EMP - what will it knock out?

[Maddie_cat]

Not sure if this is the right place to post. If not, can one of the Mods move it?
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This is going to sound daft but what exactly is an EMP? I know it is an electro magnetic pulse but what I don't understand is how it works. I can understand computers, mobile phones and leccy lines going out but what I can't understand is why batteries no longer work if they are not in use. How then does an EMP affect them? What other sorts of things does it affect? Does it affect anything with an electrical compenent even if that item is not currently in use?

Have you made a Faraday cage?

[Ian]

Don't waste your time or money.

Possibility of nEMP.
1. A nuclear weapon is required. There are not too many around in the megatonne range required for nEMP.
2. A specific weapon, high altitude burst, is required. Very, very few around, if any at all. Only ever tested by the US and USSR, 1958-1962.
3. A launch platform has to be used that reaches very high in the atmosphere. Very few people have the ability to do this.
4. Some sort of aggression is required. e.g. I really can't see the US attacking the UK or vice versa.
5. Should you have all the above, a fair number of weapons (perhaps 10-15) are required to cover the US with confidence (1/2 to 2/3 of missile based weapons are expected to fail, either delivery or completion.

Putting all that together as a package reveals that those with the availability and inclination currently number zero.

Outcome of nEMP:
1. Whilst Nemp certainly exists its effects are debatable. From the twenty one exoatmospheric tests the only damage I can find are some streetlights and a telephone exchange from 'Starfish Prime' and a rumored fire in the power plant in the city of Karaganda from Soviet test 184.
2. Many utilities are well protected these days from surges because of the threat of natural energy pulses.
3. Much theoretically vulnerable equipment will not be exposed to the effects of nEMP as it is indoors, unconnected, physically too small and so on.
4. Even if equipment was lost through nEMP much of it is not vital to life or the continuance of society or culture. We will easily carry on without television for example.

Putting all that together as a package reveals that the chance of being affected by an nEMP is vanishingly small.

Classic risk calculation deems that risk = likelihood X severity. In this case zero times vanishingly small.

In the UK ten people die every day on our roads and thousands are seriously injured.

My thesis is that the effort, time and cost one puts into preparing for the outcome of an nEMP would much better be put into, say, a yearly safe driving course or a more effective anti-sun cream to avoid skin cancer.

[chillihound]

an EMP is used to create a sudden fluctuation in the magnetic fields. it uses induction (the same thing that makes a tranformer work) to create massive currents thats overload or short out circuits. i'm not sure if it would work for smaller equipment but the for the power grid if an EMP is suspected (maybe from a solar flare) then they turn on all the stations and transformers to increase the size of the circuit. this basically allows the high current and voltage to dissapate easily. it will also allow a greater footprint to earth and the planet will absorb everything. this has only been tested on small scale with small solar flares.
an EMP can affect any electrical device. anything stored in a faraday cage will be safe. the easiest way to build a faraday cage is to use a car instead. cars are built as a faraday cage.

[Maddie_cat]

But how does it affect a battery? How would it damage that?

PS Point taken Ian!

[Arzosah]

Weren't goodly sized chunks of the Canadian electricity grid knocked out by an emp back in the 1980s or 1990s? It came on again within hours, but it didn't have *no* effect, surely?

[chillihound]

for a standard battery i can see an EMP having no real effect as long as it is not connected in a circuit. if it was it would cause the chemicals in the battery to expire their shelf life. if the battery has a PCB in it then it would certainly be destroyed.

yea ion the 80's a solar flare caused small blackouts across canada. this was only a small scale flare that we are hit by almost constantly, and its also the nature of the solar flare that causes different effects

any help?

[chillihound]

btw i am terrible at explaining things so i do apologise.

[Ian]

A battery is too small and too rugged to be affected by an EMP, nEMP, lightning or solar flare.

Consider each of the above events as an injection of energy into a circuit or component. If the item can absorb that energy or dispose of it quickly enough it will be unaffected. The amount of energy will depend on the source and how it is collected. A long wire, miles, will collect more energy than a short one, it will act as an aerial, so a small isolated item will not see much energy. When the energy enters the circuit how it affects thing will depend on the resistance the energy sees as it flows to earth following Ohms law.

