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Human head gives off smoke when electrocuted?

  1. Jul 10, 2012 #1
    I heard that when any human being is executed by electrocution (for instance on an electric chair) afterwards, smoke comes out of his head (seriously). Why does this happen? I think it's got to do with the fact that the human head has a huge number of neurons and their is a lot of electrical activity going on in the brain. But that's just what I think. What's the real reason behind this?
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  3. Jul 10, 2012 #2


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    I have read many times that it happens, but I SERIOUSLY doubt that it has anything to do with neurons ... why do you think it would?
  4. Jul 10, 2012 #3
    Neurons probably have nothing to do with it.
    This fog is probably steam, not smoke. The liquid in the human body is mostly water. There is a lot of water in the cochlear and the semicircular canals. When the water boils, the water vapor is under pressure.
    The eardrum probably holds water vapor in place for a while. However, the eardrum burst. The water vapor coming out of the ears cools down because of adiabatic expansion. Some of the water vapor leaving the ears condenses into droplets. Therefore, what comes out looks like steam.
    The high pressure water vapor shows up in other places. Not often discussed is what happens to the eyes. The high pressure water vapor sometimes makes the eyes pop out. If there wasn't a mask, you may see steam coming out of the mouth and nose. They put that mask on the prisoner for the benefit of the spectators, not the condemned.
    The only way that neurons could contribute to the steam is by contributing water. I don't know what fraction of the steam comes from the cochlea, what fraction comes from the brain itself and what comes from the blood. However, the only reason the steam comes out of the ears is because that is the shortest path out of the skull.
    Although it looks ugly, it is probably painless in most cases. If the execution isn't botched, then the inside of the brain heats up to boiling within a millisecond. There is no way the neurons in the brain can work under such high temperatures and pressures. It would like being shot with a bullet through the head. The neurons would be destroyed long before the brain could perceive of the disturbance.
  5. Jul 10, 2012 #4
    The reason why I thought smoke would be coming out of the brain due to neurons is that I thought of an electrical circuit (analagous to neurons) which when overheated (or a massive amout of electricity flows through it) starts giving off smoke. Anyway thanks for pinpoointing the real reason behind the appearance of smoke after electrocution.

    A further question. Why does smoke only come from the head? Is it because in the rest of the body water is found in liquid form whereas in the head it is also found in gaseous form?
  6. Jul 11, 2012 #5


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    Where in the head is gaseous water found?

    If this effect is true then I would think that it is because the head has 7 orifices out of a body total of 9/10 depending on sex. Also execution via the electric chair works by wetting and electrocuting the head IIRC.
  7. Jul 11, 2012 #6
    I conjectured that it is steam, not smoke. The water in the body is boiling. Hence, water vapor under great pressure is forming in the body. When the water vapor escapes, you have steam.
    A good analogy here would be between the human skull and a tea kettle. There is water, air and a little organic matter inside the tea kettle. You place it on a stove and heat it. To strengthen the analogy, make it an electric stove. Heat the water and steam comes out of the holes. There are no neurons in the tea.
    Or maybe a better analogy would be a vaporizer sometimes used to relieve colds. A container is filled with water, salt and a medicine with a low vapor pressure. An electric current passes through the solution. It heats up. Steam with vaporized medication spurts out a small hole in the container. There are no neurons in the container.
    The mist coming out of the ears is probably not smoke. The generation of smoke would require combustion, which requires oxygen. Where there is smoke there is fire. However, there is no fire in the cranium. There aren't many air pockets within the cranium. The nasal sinuses contain some air. So maybe there is some smoke generated in the sinuses. However, the mass of water far exceeds the mass of air in the skull. When that water comes to boil, the pressure of water vapor must be large. Imagine the bubbles in the brain caused by all that boiling blood. The ambient air pressure (i.e, outside the skull) is just atmospheric pressure.
    The reason it comes out of the head is that this is where most of the apertures in the body are located there. The high pressure water vapor can't break through the skull, because it is so hard. So it comes out of the small apertures. The only apertures that show are the ears.
    Note that all the body fluids are electrolytic solutions. Therefore, the fluids conduct electricity. Basically, the human body is a bag containing salt water. So the electricity has an almost straight line path from electrode to electrode.
    The neurons are more like tiny batteries than electric wires. The generate voltages between points on the surface of the brain are on the order of millivolts (i.e., 1mV = 1/1000 volt). The potential difference in an electric chair is at least 500 V. Therefore, the electric fields generated by the neurons are negligible compared to the electric fields produced by the chair electrodes.
    Last edited: Jul 11, 2012
  8. Jul 11, 2012 #7
    I have heard that the first time a doctor listens to the heart of a prisoner after the execution, some claim to hear a heartbeat. What in fact they are hearing is blood boiling in the veins and arteries.
  9. Jul 11, 2012 #8
    Do you have a source for that? It's not clear to me how boiling blood (or other body fluids) would sound like a heartbeat.
  10. Jul 11, 2012 #9
    Sorry, I don't. When I heard it though, it struck me how much power they must be pumping into the body. Wouldn't blood, being somewhat thicker than water, tend to release the vapor in larger bubbles than water. To exaggerate the difference, imagine how mud boils.
  11. Jul 11, 2012 #10
    That's speculation and not very good speculation at that. I believe PF rules apply to this forum. Heartbeats have a very specific sequence of sounds directly related to events such as valves opening and closing during the cardiac cycle. If the expansion of fluid in the major blood vessels had something to do with forcing blood though the heart (and lungs), venous blood would have to be preferentially heated. Even then, the sounds would not resemble the normal heart sounds.
    Last edited: Jul 11, 2012
  12. Jul 14, 2012 #11
    I defer to your vastly superior knowledge on the subject.
  13. Jul 14, 2012 #12
    It is true that judicial electrocution does not always kill with one or even several shocks. Examining physicians have reported hearing heartbeats after such shocks. However, to claim that boiling blood could sound like a heartbeat really requires a valid source. It doesn't take "superior knowledge" to question such a claim. It sounds ridiculous.

