Electromagnetic Pulse - EMP Myths - futurescience.com
(This helps balance out other theories about EMP's)
EMP Myths
by Jerry Emanuelson, B.S.E.E.
Futurescience, LLC
This is a page about common EMP myths.
Note: HEMP is an acronym for high-altitude nuclear electromagnetic pulse. I will begin by copying the Appendix on EMP Myths that was included in a report for Oak Ridge National Laboratories by Metatech. Afterward, I will add my own comments about additional common EMP myths.
Appendix From Oak Ridge National Laboratories/Metatech EMP Report
E1 HEMP Myths
Much of the literature on HEMP is either classified or not easily accessible. Probably because of this, some of what is openly available tends to vary in accuracy -- some, especially from the Internet, has major inaccuracies. Some discussions of HEMP have the right words and concepts, but do not quite have them put together right, or have inaccurate interpretations. Here we will discuss some common misunderstandings. HEMP has also appeared in some movies, and there are on-line discussions about possible errors in their depiction of HEMP. Here we will be concerned with E1 HEMP, and ignore misunderstandings about other types of EMP. Extremists: Some general emphasis of comments fall into either "the world as we know it will come to an end" if there is a high altitude nuclear burst, or the other extreme: "it's not a big deal, nothing much will happen". Since we really have never had a nuclear burst over anything like our current modern infrastructure, no one really knows for sure what would happen, but both extremes are not very believable. Yield: There appears to be an assumption that yield is important -- it is not for E1. The assumption that E1 is an issue only for cold war type situations, but not for terrorists or rogue nations, is false. Very big bombs might have better area coverage of high fields by going to higher burst heights, but for peak fields the burst yield is only a very minor consideration. 1962 experience: Some point to the Starfish event, and the rather minor HEMP effects produced at Hawaii by it. However, there are many problems with extrapolating that experience: 1. That was about half a century ago. Since then the use of electronics has increased greatly, and the type of sensitive electronics we currently use did not really exist back then. 2. The burst was fairly far away from Hawaii, and the incident E1 HEMP was much less than worse case. 3. The island is small -- if over the continental U.S., long transmission lines would be exposed (especially an issue for late-time HEMP). In addition, widely separated substations would have been exposed, although with electromechanical relays (not solid state). Also the yield argument has been used -- Starfish was a very big weapon, yet it did very little -- see the previous item, yield is not really very significant. Cars dying: Some say that all vehicles traveling will come to a halt, with all modern vehicles damaged because of their use of modern electronics (and one movie even had a bulk, non-electronic part dying). Most likely there will be some vehicles affected, but probably just a small fraction of them (although this could create traffic jams in large cities). A car does not have very long cabling to act as antennas, and there is some protection from metallic construction. As non-metallic materials are used more and more in the future to decrease weight and increase fuel efficiency, this advantage may disappear. Wristwatch dying: One movie critic pointed out that electronics in a helicopter were affected, but not the star's electronic watch. A watch is much too small for HEMP to affect it. Electrons present: One critic, with some awareness of the generation process, said that HEMP could not be present unless there were also energetic electrons present. This is true when one is within the source region, which exists for all types of EMP -- there are energetic electrons present. However for the HEMP, the radiation and energetic electrons are present at altitudes of 20 to 40 km, not at the ground. Turn equipment off: There is truth to this recommendation (if there were a way to know that a burst was about to happen). Equipment is more vulnerable if it is operating, because some failure modes involving E1 HEMP trigger the system's energy to damage itself. However, damage can also happen, but not as easily, to systems that are turned off. Maximum conductor length: There is a suggestion that equipment will be OK if all connected conductors are less than a specific length. Certainly shorter lengths are generally better, but there is no magic length value, with shorter always being better and longer not. Coupling is much too complex for such a blanket statement -- instead it should be "the shorter the better, in general". (There can be exceptions, such as resonance effects, which depend on line lengths.) Stay away from metal: There is a recommendation to be some distance away from any metal when a HEMP event occurs (assuming there was warning), because very high voltages could be generated. Metal can collect E1 HEMP energy, and easily generate high voltages. However, the "skin effect" (a term not really derived from the skin of humans or any other animal) means that if a human were touching a large "antenna" during an E1 HEMP event, any current flow would not penetrate into the body. Generally E1 HEMP is considered harmless for human bodies. The above is what the Metatech report for Oak Ridge National Laboratories had to say about EMP myths. Now, here is an expansion on those comments by electronics engineer Jerry Emanuelson of Futurescience, LLC. First, though, allow me to make a brief