Friday, June 04, 2010

Electrocution may be hazardous to your health

The first group of new questions from the 2010 Technician pool I'm covering are from subelement T0, which covers safety issues.  The NCVEC has been increasing the amount of safety-related content on the tests in recent years, and the new pool contains 13 new questions in this subelement.  The first of these is T0A02: "How does current flowing through the body cause a health hazard?"  I would think that most people understand that being electrocuted is bad for them, and generally something to be avoided.  However, for whatever reason, the NCVEC has decided that it's at least somewhat important for new hams to be prepared to demonstrate that they understand just why electrocution is bad for you. 

There are three main ways that electric currents within the body are hazardous.  First, any current flowing through any medium which is not a perfect conductor (which is to say, anything whatsoever) generates heat (sometimes called Joule heating).  The body's internal resistance is modest, typically between 300 and 1000 ohms; however, the skin resistance can be much higher, in the 10,000 to 100,000 ohm range depending on conditions.  A current passing through the body will heat and eventually burn tissue, preferentially at points of higher resistance; this will lead initially to burns on the skin and then later (as the skin blisters and its resistance lowers), to burns deeper within the body.  Second, many functions of cells depend on electrical charges, and the moving about of charged ions, to accomplish the purpose of the cells; electrical currents passing through these cells will tend to disrupt these electrical functions.  At very low currents (1 milliamp or less) this manifests itself as a tingling sensation.  At higher currents it will manifest as pain.  Sufficiently high currents (50 to 70 milliamps) may cause the third major effect: involuntary muscle contractions.  At even higher currents, 500 milliamps or more, the muscle of the heart can be disrupted leading to heart fibrillation, cardiac arrest, and death.

This particular question appears in the pool with an "All of the above" option.  Any experienced test-taker knows that "all of the above" is often the correct answer to any question that has such an option, and this question is no exception to that rule.  In any case, what really matters is that hams must understand that electrical voltages, even relatively low ones, are potentially dangerous, and must take precautions to avoid finding out about these effects first-hand.