Shock currents greater than the reaction current produce an increasingly severe muscular reaction. Above a
certain level, the shock victim becomes unable to release the conductor. The maximum current at which a
person can still release a conductor by using the muscles directly stimulated by that current is called the
"let-go" current. The `let-go" current varies between 4-21 milliamps, depending on the individual. A normal
person can withstand repeated exposure to his "let-go" current with no serious after effects when the duration
of each shock lasts only for the time required for him to release the conductor.
Shock currents above about 18 milliamps can cause the muscles of the chest to contract and breathing to stop.
If the current is interrupted quickly enough, breathing will resume. However, if the current persists, the victim
will loose consciousness and death may follow. Artificial respiration is frequently successful in reviving
electric shock victims.
Above a certain level, electric shock currents can cause an effect on the heart called ventricular fibrillation.
For all practical purposes, this condition means a stoppage of the heart action and blood circulation.
Experiments on animals have shown that the fibrillating current is approximately proportional to the average
body weight and that it increases with frequency.
In Table 9-1, the various hazardous current levels for ac and dc are summarized along with some of the physical
effects of each.
Summary of the Effects of Shock (9-1) (9-2)
Alternating Current (60 Hz)
Surprise (Reaction Current)
Reflex Action (Let-Go Current)