An arc flash is the light and heat produced from an electric arc supplied with sufficient electrical energy to cause substantial damage, harm, fire, or injury. Electrical arcs experience negative incremental resistance, which causes the electrical to decrease as the arc temperature increases. Therefore, as the arc develops and gets hotter the resistance drops, drawing more and more current (runaway) until some part of the system melts, trips, or evaporates, providing enough distance to break the circuit and extinguish the arc.
Electrical arcs, when well controlled and fed by limited energy, produce very bright light, and are used in arc lamps (enclosed, or with open electrodes), for welding, plasma Cutting , and other industrial applications. Welding arcs can easily turn steel into a liquid with an average of only 24 DC volts. When an uncontrolled arc forms at high voltages, arc flashes can produce deafening noises, supersonic concussive-forces, super-heated shrapnel, temperatures far greater than the Sun’s surface, and intense, high-energy radiation capable of vaporizing nearby materials.
Electric shock is the physiological reaction or injury caused by electric current passing through the (human) body. Typically, the expression is used to describe an injurious exposure to electricity. It occurs upon contact of a (human) body part with any source of electricity that causes a sufficient current through the skin, muscles, or hair. Shocks can be caused by direct or indirect contact. Contact with an exposed conductive part under fault conditions is called indirect contact. IEC requires certain degrees of ingress protection against direct contact. Indirect contact protections can be achieved by earthed equipotential bonding and automatic disconnection of supply by using fuses for example.
Causes of an arc flash
Arc flash happens when electric current flows through an air gap between conductors. Accidents caused by touching a test probe to the wrong surface or slipped tool are the most common cause of an arcing fault. Arc flashes can also be caused by:-
- Sparks due to breaks or gaps in the insulation.
- Equipment failure due to use of substandard parts, improper installation, or even normal wear and tear.
- Dust, corrosion or other impurities on the surface of the conductor.
The fault current magnetic fields make conductors to separate producing an arc. In other words, arc flash is caused by uncontrolled conduction of electrical current from phase to ground, phase to neutral, and/or phase to phase accompanied by ionization of the surrounding air. Because of the expansive vaporization of conductive metal, a line-to-line or Line-to-ground arcing fault can escalate into a three phase arcing fault in less than a 1/1000 of a second. The heat energy and intense light at the point of the arc is called arc flash.
Short circuits and arc faults are extremely dangerous and potentially fatal to personnel. The product of arc fault current and voltage concentrated in one place, results in enormous energy released in several forms.
An arc blast can cause the following injuries
- Skin burns by direct heat exposure. Arc flash generates large amounts of heat that can severely burn human skin and set clothing on fire. Temperatures at the arc can reach four times the temperature of the Sun’s surface.
- High-intensity flash can also cause damage to eyesight
- Large shock waves that can blow personnel off their feet
- Loss of memory or brain function from concussion
- Hearing loss from ruptured eardrums. The sound associated with the blast can greatly exceed the sound of a jet engine Exposure risks from flying debris. For example, shrapnel wounds from metal parts
- Shock hazard due to touching energized conductors
- Other physical injuries from being blown off ladders, into walls, etc.
Hazards from electric shock
- Effect on heart:- When ventricular fibrillation occurs, the heart stops pumping. The victim rapidly loses consciousness and dies if a healthy heartbeat is not restored by applying a second electric shock with a device called a defibrillator.
- Effect on muscles:- Muscles are stimulated by electricity. The effect of an electric shock depends on which muscles the current goes through. A current of more than 10 mA causes sustained contraction (tetanus) of the flexors, that is, the muscles that close the fingers and draw the limbs towards the body. The victim thus cannot let go of the source of current. Muscles, ligaments and tendons may tear as a result of the sudden contraction caused by an electric shock. Tissue can also be burned if the shock is lasting and the current is high.
- Electrical burns:- Electrical burns are not like burns caused by fire or by touching something hot. Electrical burns result from the heat generated by an electric current passing through the body, which literally cooks the tissue from within. Outward signs of electrical burns may be microscopic or nonexistent, and internal damage may be much more serious than the external injuries suggest. That’s the iceberg effect. Electrical marks appear at the body’s point of contact with the current. They are typically tiny charred or hard craters that do not hurt because the nerves have been destroyed. Electrical burns often have serious consequences: scarring, amputation, loss of function, loss of sensation and even death.
- Elsewhere in the body:- Electric shock can also affect the eyes, causing cataracts to develop over time. Other disorders can appear in the weeks or months following the accident, depending on which organs the current passed through.
Arc Flash and electrical shock Safety and Prevention
- Arc flash analysis must be performed prior to allowing personnel to work on energized equipment. The analysis defines the flash protection boundary distance and the type of Personal Protection Equipment (PPE) required.
- Use arc resistant equipment such as the Centerline Arc Shield from Rockwell Automation for a higher level of employee protection.
- Always hire a qualified engineer to fix the wiring system well in place with all care and caution.
- Avoid working on electric system during the damp or moist weather such as raining. Or if the main electrical system is placed near the wet area then cover it with essential material and work with caution or seek professional help.
- Always follow safety standards while working or repairing some electric system to prevent shock.
- All necessary wiring should be sealed and qualitative for better protection.
- Install main plugs and switches at normal height and out of reach of children for safety measures.
- If there is sudden fire in the house, turn off the main switch of power supply immediately and use sand or fire extinguisher to keep the fire off. However, avoid water on the electric appliances or switch while fire as it can deteriorate the situation