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Thread: DC Current Safety Threshold

  1. #21
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    Quote Originally Posted by K8MHZ View Post
    Those patients have afib and the DC is in measured pulses of around 5ms. That is totally different from the effects of steady current DC on a healthy person.
    Mark, K8MHZ

    To add to the measured levels.
    In the 70's, I worked at a university hospital, where the JHAC required testing for all electrical devices
    which might be in contact with patients. The main concern was stray currents into arteries and veins.
    The device I used was a electronic Amp-Meter which registered clearly down to 10 microAmps.
    The voltage was not the main issue, only the current flowing from a medical device which could exceed 10 microAmps.

    In my research time there,
    I commonly measured human skin-surface resistance, point to point, at 10 KiloOhms and upwards to 1 MegOhm.
    Commonly, the patient skin-resistance was found to be 50 KiloOhms.
    Given that scenario, the Calculated applied Voltage could be 0.5 Volts.
    That is 0.5 Volts applied in a laboratory experiment.

    Given that some leakage could be via in-the-vein connection, the resistance of the system drops to the 10 KiloOhm range.
    (1) D.C. could cause heart contractions, similar to a defibrillator, if momentary.
    (2) A.C. could cause heart fibrilations, known as multiple-nodes-of-contraction,
    wherein the atria will show chaotic depolarisation with multiple foci.
    Visually, this appears to be a dozen points of contraction, instead of one single contraction for a heart-beat.

    It has been a very long time passing, since those experiences.
    But, it should be obvious that testing for electrical leakage
    flowing from devices/equipment
    is a serious concern.

    This is a good thread. Thank you for the contribution, Mark.
    Since 1958, I have been K4KKQ.
    Glene77is, Memphis, TN. .....Electricity.is.Shocking.....׺`_

  2. #22
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    [QUOTE=drcampbell;1845402]Actually, it depends on the frequency. 50-60 Hz is the most dangerous, requiring about half as much current as DC to inflict the same harm. 400 Hz is about equally dangerous as DC. and increasing frequencies are increasingly less dangerous.

    DrCampbell,
    Good points. There must be more measurement presented in order to keep this discussion rationale.
    As you pointed out with measured frequency : 60 Hz is more dangerous than 400 Hz.

    The pulse nature ( 5mS ) for a Defib waveform is certainly the reason that it unifies the muscle contractions of the heart.
    The long term application of D.C. will certainly impose a long-term contraction on the heart, leading to death.
    Short pulses of A.C. (60Hz) can lead to multiple nodes of contraction in the atria, possibly leading to Fibrillation.

    If you love life, then work with electricity carefully.
    If you want to meet St. Peter today, then grab two wires.
    Glene77is, Memphis, TN. .....Electricity.is.Shocking.....׺`_

  3. #23
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    Quote Originally Posted by Sahib View Post
    May be high frequency current flows along skin due to 'skin effect' not passing through internal organs, making it less dangerous?
    Sahib,

    I work with radio equipment every day.
    Skin Effect is a reality, and becomes measurably important when the frequency passes above 1 Mega Hz.

    The difference in resistance between D.C. and A.C. (60Hz) is less than 0.12 % .
    D.C. measurements and A.C. measurements are very much the same.

    Not much skin effect if daily electrical work,
    if you are accurately measuring,
    or if you are calculating by use of electrical equations.
    Glene77is, Memphis, TN. .....Electricity.is.Shocking.....׺`_

  4. #24
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    Quote Originally Posted by glene77is View Post
    Mark, K8MHZ

    To add to the measured levels.
    In the 70's, I worked at a university hospital, where the JHAC required testing for all electrical devices
    which might be in contact with patients. The main concern was stray currents into arteries and veins.
    The device I used was a electronic Amp-Meter which registered clearly down to 10 microAmps.
    The voltage was not the main issue, only the current flowing from a medical device which could exceed 10 microAmps.

    In my research time there,
    I commonly measured human skin-surface resistance, point to point, at 10 KiloOhms and upwards to 1 MegOhm.
    Commonly, the patient skin-resistance was found to be 50 KiloOhms.
    Given that scenario, the Calculated applied Voltage could be 0.5 Volts.
    That is 0.5 Volts applied in a laboratory experiment.

    Given that some leakage could be via in-the-vein connection, the resistance of the system drops to the 10 KiloOhm range.
    (1) D.C. could cause heart contractions, similar to a defibrillator, if momentary.
    (2) A.C. could cause heart fibrilations, known as multiple-nodes-of-contraction,
    wherein the atria will show chaotic depolarisation with multiple foci.
    Visually, this appears to be a dozen points of contraction, instead of one single contraction for a heart-beat.

    It has been a very long time passing, since those experiences.
    But, it should be obvious that testing for electrical leakage
    flowing from devices/equipment
    is a serious concern.

    This is a good thread. Thank you for the contribution, Mark.
    Since 1958, I have been K4KKQ.
    Nice to make your acquaintance. Thank you for that info, it's great!
    Cheers and Stay Safe,

    Marky the Sparky

  5. #25
    Join Date
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    Location
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    Posts
    6,843
    Fairly decent overall treatise on the subject, confirming research data I had seen elsewhere when I was on a design team for a device that was going to be used in kidney dialysis.

    http://www.wikilectures.eu/index.php...AND_HUMAN_BODY
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  6. #26
    Join Date
    Jul 2017
    Location
    Western Grove, AR Newton County
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    DC Current Safety Threshold

    This has been a good discussion but I haven't seen this angle.

    In the past, Welding Machines often had 70 to 80 Volts DC output. When OSHA came into being in April 1971 it appears they researched some Welder (persons) deaths. OSHA came out with the 50 Volt Max on Commercial Welders shortly after that. I have used old (pre-OSHA) Welders on wet ground / earth and felt a tingling when changing Rods but never knew of anyone that had become a fatality from the older machines. Still, the evidence must have been there for OSHA to make such a drastic change. The OSHA guidelines don't call for a Maximum Current, just the Maximum Voltage.
    JimO

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