The two most likely reasons for an EMP are a nuclear explosion or solar flare. This post discusses the damage an EMP may cause and actions that you can take to prevent or manage the results of the EMP. A large Electromagnetic Pulse EMP would cause widespread problems. This post is part of our Common Sense Preparedness series, where our goal is to help you be prepared for whatever life throws at you.
What is an EMP (Electro Magnetic Pulse)?
An EMP or Electro Magnetic Pulse is a wave of electromagnetic radiation. An EMP does not directly hurt people, but an EMP interacts with power lines, metal, conductive materials and electronics and causes power spikes. In very large events an EMP can cause electronic systems failures. A large one could knock out power or kill electronic equipment. An EMP can be caused by many things. The two most likely EMP threats are a nuclear explosion or solar flare.
What could an EMP damage?
Depending on the power of the explosion or solar flare, an EMP could damage:
- TVs, radios and other broadcast equipment
- Power grid transformers and substations
- Telephones (land lines) and mobile phones
- Vehicle and aircraft control systems
- Computers and all internet connected devices
- Satellites potentially within the range of the EMP
Anything electronic or powered by electricity could be damaged by an EMP. The damage will vary with the size of the EMP and how close you are to the center of the energy from the EMP.
What is the difference between Solar and Nuclear EMP?
A nuclear EMP is a more energetic and has a shorter burst. A solar flare EMP may also be referred to as a Coronal Mass Ejection (CME) or a geomagnetic storm. Solar flares vary widely in intensity from simply causing bright “northern lights” to potentially destroying some or all of the power grid. Smaller EMPs may cause power grid blackouts. Solar flares can last much longer than nuclear EMPs.
Nuclear EMP Summary (High Altitude EMP)
With the proliferation of nuclear weapons, the likelihood of a nuclear EMP increases. A nuclear EMP requires a nuclear weapon delivered by a rocket, high flying aircraft or ICBM. The nuke is detonated high in the air (referred to as an “air burst” or atmospheric burst) to create the EMP. In a worst case, the nuke is detonated in the upper atmosphere, approximately 20 miles up. A large 1 kiloton to 2 kiloton nuclear electromagnetic pulse like this would be very serious. A nation state or rogue state such as North Korea or Iran are the most likely cause of an atmospheric nuclear burst (EMP). There are other ways to create small directed EMPs but we are not covering them in this post.
The atmospheric nuclear explosion itself would create little to no physical destruction. The gamma radiation would be fairly far away so its direct impact would be limited. However, the air burst nuke would create a widespread EMP and some limited fallout. That large EMP would destroy or at least damage the electrical grid. It would also destroy electronics within the EMP area. Nearly all vehicles with electronic systems would fail when exposed to the EMP. With the level of damage depending on how close and how powerful the blast is. Of course the location and protection of the vehicle impact the level of possible electronics damage.
Basically, a fast burst, high energy nuclear EMP damages or destroys all nearby non-shielded electronic devices (cell phones, refrigerators, generators, inverters, TVs, radios, cars, etc) within its area of effect in a few seconds.
Note: In nuclear weapon tests the EMP doesn't expand in simple circles. The earth's magnetosphere deflects and interacts with the blast, causing the waves to spread more strongly away from the poles and may vary widely. The pulse is concentrated more strongly in a semi-circular band, as shown in the image above. The earths magnetic field deforms the explosion. The graphic is only an estimate – and would vary in the real world based on size/altitude/atmospheric state/magnetosphere and other variables.
How long would it take to recover from Nuclear EMP?
The time to recover from an nuclear EMP could be hours, days, weeks or months. Recovery would vary depending on the scope, location, size and type of explosion, and altitude of the EMP attack. The scope of damage to the electrical grid and technology infrastructure nationally would be a big factor in recovery time. If the blast was small enough or far enough away, vehicles may be disabled temporarily but could be restarted. There is no clear, easy way to predict impact, duration and scope of an EMP.
The biggest risk is a multi warhead nuclear EMP attack resulting in multiple atmospheric nuclear bursts. Multiple bursts spread out over the USA would likely cripple if not destroy the entire power grid. A total power grid failure would require months to even years of recovery work. If the power grid fails, water and natural gas also fail soon after the burst.
Could a surface nuclear blast cause an EMP?
