), combining blunt impact with field-proven TASER NMI.
TASER C2™ ECD
The TASER C2 is designed for personal protection. Utilizing the same
technology as law enforcement models, the TASER C2 is designed to have
strong take down power.
10
Also, the M26 records a datapoint entry with each five (5) seconds of continuous
device discharge.
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BASIC TASER DEVICE OPERATIONS
It is common for people to ask, “How can the TASER device generate 50,000 V
from 12 V or less at the battery of cells (for the TASER M26)?” The answer is
that TASER devices use a series of transformers and capacitors, together with
the principles of physics (P = I * V).
Transformers: Analogy: An Electrical Lever
There’s a well-known stunt performed by acrobats using a “see-saw” device as a
lever. Two acrobats jump from a given height (say 10 feet) onto one side of the
lever. On the other side, a single acrobat is launched twice as high into the air.
The lever transfers the momentum of the two acrobats into one acrobat, sending
him twice as high.
Figure 14 Understanding Transformers Analogy
One can think of a transformer as an electrical lever. As electrons enter one side
of the transformer from a certain voltage (similar to the height of the acrobats’
jump), the leverage ratio of the transformer transfers this energy to electrons on
the output side of the transformer. Depending on the design of the transformer, it
can either step-up the output voltage, or step it down. In either case, the
transformer is constrained by the power input (P = I * V).
In its simplest form, the transformer “trades” volts for amperes, or vice versa. In
the example above, if 2 amperes of current at 10 volts are delivered into this
transformer, 1 ampere of current at 20 volts will be the output. (Note that in the
real world, transformers are not 100% efficient, so the actual output will be
slightly less than the input.)
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THE TASER DEVICE CIRCUIT: AN ILLUSTRATIVE LOOK
The battery of power cells is the power supply in any TASER device. In this
illustrative example, the battery of cells function like a water faucet, supplying the
power to the circuit. The “pressure” out of the battery of cells in the M26 is
roughly 10 volts (it drops from 12 volts, or less, as the battery of cells is loaded)
and the current is roughly 4 amperes; hence the total power from the batteries is
roughly 40 watts.
Figure 15 An Illustrative Representation of the TASER M26 Circuit
The electric current from the battery of cells is directed into a transformer
(Transformer 1) that steps up the voltage by a factor of roughly 200, from 10 to
2,000 volts. As the transformer steps-up the voltage by 200x, it also steps-down
the current by 200x, from 4 amperes input to roughly 0.02 amperes (the actual
output is less, about 0.013 amperes due to inefficiencies).
The output of Transformer 1 is connected to a capacitor. A capacitor is a device
that stores electric energy, just like a bucket would store a flow of water. Similar
to a bucket, a capacitor can only hold so much energy. Once the capacitor is full,
it dumps its energy into Transformer 2. Transformer 2 steps the voltage up again,
from 2,000 volts to a peak of 50,000 volts. Similarly, the current drops again to an
even lower output current.
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One important note – the 50,000 volts is a peak potential voltage, or open circuit
voltage; it is not what is actually delivered to the person on the receiving end.
Again considering the water analogy, the wires from the TASER device to the
target are like hoses that carry the current. If a section of plastic wrap is placed
over the end of a garden hose, the pressure will build up inside the hose. At
some point, the plastic wrap will finally burst, and the water will flow out the end.
When the plastic bursts and the water starts to flow out, the pressure inside the
hose drops, and the pressure of the water flowing out is actually lower than the
peak pressure that developed within the hose itself.
In a TASER ECD system, the wires do not always make contact with the skin of
the target. If there is an air gap between the darts and the body of the subject,
the air gap will function as a barrier, just like the plastic wrap on the hose. The
voltage (pressure) will build up inside the TASER wires until it can break through
the barrier (the maximum would be 50,000 volts, which can break through a
barrier of approximately 2 inches of air gap). Once the barrier is breached, the
voltage (pressure) drops immediately as the current flows through. In the case of
the TASER M26, the maximum voltage delivered across the body of the target is
about 5,000 volts, with only 1.44 volts average (one-second baseline). In the
case of the TASER X26, the maximum voltage delivered across the body of the
target is about 1,200 volts, with only 0.84 volts average (one-second baseline).
The big picture from this illustrative look at the TASER device is to understand
that at each level, as the voltage is increased, the output current is decreased.
