What is an Electromagnetic Pulse?

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ELECTROMAGNETIC PULSE

WHAT IS IT, WHEN DOES IT HAPPEN, AND WHAT ARE THE RESULTS?

1. What is an electromagnetic pulse (EMP)?
   • An electromagnetic pulse is an extremely powerful burst of electromagnetic energy capable of causing damage and/or disruption to electrical and electronic equipment.
2. What causes an electromagnetic pulse
   • There are several causes:
     • Detonation of a nuclear bomb
     • A Solar flare
     • A device intended to cause an EMP
     • A close lightning stroke
     • A massive powerline short circuit
3. How far away can an EMP cause damage?
   • This depends on the cause of the EMP and the kind of equipment that is damaged A table of devices, EMP sources, and approximate maximum distances follows:
     

     	CAUSE OF ELECTROMAGNETIC PULSE
     DEVICE DAMAGED	Nuclear Bomb	Solar Flare	EMP Source	Lightning	Short Circuit
     Radio with longwire antenna	2.5 Mm*	Anywhere*	Unlikely	1 km	100 m
     Radio with internal antenna	2.5 Mm*	Unlikely	2 m	100 m	10 m
     Computer (damaged)	2.5 Mm*	Unlikely	2 m	Depends**	Depends**
     Computer (rogue program counter)	Anywhere*	Anywhere*	6-10 m	Depends**	Depends**
     Computer network (damage)	2.5 Mm	Anywhere*	6-10 m	1 Km††	100 m** ††
     Computer network (disrupted)	Anywhere*	Anywhere*	10-25 m	5 Km††	500 m††
     Car engine computer (damaged)	2.5 Mm*	Unlikely	2 m	5-10 m	5-10 m
     Modern stereo (no antenna)	2.5 Mm*	Unlikely	2 m	100 m**	10 m**
     Radio or TV station	2.5 Mm	Unlikely	Unlikely	500**	50**
     Power line (length 1 Km)	250 km	Unlikely	Unlikely	No***	No***
     Power line (length 20 Km)	1 Mm	Anywhere*	No	No	No***
     Power line fuse	2.5 Mm	Anywhere*	Unlikely	No***	No***
     AC power plant generator	250 Km	Anywhere*	No	No	No***
     DC commutator power generator	250 Km	Anywhere*	No	No	No***
     DC rectifier power generator	2.5 Mm	Anywhere*	No	No	No***
     Switching DC power supply	2.5 Mm	Anywhere*	4 m	500 m**	200 m**
     Rectifier DC power supply	1 Mm	Anywhere*	No	50 m**	20 m**
     Dimmers	2.5 Mm	Anywhere*	Unlikely	500 m**	200 m**
     Semiconductor controllers	2.5 Mm	Anywhere*	Unlikely	500 m**	200 m**
     New Technology lightbulbs†	2.5 Mm	Anywhere*	2 m	500 m**	200 m**
     Incandescent lightbulbs	1 Mm	Anywhere*	Unlikely	50 m**	20 m**
     Old style fluorescent lightbulbs	1 Mm	Anywhere*	Unlikely	50 m**	20 m**
     Relays	1 Mm	Anywhere*	Unlikely	20 m**	10 m**
     Cellular phones	2.5 Mm	Anywhere*	4 m	100 m**	50 m**
     Cellular phone towers	2.5 Mm	Anywhere*	Unlikely	50 m**	20 m**
     Meters	2.5 Mm	Anywhere*	6 m	500 m**	200 m**

     * The earth itself blocks the EMP. Must have nearly a line-of-sight relationship with the source.
     ** Distance depends on what the device is connected to, and whether the EMP can arrive through power line induction.
     *** Can happen through a direct connection to the fault, but not through the EMP generated by it.
     † Compact Fluorescent Lamps (CFL), Light Emitting Diodes (LED), and other types.
     †† Distance from closest point of network.