comment about the awful EMP myths generated by movies and television. That situation is so bad that the United States Air Force Space Command commissioned Bill Nye, The Science Guy to make a video for the Air Force called "Hollywood vs. EMP." Apparently, the Air Force wanted to make sure they had a way to concisely remove popular EMP myths from the minds of those people that we most depend upon to be prepared to deal with the real thing. That video is not available to the public. Now, more on common myths: Nuclear Weapon Yield: The E3 component of nuclear EMP, which induces geomagnetic currents in much the same way as a severe solar storm (by causing short-term movements of the earth's magnetic field), is very roughly proportional to the total energy yield of the weapon. The E1 component of high-altitude nuclear EMP is dependent upon the gamma ray output of the weapon. E1 is dependent upon several aspects of the gamma ray output. The gamma ray output of the bomb can often be increased by sacrificing some of the total energy yield. For example, making the casing of the bomb much thinner can greatly increase the gamma ray output, but can cause the weapon to blow itself apart before the nuclear reaction is complete, reducing the total energy yield. Nuclear weapons are complex weapons, and there are several techniques for optimizing different components of EMP. E1, E2 and E3: Most EMP myths originate because people do not understand about the three components of nuclear EMP. The difference between E1 and E3 is especially important. I have a separate page explaining E1, E2 and E3. To a certain extent, all nuclear weapons will generate all of these components of EMP, especially when detonated at high altitude. It is especially important to note that solar storms are only known to produce an E3 component at ground level. (Solar storms can damage electronics in space, but the mechanism is different from the nuclear weapon mechanism for generating E1.) A severe solar storm could knock the large sections of the electrical power grid out for years, but solar storms would not damage electronics equipment at ground level that is not connected to the electrical power grid or other very long lines. Myth: EMP must obey the inverse square law, and therefore has only limited range. Fact: There is some truth to the belief that the law of physics known as the inverse square law applies to nuclear detonations, but it is not relevant to most cases of nuclear EMP. There are several reasons for this. One reason is that, although the nuclear weapon may be detonated far away, the E1 EMP is generated in the atmosphere overhead. Most of this E1 generation is in a region of the stratosphere between 20 and 40 kilometers overhead. (That is about 12 to 24 miles overhead.) This region is commonly called the source region in scientific articles about EMP, since it is the source of most of the E1 EMP. A second thing that makes the inverse square law less relevant is that there are saturation effects that limit high-altitude EMP to about 50,000 volts per meter. These saturation effects mean that the intensity of the E1 EMP is fairly uniform over an extremely large area, regardless of the intensity of the gamma radiation hitting the source region. A third thing that makes the inverse square law less relevant is that the inverse square law applies to the total energy density expanding outward from a single point. The damage generated by the E1 EMP is dependent upon the electric field intensity in volts per meter (or the magnetic field intensity in amperes per meter). These destructive components are linearly proportional to distance. If the inverse square law applied to EMP in the way that many people argue, then radio and television broadcasting would only be effective very close to the transmitting site. Myth: Multiple EMP detonations can be used in a single attack to enhance E1. Fact: Multiple nuclear EMP detonations can add to the effectiveness of the geomagnetic disturbance due to the E3 component. Multiple nuclear EMP detonations can also help to insure coverage of a continent-sized area when one detonation wouldn't work, or wouldn't be high enough in altitude for the intended area of coverage. There is one very significant problem with multiple nuclear detonations, though. The first nuclear detonation will ionize the source region in the stratosphere over the line-of-sight area, making this part of the mid-stratosphere conductive. This turns this critical part of the atmosphere into somewhat of an electromagnetic shield, and renders it incapable of generating further E1 EMP for a period of time. This period of time will range from a few minutes to an hour or more, depending upon a number of factors. The important thing to remember is that for multiple high-altitude detonations, even if they are timed to be simultaneous using atomic clocks, the E1 components will not add. The E1 as a result of second and subsequent detonations may even be negligible, depending upon a number of factors. Myth: During the 1960s, the AT&T Long Lines Division was partially hardened against EMP, therefore the 21st century telephone system is completely resistant to EMP. Fact: This myth, like many others, is quite bizarre, since it involves a company that has not existed in a very long time; and most of the technology that they used has not been used in a long time. I only mention this myth here because I have heard it so many times. There are many other versions of this myth which assert that since some 30-year-old (or older) technology was EMP-resistant that current technology is also EMP resistant. These myths get things exactly backward. The actual