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Electrical Forum - What Kills
Citat:
Most personnel are aware that there is a danger of electrical shock, even electrocution. It’s the one electrical hazard that most electrical safety standards have been built around. However, few really understand just how little current is required to cause injury, even death. Actually, the current drawn by a 7 1/2 watt, 120 v lamp, passing across the chest, from hand to hand or foot, is enough to cause fatal electrocution.
Consider the human body as a resistor with a resistance R (hand to hand) of just 1,000 ohms. The voltage V will determine the amount of current passing through the body:
While 1,000 ohms may appear to be rather low, even lower levels can be approached by someone having sweat-soaked cloth gloves on both hands, and a full hand grasp of a large energized conductor and a grounded pipe or conduit. Moreover, cuts, abrasions or blisters on hands can negate skin resistance, leaving only internal body resistance to oppose current flow. A circuit in the range of 50 volts could be dangerous in this instance.
Ohm’s Law: I (Amperes) = V (Volts) / R (Ohms)
Example 1: I = 480 / 1000 = 480 mA (or 0.480 amps)
The most damaging path for electrical current is through the chest cavity and head. In short, any prolonged exposure to 60 Hz current of 10ma or more may be fatal. Fatal ventricular fibrillation of the heart (stopping of rhythmic pumping action) can be initiated by a current flow of as little as several milliampers (mA). These injuries can cause fatalities resulting from either direct paralysis of the respiratory system, failure of the rhythmic heart pumping action, or immediate heart stoppage.
Responses to 60 Hz. AC Current
Tingling Sensation 0.5 - 3 mA
Muscle Contraction and Pain 3 - 10 mA
“Let Go” Threshold 10 - 40 mA
Respiratory Paralysis 30 - 75 mA
Heart Fibrillation and May Clamp Tight 100 - 200 mA
Tissue and Organs Burn Over 1,500 mA
Consider the human body as a resistor with a resistance R (hand to hand) of just 1,000 ohms. The voltage V will determine the amount of current passing through the body:
While 1,000 ohms may appear to be rather low, even lower levels can be approached by someone having sweat-soaked cloth gloves on both hands, and a full hand grasp of a large energized conductor and a grounded pipe or conduit. Moreover, cuts, abrasions or blisters on hands can negate skin resistance, leaving only internal body resistance to oppose current flow. A circuit in the range of 50 volts could be dangerous in this instance.
Ohm’s Law: I (Amperes) = V (Volts) / R (Ohms)
Example 1: I = 480 / 1000 = 480 mA (or 0.480 amps)
The most damaging path for electrical current is through the chest cavity and head. In short, any prolonged exposure to 60 Hz current of 10ma or more may be fatal. Fatal ventricular fibrillation of the heart (stopping of rhythmic pumping action) can be initiated by a current flow of as little as several milliampers (mA). These injuries can cause fatalities resulting from either direct paralysis of the respiratory system, failure of the rhythmic heart pumping action, or immediate heart stoppage.
Responses to 60 Hz. AC Current
Tingling Sensation 0.5 - 3 mA
Muscle Contraction and Pain 3 - 10 mA
“Let Go” Threshold 10 - 40 mA
Respiratory Paralysis 30 - 75 mA
Heart Fibrillation and May Clamp Tight 100 - 200 mA
Tissue and Organs Burn Over 1,500 mA
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