WHAT'S AN ARC FLASH?
An electric arc is a brief, but lethal hazard which expels large amounts of deadly energy. In jargon, such incident causes an ionization of the air that will cause serious harm to equipment and people. Damage is caused by both the explosion and the heat radiating from the blast of vaporised materials.
Within fractions of a second, the explosion of an electric arc may reach temperatures exceeding 19000 degrees Celsius. This is roughly 4 times hotter than the surface of the sun. This heat can cause serious, even fatal burns, as well as ignite clothing and other nearby material and objects. Such high temperatures vaporise all materials like water (present in the air as humidity) and liquefies metal parts in the vicinity of the incident, such as copper and aluminum. This in turn means a massive volume expansion that results in explosive pressures and sound waves which form one of the biggest dangers of an arc flash incident.
SIMPLIFIED STATS OF AN ELECTRIC ARC:
- Duration of an electric arc is relatively short, often not longer than 0.5 second
- The temperature that is unleashed is approximately 19000°C
- The noise level of an electric arc could go up to 165dB
- One of the biggest dangers of electric arc is the volume expansion of materials as a result of the high temperature. The extreme heat vaporises all materials like water and copper. Water increases volume with a factor 1670. Copper expands in its vaporized circumstance 67000 times its original volume. The shockwave as a result of the arc flash can be higher than 2000 lbs/sq. ft
It goes without saying, that proper PPE can make the difference between life and death, or at least contribute significantly in the reduction of burn wounds.
In the core, the protection from electric arc is not so much different from the protection against the burn injuries that are caused by a flash fire. In both cases it is the aim to protect wearers against thermal hazards that could result in 2nd degree burn wounds or worse.
It is the nature of the hazard that makes flash fire protection different from electric arc protection.
WHAT TO LOOK FOR IN FR WORKWEAR?
In principle, arc rating measures the amount of heat the flame-resistant fabric blocks when exposed to electric arc. An arc rating is the number of calories that the garment is expected to 'absorb' if exposed to an electric arc.
Arc rating is the level of protection provided to you, the wearer. A calorie is the unit of measure of the heat energy of an arc flash and the protective level of FR clothing. The bigger the calorie number, the greater the heat energy level of arc flash and the greater the protective level of the clothing. You will be protected from an electric arc if your clothing has a higher calorie arc rating than the calories of heat generated by the arc.
Minimum Arc Rating Levels (cal/cm2):
| PPE 1 4.0 |
PPE 2 8.0 |
PPE 3 25.0 |
PPE 4 40.0 |
SO WHAT DOES IT MEAN?
In basic terms, the higher the calorie arc rating the better protection the garment will provide.
While it does not matter if the fabric has an ebt or ATPV value, it is important to pay attention to the calorie level the fabric can support - This is shown in cal/cm2
As there are no definitive Australian Standards that cover the use of FR Workwear onsite, WORKIT has adopted the NFPA 70E American Electrical Standard for levels of protection required and designing of the garment.
EN 1149 Protective clothing - Electrostatic properties (Anti-static)
The European standard (EN 1149) consists of different parts that specify requirements and test methods to measure protection against static electricity or charge decay, with EN 1149-5 describing performance requirements. The garment shall be constructed so all outer surfaces is made of electrostatic dissipative material. Conductive components as zippers and buttons shall be hidden by non conductive material.
BS EN 1149-1 - The maximum acceptable resistance specified is ≤2.5 ´ 109 W measured on at least one surface.
BS EN 1149-3 - The shielding factor should be greater than 0.2 and/or the half decay time be less than 4 seconds.
Protective clothing shall always be worn with electrostatic dissipative footwear.
Anti-static Properties
Garments rated as anti-static have the ability to discharge any build-up of electricity instantly; they do not in affect hold an electrical charge. This charge can come from different synthetic fabrics rubbing against each other, badly earthed electrical products and numerous other sources. The main reasons certain industries insist on anti-static gear are firstly that a spark would readily ignite any petro-chemical vapors, causing an explosion, and secondly, some equipment such as computer memory chips and components are able to be rendered useless by static electricity.
Natural fibers such as cotton are naturally good at preventing static charge build-up above freezing point, and therefore would be of benefit to someone looking for limited protection against these risks.
For a more guaranteed protection against static discharge, it is necessary to either chemically coat the material (which washes out after 12 to 15 washes), or to weave conductive thread into the garment, like we have done with all WORKIT FR garments.
EN50534 / NFPA 70E Electrical arc flash protection
These standards include specifications on Garment Design and Protection Factor in the event of high voltage arc strike. According to the North American association, the National Fire Protection Association (NFPA) 70E Hazard Risk levels (now referred to as PPE levels), the minimum requirements for PPE1 is 4.0 cal/cm2 and PPE 2 @ 8.0 cal/cm².
We design and manufacture WORKIT FR garments to PPE1, PPE2 and PPE3 requirements for Australian industry, and these ratings are clearly marked on the outside of each garment for easy reference.
Arc Thermal Protection Value Rating (ATPV Rating)
This rating is stated where a fabric gives the wearer protection against the heat generated by an electrical arc from high voltage equipment. The surface temperature at the point of contact of such an arc can reach temperatures greater than 10,000oC, and obviously cause severe if not fatal burns without some protection against this.
Our WORKIT FR garments have a rating exceeding the minimum requirements of Australian companies for protection against 2nd degree burns. The rating of the materials used are based on the period of time it takes for the required test voltage arc to cause 2nd degree burns to the wearer.
The fabric helps prevent serious burns by turning into a fluffy carbonized deposit that sits against the wearer and reduces the heat transmitted directly to the wearer.
To meet higher required ratings (where voltages worked around are considerably higher) the wearer of the garment must either use a specialized suit which may include a full hood, or layer other such ATPV rated garments underneath to provide further layers of protective “fluff” in the event of an arc flash. This is similar to comparing thin and thick Pink Bats - the thicker the insulation, the less heat escapes, or in this case, the less the heat penetrates.
As there are no definitive Australian Standards that cover the use of FR Workwear onsite, WORKIT (like most brands) has adopted the NFPA 70E American Electrical Standard for levels of protection required and designing of the garment.
We employee third-party testing laboratories in both Canada and Spain to help navigate the standards are prove the garments ability to mitigate burn risk by using the ATPV 70E testing regime.
All test data and certification is open to view to our client base to assist with their own site based risk assessments.
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