Electric Shock
What current does to the body, and what determines severity.
12 min
Electric shock occurs when current passes through the body. Severity depends on the current, the path it takes, the duration of contact, and the frequency.
Effects of alternating current at mains frequency
| Current | Typical effect |
|---|---|
| 1 mA | Perception threshold |
| 5–10 mA | Painful; muscular reaction |
| 10–20 mA | Muscular contraction — the casualty may be unable to let go |
| 30 mA | Typical residual current device trip threshold |
| 50 mA and above | Risk of ventricular fibrillation; potentially fatal |
| Higher currents | Cardiac arrest, severe internal and external burns |
The path matters
Current from hand to hand, or hand to opposite foot, passes through the chest and is the most dangerous path. This is why one-handed working, where practicable, is a recognised precaution.
Conditions that increase risk
Wet or damp conditions, sweating, confined or conductive locations such as tanks and boilers, contact with earthed metal, and damaged footwear all lower the body's resistance and raise the current for a given voltage. A voltage that would be survivable in a dry workshop can be lethal inside a metal vessel.
Secondary injuries
Many electrical injuries are not caused directly by the current. The involuntary reaction to a shock causes falls from ladders and platforms, contact with moving machinery, and dropped tools, and these secondary injuries are frequently more serious than the shock itself.