Effects of Electric Current on the Human Body

Electric current can have significant effects on the human body, ranging from mild shocks to fatal injuries. Understanding these effects is crucial for both safety and designing electrical systems. Below is a comprehensive breakdown of how electric current impacts the body and the variables that determine its severity.

What Happens When Electric Current Passes Through the Body?

When electrical current passes through the human body, it stimulates the nervous system, causing an electric shock. The intensity of this shock depends on:

• Strength of the Current: Higher currents result in more severe effects.
• Path of Current Flow: The route taken by the current (e.g., hand-to-hand or foot-to-foot) significantly affects its impact.
• Duration of Contact: Longer exposure to electrical current increases the risk of severe injury.

In extreme cases, electric shocks can disrupt the normal functioning of the heart and lungs, leading to unconsciousness or death.

Safe and Dangerous Current Levels

1. Below 5mA: Generally considered safe.
2. 10mA - 20mA: Dangerous, causing a loss of muscular control.
3. Above 100mA: Potentially fatal, as it can stop the heart from pumping blood and cause respiratory paralysis.

Key Formula:
The leakage current $I = \frac{E}{R}$, where:

• E: Supply voltage
• R: Body resistance

Example Calculation:

For a 230V supply and an assumed body resistance of 20kΩ:

$$I=\frac{230}{20,000}=11.5mA$$

This current is enough to cause severe injury or even death.

Human Body Resistance

• Dry Skin Resistance: Ranges from 70kΩ to 100kΩ per square cm.
• Wet Skin Resistance: Drops drastically to 700Ω to 1000Ω per square cm.

Critical Insight: A wet body is far more vulnerable to electric shock. For example, a 100V supply can be as dangerous to a wet body as a 1000V supply to a dry body.

Effects of Current Flow Through Different Paths

1. Hand-to-Hand or Foot-to-Foot Current Path

• Perception Threshold: At 1mA, a slight tingling sensation is felt.
• Let-Go Current:
  • 9mA for males
  • 6mA for females
• 20mA - 100mA: Causes painful muscle contractions and physical injury but does not stop heart or lung function.
• Above 100mA: Can result in:
  • Heart failure (ventricular fibrillation)
  • Respiratory paralysis
  • Severe burns

2. High-Frequency Currents

High-frequency currents (e.g., 100 Hz and above) have unique effects:

• Reduced Sensation: Shock perception diminishes at higher frequencies.
• Internal Burns: Despite reduced sensation, internal burns can occur, proving fatal in severe cases.

AC vs. DC Effects

• AC Current: At common frequencies (25–60 Hz), AC is more dangerous than DC for the same RMS value.
• DC Current: Generally less harmful but still poses significant risks at high levels.

Voltage and Risk Factors

• Even 50V AC can produce a dangerous current of 50mA, especially with wet skin.
• Survival depends on factors such as:
  • Skin dryness
  • Insulating clothing
  • Wearing rubber-soled boots

Key Takeaways

1. It’s the Current, Not Voltage, That Kills: The severity of an electric shock is determined by current, resistance, and exposure time.
2. Wet Skin Increases Risk: Always take precautions to stay dry when handling electrical equipment.
3. High-Frequency Risks: Though less perceptible, high-frequency currents can cause severe internal injuries.

Understanding these principles can help minimize risks and improve safety practices around electrical systems. Always use proper insulation and safety equipment to protect yourself from electric shocks.