Electric Arc
The injuries that can result from an arc flash are degrees of burns, respiratory system damage, penetration of the skin by flying debris, hearing loss and internal injuries caused by the force of the blast.
ELECTRIC ARC STANDARDS
When workers cannot work de-energised, it is imperative they have suitable and adequate flame resistant (FR) and arc rated (AR) workwear, which matches the potential arc flash hazard they are working with. Workwear, which is not FR/AR will most likely continue to burn after the onset of ignition, resulting in the fabric perhaps dripping and melting into the skin, only increasing the severity of the injuries. FR/AR workwear can under certain circumstances ignite, however it will self-extinguish after the ignition source, that is, the flame or arc has ceased.
Heat generated from an electric arc is capable of reaching temperatures of around 4000°C (7232°F) thus, producing a significant amount of calories. Arc flash temperatures can reach or exceed 35000°F at the arc terminals.
To match FR/AR workwear to the potential arc flash hazard, end users must undertake arc flash hazard assessments to determine the potential incident energy and arc flash boundary their workers are exposed to. Corporations must then choose arc rated clothing and head protection that has an ATPV (or Ebt) equal to, or greater than, the calculated hazard level. The Ebt (Energy Break-open Threshold) is the incident energy on a material that results in a 50% probability of the material breaking open. The Ebt is the reported arc rating when it is lower than the ATPV.
NFPA 70E
PURPOSE
The National Fire Prevention Association (NFPA) develops and publishes more than 300 consensus codes and standards intended to eliminate death, injury, property and economic loss due to fire, electrical and related hazards.
The purpose of the standard is to provide a practical safe working area for employees relative to the hazards arising from the use of electricity.
SCOPE
NFPA 70E addresses electrical safety-related work practices for employee workplaces that are necessary for the practical safeguarding of employees relative to the hazards associated with electrical energy during activities such as the installation, inspection, operation, maintenance and demolition of electric conductors, electric equipment, signaling and communications, conductors and equipment and raceways. This standard also includes safe work practices for employees performing other work activities that can expose them to electrical hazards, as well as safe work practices for the following.
- Installation of conductors and equipment that connect to the supply of electricity.
- Installations used by the electric utility, such as office buildings, warehouses, garages, machine shops and recreational buildings that are not an integral part of a generating plant, substation or control centre.
STANDARD FOR NFPA 70E SAFETY REQUIREMENTS FOR EMPLOYEE WORKPLACES
NFPA 70E TABLE 130.7 (C)(16) PERSONAL PROTECTIVE EQUIPMENT (PPE)
|
|---|
PPE CATEGORY | PPE | MINIMUM ARC RATING (CAL/CM2) |
1 | SINGLE LAYER OPTIONS - Arc rated long-sleeve shirt and trousers or arc rated coverall. | 4 |
2 | SINGLE LAYER OPTIONS - Arc rated long-sleeve shirt and trousers or arc rated coverall. | 8 |
3 | Arc rated long-sleeve shirt, arc rated trousers, arc rated coverall, arc rated arc flash suit jacket, arc rated arc flash trousers, arc rated jacket, parka, rainwear or hard hat liner. | 25 |
4 | Arc rated long-sleeve shirt, arc rated trousers, arc rated coverall, arc rated arc flash suit jacket, arc rated arc flash trousers, arc rated jacket, parka, rainwear or hard hat liner. | 40 |
Some corporations simplify compliance to NFPA 70E by implementing everyday uniform programs that meet the requirements of NFPA 70E PPE CAT 1 and 2 as a single layer by adopting the provisions set out in the table above. This can alleviate employer concerns about leaving the difficult decision of determining whether a specific routine electrical task is PPE CAT 1 or 2 in the hands of the employee. To supplement everyday uniforms, additional arc rated PPE is available for higher energy PPE CAT 3 and 4 level situations.
ASTM F1891
PURPOSE
This standard is used for compliance with OSHA 1910.269, NFPA 70E and CSA Z462. ASTM F1891, Standard Specification for Flame and Arc Resistant Rainwear, outlines the minimum physical, arc flash and thermal performance criteria for rainwear used by workers with a risk exposure to momentary electric arcs. The ASTM F1959 test is followed with both the Arc Thermal Performance Value (ATPV) and Energy Break-open Threshold (Ebt) results being reported. The material is exposed to twice the arc rating to ensure no melting and dripping of the rainwear will occur. ASTM F1959 has a minimum arc rating of 5 cal/cm2.
Tests must be performed before and after 5 wash cycles, with the exception of the arc test. As in ASTM F1506, the arc test is considered a design test and only needs to be repeated after a change in the material. All other testing must be performed annually for compliance.
STANDARDS
| SECONDARY PPE | |
| STANDARD | TITLE |
| ASTM 1506 | Standard Performance Specification for Flame Resistant and Arc Rated Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Hazards |
| ASTM D6413 | Standard Test Method for Flame Resistance of Textiles (Vertical Test) |
| NFPA 70E | Handbook for Electrical Safety in the Workplace |
| ASTM F1959 | Standard Test Method for Determining the Arc Rating of Materials for Clothing |
| IEC/EN 61482 | Protective Clothing Against Thermal Arc Hazards of an Electric Arc |
| RAINWEAR | |
| STANDARD | TITLE |
| ASTM F1891 | Standard Specification for Arc and Flame Resistant Rainwear |
| ASTM F1449-20 | Standard Guide for Care and Maintenance of Flame, Thermally and Arc Resistant Clothing |
| IEC/EN 61482 | Live Working - Flame Resistant Materials for Clothing for Thermal Protection of Workers - Thermal Hazards of an Electric Arc - Part 1: Test Methods |