Low voltage: <600V
High voltage: >600-750 V
Humans more sensitive to alternating currents esp 39 – 150 cps
Amperagae is most important factor
A = V/R
Household 110-120 V
High voltage lines 7500-8000 V
High tension lines 100,000 V or higher
Direct contact not needed! 1,000 V line can arc through air few mm; 5,000 V – 1 cm; 20,000 V – 6 cm, 40,000 V – 13 cm and 100,000 V – 35 cm
Dry skin 100,000 ohms
Moist skin 1,000 ohms
Moist thin skin 100 ohms
Mechanism of death:
low voltage – v fib
high voltage – electrothermal injury or respiratory arrest from paralysis (due to central damage to respiratory center by hyperthermic effects of current)
|15 - 17 mA||contracture "no-let-go"|
|50 mA||contracture of all muscles, resp paralysis and death|
|75 - 100 mA||v. fibrillation|
|1 A||ventricular arrest|
Examples: 120V current, 1000 ohms resistance, 120 mA reach body; 5 sec to v. fib; if skin moist & thin, 100 ohms, 1200 mA (1.2A) reach body and 0.1 sec to v. fib
Muscle contractions may cause fractures: scapula, humerus, femoral neck, T12 and L1. May arch back and neck backwards.
Burns present in all cases of high-voltage, but only 50% of low voltage electrocution.
Cannot differentiate antemortem from postmortem electrical burns.
Scanning EM can detect small particles of metal from the conducting surface.
Ground-Fault Current Interrupters: monitors current flow and detects a 5 mA difference (required in kitchens, bathrooms and outside outlets). Circuit breakers detect a 15 mA differece.
Most indibiduals hit by lightning do survive. 1,000 A or more.
Cutaneous burns not severe, but always present.
81% rupture tympanic membrane.
Metal objects magnetized.
“Lichtenburg” figures: arborescent or fern-like injury to skin. Present 1 – 24 hrs erythema, then fades. Not burns