    Last edited: Jul 14, 2012
  14. Jul 17, 2012 #13
    It sounds like wishful thinking. I hypothesize that the coroner wants to believe that the body is dead before he starts cutting. The executioner would like to believe that he delivered a clean kill. So they interpret the beating of a heart as "boiling".
    There would be other effects apparent if the blood were so hot. If the blood were boiling, there would be steam coming out of every orifice in the body. If the blood was so hot inside to be boiling, then the skin would be too hot to touch. Furthermore, the insides of the deceased would be caramelized.
    I suspect that the coroner didn't want to check for those things before cutting. Vivisection is not an acceptable coup de grass.
  15. Jul 31, 2012 #14
    FWIW, to a layman, the heartbeat of a person who is near death and/or experiencing cardiac distress can sound sufficiently unlike a healthy heartbeat for a sound of the kind skeptic2 suggested (boiling mud) to be mistaken for such. But there are several ways in which that set of circumstances shouldn't apply to the situation in question, so... :)
  16. Jul 31, 2012 #15
    I understand the laws in the US require trained medical personnel to confirm the absence of a heartbeat as an indicator of death, not lay people. In any case, given the gravity of execution, I asked for a source. None was provided. I didn't say it was impossible, especially if someone doesn't know what they're doing.
    Last edited: Jul 31, 2012
  17. Aug 24, 2012 #16
    Could it be the hair igniting?
  18. Aug 24, 2012 #17
    No. The aerosol plume comes out of the ears. This has been witnessed many times.
    Most electrocutions are preceded by shaving the head under the electrodes. Thus, the electric current never comes in direct contact with the hair. So the hair probably has nothing to do with it.
    The white plume coming out of the ears is either steam or smoke. I am not sure whether the aerosol plume is steam or smoke. The OP called it a "smoke plume". My conjecture is that is most likely to be steam. I doubt that the electric current can burn once it is below the skin. However, there are plenty of body fluids containing water. Increased evaporation of water in the body can create water vapor under high pressure. This can produce steam.
    When I say steam, I am talking about condensation of water vapor to form water vapor droplets. I don't think the body fluids have to reach the boiling temperature to produce steam. The body fluids just have to reach a temperature high enough to speed up the rate of evaporation. Confined by the body, the water vapor would be at high temperature and pressure. The water vapor would experience "free expansion" coming out of the ears. The drop in pressure would cool the water vapor. The sudden cooling would cause water droplets to condense from the vapor.
    Of course, I don't know for sure. However, it is an interesting problem in thermodynamics.
    Last edited: Aug 24, 2012
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