Arc Flash: What it is and How to Protect Against It
Arc flash events pose grave dangers to electrical workers, with the potential to cause life-altering injuries, fatalities, and substantial damage to equipment. In this article, we'll explain when and why Arc faults occur, and how to protect yourself against injury using the right Personal Protective Equipment (PPE).
What is an Arc Flash?
An Arc Flash or arc fault happens when electric current flows through air gaps between conductors, causing a short circuit.
When does it occur?
Arc Flashes often occur when racking in a breaker, performing switching, due to insulation failure, or accidents caused by touching a test probe to the wrong surface or slipped (non-insulated) tools.
What makes up an Arc Flash?
In its most basic form, an Arc is made up of four elements; thermal energy (heat), acoustical energy (sound), pressure wave and debris. Each of these elements can cause serious injury or death to a person.
The dangerous part
The most dangerous part of an Arc Flash incident is the fact that it creates temperatures high enough to burn skin, but also ignite non-Arc-rated clothing. Burns due to burning clothing are the most serious, involve large percentages of the body and are more often than not fatal.
Timed Sequence Over One Second of the Arc Flash
- Test Set Up
- 37cal/cm² or 10kA/1sec rated Arc Flash jacket ready for testing
- The garment has never been worn, however has been laundered industrially 50 times
- The garment is a dual layer Proban construction, of 330gsm per layer
- The initial Arc Flash ignition is anywhere between 9,000º & 20,000º C
- The copper in the switchboard is vaporised and expands to over 40,000 times its solid volume
- Plasma is generated by the arc putting the garment under immense heat and pressure
- The arc continues for 1 full second, as a result of high fault current and slow trip times
- The mannequin is equipped with temperature sensors, none of which may surpass levels that would cause second degree burns
- The garment cannot break open at all or it will fail the test
- The garment passes this test at 10kA/1sec or 37cal/cm²
- No part of the garment breaks open, and no temp sensor register
a second degree burn value - A worker wearing this garment with other appropriate PPE would have had none, or only minor injuries
Arc Flash Protection: NFPA 70E
NFPA 70E is the world’s leading standard on Arc Flash protection and risk mitigation. Part of the standard is a list of categories (refer to the chart below) designed to advise and determine protection categories for Personal Protective Equipment (PPE).
An Arc Rating is the value attributed to materials that describes their performance when exposed to an electrical arc discharge.
The Arc Rating is expressed in calories per square centimetre (cal/cm²) and is derived from the determined value of the Arc Thermal Performance Value (ATPV).
The PPE should always be selected to match or exceed the PPE Category rating of the equipment worked on.
NFPA 70E® Standard for Electrical Safety in the Workplace 2024 Edition |
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Table 130.7(C)(15)(c) Personal Protective Equipment (PPE) | ||
PPE Category |
PPE |
Req. min. Arc Rating (ATPV*) (cal/cm²) |
Arc-rated long-sleeve shirt and pants or arc-rated coverall Arc-rated face shield or arc flash suit hood Arc-rated jacket, parka, high-visibility apparel, rainwear, or hard hat liner (AN) |
Arc-Rated Clothing, Minimum Arc Rating of 4 cal/cm2 (16.75 J/cm²) |
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Arc-rated long-sleeve shirt and pants or arc-rated coverall Arc-rated flash suit hood or arc-rated face shield and arc-rated balaclava Arc-rated jacket, parka, high-visibility apparel, rainwear, or hard hat liner (AN) |
Arc-Rated Clothing, Minimum Arc Rating of 8 cal/cm2 (33.5 J/cm²) |
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Arc-rated long-sleeve shirt (AR) Arc-rated pants (AR) Arc-rated coverall (AR) Arc-rated arc flash suit jacket (AR) Arc-rated arc flash suit pants (AR) Arc-rated arc flash suit hood Arc-rated gloves or rubber insulating gloves with protectors (SR) Arc-rated jacket, parka, high-visibility apparel, rainwear, or hard hat liner (AN) |
Arc-Rated Clothing Selected so that the System Arc Rating Meets the Required Minimum Arc Rating of 25 cal/cm2 (104.7 J/cm²) |
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Arc-rated long-sleeve shirt (AR) Arc-rated pants (AR) Arc-rated coverall (AR) Arc-rated arc flash suit jacket (AR) Arc-rated arc flash suit pants (AR) Arc-rated arc flash suit hood Arc-rated gloves or rubber insulating gloves with protectors (SR) Arc-rated jacket, parka, high-visibility apparel, rainwear, or hard hat liner (AN) |
Arc-Rated Clothing Selected so that the System Arc Rating Meets the Required Minimum Arc Rating of 40 cal/cm2 (167.5 J/cm²) |
*ATPV = Arc Thermal Performance Value
** NFPA = Nation Fire Protection Association (USA)
AN: as needed (optional).
AR: as required.
SR: selection required.
Arc Flash Protection: NENS 09
ENA NENS 09-2014 is the National Guideline for the Selection, Use and Maintenance of Personal Protective Equipment for Electrical Arc Hazards and supersedes NENS 09 - 2006.
Scope
The guide provides a basic overview of the physical attributes of an arc hazard and applies to the selection, use and maintenance of PPE for work where electrical arc hazards may be encountered during the operation, construction and maintenance of electrical apparatus within an Electricity Network. This guideline is limited to protective clothing, eye and face protection, head protection, hand protection and safety footwear.
Additional PPE and equipment may be required for specific tasks e.g. HV live line work, working at heights, in confined spaces or
with hazardous materials, etc.
The Guideline also covers the clothing and apparel designs, the minimum performance levels used and the methods of testing to determine the performance levels.
The Guideline does not consider protection from electric shock or tests for the electrical conductivity of the associated PPE. The Guideline does not consider protection against other hazards, e.g. chemical, biological, noise and radiation hazards.
Objectives
The Guideline sets the minimum criteria for the selection, use and maintenance of Personal Protective Equipment (PPE) used to protect workers and others against the electrical arc hazards within the electrical supply industry.
The Guideline supports the objectives of the National Electricity Network Safety Code (ENA DOC 001) issued by the ENA to promote nationally consistent practices within the Electricity Supply Industry.
Application
The Guideline applies to workers within the electricity supply industry who are required to work on or near Low and High Voltage electrical apparatus.
Selecting the appropriate PPE for an Arc Hazard |
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Arc Rated Base Garments |
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Protective garments for the workers should provide limited arc protection (CAT 1 – 4 cal/cm²) for the workers entire upper and lower torso, arms and legs. E.g. Shirts, trousers and coveralls. |
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Arc Rated Outer Garments
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Where higher levels of arc protection are required, this may be achieved by the use of arc rated outer garments worn over base garments, such as: Coveralls, Switching Coat, Leggings, Switching Jacket, Overpants and Bib & Brace Coveralls. |
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Eye, Face and Head Protection |
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Safety glasses should be worn at all times where there is the possibility of exposure to incident energy above 1.2 cal/cm². They should comply with the requirements of AS/NZS1337.1 or AS/NZS1337.6, be manufactured with medium impact resistance, have a non-conductive frame, a wraparound design or be fitted with side shields. |
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Hard Hats / Safety Helmets |
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Should comply with AS/NZS 1801 and be selected and used in accordance with AS/NZS 1800. They should also be Type 1 construction and comply with clause 4.4 (Electrical resistance test) of AS/NZS 1801. |