Basics of Nerve and Muscle Stimulation
As mentioned previously, the body’s neurons conduct electrical stimuli to and
from the brain. When a neuron is in its resting state, electrically charged ions are
pumped across the cell membrane such that net positive charge collects outside
the membrane and a net negative charge collects inside the membrane. In this
state, the membrane serves as a charged capacitor. When the nerve cell is
stimulated, channels in the membrane open up temporarily, allowing the positive
ions to temporarily rush across the membrane (opposites attract). At this moment
in time, the voltage potential across the membrane briefly flips polarity as the
charge balance reverses. This process is called an action potential. As an
action potential occurs in one section of the cell membrane, the change in the
electric fields causes the adjacent section of the membrane to depolarize. The
result is a chain reaction of action potentials cascading down the length of the
neuron, thereby carrying an electric impulse along the neuron.
One important point to understand about action potentials is that they come in
only one magnitude. For each neuron, there is a threshold stimulation level.
Once this threshold is attained, an action potential will occur. There are not
different intensities of action potential, they are an “All-or-None” phenomenon. In
other words, there is no such thing as a partial or weak action potential. Either
the threshold potential is reached and an action potential occurs, or it is not
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reached and no action potential occurs. (As an example, either a light switch is
turned on or it is turned off … it is not [in this case] a “dimmer” switch.)
Each neuron can only deliver one magnitude of impulse. Whether a muscle
contraction will be strong or weak is not a function of the magnitude of the
impulses of the connected neurons (again, there is no difference between
impulses). The difference is the pattern of impulses delivered.
The section below describes the process by which these nerve impulses cause
muscular contractions:
The Neuromuscular Junction
Nerve impulses (action potentials) traveling down the motor neurons of the
sensory-somatic branch of the nervous system cause the skeletal muscle
fibers at which they terminate to contract. The junction between the terminal of a
motor neuron and a muscle fiber is called the neuromuscular junction. It is simply
one kind of synapse. (The neuromuscular junction is also called the myoneural
junction.)
The terminals of motor axons contain thousands of vesicles filled with
acetylcholine (ACh). When an action potential reaches the axon terminal,
hundreds of these vesicles discharge their ACh onto a specialized area of
postsynaptic membrane on the fiber. This area contains a cluster of
transmembrane channels that are opened by ACh and let sodium ions (Na+)
diffuse in.
The interior of a resting muscle fiber has a resting potential of about −95
millivolts (mV). The influx of sodium ions reduces the charge, creating an end
plate potential. If the end plate potential reaches the threshold voltage
(approximately −50 mV), sodium ions flow in with a rush and an action potential
is created in the fiber. The action potential sweeps down the length of the fiber
just as it does in an axon.
No visible change occurs in the muscle fiber during (and immediately following)
the action potential. This period, called the latent period, lasts from 3–10
milliseconds (ms). Before the latent period is over, the enzyme
acetylcholinesterase breaks down the ACh in the neuromuscular junction (at a
speed of about 25,000 molecules per second) the sodium channels close, and
the field is cleared for the arrival of another nerve impulse. The resting potential
of the fiber is restored by an outflow of potassium ions. The brief (1–2 ms)
period needed to restore the resting potential is called the refractory period.
Tetanus
The process of muscles contracting takes some 50 ms; relaxation of the fiber
takes another 50 to 100 ms. Because the refractory period is so much shorter
than the time needed for contraction and relaxation, the fiber can be maintained
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in the contracted state so long as it is stimulated frequently enough (e.g., 50
stimuli per second).
Such sustained contraction is called tetanus. When shocks are given at one per
second, the muscle responds with a single twitch. At five per second and 10 per
second, the individual twitches begin to fuse together, a phenomenon called
clonus. At about 50 shocks per second, the muscle goes into the smooth,
sustained contraction of tetanus.
Clonus and tetanus are possible because the refractory period is much briefer
than the time needed to complete a cycle of contraction and relaxation. Note that
the amount of contraction is greater in clonus and tetanus than in a single twitch.
As we normally use our muscles, the individual fibers go into tetanus for brief
periods rather than simply undergoing single twitches.
How the TASER Device Does What It Does to the Body
TASER devices deliver very short duration electrical pulses at a rate of
approximately 15–25 pulses per second. As mentioned earlier, the first
generation stun devices such as the TASER TF-76 and the AIR TASER 34000
only delivered sufficient charge in each pulse to stimulate the sensory nerves
close to the skin. Very little motor nerve stimulation occurred, resulting in
relatively low effectiveness against focused, motivated, or pain-resistant subjects.
The TASER M26 and X26 deliver a similar train of electrical pulses, also at
approximately 15–25 pulses per second. However, the M26 and X26 devices
deliver more electrical charge in each pulse. This higher charge results in deeper
nerves, such as motor nerves, being stimulated. As a result, the motor nerves
between the two electrodes fire at a rate of roughly 20 pulses per second.
This stimulation rate is sufficient to cause clonus, where the individual twitches
fuse together into a sustained contraction. However, it is well below the 50–60
pulses per second required to cause complete tetanus (a smooth, continuous
contraction of the muscle tissue). Accordingly, the stimulation from the TASER
device does cause less muscle contraction than the types of contractions caused
voluntarily by the brain.
