Electrocution is a leading cause of construction fatalities. Electrical shock occurs when current flows through the body and can cause cardiac arrest, respiratory failure, or severe burns. The severity depends on voltage, current, duration of contact, and path through the body. AC (alternating current) is more dangerous than DC at the same voltage; 60 Hz AC (standard in North America) is particularly hazardous. Currents as low as 50 mA (0.05 amps) can cause cardiac arrest. Voltages above 50V are considered dangerous. Construction sites use various voltage levels including 120V, 208V, 240V, 277V, and 480V or higher. All electrical work must be performed by qualified persons trained on electrical hazards. Lockout/tagout procedures de-energize equipment before maintenance. Wet conditions increase hazard; wet skin and wet ground reduce electrical resistance, allowing higher current flow. Portable electrical tools used in wet areas require GFCI (ground fault circuit interrupter) protection. GFCI devices detect leakage current and shut off power in milliseconds, preventing serious shock. All temporary electrical installation must use GFCI protection. Extension cords must have three-wire grounding plugs that cannot be altered. The ground wire provides an alternate path if insulation fails. Damaged cords with exposed conductors must be removed from service. Generators must be properly grounded. Neutral and ground must be bonded at the first source (generator or service entrance) but not bonded downstream. Double bonding causes dangerous current flow. Electrical distribution must have proper guarding. Live conductors above work areas must be at least 15 feet above finished floor. Proper clearance prevents accidental contact.