Electric shock data
The table found in the Bussmann handbook
differs slightly from the one available from MIT: for the DC
threshold of perception (men), the MIT table gives 5.2 mA
while the Bussmann table gives a slightly greater figure of
6.2 mA. Also, for the "unable to let go" 60 Hz AC threshold
(men), the MIT table gives 20 mA while the Bussmann table
gives a lesser figure of 16 mA. As I have yet to obtain a
primary copy of Dalziel's research, the figures cited here
are conservative: I have listed the lowest values in my
table where any data sources differ.
These differences, of course, are academic.
The point here is that relatively small magnitudes of
electric current through the body can be harmful if not
lethal.
Data regarding the electrical resistance of
body contact points was taken from a safety page (document
16.1) from the Lawrence Livermore National Laboratory, citing
Ralph H. Lee as the data source. Lee's work was listed here
in a document entitled "Human Electrical Sheet," composed
while he was an IEEE Fellow at E.I. duPont de Nemours & Co.,
and also in an article entitled "Electrical Safety in
Industrial Plants" found in the June 1971 issue of IEEE
Spectrum magazine.
For the morbidly curious, Charles Dalziel's
experimentation conducted at the University of California
(Berkeley) began with a state grant to investigate the
bodily effects of sub-lethal electric current. His testing
method was as follows: healthy male and female volunteer
subjects were asked to hold a copper wire in one hand and
place their other hand on a round, brass plate. A voltage
was then applied between the wire and the plate, causing
electrons to flow through the subject's arms and chest. The
current was stopped, then resumed at a higher level. The
goal here was to see how much current the subject could
tolerate and still keep their hand pressed against the brass
plate. When this threshold was reached, laboratory
assistants forcefully held the subject's hand in contact
with the plate and the current was again increased. The
subject was asked to release the wire they were holding, to
see at what current level involuntary muscle contraction
(tetanus) prevented them from doing so. For each subject the
experiment was conducted using DC and also AC at various
frequencies. Over two dozen human volunteers were tested,
and later studies on heart fibrillation were conducted using
animal subjects. |