As noted before, both nerve cells and muscle cells can be stimulated with
electricity (both nerve and muscle cells use action potentials during stimulation).
The mechanism of stimulation from the TASER devices is not direct electrical
stimulation of muscle tissue, but stimulation of motor nerves which then stimulate
muscles in a nerve-mediated mechanism. This has been demonstrated in
laboratory testing wherein a test animal was administered a drug which blocked
the neuronmuscular junction (similar to curare). Before the drug administration,
the application of the TASER device caused significant muscular contractions.
After the drug administration, the TASER device application caused insignificant
muscle reaction, demonstrating that the mechanism of effect is mediated by the
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motor nerves not a direct electrical stimulation of the muscle tissue. This is an
important concept in that the muscle contractions are mediated by the
neuromuscular junction, just as in normal activity.
Figure 16 Air Force Research Lab Tests Show TASER M26 Muscle Contractions at 40% or
less of Maximum Contraction Force
In fact, a study by Dr. James Jauchem at the Air Force Research Laboratory
(AFRL) found that the intensity of the muscle contractions caused by the TASER
M26 could be increased to more than 250% of the level of contraction from the
field production M26. Accordingly, the M26 generates a muscle contraction
approximately 40% or less than the maximal contraction attainable with more
aggressive waveforms. The X26 has been tuned to deliver a contraction roughly
5% greater than the M26 – a level still well below even 50% of the maximal
contractions found in the AFRL study.
While the TASER device-induced contractions are sufficient to interfere with and
impair voluntary movement and cause incapacitation in the majority of
applications, they are still within the normal operating range of voluntary muscle
movements associated with strenuous activities such as weight lifting, wrestling,
or other athletic, sports, or exertion activities.
TASER Device Outputs and Comparisons
Figure 17 is a graph depicting the current output of a single AIR TASER 34000
pulse compared to a TASER M26 pulse. The vertical axis is the magnitude of
electric current. The horizontal axis is time, measured in microseconds (1
microsecond (µs) = 0.000001 seconds).
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Current [A]
E+00
1.00E-05
2.00E-05
3.00E-05
4.00E-05
5.00E-05
6.00E-05
7.00E-05
8.00E-05
9.00E-05
Time (sec)
M26 Taser Current [A]
M34000 Taser Current [A]
Figure 17 Comparison of Current Output of AIR TASER 34000 and TASER M26
Note that for a very brief period of time (about one microsecond), the peak
current output from the AIR TASER 34000 reaches about 8 amperes (remember
that a strong static shock can reach a peak of 30–37.5 amperes). However, the
duration of the primary phase of the impulse is extremely short – roughly five
microseconds. This is about 1/200,000th of one second. To give you an idea of
how short this pulse duration is: if you stacked 200,000 sheets of standard copier
paper, the stack would be roughly 50 feet tall. If this stack of paper represented
just one second in time, the duration of the primary phase of the AIR TASER
34000 pulse would be the width of just one piece of paper from the 50-foot-tall
stack of 200,000 sheets!
Because the pulse duration is so extremely short, the amount of electrical charge
actually delivered is quite small. Consider if you turn on a faucet, even at a very
high flow rate, but you turned it back off after 0.000005 seconds. Even though
the flow rate for that moment in time might be high, a very small amount of water
would actually have time to flow out – probably just a drop.
In looking at the same chart again, since the vertical axis is the flow rate and the
horizontal axis is time, the amount of actual charge delivered can be calculated
by taking the area under the curve.
In the case of the AIR TASER 34000, the charge in the primary pulse is roughly
0.00003 coulombs (C) (or 30 microcoulombs [µC]). The charge in the entire pulse
Rev: F
November 10, 2008
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(including both the positive and negative phases) is roughly 70 microcoulombs
(µC). However, it is the charge in the first phase that appears to be the most
important for causing peripheral nerve stimulation. Once the current changes
polarity, it is actually shifting charge in the opposite direction. Hence, if the nerve
cell has not reached its action potential threshold during the first phase, the
second negative phase actually works against it. Therefore, it is the charge in the
primary phase that is most relevant. However, in the interest of conservatism for
rating purposes, the entire charge delivered will be considered. Since the device
pulses roughly 15 times per second it will deliver 70 microcoulombs (total
rectified charge) * 15 pulses per second = 1,050 microcoulombs per second.
Since current is the flow rate of charge, 1,050 microcoulombs per second = 1,050
microamperes = 1.05 milliamperes.