facts are that the main reason that the EMP threat is increasing is the fact that electronic devices are becoming more sensitive to EMP every year. Myth: Small transistorized radio receivers would survive a nuclear EMP attack. Fact: In many areas affected by an EMP attack, many small solid-state radio receivers probably would survive if their antennas were not extended and they were not connected to any external wires. Many other unprotected radio receivers probably would not survive, though. Where most people go wrong is the source of the information for their belief that radio receivers would survive. One source for the belief is the testing of small transistorized radios that was done during the 1970s. That testing cannot be extrapolated to today's solid-state receivers, which usually use integrated circuits that are much more sensitive to EMP than the receivers of the 1970s that used much more rugged discrete transistors. More recent testing of portable professional two-way radios has shown that they were resistant to EMP up to quite high levels. Two-way radios must have sophisticated filtering to protect the receive circuits. Otherwise, the receive circuits would be blown as soon as the transmit button is pressed. One cannot extrapolate the EMP resistance of professional two-way radios to all other solid-state radio receivers, especially inexpensive consumer radios. Myth: EMP is not a problem since there are many ways to protect against it. Fact: There are many ways to protect against EMP, but they are very rarely being used, especially in the civilian infrastructure. In an effort to save money in the short term, most companies do not even have any effective protection against lightning. A major television station in the city where I live spent several days off the air due to lightning damage in 2010. Two years earlier, I had been in the station manager's office and had told the station manager and the acting chief engineer that the station was very deficient in lightning protection, and I told them exactly what to do about it. My advice was completely ignored. The myth that EMP is not a problem since there are many ways to protect against it is similar to the problem that many people have with preventive medicine. I have known many people with a "silent" medical condition such as high blood pressure. These people have been prescribed a blood pressure medication, and they have purchased the medicine, but they do not use it. They seem to think that a bottle of blood pressure medication setting in their cabinet will help their condition; but it won't help if they don't use it. The fact that critical infrastructure could be protected is irrelevant if that protection is not used. Myth: EMP is a new kind of weapon. Fact: EMP is seen as a secondary effect of all types of nuclear weapons, and was a problem in the very first nuclear weapons test in July, 1945. The official technical history for that first nuclear test states, "We can understand the difficulty of transmitting signals during the explosion when we consider that the gamma rays from the reaction will ionize the air and other material within hundreds of yards. Fermi has calculated that the ensuing removal of the natural electrical potential gradient in the atmosphere will be equivalent to a large bolt of lightning striking that vicinity. . . . All signal lines were completely shielded, in many cases doubly shielded. In spite of this many records were lost because of spurious pickup at the time of the explosion that paralyzed the recording equipment." As I stated on another page on this site, consider this Cold War era quotation from a widely-read and highly-respected publication: "The United States is frequently crossed by picture-taking Cosmos series satellites that orbit at a height of 200 to 450 kilometers above the earth. Just one of these satellites, carrying a few pounds of enriched plutonium instead of a camera, might touch off instant coast-to-coast pandemonium: the U.S. power grid going out, all electrical appliances without a separate power supply (televisions, radios, computers, traffic lights) shutting down, commercial telephone lines going dead, special military channels barely working or quickly going silent." -- from "Nuclear Pulse (III): Playing a Wild Card" by William J. Broad in Science magazine, pages 1248-1251, June 12, 1981. The reason that EMP is getting more attention now is that the critical infrastructure that sustains our lives is becoming increasingly sensitive to the effects of EMP. This is happening because electronics is becoming more sensitive to EMP all the time, and critical infrastructures are becoming increasingly dependent upon electronics. The next myth is what I call the either-or myth with regard to electromagnetic shielding. The myth is the belief that either an electronic device is resistant to EMP or that it must be enclosed in a military-grade faraday cage. This myth is so bizarre that I heard it for years before I realized that many people actually believe it. Unfortunately, many of the "professionals" working in the EMP field seem to be responsible for spreading this myth through careless comments. If a device has a damage threshold of an EMP field of 20,000 volts per meter, then reducing the electromagnetic field by a factor of 3 or 4 will be enough to protect it from known weapons, and shielding it by a factor of 10 will protect it from the super-EMP weapons that are believed by many to exist. A very efficient 80 db. faraday cage would reduce the EMP by a factor of 10,000. In other words, it would reduce a 20,000 volts per meter EMP field to 2 volts per meter. This high level of shielding is