     1 m   = 3.28 ft 1 Km  = .621 mi 1 Mm  = 621 mi

     1 ft  = .3048 m 1 mi  = 1.609 Km 1 Kmi = 1.609 Mm

4. How likely is an electromagnetic pulse?
   • This depends on where you are and what is going on:
   • A nuclear explosion is an extremely rare event. Unless terrorists set off a nuclear explosion, there probably will not be one.
   • A solar flare is a common occurrence, but one that does damage is rare. But it is the most common thing that the average person might encounter.
   • Only if a police chase is passing you on a highway do you need to be concerned about an EMP device.
   • A lightning strike close enough to cause an EMP is quite rare. Usually any EMP would come in on power or communication wiring, rather than through the air. This is what surge protectors are for.
   • A power line short EMP is rare. Unless it is very close, surge protectors take care of most of them.
   • One caution: When using surge protectors. Make sure the SAME surge protector is used for both power and communication wiring.
5. When was electromagnetic pulse discovered?
   • There were several instances:
   • Enrico Fermi predicted that EMP would be an effect of the Trinity bomb test. His prediction was demonstrated when the EMP from the test destroyed some recording instruments used for measurements during the test, even though signal cables were shielded against it.
   • Automobile engines stopped running in New Mexico and Nevada at the exact times of the ground tests in those states. The engines were not damaged, and were started normally seconds later. This was before transistor ignition.
   • The US held a nuclear test in space in July 1962. A 1.4 Megaton bomb was detonated 250 miles above sea level. It caused damage to orbiting satellites and equipment on the ground within 1500 miles. This includes damage to streetlights, radios, and telephone relay equipment in Hawaii. It also set off many burglar alarms there.
6. How does damage or improper operation happen to electronic equipment?
   • The electromagnetic pulse induces large currents in conductors that are part of or are connected to the equipment. These high currents can do the following:
     1. Induce voltages high enough to arc from one conductor to another, damaging whatever is connected to them.
     2. Induce voltages high enough to arc from a conductor to a device, damaging the device.
     3. Exceed the current-carrying capabilities of conductors or components in the device, damaging them.
     4. Induce voltages that exceed the voltage limitations of components in the device, damaging them.
     5. Induce voltages that exceed the breakdown voltage of insulation in the device, damaging other components.
     6. Cause voltage spikes that move atoms around in the doping of semiconductors, ruining them.
     7. Cause voltage spikes that puncture through the metallic oxide gates in semiconductors, ruining them.
     8. Cause all of the sparkplugs in an internal combustion engine to fire at the same time, stopping the engine.
     9. Damage the semiconductors in an electronic ignition system, stopping the engine and keeping it from running again.
     10. Blow fuses in electric power transmission lines, putting them out of service until the fuses are replaced.
7. What equipment is most susceptible to EMP?
   • The following equipment is likely to be damaged by EMP:
   • Computers and computer equipment
   • Appliances containing microprocessors
   • Automobile electronic ignition
   • Automotive computers and electronics
   • All digital TV equipment.
   • Radio, TV, stereo, and recording equipment containing semiconductors
   • Semiconductor electronics (installed)
   • Semiconductor electronics (not installed)
   • Switching power supplies
   • Cellular phones
   • Cellular phone towers
   • LED and compact fluorescent light bulbs
   • Incandescent light bulbs (requires a much bigger EMP than electronic bulbs)
   • Powerline fuses
   • Power generation electronic controls
   • Powerline distribution equipment and transformers
   • Long distance electric transmission lines (insulators)
   • Generators, but only if their current or voltage limits are exceeded
   • Radio and TV transmitters
   • Microwave communication equipment
   • Radar equipment
   • Electronic telephone equipment
   • Satellites and satellite ground stations
   • Anything with a longwire antenna
   • Photovoltaic solar cells
   • Most electronic sensors
   • TV cameras
   • Microphones
   • Tape recordings
   • Computer disks
   • Flash drives
   • Avionics
   • Electronic flashlights and power failure lights
   • Most electronic factory equipment
   • Batteries connected to equipment
   • Meters
8. What equipment is likely to be immune to EMP, unless it is very strong
   • The following equipment is not likely to be damaged by EMP:
   • Equipment stored inside metal cases with no openings
   • Ordinary electric wiring in a building (unless the pulse is carried into the building by wires)
   • Vacuum tube equipment with no semiconductor devices
   • Old-style electric telephone equipment
   • Most electric motors, but only if current limits and insulation voltages are not exceeded
   • Automobiles with no semiconductor devices
   • Non-electronic record turntables and pickups
   • Phonograph records
   • Mechanical equipment
   • Punch cards and card punches
   • Electromechanical wire service equipment
   • Incandescent light bulbs that are not installed
   • Incandescent flashlights
   • Compact disks
   • Most non-semiconductor electronic parts that are not installed
   • Magneto ignition systems
   • Relays
   • Diesel engines without electronic injection (other than the starters)
   • Most mechanical and chemical factory equipment, unless damaged by effects of the EMP (e.g. jammed parts)
   • Batteries not connected to circuits
9. What is a rogue program counter?
   • A rogue program counter is a glitched microprocessor running the wrong code:
   • Most microprocessors have instructions that use more than one byte in memory.
   • Each instruction has an operation code byte. It may be followed by one or more addressing bytes (see diagram).
   • A pointer called the program counter steps through the bytes and gives the microprocessor the instructions to follow.
   • An electrical disturbance can cause the program counter to jump to a random location in the computer's memory. The random location could be any of the following:
     1. A location containing data instead of a program.
     2. A location that has never been loaded since the computer was turned on, and contains random values.
     3. A location in the wrong program.