A terrorist group would have trouble successfully setting off a high altitude air burst and would likely use a ship and float in a nuke to a major port city. The lower altitude greatly restricts the range of the EMP damage. Unfortunately the proximity to the ground increases local physical damage, gamma radiation and fallout. A dirty bomb would tend to be devastating locally, but would not result in a widespread EMP. See also “Nuclear Radiation Exposure – Dealing with Radiation Risks“.
Nuclear EMP Details
The amount of energy created in a nuclear EMP is difficult to calculate. We can estimate EMP energy based on historical nuclear tests. A nuclear test using a 1.47 megaton bomb was detonated in 1962, about 400 kilometers (250 mi) in the mid-pacific ocean. The test was called “Starfish Prime” . The nuclear detonation caused electrical damage 800 to 900 miles away in Hawaii. If the same 1.4 megaton nuke was detonated off the US, it is estimated it would have created a 22 to 30 kV/m pulse at the core of its blast. A modern hydrogen bomb is 3 kilotons all the way up to 1.2 megatons, so the amount of EMP from one of these would vary greatly. You can use the kiloton ratio to estimate the range of the EMP and impact in kV/m.
Aircraft may be impacted, but the metal fuselage would function partially as a Faraday cage, so aircraft would not necessarily susceptible, again depending on proximity and many other variables. The electronics in a car or truck would likely survive .25 kV/m EMP blast (especially if it’s not running), but higher than .25kV/m would damage or destroy the electronics.
The distance from the detonation, the altitude and the magnetosphere will determine the amount of damage to electronics. Ultimately the area in the blast would very likely see a regional electrical grid failure. A functional vehicle would not necessarily do you any good if the gas stations can't pump.
Solar Flare Summary
A solar flare or Coronal Mass Ejection (CME) created by the sun through normal activity results in electromagnetic radiation that travels through space. That solar CME wave results in an EMP if it hits our atmosphere. Small solar flares hit earth regularly, but medium ones are rare and huge ones are extremely rare. A really big solar flare could occur any time and they are highly unpredictable and extremely rare.
Scientists would detect a coronal mass ejection (CME) and have time to issue a warning. It takes about 5 days for a CME to reach earth. The CME would create a geomagnetic storm or EMP on earth, also referred to as a geomagnetic disturbance (GMD). Our magnetosphere protects us from most solar radiation and EMP effects. A larger solar flare can get through the magnetosphere and impact the earths surface.
A very large, extended Solar Flare EMP could destroy some or all of the high voltage backbone transformers. These transformers are critical to the U.S. electric grid. Even if only a few hundred of the larger transformers were destroyed it would likely disable the entire interconnected system for weeks or even months. Small electronics could survive a solar flare, cell towers could, some cellphones may survive also but the power grid damage for an extended event is the bigger problem. In general a large long lived solar flare would be far worse than a single nuclear EMP.
You can actually get warnings and alerts for known solar flares here are some references:
- Solar Alerts App https://itunes.apple.com/us/app/solar-alert-protect-your-life/id513766293?mt=8
- NWS Space Weather https://www.swpc.noaa.gov/products/alerts-watches-and-warnings
- Flare Aware https://flareaware.com/
How long would it take to recover from Solar EMP?
The recovery time for small solar EMP could be days to weeks (like 1979 in Canada). The time to recover from a large solar flare EMP could be months to years. The effects of an EMP vary widely depending on the scope, weather, grounding, location, intensity and length of the burst. The largest risk is damage to the electrical grid and technology infrastructure. A major EMP would not directly kill people but the resulting loss of power and communications would result in short and possibly severe long term impacts. It could also disable or destroy some satellites if the flare was strong enough.
Solar Flare Details
The largest recorded CME was the 1859 Carrington event. It lasted multiple days and impacted the entire planet. It caused telegraph wires in the United States to burst into flames, starting fires along the telegraph lines. Telegraph machines scorched paper printouts, gave operators electric shocks, and transmitted gibberish. Telegraphs continued working for hours even after being unplugged from the batteries that powered them. For two days, the light show (northern lights) and electromagnetic storm continued, then faded. A repeat of this event would be disastrous to our modern global electronics dependent environment, impacting part or all of the entire planet. The scope of a larger flare would be absolutely devastating .
Recent EMP Event
In 1979 there was a small solar flare that caused Toronto to be without power for an entire day. There was also a smaller flare that knocked out power in the entire province of Quebec in 1989. The odds of these events are hard to predict, but the likelihood is as high as 1 in 8 for the next 10 years (varying with the solar cycle).