necessary for some applications, but not for the average consumer. For many applications, an imperfect shield is quite helpful and may be all that is necessary. This myth is analogous to saying that if a coat doesn't keep you from being cold during a winter blizzard that you might as well just rip your coat off and go shirtless while out in the snowstorm. Asking how much shielding that you will need is like asking how much of a coat you will need in the winter. (It depends upon how cold it will get, and upon how sensitive you are to the cold.) Myth: Solar storms only affect the side of the earth that is facing the sun at the time that the storm arrives. Fact: Solar storms, especially the most severe solar storms, tend to disturb the entire magnetic field of the earth. The effect of the solar storms tends to be much greater near the geomagnetic poles, but it matters little whether it is night or day. When the electrical power grid of Quebec was shut down by a solar storm on March 13, 1989, the power grid was operating normally at 2:44 a.m. It went from normal operation to complete shutdown in the middle of the night over a span of only 92 seconds. Myth: There are scientists who can predict the probability of a severe solar storm or nuclear EMP over a 5 or 10 year time frame. Fact: Most of the attempts by the world's best solar scientists to predict solar activity over a 2 to 10 year time frame have proven to be quite embarrassingly wrong. The prevalence of severe solar storms on time scales of centuries is much better known. In the spring of 2011, several noted solar scientists predicted that the forthcoming solar maximum would likely fizzle, and that we may be heading for something like the Maunder Minimum of a few centuries ago or the more recent Dalton Minimum. Shortly after these predictions were reported in the news media, the sun began emitting a number of M and X class solar flares. Fortunately, none of the stronger solar flares were aimed directly at the Earth, but this increased solar activity did demonstrate the considerable difficulty in relatively short term predictions. There is a similar difficulty behind predicting the probability of nuclear EMP attacks. Such an attack would be a surprise attack. The most reliable characteristic of surprise attacks are that they are a surprise! I've seen a remarkable number of writings and videos about what to do if a nuclear EMP attack is imminent. If you are the average civilian, though, I do not think that you are likely to be receiving a courtesy telephone call from an attacking nation. It is fairly easy to predict that the ability to produce both nuclear weapons, and the ability to send them to the necessary altitude, will be greatly increasing over the coming years. It is not so easy to predict whether any entity will actually make use of that capability to carry out an EMP attack. Myth: Severe solar storms can damage automobiles and trucks. Fact: Solar storms, no matter how severe, will not damage vehicles. This is a myth that has arisen in the past few years, and that just will not go away. (If you have an electric car, and it is plugged in to the electrical grid for charging, it is conceivable, though very unlikely, that it could be damaged.) A nuclear EMP can damage automobiles through the E1 component, which is not present on the surface of the Earth during a solar storm. The voltages induced in automobile wiring by a severe solar storm would be less than 0.1 volt, and would be slowly increasing DC-like voltages. A typical automobile experiences voltage changes that are much greater, and that change much more rapidly, every time that the engine is started. Severe solar storms have been experienced in relatively small areas of our planet at high latitudes during the years since automobiles have relied heavily on microelectronics. There were billions of dollars in damage to high-latitude electrical grids in the solar storms of 1989. That damage was mainly in Quebec, in northern Europe and to one very large transformer in New Jersey. In 2003, a solar storm in South Africa damaged at least 14 major transformers in the South African power grid. That solar storm left large parts of the South African power grid crippled for months. None of these solar storms resulted in reports of damage to automobiles. Myth: A Faraday cage will protect against a solar storm. Fact: There is some truth to this if you are designing a satellite or if you are located on the Moon or on Mars. If you are located on the surface of the Earth, a Faraday cage will protect only against the E1 and E2 components of nuclear EMP, and will do no good at all against a severe solar storm. Myth: When an EMP hits the ground, the induced electric currents either head directly toward the center of the earth or they just vanish from existence. Fact: When EMP (or lightning) hits the ground, the currents tend to spread out horizontally. These ground currents can do great damage, especially to underground cables of all kinds. Metal conduits are of little help, and may actually make the situation worse by providing a path for underground currents which can, in turn, induce large voltage spikes on the underground lines inside of the conduits. A large amount of damage has actually occurred due to these underground currents, due to both lightning strikes and nuclear EMP. This is one reason that so much of the information on the internet on grounding and on underground cabling is pure nonsense. Large variations in soil conductivity makes the ground current situation even more complex. There are lots more EMP myths. (They seem to be endless.) I will have more later. |
No comments:
Post a Comment