An arc flash or arc blast incident is a kind of lightning in an electrical circuit that results from a fault in a high current electrical system, regardless whether this is a low, medium, or high voltage system. The ‘lightning' comes from ionized das, so called plasma, explains Chris Ross of J&K Ross
An arc flash can be hotter than the surface of the sun. Typically, the arc flash is triggered, for example, when a short circuit occurs in electrical switch gear, often during maintenance work. An arc flash can only occur if the fault current is very high - several tens of thousands amps. The massive energy released in the fault instantly vaporises the metal conductors involved, blasting molten metal and expanding plasma outward with extreme force. In addition to the explosive blasts of such a fault, much of the deconstruction arises from the intense radiant heat produced by the arc.
Everybody knows artificial electrical arcs from arc welding - physically seen - an arc flash is the same but with magnitudes of higher intensity. The metal plasma arc produces tremendous amounts of light energy from far infrared to ultraviolet. Surfaces of nearby people and objects absorb this energy and are instantly heated to vaporising temperatures. The effects of this can be seen on adjacent walls and equipment; they are often ablated and eroded from the radiant effects.
Globally accepted studies with regard to the distribution of thermal injuries have shown apart from the hands, the head and face are top of the list of this concerning ranking.
Plastic shields manufactured from polycarbonate, propionate or acetate providing sufficient thickness can protect against:
- Conventional heat (the plasma heat ball)
- Fragments (primarily or secondarily released by the explosion)
- Molten particles (e.g. from electrodes, "arc feet")
However they are designed to let electromagnetic radiation pass through. With ultra-violet filters (UV blocker) a part of this tremendous energy can be absorbed but scientific findings have proved that this is by far not enough. The intensity of visible light is high enough too irreversibly injure human eyes and the infra-red (IR) radiation can burn eyes and skin. For optimal protection we need an ‘intelligent' face protection providing:
- Contrast enhancement
- High visible light transmission (up to VLT 70%)
- True colour impression for a broad range of visible light. Under normal circumstances the highest possible absorption of radiation from UV to IR.
By using the innovative process of ablation the proprietary ablative materials absorb the arc flash's energy layer by layer through a controlled dissociation process and make the Arc Shield give up its surface. Subsequently, Paulson improved this protection mechanism by using nanotechnology; a further significant milestone following years of intensive research and testing.