What Does
Shrapnel Mean?
Shrapnel are sharp pieces of metal that are propelled at high speed due to an explosive force or an arcing fault.
Electrical workers close to an arc flash event are prone to injury from shrapnel. Because of this, anyone who might be in proximity of an arc flash must wear protective equipment that will not only protect them from heat and electricity, but also fragments of metal.
Safeopedia Explains Shrapnel
An arc flash occurs when light and heat are discharged due to a fault in an electrical circuit. The arc gets progressively hotter, reducing the electrical resistance and drawing more current till some part of the system trips, melts, or evaporates.
A supersonic shockwave is produced when the uncontrolled arc vaporizes the metal conductors, causing an arc blast. The result can be deafening noise, supersonic concussive forces, superheated shrapnel, high energy radiation, and extreme temperatures.
Causes of electrical arcing include:
- Overloaded circuits in a panel – Excess current can cause the circuit breaker to malfunction, allowing the current to continue flowing
- Faulty panels – Defective circuit breakers and other design flaws in an electrical panel can contribute to arcing incidents
- Excessive fuses in the box – A box with too many fuses will allow additional current to flow through the circuit, causing overheating and arcing
Shrapnel Generation in Arc Flash Events
The explosive force generated by an arc blast is capable of turning metal objects into projectiles that can injure or kill anyone present in the area. The mass, shape, and velocity of the shrapnel depends on the type of equipment involved, the energy available, and the mode of failure that caused the arc flash event.
The extreme temperature from the arc flash causes the explosive expansion of the surrounding air and the metal in the path of the arc. Copper is known to expand 67,000 times when it turns from solid to vapor state, causing high pressure, deafening sound, and shrapnel. The pressure generated can exceed thousands of pounds per square foot, causing extensive damage to people and property. Molten metal and material expelled away from the arc path at speeds over 700 miles per hour (mph) are capable of completely penetrating the human body.
Protecting Against Shrapnel from Arc Flashes
Arc-rated garments can provide workers with protection within the arc flash boundary. They are, however, only meant to protect against burns and are not adequate for other arc-related hazards. Additional PPE is required to safeguard workers against shrapnel injuries.