If it sees a high resistance (or accurately, impedance) a high voltage and low current will ensue which may damage items that are sensitive to voltage like integrated circuits and computer chips. Should the energy see a low resistance (impedance) to earth, the voltage will be low but the current high destroying printed circuits and wires.

The actual energy is really very small but arrives over a very short space of time, thousandths of a second, and consists of a wide range of frequencies. Both make the energy difficult to stop or divert. For example a nEMP injected into a cabinet might be decaying at the input before it has reached the earthpoint, even at the speed of light, so the whole of the energy at that point is on or in the cabinet.

[Maddie_cat]

Thx for that guys. Believe I now u/s how it works.

[Dr_zoidberg]

I think by preparing for an EMP we should define what kind. There are 3 components that make up an Electromagnetic pulse. E1, E2 and E3.

The E1 pulse lasts for no more than 1000 nanoseconds and is created by a nuclear blast in the upper atmosphere. In this case we've seen these before. Starfish Prime test in 1962, where a 1.4 megaton bomb detonated at 250 mile altitude knocked out street lights and telephones in Hawaii over 900 miles away! And test 184 over Khazakstan (a 300 kiloton detonation).

The one thing that should be noted about the American and soviet tests was that they used multistage thermonuclear weapons. Which are somewhat inefficient at making an EMP. These E1 pulses are created when gamma rays from the nuclear blast strip atoms of their electrons in the upper atmosphere (via a process known as the Compton effect) this creates a huge wave of electrons traveling towards earth at near relativistic speeds. Creating a voltage spike at ground level (around 50,000 volts per meter). Anything metal acts as an aerial to this surge. Anything with transistors in will become a brick. Modern transistors are far too fragile to survive such a surge. The problem today is, that there is very little which doesn't have transistors in.

However there have been rumors for many years of super EMP weapons maintained in the nuclear stockpiles of the great powers. These would probably work by creating as many gamma rays as possible. Of which a pure fission bomb would be better at. (Hiroshima and Nagasaki were fission bombs) All nuclear weapons are fission bombs. But most use the energy created by a fission chain reaction to start a fusion reaction which is much more powerful. However a scaled up fission bomb could create voltages of 200,000 volts per meter at ground level. The British actually detonated one of these large fission bombs which had a yield of 700 kilotons to fool the Americans that they actually had working fusion weapons back in the 1950's.

In the event of an E1 pulse the power grids and phone systems will absorb huge fast traveling currents. In the soviet tests for example. They found all the over-voltage protectors in the phone lines had fired and yet it hadn't stopped the surge. Same with fuses. A phenomenon called fatigued fuse had been observed where the fuse wire can carry a very brief current many hundreds of times its maximum tolerance for a very short time and not even burn out. Everything from the big heavy duty breakers and switchgear in the grid right through to your fuse box at home will fail to stop the E1 pulse. Even if it's not hooked up to the grid a high altitude EMP will fry it all. None of the surge protectors that your precious electronics are hooked up to will work fast enough to stop the surge. Not that that will matter because they will get fried anyway. Even if they're turned off.

The E2 component of the pulse is somewhat similar to those created by lightning and other natural phenomena. But in the case of EMP it would be created by residual gamma rays in the upper atmosphere sending more high velocity electrons our way. Some equipment may be shielded and designed to deal with these. However most of this would have already been overwhelmed by an E1 pulse. This phase could last up to 5 seconds.

E3 pulses are a residual effect of an EMP. It lasts from tens to hundreds of seconds and is caused by the earths magnetic field lines being heaved out of the way by the pulse and then moving back into place. This has the effect of inducing giant currents in large conductors like power grids. In the starfish Prime test Hawiis power grid was too small to be affected by these. However during in test 184 in Kazakhstan the E3 pulse did the most damage.

