Effects of current passing through the human body

From: johnh@macadam.mpce.mq.edu.au (John Haddy) Newsgroups: sci.electronics Subject: Electrical Safety Date: 2 Mar 1994 06:20:49 GMT Organization: Macquarie University, Sydney Australia NNTP-Posting-Host: macadam.mpce.mq.edu.au I wrote the following in response to a thread of a thread with the topic Jacob's Ladders. However, since I feel that the information should reach a wider audience, so I've reposted it with a new topic.

===============

It always amazes me how long it will take before somebody presents attributable data for questions on sci.electronics. What's more shocking (sorry!) is the amount of suspect "I think ..." responses I've seen to such an important field as electrical safety.

From Australian Standard AS3859-1991, based on IEC479-1(1984) and IEC479-2 (1987) "Effects of current passing through the human body":

Table 1:

Total Body Impedance

                        Values for the total
                        body impedance (ohms)
                        that are not exceeded
                        for a percentage
                        (percentile rank) of
Touch Voltage           5%      50%     95%
(V)                     of the population

25                      1750    3250    6100
50                      1450    2625    4375
75                      1250    2200    3500
100                     1200    1875    3200
125                     1125    1625    2875
220                     1000    1350    2125
700                     750     1100    1550
1000                    700     1050    1500
Asymptotic value        650     750     850

"The values of the total body impedance given in Table 1 are valid for living human beings and a current path hand to hand or hand to foot for large contact areas (50cm^2 to 100cm^2) and dry conditions.

"At voltages up to 50V, values measured with contact areas wetted with normal water are 10% to 25% lower than in dry conditions and conductive solutions decrease the impedance considerably down to half the values measured in dry conditions.

"At voltages higher than approximately 150V the total body impedance depends only slightly on humidity and on the surface area of contact."

From the same document:

Describing the four zones of physiological effects for a.c. currents:

(extracted from Table II)

Zone 1

Usually no reaction effects

Zone 2

Usually no harmful physiological effects

Zone 3

Usually no organic damage to be expected. Likelihood of muscular contractions and difficulty in breathing, reversible disturbances of formation and conduction of impulses in the heart, including atrial fibrillation and transient cardiac arrest without ventricular fibrillation increasing with current magnitude and time.

Zone 4

In addition to the effects of Zone 3, probability of ventricular fibrillation increasing up to about 5% (curve c2), up to about 50% (curve c3) and above 50% beyond curve c3. Increasing with magnitude and time, pathophysiological effects such as cardiac arrest, breathing arrest and heavy burns may occur."

This table references Figure 5 of this document, "Time/current zones of effects of a.c. currents (15Hz to 100Hz) on persons.", which I cannot draw due to the nature of the curvy lines, etc.

Summary

In summary, Zone 1 lies in the region less than 0.5mA body current, for all durations. Zone 2 extends to about 500mA at 20ms or less duration, to 20mA at 1000ms duration and to 10mA at 10000ms duration. Zone 3 (to curve c2 mentioned) extends from the Zone 2 boundary to 1000mA for 10ms duration, 200mA for 500ms duration and 50mA for 10000ms duration.

I really do recommend that _anybody_ playing with mains powered circuits should get hold of a copy of their country's standard and read it.

JohnH

----------------------------------------------------------------------------

      |  _  |_   _   |_|  _   _|  _|              Electronics Department
    |_| (_) | | | |  | | (_| (_| (_| \/           School of MPCE
    ---------------------------------/-           Macquarie University
                                                  Sydney, AUSTRALIA 2109

    Email: johnh@mpce.mq.edu.au, Ph: +61 2 805 9090, Fax: +61 2 805 9128

----------------------------------------------------------------------------