What is the safe amount of current (electricity) that can flow into the human body?

According to IEEE Std 1246™-2002;

Humans are highly sensitive to electrical current, primarily because their body nervous system is electrically stimulated. The magnitude of current that a body can tolerate depends on frequency, duration, and physical condition of the body. It is the consensus of researchers, however, that generally for frequencies above 25 Hz and for a duration of a few seconds, the threshold of perception is 1 mA. A current of 9 to 25 mA makes it difficult for a person to release their grip from a power circuit, and at 30 mA muscular contractions can make breathing difficult. At higher currents, a person’s heart can cease to function (ventricular fibrillation).

As previously stated, the magnitude of current a body can tolerate depends to a great extent on the duration of the shock. Researchers have concluded that 99.5% of all persons could withstand, without ventricular fibrillation, currents with a magnitude determined by Equation (1) or Equation (2):

IB = 0.116/sqrt(Ts) for a 50 kg (110 lb) body (1)

or
IB 0.157/sqrt(Ts) for a 70 kg (155 lb) body (2)

where
IB is the rms magnitude of body current (Amperes),
Ts is the duration of current exposure (seconds).

Generally, Equation (1) is used for a more conservative approach. However, one may use Equation (2) provided that the average population weight can be expected to be at least 70 kg (155 lb).




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