Robert et al,
You have received quite a bit of good information already from the
folks here on the PSNet. I'll try to, hopefully, add something new here.
The research on electric shock effects has been ongoing since the
development of electricity for commercial purposes. The basic data used
today comes from work done primarily in the 30's, 40's and 50's - so it has
been around for some time. Ongoing work since has attempted to fill in the
gaps in our understanding of these effects; there were a couple of
symposiums in the 80's providing updated information in many areas. The
basic work, however, stands and is a monument to the early researchers
seeking answers to questions on electric shock.
The development of modern electrical/electronic medical equipment
has spurred the development of specific requirements for that class of
equipment. Their requirements are not contained within the usual resources
- e.g. IEC 60479, Effects of current on the human body... This work is
ongoing (see the IEC website (www.iec.ch) for the details of the issued
documents as well as a description of the continuing work). The application
of electronics to new uses has made this field challenging and considerable
ongoing work is continuing within this committee. The application of
semiconductors to mains circuits has complicated the waveforms that may be
accessible to users (not sinusoidal any more) and work is ongoing to better
understand that and provide proper details to control the level of electric
shock allowed in equipment. Simplification is desired - specifically
specifying safe voltage - which adds considerable complication to the quest.
Finally, it is almost impossible to conduct electric shock experiments any
more because of both legal and political pressure; development of better
modeling is the best way forward and some basic work is ongoing today.
The application of a pulse or pulses raises questions of its own.
Requirements for single pulses are laid out in IEC 60479 - the chart
deals with capacitance, charge and energy as a function of voltage showing
the range between threshold of perception and threshold of pain. That data
assumes the pulse is applied to the skin and not internally. Internal
pulses are a different matter. Have you ever seen a picture of the small
paddles which are applied directly to the heart to defib or restart it after
surgery? Moreover the applied current is very small compared to that applied
on the outside with the usual paddles. The total charge has to be small
also and the voltage can be much lower to do the job.
The application of multiple pulses within the heart period also
requires special attention as the heart needs to cycle to recover its
internal ability to withstand a pulse without going into fibrillation. This
is described in IEC 60479.
For medical applications you must reference their specific
requirements in IEC 60601 or go back into their literature and determine if
additional information is present supporting your specific need.
You are asking good questions. Focus on your application - specific
requirements will apply. Find these and apply them to your design to have
an acceptable application.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety Engineer
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201 fone/fax
p.perk...@ieee.org
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