Since the pulse intensity from the AIR TASER 34000 was found to be insufficient
to cause motor neuron mediated stimulation of muscle, a new pulse waveform
was developed for the TASER M26. Note that the M26 delivers a pulse that is
both taller and wider than the AIR TASER 34000. Accordingly, the total charge
delivered from the M26 pulse is also higher, roughly 85 microcoulombs (µC). At a
nominal pulse rate of approximately 20 pulses per second, this equates to an
average rectified current of 3,600 microamperes = 3.6 milliamperes (0.0036 A).
Due to all the equipment law enforcement officers must carry, it was reportedly
difficult for officers to fit the TASER M26 on their duty belts for full-time carry.
Accordingly, the company set out to develop a smaller TASER device that could
still cause a similar amount of motor-nerve mediated muscular incapacitation.
The result was a more complex waveform using “Shaped Pulse™” Technology.
(For more details on Shaped Pulse™ Technology, see TASER Training CD/DVD
version 10+.) A new waveform developed using Shaped Pulse Technology,
which delivered a comparable amount of charge to the waveform from the
TASER M26, was implemented in a new device called the TASER X26,
introduced in May of 2003.
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Electrical Waveform Comparison of M26 and X26
20
15
Current [A]
10
5
0
-5
-10
0
10
20
30
40
50
60
70
80
90
100
Time [us]
X26 Waveform
M26 Waveform
Figure 18 Comparison of Current Output of ADVANCED TASER M26 and TASER X26
Note that the TASER X26 uses a lower peak current than the ADVANCED
TASER M26, but a longer pulse duration. As a result, the X26 delivers a roughly
comparable amount of electrical charge in each pulse. In laboratory experiments,
the output of the TASER X26 was designed to cause approximately 5% stronger
muscle contractions than the M26. The X26 delivers roughly 100 microcoulombs
(µC) per pulse, at a pulse rate of 19 pulses per second (pps), for an average
rectified current of 2,100 microamperes (µA) or 2.1 milliamperes (mA) (or 0.0021
A). (Note, the primary phase of the X26 is actually negative in polarity compared
to the main pulse – however most of the charge delivered is of the same polarity,
one of the reasons that the X26 waveform is more efficient.)
These patented pulse waveforms have proven highly effective at incapacitating
even the most aggressive subjects while minimizing the risk of serious adverse
effects. Due to the extremely short pulse durations used in TASER pulses, the
charge per pulse and average current are miniscule when compared to
continuous outputs such as AC currents from a wall outlet, industrial equipment,
or power lines.
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TASER Risk Benefits
TASER device deployments have been shown to dramatically reduce officer and
suspect injuries. More information can be located on the field use reports, risk
analysis PowerPoint presentations, published studies, etc.
Use of Force Data
Real World TASER Program Results
Orange County Sheriffs, Florida
# of Incidents
600
Dept
500
Cincinnati PD
R
SE
A
T
400
300
Austin PD
Orange County SO
CharlotteMecklenburg
100
Cape Coral PD
0
2000
300
263
Physic al
78
75
0
1
62
60
27
21
13
12
0
3
228
482
# of Incidents
1999
Chemic al
Impac t
K9
Batons
TASER
6
4
2
2001
52
13
154
70
2
Ð 70%
Ð 53%
Ð 40%
Ð 80%
Ð 67%
Ð 24%
Topeka PD
Omaha
Ð 23%
Ð 80%
Ð 59%
Ð 83%
Ð 46%
Ð 18%
Lethal Force
Force
Complaints
Ð 50%
Ð 32%
Ð 54%
14 “saves”
Ð 25%
Ð 78%
Ð 79
19 “saves”
Ð40%
Ð 46%
-
48
70
4
Year
5
2002
Firearms Use
221
Suspect
Injuries
Phoenix PD
Columbus PD
200
14
12
Rounds
10
8
Officer
Injuries
Miami and Seattle: Over 12 Months without a Lethal Force Shooting
Shooting
0
0
Comparison of Injuries
Risk vs. Benefit
TASER Technology Reduces Injuries
80%
78%
78%
80%
70%
60%
60%
50%
Suspect
Injured
45%
36%
29%
30%
20%
16%
20%
21%
29%
18%
11%
10%
Swarm
0% 0%
Chemical
Spray
Kick
Baton
Punch
Flashlight
0%
Misc. body
force
5%
Officer
Injured /
Affected
TASER
40%
Force Type
Source: Study of Use of Force at Los Angeles Police Department, Capt. Greg Meyer.
Statistics are for 7-Watt TASER technology deployed at LAPD.
Original Study Available at http://home.earthlink.net/~gregmeyer/injury.html on the internet.
Figure 19 Examples of TASER Risk Benefits
DEGREE OF CERTAINTY
While many of the statements in this document are factual in nature, or directly
out of high school sciences revisited, any expert opinions are to a reasonable
degree of scientific, medical, and/or professional certainty.
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November 10, 2008
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