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The context of the question is camping and sleeping outdoors in the unprotected elements. If you’re sleeping in a tent close to the ground, and lightning directly strikes your tent or the vicinity within up to 100m of it, what minimum safe electrical resistance (in Ω.m) would the material(s) between the bare earth and you (such as tent base, sleeping mat, sleeping bag etc - however many pieces, the resistance in total), be?

Knowing this minimum Ω.m resistivity (of worst case scenario where one side of your whole naked body, including proximity to vital organs, is in contact with such material connecting you to the ground and the lightning is direct), can help determine what materials may be suitable to safely choose from when considering lightning protection.

I will point to this wikipedia collation as a reference for the apparent electrical resistivity os materials (at 20° C).

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The usual method of lightning protection is to convince the lightning strike to follow a less harmful path than through the item being protected. Hence, lightning rods and lightning arrestors.

Ohm's law resistivity assumes linear behavior- this is not what happens when you have enormous voltages and currents at play. Air is supposed to be a pretty good insulator, but lightning reaches through it. Many meters of air. A thin bit of polyethylene film is an almost perfect insulator, but a few thousand volts will punch a hole through it. At high current it will carbonize and become a pretty good conductor. A lightning strike is hundreds of thousands of volts and tens of thousands of amperes typically.

That said, there may be information available on what ground conditions are like. Geophysical surveys looking for natural resources sometimes use EM methods to find ground conductivity such as this map of Electromagnetic Ground Conductivity. It will vary greatly depending on what is under the ground.

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  • \$\begingroup\$ That's superb summarised information. Thank you. So I am to conclude that even a rubber air mattress wouldn't offer any meaningful protection over a (much more electrically conducting) cotton blanket (even for strikes 50 meters away and dissipating across the ground), and that much much more of a factor is measures like not being near trees/hills/high points, etc.? \$\endgroup\$ – user22246 Mar 25 '14 at 6:43
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    \$\begingroup\$ Yes, that is correct. \$\endgroup\$ – Spehro Pefhany Mar 25 '14 at 6:44
  • \$\begingroup\$ Oh, just edited my comment to include 'even for strikes 50 meters away and dissipating across the ground', wouldn't it still offer meaningful difference for strikes to trees less than 100m/50m from you? \$\endgroup\$ – user22246 Mar 25 '14 at 6:45
  • \$\begingroup\$ I realised this question was outside the parameters of the actual question. I've now edited it to include the area around you, not just direct hit, given I now realise that's actually more (or at least just as) likely a scenario with lightning striking you when camping in the open... \$\endgroup\$ – user22246 Mar 25 '14 at 7:13

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