Safety Methods Protect Underwater Welders

Underwater "wet welding" requires more precautions than shop floor. welds. Underwater wet welding is generally safe, however, the diver/welder must take certain precautions to prevent electrical shock hazards.Underwater wet welders use direct current (DC) power supply, not alternating currents (AC). A knife-switch is used to break the current when the diver is not welding.

Most welders are conditioned to stay dry when welding. Others, with training and special safety measures, weld underwater in lakes, rivers, and oceans.

Underwater "wet welding" requires more precautions than shop floor. welds. Underwater wet welding is generally safe, however, the diver/welder must take certain precautions to prevent electrical shock hazards.Underwater wet welders use direct current (DC) power supply, not alternating currents (AC). A knife-switch is used to break the current when the diver is not welding. The underwater welder should always wear a rubber dive suit and gloves to avoid electric shock, a welding lens is required to protect the diver/welder from ultraviolet light. Welders use specially designed electrodes and electrode holders for underwater applications. Safety for underwater welders begins with training at a commercial dive company's location or at a school offering courses to familiarize divers with what to expect in underwater welding environments.

Shock and Ohm

The susceptibility of the body to shock is proportional to the current entering the body. According to Ohm's Law, current is determined by the voltage and the circuit resistance (I=E/R, where I=current, E=voltage, and R=resistance). Thus, the body's resistance determines the current entering the body since voltage in a circuit is constant.

Robert Murray, manager Naval Special Warfare SEAL Support Programs, Naval Sea Systems Command, Washington Navy Yard explains the basic differences between using electrical equipment in air or in water. "Air, an insulator, protects the individual from shock unless he contacts the fault, becoming part of the electrical circuit, and diy skin provides a substantial measure of protection."

A dry, 150 lb person in air has a resistance limb-to-limb of approximately 3,500 ohms. A wet diver has a limb-to-limb resistance of approximately 500 ohms for voltages over 50 and 750 ohms for voltages less than 50. The only exception to these values: the front-to-back of the chest area resistance is 100 ohms regardless of voltage.

For example, a diver with current entering and leaving through a leg may experience muscle contractions impairing mobility. That same current flowing through his chest cavity may generate muscle contractions causing asphyxiation or ventricular fibrillation, resulting in death.

A hazardous electrical shock comes from three actions - circuit current, a fault in the electrical system, and the individual exposed to the fault.

Proper Precautions

Safety procedures work. Since the 1930s, Navy divers have been welding and working with electrical power for lights, weld inspection tools, and other equipment. During that time, the Navy reports only one death due tounderwater electrocution, an accident during training in 1942.

What makes underwater wet welding an acceptable risk hazard is the low DC voltage that is nominally used (combined with common sense). "Welding with 30V DC and limb-to-limb wet body resistance of 750 ohms, the diver/welder will be within the safe current limit if he inadvertently becomes part of the circuit," says Murray

With current safety procedures, electrodes designed for wet welding, and wet weldingtechniques combined with modern welding power sources and equipment, welders can produce weld quality comparable to surface welds.

Sumber : Harris, Richard. "Safety Methods Protect Underwater Welders". 27 Januari 2014. http://search.proquest.com/docview/213276362?accountid=31562