Electricity has long been recognized as a serious workplace hazard, exposing employees to electric shock, electrocution, burns, fires, and explosions. Hundreds of deaths and thousands of injuries occur each year on the job due to electrical shock and arc flash, yet almost all of these tragic events are preventable.
In addition to being properly qualified for the task at hand, personal protective equipment (PPE), including arc flash rated clothing, can provide additional safeguards against the hazards posed by working around electrical energy.
NFPA 70E
NFPA 70E covers electrical safety requirements for employees, including the proper selection, use, and care of personal protective equipment (PPE). The document describes safe work practices for electrical construction and maintenance but does not specify how to safely design or install electrical systems.
Important NFPA 70E Articles
- Article 100 – Definitions
- Article 110 – General Requirements
- Article 120 – Establishing an Electrically Safe Work Condition (ESWC)
- Article 130 – Work Involving Electrical Hazards
Who is Qualified to Work on Electrical Equipment?
It is important to note that a person can be considered qualified with respect to certain equipment and methods, but still be unqualified in other situations. A person could be qualified to perform one work task and not be qualified to perform a different task on the same piece of equipment.
The NFPA 70E 2018 definition of a qualified person is: “One who has demonstrated skills and knowledge related to the construction and operation of electrical equipment and installations and has received safety training to identify the hazards and reduce the associated risk.”
Electrical workers who meet the definition of a “qualified electrical worker” will be able to:
- Determine the nominal voltage for the equipment or system.
- Determine the required approach distances for electrical shock and burn hazards.
- Distinguish exposed energized conductors and circuits from other parts of the equipment.
- Properly select, care for and use the appropriate personal protective equipment for both shock protection and arc flash protection.
Arc-Flash
Numerous workers are injured and/or killed each year while working on energized electrical equipment. Arc-flash is a type of electrical explosion that results from a low-impedance connection to ground or another voltage phase in an electrical power system.
Temperatures can reach or exceed 35,000 °F (19,400 °C) at the source of the arc. The radiant energy released by an electric arc is capable of permanently inuring or killing a human being at distances of up to ten or even twenty feet.
NFPA standards require a label on electrical equipment that warns qualified persons of potential arc flash hazards if that equipment is likely to require examination, adjustment, servicing, or maintenance while energized.
Approach Boundaries
Short circuit and coordination studies are performed to determine the available energy of an electrical system and the expected clearing time of protective devices, the arc-flash hazard analysis selects the working distances and calculate the incident energy at each fault location at the prescribed working distance. Based on this information, the arc-flash hazard PPE category for the calculated incident energy level can be specified along with the flash protection boundary at each fault location.
Arc Flash Boundary
The arc flash boundary is the minimum “safe” distance from exposed energized conductors or circuit parts that has the potential for an arc flash. The arc flash boundary is calculated to 1.2 calories/cm2 of incident energy. That’s the distance where a worker without appropriate PPE would receive second-degree burns.
Limited Approach Boundary
Within this boundary, the exposure to arc flash risk increases and it is possible to be exposed to a shock hazard. Appropriate PPE should be worn by qualified workers in the limited space (space between the limited approach boundary and the restricted boundary). Non-qualified workers should stay outside of this boundary unless wearing proper PPE and being escorted by a worker with specialized training.
Restricted Boundary
The area closest to the live, exposed equipment is within the restricted boundary. In order to pass this boundary, you must be a qualified worker with the proper training and PPE. If you need to perform work on the energized equipment, you may also need a work permit and documentation.
Arc Flash Clothing
Flame resistant (FR) clothing significantly reduces burn injuries, which can save lives in the event of an arc-flash incident. Protective clothing includes items such as shirts, pants, coveralls, hoods, jackets, rainwear, and parkas.
The arc flash rating is called the Arc Thermal Performance Value (ATPV), which is expressed in calories per square centimeter (cal/cm2) or joules per square centimeter (J/cm2). Clothing is available with ATPV ratings from approximately four to greater than 50 cal/cm2 (16.7 to 209 J/cm2).
| Hazard Risk Category | Minimum Performance |
|---|---|
| HRC 1 | 4 cal/cm2 |
| HRC 2 | 8 cal/cm2 |
| HRC 3 | 25 cal/cm2 |
| HRC 4 | 40 cal/cm2 |
Some clothing might need to be dry cleaned if contaminated with grease or certain solvents. The flame resistance of chemically treated garments can decrease with the number of washings, and failure to remove grease and solvents from inherently flame resistant or chemically treated PPE could compromise its protective properties.
Rubber Gloves
Insulating rubber gloves are among the most important articles of personal protection an electrical worker can wear. Protective gloves are categorized into six classifications, each based on the approved voltage levels the gloves can provide protection for.
In order to maintain the highest level of protection and ensure long life, it is essential that rubber goods are properly cared for and stored. Before each use, rubber goods should be visually inspected for holes, rips or tears, ozone cutting, UV checking and signs of chemical deterioration, contamination, physical damage and embedded wires.
To provide the necessary mechanical protection against cuts, abrasions and punctures, leather protector gloves should always be worn over insulating rubber gloves. Leather gloves only protect the rubber and do not protect the user against electric shock.
