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Many questions (and answers) about seem to focus on avoiding being hit directly by lightning but don't consider being close to where it hits the ground. Granted, it may be intentional (ie: keeping a narrow scope) but it got me thinking:

What do I have to be aware of if lightning strikes close to me?

And just how close is too close? Is there any real difference if it hits me or if it falls at an arm's length?

For example:

  • I once heard that if it falls really close (but doesn't hit me directly) I'd be deafened. Temporarily, unless there's serious damage to my ear. And I'd probably be disoriented (which could be a risk in itself).
  • I read that electricity from lightning often travels through the ground's edges and bends (especially if wet); so one shouldn't be too close to a wall or cliff. Also, falling rocks could be an issue here.

I'm sure there are lots of things I should be aware of and not only the ones I mention.

  • 1
    One this to be aware of is that if can fall close then it could also hit you. – paparazzo Jul 12 '16 at 4:22
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It seems you are asking about risks of lightning striking close by, but not directly on you. In other words, the lightning current isn't passing thru you on its way between the ground and the sky.

There are certainly risks. I think the two main ones are flying debris and ground currents.

The current in lightning is very high, can heat things above the boiling point of water during the short time of the lightning strike. The steam pressure causes things to explode or to be ejected. The bark of trees can be exploded outward, for example. I know someone who saw lightning strike a stone wall by the side of a road, and some of the rocks get ejected onto the road. You can certainly get hurt from flying debris within a few meters, probably up to 10 meters or so.

Ground currents can cause electrocution, but not by getting directly hit by the lightning. Again, the current in lighting is very high. This current fans out when it enters the ground. It doesn't just go to zero immediately. There will still be substantial currents some distance from where the lightning hit the ground. Also the ground is not uniform, so the current does not spread out uniformly and can be channeled by geographic features. All this means the ground currents can still be substantial up to a few 10s of meters away from where the lighting hit the ground.

The reason ground currents matter is because they cause a voltage drop across the ground. This voltage drop is proportional to the current and inversely proportional to the resistivity of the ground. You don't really care about the current going thru the ground beneath you, but you do care about the voltage difference this current causes along the ground. For example, if the current causes 1000 volts/meter underneath you, and you are standing with your two feet ½ meter apart oriented in line with that current, then your feet get exposed to 500 volts.

This therefore indicate three things you can do to minimize shock from ground currents due to lighting that might strike nearby:

  1. Present the smallest "footprint" across the ground as possible. This minimizes the voltage across the ground that you are exposed to for the same ground current.

  2. Insulate yourself from the ground as much as possible. If you have a foam pad with you, for example, sit on it on the ground instead of directly on the ground. It won't be a perfect insulator, but this is all a probability game anyway. More insulation gives you a higher chance of not getting hurt.

  3. Find a spot ground currents are less likely to travel over. This can be tricky, so in some cases you skip this. For example, sitting on a rock outcrop that itself has a small footprint can be helpful. Of course if that puts you higher up on a flat plane, then that's a bad idea since it increases the chance of a direct hit. A direct hit is always worse than shock due to ground currents. If you're not sure about this, skip it.

  • There is also the possibility that the electromagnetic fields from a nearby strike could interfere with brain and/or heart function and cause respiratory arrest. – aucuparia Jul 12 '16 at 15:35
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Close enough to shock i.e. an indirect strike

According to the National Lightning Safety Institute lightning has been observed to arc out 40 meters and how far it conducts varies.

Possible outcomes

  • Death
  • Concussive injury
  • Burns
  • Lichtenberg figures
  • Blunt force trauma
  • Cardiac Arrhythmias
  • Kidney damage
  • Cataracts
  • Eardrum damage
  • Lower extremity paralysis

Not shocked but within a mile

  • Increased risk of wildfires.
  • In the old days, stampedes could be caused by lightning strikes.
  • Thunder will make it hard to sleep.

For more information, I would suggest the Wikipedia article and this paper by the National Lightning Safety Institute

XKCD: Conditional Risk

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