These huge currents burn out the transformers in the power grid. In the UK power grid for example requires large numbers of transformers to change the voltages between 400,000 volts, 250,000 volts, and 11,000 volts. These transformers are enormous pieces of equipment. I know of no companies which make larger ones operating in the UK. In my job i've been made aware that there are many of these transformers in all parts of the grid that are well past their design lifetime. I cycle past some transformers in my area that are leaking large amounts of oil into the canal. A sign they are on their way out. A couple years back another big substation up the road caught fire due to a similar thing.

The worrying thing about an E3 pulse is that these are also caused by severe geomagnetic storms. This is caused by the sun spitting out a CME (coronal mass ejection) like a solar flare but on steroids. Trillions of tons of plasma are hurled towards the earth at millions of miles an hour. This collides with the earths magnetic field having the same effect.

This caused a mass blackout in Quebec in Canada in 1989. It left more than 6 million people without power for several days. However the 1989 storm was a damp squib compared to the storm of 1859. The northern lights were seen as far south as Panama City. Telegraph lines burned out and caught fire. And wireless operators could hear nothing over the static for days. Although E3 pulses have no effect on cars. A solar storm would probably not destroy portable appliances with transistors. But by destroying the grid which supplies them all, they would effectively be useless. Its more a matter of when than if when it comes to one of these storms.

If we're looking at the risk of one of these events. I don't think we're quite living in an era of nuclear terrorism. Not yet anyway.

In 1945 when the first nuclear weapons were detonated it took the worlds best and brightest 4 years and hundreds of billions of dollars to build 3 bombs. The cats out of the bag now. A small team of people with backgrounds in engineering and fabrication could probably make a crude nuclear weapon for a couple million dollars. Most of the work is acquiring the fissile material in the core of the bomb. I'm reasonably confident of there being a nuclear terrorist attack some time in the 2020's.

To create a high altitude EMP one must also achieve altitude. At the moment the rockets which are able to do that are the preserve of the military and government space agencies of the world. However i think we're in the early stages of a boom in commercial spaceflight. The private company SpaceX is already using the Falcon 9 rocket to launch cargo to the ISS. It has a space capsule in the early stages of development and a rocket on the drawing board which would be even more powerful than the Saturn V. There's nothing especially expensive about rockets. It's just that the companies that manufacture them are bloated defense industry entities which don't obey the same rules of business as everyone else does. In 15 years time a rogue nation or international terror group might well be able to buy a couple kilos of plutonium and a rocket to launch their make shift warhead with for the price of a corporate jet.

Also a car is not a Faraday cage. Its not grounded and it has giant gaping holes in the metal frame. I would suggest a very old desiel car

I think there's a distinction to be made between a true Faraday cage and EM shielding. For a novice a Faraday cage isn't really possible. But building something with suitable EM shielding is.

The best way to build one would probably be 2 main layers of shielding that would form a circuit. The best electrical conductors are gold and silver. But these are prohibitively expensive. Apparently Copper and Aluminium are good at sheilding out the frequencies damaging to electronics. I would use a copper mesh on the outside and Aluminium on the inside and insulate them from each other but design the box so when you put the lid on it completes the circuit. I'd also store all the various electronics in smaller boxes inside insulated in a similar manner. That way there are many layers of sheilding between your stuff and the pulse.

I've heard the story that EMP damages batteries before. I'm not sure why it would. But better safer than sorry i suppose. LED's are very sensitive to EMP. Compact fluorescent bulbs, not so much. Hard Drives. To keep your data safe for when there are computers again. Although it would be safe outside a Faraday cage or shielding on disk. A pocket calculator (because using a slide rule sucks). Depending on how much you want to sheild, maybe a generator, power tools, a laptop. These things could come in handy for the years it takes until all of our grids and gadgets are replaced and working again.

While having an old car (pre-1970's) will help there are still problems. During test 184 soviet military diesel generators suffered dielectric breakdown. So i imagine the alternator could be damaged in an old car. Fuses could be blown. But it's not difficult to repair an older car. A modern one would be useless. There's nothing on a modern car not dependent on sensors and the engine management system. Older diesels are probably best as they have a less complex electrical system compared to older petrols which still have plugs. etc.