Protect devices from an EMP
You can shield or protect devices by protecting them from the pulse. Here are three ways:
- Building a Faraday cage (a shield that redirects power to ground) using a conductive metal container that is grounded.
- Grounding a “shell” around them and isolating them from the electromagnetic radiation/power spikes
- Using industrial grade ground fault isolation
Here are some basic protection options:
- Foil wrap: A simple Faraday cage can be made by COMPLETELY covering an object with aluminum foil. Wrap your radio with cloth or other insulation, then wrap that with a double layer of aluminum foil (to ensure no gaps). Ensure that this shell is well grounded (electrical ground). If you don't know what an “electrical ground” is, find someone who does.
- Garbage Can or other metal container: A large fairly cheap Faraday cage can be a steel garbage can with a couple of grounding rods. The steel of the garbage can interacts with the EMP and creates a voltage/current spike that is then grounded. That redirects the electrical charge, protecting whatever is inside the garbage can. A Faraday Cage can be used to store radios and other susceptible electronic devices.
- Metal Roof: A house with a extremely well grounded metal roof could protect from an EMP, depending on the power of the pulse, because it could effectively “shield” the house by interacting with EMP and then re-directing the resulting voltage/current spike to the heavy ground wires (like lightning). A multi-day solar flare would create ongoing voltage/current. A nuclear explosion would create a spike more like a lightning strike, independently hitting everything within line of sight. Note: A grounded metal roof alone doesn't fix the problem, because power line spikes could negate any benefits a metal roof would provide.
- These items were designed specifically to shield from EMPs:
What to prepare for?
The best course of action for most people is to focus on events such as a 72 hour power outage. Short duration trouble is more likely than long term problems. It is possible but quite unlikely that a global event could occur due to: a solar flare, major meteor storm, pandemic, major volcanic activity, war or any number of other catastrophes. We suggest you first plan for the far more likely snowstorm, power outage, tornado, earthquake or hurricane.
Prepare for likely events first. Then if you have the resources and understanding prepare for the less likely ones like a solar or nuclear EMP.
Preparing for a small EMP
Prepare as you would for a hurricane, tornado, earthquake or other extended natural disaster. The government recommends we have 72 hours, we recommend 7 days to start, 30 days as a target and your stretch goal of 1 year. Stockpile food and water, fuel, prescriptions, general medical supplies, personal hygiene items – the basics you need to survive. Plan for cooking, shelter, self defense, heating, cooling, clothing, hygiene, handling medical emergencies and garbage disposal as if you were camping without power. Having a 72 hour to 1 year food and supplies stash can serve you regardless of the event, even as simple as a job loss.
- 20 Things I Wish I Had Before the Flash Flood Emergency
- When the Power Grid Fails – 10 Things You Need to Prepare
- Storage and Shelf Life of Over the Counter Medication
There's a lot of overlap between different types of emergency preparedness.
Preparing for a large EMP
This is harder. The time to recover from a large EMP would depend on location and many other variables. It could be weeks, to many months or in a worst case scenario, years. There would also be chaos as supplies dwindle, and the military would likely be called in to maintain order. We've all seen how quickly grocery stores empty during emergencies, and supply lines would be cut. Effectively, you would need to be prepared to live without power, i.e. living off-grid, for a few months to a year or more.
If you are preparing for a single nuclear EMP, the recovery time would be quicker. For a large solar EMP or multiple nuclear bursts the recovery time would be much longer. With a global, multi-day major solar flare CME EMP, it would be many months or even years before we would recover.
Basically, you would need to prepare to live an 1800s lifestyle – wood stove, handtools and no electrical power. You would need hand tools and equipment necessary to garden, hunt, prepare food without electricity or gasoline. You would need a good stock of books, tools, medicine, and learn a LOT of skills.
The other option is to store a completely protected and isolated power generation system, solar, bio diesel equipment, gasification, wind etc. and know how to put it together after the event. If you are planning on keeping modern conveniences you will need to a full electrical power generation system protected from the EMP and spare parts. A Faraday cage around solar panels, bio diesel equipment and/or a wind generator are your best bet, since you won’t be able to get gasoline or natural gas. Box up everything electrical in Faraday Cages.
