This works well unless you are working with high voltages (and low power), In my early R&D days I was taught that, if in doubt, (AND AFTER waving an earthed conductor all over the circuit) to keep my left hand in my pocket and stand on my right leg. If something din go horribly wrong the current would not cross the body and was slightly less likely to pass through the heart.
Fortunately I never got the 'chance' to prove it true or false - but - hey - any end is better than none. Think of all those "lucky" rabbits feet that have been sold. My answer - if they were that lucky then the rabbit would still be wearing them. Best regards Gregg PLEASE NOTE NEW NUMBERS P.O. Box 310, Reedville, Virginia 22539 USA Phone: (804) 453-3141 Fax: (804) 453-9039 Web: www.test4safety.com -----Original Message----- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Rich Nute Sent: Tuesday, November 13, 2001 9:13 PM To: Product Safety Technical Committee Subject: AC, DC definitions and safety Hi Ted: > The electrician's rule of thumb when working on domestic wiring was to > always check the wire is dead, even though you isolated it, in case of > bridging or faulty connection. The technique used was to brush the > exposed conductor lightly with the back of the fingers. Any AC present > will be noticeable as a tingle. DC would cause contraction of hand > muscles which would cause the hand to withdraw from the conductor. The technique of brushing lightly avoids a low- resistance connection to the body which would occur with a tight or solid connection. The back of the hand has more hair, fewer sweat glands, and higher resistance than other parts of the body. So, this, too, tends to avoid a low-resistance connection. Both ac and dc would cause a tingle; in this situation, the protection is by means of a high- resistance connection which limits the current, and the electrician maintains control of his muscles regardless whether ac or dc. > The same teacher explained that this precaution saved lives. Should the > hand be allowed to grasp a live conductor the paralyzing effect of DC > would be more likely to cause injury, shock or death because the effect > of the current on the hand muscles when grasping would increase the grip > and prevent the hand being opened to break the circuit. In this case it > is precisely tetanus of the body which is dangerous because it > interferes with the ability to move away from the hazard. Dc may cause a single contraction, but not continuous contraction. In my experience, the dc tends to throw you away from the source. Charles Dalziel reports in his experiments that his subjects chose not to let go of dc (and they could!) because of the severe pain at the moment of letting go. I studied Reilly (again) and found no reference to tetanization due to dc. Reilly says that "As sinusoidal frequencies approach dc, it becomes quite difficult to stimulate peripheral nerves. Stimulation may be elicited at the onset of direct current as with any rectangular pulse. However, following the onset of direct current, additional stimulation of... skeletal muscle is not so easily achieved..." > Power is hazardous to health in all its forms. I would say that ENERGY is the key parameter, not power. Defibrillators are calibrated in joules, and essentially apply a corrective pulse to the heart to contract the heart muscle and then let it resume normal rythyms. Because we can easily do so, the limits in safety standards are in terms of voltage and current which can be sensed. Sensation levels are very much below the injury level (where energy becomes important). Best regards, Rich ref: Reilly, J. Patrick Applied Bioelectricity from Electrical Stimulation to Electropathology ISBN 0-387-98407-0, Springer-Verlag, New York ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
