Clothing for protection against Electric Arc
Standards IEC 61482-1-1:2019 and IEC 61482-1-2:2019 specify the requirements and test methods to which protective clothing and materials related to heat and flame-resistant clothing for workers exposed to electric arc must be subjected.
The garment is subjected to specific tests according to the regulations, which determine:
- The ATPV (Arc Thermal Performance Value) and EBT (energy breakopen threshold) value;
- The arc flash protection class.
What’s Electric Arc?
The electric arc is a continuous high-voltage electric discharge that occurs between two conductors accidentally and unexpectedly. This electrical discharge is accompanied by a strong glow and intense heat and often a wave of high pressure, noise and toxic fumes.
An electric arc can occur:
- For system overvoltages;
- For melting overloaded conductors;
- Due to the presence of moisture or conductive dust that interfere with the surface insulation of an insulator.
The temperatures resulting from the electric arc can exceed 10,000°C and can cause fires with explosions, metal vaporization, intense emission of ultraviolet rays and the formation of toxic gases and noise.
These factors cause damage to the user with different severity depending on the health of the operator and the time and mode of exposure to the electric arc. This can result in:
- Increased pressure;
- Toxic influences caused by melting of the casings;
- Cardiac arrest;
- Second or third-degree burns, which are the most common injuries
- Fractures or damage to internal organs;
- Involuntary muscle contraction, that can cause sudden and dangerous movements, falls and other accidents.
The creation of an electric arc represents a severe, potentially lethal risk.
The energy produced by the electric arc can ignite standard protective clothing, so workers exposed to this risk must be adequately protected. These garments are mainly used by personnel who come into contact with electrical cabinets or panels, or by electricians who are always in contact with conductive materials or electrical systems. Other workers at risk from the electric arc are operators of chemical plants and refineries.
The protective workwear designed to guarantee safety in jobs in the potential presence of an electric arc must comply with the test methods according to the IEC EN 61482-1-1:2019 standard.
- The ATPV value (Arc Thermal Performance Value) represents the maximum thermal energy that a fabric can withstand before the worker suffers second-degree burns;
- The EBT (energy limit of breakage) value indicates the maximum exposure to energy that a garment can sustain without breaking.
The arc resistance of a tissue is therefore equivalent to its ATVP or EBT.
According to the IEC EN 61482-1-2:2019 standard, the test is carried to the closed arc: an electric arc is reproduced in a very confined environment and with special electrodes, in which the fabric is exposed.
This test classifies the fabrics into two classes:
- Class 1, the fabric must remain intact at 4 KA short circuit condition for a time of 0.5 seconds, protecting the operator from second-degree burns;
- Class 2, the fabric must remain intact at 7 KA short circuit conditions for a time of 0.5 seconds, protecting the operator from second-degree burns.
The arc resistance of a garment is equivalent to the Class of the fabric it is made of.
More on the IEC 61482 standard
THE STOLL CURVE
The Stoll Curve is a mathematical model that allows us to quantify the response of human skin and tissues to heat energy sources.
When the tissues pass from 36°C (blood temperature) to 45°C, burns begin to occur, after 50°C the damage to the skin is 100 times faster than 45°C, while at 72°C the skin undergoes instant complete destruction.
As a result of these studies, special calorimetric sensors have been developed that reproduce the reaction of the skin to exposure to flames and, placed on fabrics or mannequins and subjected to the closed arc test, predict the beginning of second or third-degree burns.
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