Practical things you can do that would help in small and large emergencies…
Consider joining regional and national emergency communications, such as your local ARES/RACES program. (ARES = Amateur Radio Emergency Service. RACES = Radio Amateur Civil Emergency Service.) Get a shortwave radio and EMP protect it. More information here: https://en.wikipedia.org/wiki/Amateur_Radio_Emergency_Service
Get First Aid and medical training, and you can use those skills for a storm, EMP or car accident. See Red Cross training programs, YMCA or YWCA, or check out your local vocational tech schools. Participate with your local EMTs. Volunteer to assist in local preparedness exercises. Buy or build a First Aid Kit that would serve you, your family and if you have the funds, your community.
If you don’t have basic carpentry skills, consider learning those skills. Get supplies and tools necessary to repair, improve or worse case, create shelter. Get camping gear, a tent inside a cold house will stay warmer than the house alone or the tent outside.
Stockpile at least 3 days of the foods you regularly eat. Once you have 3 days, build up to 3 weeks, and so on. (See “Top 10 Real Foods to Store Without Electricity“.) Extra stored food is useful for a snow storm, tornado, short power outage or even simply feeding your family while you hunt for a new job. Don't forget to have a way to cook your food, too. See “Emergency Cooking – 10 Ways to Have a Hot Meal When the Power Goes Out” for more information.
For those who have livestock or pets, don't forget about their needs, too.
You must have at least one gallon of potable (drinkable) water person per day. Store at least a week of water, or have a guaranteed way to get water without electricity. Get a bathtub water bladder and fill it IMMEDIATELY after any power event (or before if you have warning, such as a snowstorm or Solar EMP). Purchase a Berkey water filter or other water gravity fed filtration system. The higher end filters are good for an EMP or any other natural disaster. Get LifeStraw personal water filters to carry instead of water. See”Emergency Water Storage and Filtration – What You Need to Know Before Emergencies Hit“. Again, if you have livestock or pets, plan for their needs, too. Hand pumps and large scale water storage will be essential for large numbers of animals or large animals.
BASIC TOOLS & SUPPLIES
Get a good basic tool kit (hammer, knife, screwdriver, etc.). Ensure you have tarps, duct tape and fire extinguishers. Consider other items like a bike pump and a crank cellphone charger/flashlight/radio. Think about what would you need if the power was out for days or weeks? Think about people powered options for making basic repairs.
During an extended event, people causing trouble will likely be armed. Emergency services such as the police will likely be overwhelmed and difficult or impossible to reach. If you obtain a firearm, get proper training to use and maintain it. Consider other options such as pepper spray if you don't feel confident with a firearm or they are prohibited in your area.
Establish good relations with neighbors before emergency situations, so you know someone has your back. (And you have theirs.) Community is how we have survived for 10s of thousands of years. Build your community.
It is possible a household generator would still function after a small EMP, so having the generator and some extra gas, or propane, could allow you to have limited power while the grid is repaired. This would be useful in storms also. A solar USB charger can keep devices that survived the blast running without grid electricity. This assumes you store the electronic devices in a protected location.
Be prepared for toilets to stop functioning. You can use waste bags that fit into a conventional toilet, or a dedicated emergency toilet. See “DIY Portable Toilet, Plus Tips to Get Rid of Smells” for detailed emergency loo tips. Consider a gravity fed solar shower, and make sure you have a clean source of water for hand washing. Solar ovens can do double duty, cooking food and sterilizing water.
What You Need to Do – For EMPs and Other Large Disruptions
The basics are still the best:
- Have water storage and water filtration available
- Stockpile the foods you eat regularly and rotate your stock
- Determine your most basic shelter and clothing needs (clean underwear and socks are priorities)
- Learn necessary skills, such as first aid training, to take care of yourself, your family, and your community
Many of us have seen first hand how emergencies bring out the best and worst in people. Having the tools and skills you need to get things done is never a bad investment.
- Partial Starfish Prime report: http://www.dtic.mil/dtic/tr/fulltext/u2/a955411.pdf
- When the Power Grid Fails
- Surviving Without the Grid – Emergency Backup Power
- Emergency Power Options for Your Home – Gas Generators and More
- Emergency Cooking – 10 Ways to Have a Hot Meal When the Power Goes Out
This post was written by August Neverman IV. August is the Chief Information Officer and Information Security Officer of Brown County Wisconsin. August served on several emergency preparedness teams during his tenure at a local hospital, as well as undergoing emergency response training during his time with the Air National Guard.
Originally published 2013 and last updated March 2019.