Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Lightning's Lethality

  1. Aug 27, 2012 #1
    Does anybody know why lightning doesn't kill any living thing it touches if it is supposed to be four or five times hotter than the sun and has a huge amount of voltage? The heat alone should be able to kill living things instantly, right?
  2. jcsd
  3. Aug 27, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Wait, what? There have been reports of people killed by lightning! What do you mean that it doesn't kill any living thing it touches? Where do you get such an idea?

  4. Aug 27, 2012 #3


    User Avatar

    Staff: Mentor

    I think (but am not sure) that he is asking how come it doesn't *always* kill whatever it strikes.

    If so, it just depends on how much of the current goes through the critical parts of the body (brain and heart). If for some reason most of the current bypasses the person's core (or animal's core), then they may survive the strike...
  5. Aug 27, 2012 #4
    Yes, that is what I meant. Sorry for not phrasing the question right.

    I get what your saying. I was wondering the exact process though. I understand that all the current doesn't travel through the body, even with a direct hit by lightning, but if the lightning is so hot, that should be independent of the current, right? The heat should have exploded the water inside your body the same way it explodes clothes outside the body and inside trees, destroying them.

    Unless when they say that the temperature of a lightning bolt is five times the sun, they really mean that it has the potential to reach five times the heat of the sun if the current is allowed to move freely through whatever it touches.

    Just trying to sound it out, but when I think about it a lightning strike is not that much more lethal than a gunshot unless the survivors simply aren't ever hit by a direct lightning bolt. That would explain some things.
  6. Aug 27, 2012 #5


    User Avatar
    Gold Member

    Just like if you take a blow torch to your hand, it doesn't kill you, it demolishes your hand. With lightning, the heat only spikes where the current travels, so of it doesn't hit vitals, it's less likely to kill you.

    Lightning can take different paths depending on where it finds ground, or the lowest potential path.
  7. Aug 27, 2012 #6


    User Avatar

    Staff: Mentor

  8. Aug 28, 2012 #7
    I read through that link and it instructs to take safe shelter, but it doesn't really describe safe shelter.

    If I'm up on a mountain, what should I do to be safe? It says stay away from trees, but I know you also don't want to isolate yourself.

    I know from a physical perspective, lighting will strike the path of least resistance. Air has a very high resistivity compared to most solids/liquids, so being higher up is therefore dangerous. I'd guess that human resistivity is lower than that of wood, or rock, so you'd need to be significantly lower than the surrounding wood/rock, so that your elevation difference will outweigh the lower resistivity of your body.
  9. Aug 28, 2012 #8


    User Avatar

    Staff: Mentor

    It provides links to many sources, you need to read about the links.

    For example that page links to this one for safety.


  10. Sep 1, 2012 #9
    I've often wondered this too why lighting doesn't kill you with the heat if nothing else. My guess is that perhaps this is the temperature directly on the lighting arc itself. Air has very high resistance, people have less resistance so not as much heat would be generated passing current through you.

    Also air is very low density so it may burn you where the lightning hits you but it would dissipate quickly like tin foil coming out of the oven.

    I think I've heard people indeed do have burn where the lighting goes in and out which would make sense.

    Also I've read they're often burnt where they had moisture on their bodies from the moisture vaporizing. While it burns them it also probably protects them from more serious injury by throwing off the heat.

    It reminds me of trying to strike an arc with a stick welder and sticking the rod the arc strike instantly melts the metal and sticks the rod and the base metal together. If you leave it there for a couple seconds it'll get hot from the current flow but not that hot because the real heat comes from the current passing through the air gap between the two metals.
  11. Sep 1, 2012 #10


    User Avatar

    Staff: Mentor

    You could read the answers in post #6.
  12. Sep 2, 2012 #11
    There are 2 possible ways lightning can damage you. 1 is the immediately arrhythmia in the heart from the lightning, which why ER's will always check your ECG first. 2 is the burn itself, which is not actually the surface burn. The electrical current travels in the body and slowly releases heat and burns on the inside, which takes some time and also is the most severe kind.
  13. Apr 12, 2013 #12
    Lightning is not intrinsically hot. It generates heat as a result of its passage through resistive media that dissipate the energy. In the human body the highest resistance and heat occurs on the skin. Inside the body the resistance is relatively low so less heat is dissipated internally. The lightning also spreads out inside the body which reduces the resistance further and dissipates the heat over a larger volume. Of course if the strike is powerful enough it can still cook you.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook