^ Electric Shocks, Fumes, & Sparks are Major Hazards in Welding (Image Courtesy: Oliver Sved at BigStock.com)
A Shocking Experience
Shaken and completely stirred! Perhaps, the best way to recount the feeling of electric shock you might have experienced. Hopefully, you won’t have to go through the ordeal again.
Flawed equipment and low safety consciousness, sadly, ensures that many do. Around 1,000 people are electrocuted (die from electric shocks) annually in the United States alone. Death apart, electric shocks can result in numerous debilitating disorders.
Hot Jobs such as welding, cutting, and brazing create health and safety hazards for over 500,000 workers and cause 4 deaths per 1,000 workers over a working lifetime according to U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA).
The Dynamics of Electric Shocks
Perils involved in hot work jobs are:
- Electric Shock
- Toxic Atmosphere
- Ultraviolet or Optical Radiation
In the most elementary of terms, you get a shock when you touch two objects that have an electric potential difference between them. Current flows between two points when there is a potential difference between them. Voltage is the potential difference between two points.
Our bodies react as a mixed solution of electrolytes inside a leather container when exposed to electricity. Water and other bodily fluids with dissolved salts act like electrolytes and therefore allow current to pass.
Generally, alternating currents (AC) are 2-3 times more lethal than direct currents (DC). Depending on other factors, voltage of 50V is enough to injure or kill. Humans can feel a current as low as 1 milliampere (mA) while currents of 100mA can be fatal.
Electricity used for welding comes as:
- single phase 120V / 240V
- three phase 575V in Canada and 480V in the U.S.
Arc welding with AC generates weld currents of over 150amps. Voltage across the arc is usually around 23-33V. Open Circuit Voltage (voltage when not welding, no-load voltage) can range from 20V to 100V. It is the highest voltage the electrode attains. Voltage inside the weld equipment is greater, from 120V to 575V.
Primary Electric Shock is the one you get from the input voltage. Typically, this happens when you touch the lead or other electrically active component inside a weld machine with its power turned on and when another part of your body touches grounded metal.
You get Secondary Electrical Shock if you touch a live part of the welding electric circuit while another part of your body touches the metal-being-welded.
TIG (Tungsten Inert Gas) and MIG/MAG (Metal Inert Gas / Metal Active Gas) welding is safer because the operator switches the welding current on and off using the foot or trigger switch. High frequency welding is more electric shock prone.
Causes . . .
According to the Guide for Safety at Work – Electric Shock Hazard of Manual Electric Arc Welding, causes for electric shocks include:
- neglecting the hazards
- unsafe weld equipment
Typically, this transforms into:
- replacing welding electrode with bare hands while leaving the welding transformer on
- leaning or sitting on the welding workpiece connected to the welding return cable
- unintentionally touching a live part of the welding electric circuit
- welding while standing on flooded or wet ground
- welding the underside of the workpiece while lying on the floor
In arc welding, you connect one output terminal of the welding transformer to the electrode holder and another to the workpiece. The former is the welding cable and the latter is the welding return cable.
It is the voltage difference between the two that creates the arc. You get an electric shock if any parts of your body touch both these terminals at the same time, directly or indirectly.
Stray Welding Currents are those that return to the welding transformer by a path other than the return cable. These constitute an additional electric shock hazard. Such pathways include:
- earthing / protective earth (PE) / grounding conductors of the weld equipment or other electrical equipment in the vicinity
- pipework and metal fittings
- slings, wire-ropes, and chains
- motor bearings
Structures such as pipelines and under-construction-ships are, by their very nature, connected to the earth and thereby amplify stray currents. Flimsy insulation of the return cable does the same.
Metal floors or metal pieces strewn across the shop floor hike the electrocution hazard. Welding in confined spots such as tanks or the underside of pipelines in a sitting, lying, or kneeling position is similarly dangerous.
. . . and Consequences
Depending on the route the current takes to pass through the body, the quantity of current, and the duration of exposure, consequences can be:
- Burns including superficial skin burns as well as internal burns. Voltages of 500-1,000V cause the latter that may aggravate into organ damage and even death. The treatment for internal burns is complicated and healing is painfully slow
- Pain in the chest and abdomen can be starting point for horrendous internal injuries
For example, a fall in blood pressure and disturbance in the body’s electrolytic and fluid balance may trigger the release of myoglobin and cause kidney failure
- Nervous Impairment as currents interfere with the electric signals that our nervous system uses regularly to transmit and receive
- Muscle Paralysis is the next, graver stage of nervous impairment. Prolonged and serious shocks can cause loss of ability to perform voluntary actions
- Heart Attacks usually follow Ventricular Fibrillatione. the uncoordinated contraction of heart muscles. The heart does not pump blood properly and the situation can easily worsen into death
Current flow between the left hand and the torso is most lethal, for it passes through the heart. That apart, even minor shocks can cause you to trip and fall. Although this sounds innocuous, it is not as a fall from an elevated location can assume lethal and even fatal proportions.
Electric shocks during welding are a multifaceted threat and you have to counter it with a nuanced approach with loads of prudence and eternal vigilance.
Want to know more on the perils inherent in welding? Visit our blog. Apart from knowing a lot of welding, we also practice it. Contact Kemplon Engineering for fantastic marine fabrication services, marine pipe fitting, and large scale custom metal fabrication.