A shock from a welder can be fatal, despite the relatively low voltage involved in the welding circuit. The primary danger stems from contact with the electrically live parts of the welding circuit, known as a welding shock, which occurs when a person becomes part of the electrical path. The open-circuit voltage (OCV)—the voltage present before the arc is struck—is generally between 20 and 100 volts. This is often enough to drive a lethal current through the body under certain conditions.
The Lethal Mechanism: Current, Voltage, and Resistance
The key factor determining the severity of an electric shock is the amount of current, or amperage, that flows through the body, not the voltage alone. A current as small as 100 milliamperes (mA) is sufficient to cause ventricular fibrillation and death. Voltage is the driving force, but the current that flows is controlled by the body’s electrical resistance.
The skin acts as the body’s main insulator, providing high electrical resistance when dry. However, moisture from sweat, rain, or damp clothing drastically lowers this resistance, allowing significantly more current to pass through the body at the same voltage. For example, a welder’s open-circuit voltage of 70 volts could be harmless with dry skin, but become lethal when the skin resistance drops dramatically in a wet environment.
When resistance is low, even the low voltages typical of a welding circuit can push a dangerous amount of current through the body. The danger increases substantially if the electrical current path includes the heart, such as hand-to-hand or hand-to-foot contact. Wet or humid conditions are dangerous in welding because the body’s natural defense against electricity is compromised.
Welding Methods and Shock Risk Differences
The type of current produced by the welding machine affects the physiological impact and the overall shock risk. Alternating Current (AC) is considered three to five times more hazardous than Direct Current (DC) at the same voltage level. AC is more dangerous because its constant change in direction (50 or 60 Hz) is highly effective at disrupting the heart’s electrical rhythm.
AC current often causes muscle tetany, an uncontrollable muscle contraction that prevents the person from letting go of the energized object. DC current tends to cause a single convulsive contraction, which may sometimes throw the person clear of the electrical source. However, DC is far from safe, and a high-voltage DC shock can still be severely damaging or fatal.
Some welding processes, such as Gas Tungsten Arc Welding (GTAW or TIG), utilize High-Frequency (HF) current for arc starting. While the HF current itself is very low, it introduces a unique shock risk because it uses a high-voltage, high-frequency pulse to ionize the air gap. This high voltage can create a painful, startling secondary shock, which may lead to serious injury if the welder falls or makes contact with another live part.
Immediate Physiological Impact of Electric Shock
When electric current passes through the body, the immediate consequences are both electrical and thermal. The most common cause of death from electric shock is the disruption of the heart’s natural electrical signals. This can induce ventricular fibrillation, where the heart’s lower chambers quiver rapidly, ceasing to pump blood.
Current passing through the chest can also cause respiratory paralysis, stopping the muscles responsible for breathing and leading to asphyxia. Furthermore, internal tissues resist the flow of current, which generates heat. This thermal effect causes severe internal and external burns, damaging muscles, nerves, and internal organs along the current’s path.
The severity of the injury depends on the magnitude and duration of the shock, and the path the current takes through the body. Even a brief, low-current shock can be dangerous if it passes through the heart during a vulnerable phase of the cardiac cycle. Immediate medical attention is necessary after any significant shock, as delayed cardiac issues can occur hours later.
Essential Safety Practices to Prevent Fatal Shock
Preventing fatal shock relies on maintaining the body’s electrical resistance and ensuring the integrity of the welding equipment. Welders must use dry, insulated gloves and protective clothing to create a barrier between their skin and the welding circuit. It is important to inspect all cables, electrode holders, and ground clamps regularly for damaged insulation or frayed wires.
The work environment must be kept as dry as possible, as moisture is the biggest contributor to lowered body resistance. If welding in wet, humid, or confined spaces is unavoidable, additional safety measures must be employed, such as using insulating mats and rubber boots. Never stand in water or on damp ground while welding.
Proper grounding of the workpiece is important to ensure the current follows the intended path back to the power source. Many modern welding machines include a Voltage Reduction Device (VRD) that lowers the open-circuit voltage to a safer level (typically 12 to 25 volts) when the machine is on but not actively welding. Welders should never touch the electrode or metal parts of the electrode holder with bare hands or wet gloves.