     4. An addressing byte in a program, causing the program counter to treat it as an instruction. The program counter is now out of registration with the program, reading the wrong bytes as instructions.
     The microprocessor is now executing unintended "instructions" instead of the intended program.
   • The microprocessor has no way of knowing that it is not running the correct program.
   • This is one cause of a program that is "no longer responding."
   • This can cause the computer to do anything. But it usually causes the intended program to do nothing.
   • This continues until power is removed from the microprocessor, or until a time sharing system stops the process.
   • Removing power from the microprocessor, and then restoring it several minutes later, causes normal operation to resume.
   • Since the program counter is not running the correct code, any logging system will not make any entries.
   • Special watchdog hardware can monitor the computer and restart it if the program counter goes out of bounds.
10. What is an EMP Source
    • An EMP source is a device that intentionally produces a small EMP. There are three kinds:
    • A small device used by police to disable a fleeing vehicle (the source shown in the table)
    • A source used to test equipment for resistance to EMP (classified strength)
    • A weapon intended to disable enemy equipment (classified strength)
11. Once a large EMP happens, what can be done to restore power, communications, and transportation?
    • Any engine with a magneto will probably still work. A portable generator with such an engine, given fuel, will work, provided it was not connected to a load before the EMP.
    • Military equipment designed to survive EMP will probably work, provided it has power.
    • Unless the EMP was extremely strong, automobiles without electronic ignition will probably work.
    • Unless the EMP was extremely strong, electronic equipment with tubes (no solid state components) should work.
    • Unless the power transmission lines are damaged, power can be restored with the following procedure:
      1. Disconnect transmission lines to systems served by other generators.
      2. Disconnect or bypass any synchronizing and speed control electronics, which were likely destroyed.
      3. Rig manual controls to replace the electronic ones that were destroyed.
      4. Disconnect individual customers until the individual electrical systems can be inspected.
      5. Start the generator. The line frequency will be wrong, but there will be power.
      6. Replace blown fuses in transmission lines.
      7. Reconnect customers a few at a time.
      8. Do not restore grid connections connecting generators together. They will cause phase errors and blow breakers.
    • Unless the communication lines are damaged, communication can be restored with the following procedure:
      1. Wait until power is restored.
      2. Disconnect, replace, or bypass damaged computers, routers, switches, and hubs.
      3. Rig manual controls to replace the electronic ones that were destroyed, if possible.
      4. Disconnect individual customers until the individual systems can be inspected.
      5. Start the network one component at a time. Test it after each component in added.
      6. Test each transmission line before using it.
      7. Reconnect customers one at a time.
      8. Do without some parts of the system until they can be replaced.
    • While transportations ways are not usually damaged, equipment needed to run it can be:
      • Highway
        1. Post temporary controls and flagmen until automatic signals can be repaired or replaced.
        2. All LED traffic signal lamps will probably not work. Replace them with whatever is available.
        3. Individual vehicles will have to be repaired.
        4. Motorcycles and Diesel vehicles will probably work if not computer controlled.
        5. Suspend environmental laws to allow vehicles to be rigged to work. The environment is probably destroyed anyway if a nuclear bomb exploded.
        6. Do without some parts of the system until they can be replaced.
      • Rail
        1. Post temporary controls and flagmen until automatic signals can be repaired or replaced.
        2. All LED signal lamps will probably not work. Replace them with whatever is available.
        3. Individual vehicles will have to be repaired.
        4. Diesel vehicles will probably work if not computer controlled.
        5. Do without some parts of the system until they can be repaired or replaced.
      • Air
        1. Do without air transportation until air traffic control can be restored.
        2. Individual vehicles will have to be repaired.
        3. Suspend environmental laws to allow vehicles to be rigged to work. The environment is probably destroyed anyway if a nuclear bomb exploded.
        4. Do without some parts of the system until they can be replaced.
      • Ships
        1. Post temporary controls and flagmen in patrol boats until navigation equipment can be repaired or replaced.
        2. All LED and CFL navigation lamps will probably not work. Replace them with whatever is available.
        3. Individual vehicles will have to be repaired.
        4. Magneto motorboats and Diesel vehicles will probably work if not computer controlled.
        5. Suspend environmental laws to allow vehicles to be rigged to work. The environment is probably destroyed anyway if a nuclear bomb exploded.
        6. Do without some parts of the system until they can be replaced.
12. What can be done to prevent damage due to EMP?
    • Shield wiring connected to sensitive equipment, or enclose wiring in metal conduits. Ground the shields.
    • Fuse long wires and cables.
    • Increase the current carrying capacity of the building ground.
    • Avoid the use of semiconductors where possible.
    • If semiconductors are used, make sure they are rated at maximum voltages and currents at least 10 times the values actually in use.
    • Use large ferrite beads on power wiring.
    • Bypass suitable electronics to ground with capacitors rated for several thousand volts and heavy currents.
    • Design circuitry to be resistant to high voltages and currents.
    • Provide battery backup power for essential equipment.
    • Provide the above protections to essential equipment, such as emergency communications and traffic signals.
13. What can be done in advance to make restoration easier after an EMP?
    • Stock replacement equipment and parts in metal containers or rooms.
    • Wrap replacement parts in aluminum foil.
    • Keep a stock of batteries. And rotate the stock, so the newest ones are not taken out and used first.
    • Stock up on light bulbs that are not CFL or LED.
    • Take steps to prevent damage.