Chapter 3 – Electrical Safety
The table of electric currents and their various bodily effects was obtained from online sources: the safety page of Massachusetts Institute of Technology , and a safety handbook published by Cooper Bussmann, Inc. In the Bussmann handbook, the table is appropriately entitled Deleterious Effects of Electric Shock and credited to a Mr. Charles F. Dalziel. Further research revealed Dalziel to be both a scientific pioneer and an authority on the effects of electricity on the human body.
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 were 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 around, brass plate. A voltage was then applied between the wire and the plate, causing current 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.