FLame Resistant (FR) Coverall Rating Guide
Flame Resistance Overview
What Are Flash Arcs
Arc flashes are a phenomenon where a flashover of electric current leaves its intended path and travels through the air. Dust, dropping metal, accidental touching, condensation, material failure, corrosion, or poor installation are some causes of arc flashes. Serious injury and even death can occur when a person is near an arc flash. Other outcomes include burns, fire, flying objects (molten metal), blast pressure of 2,000+ psi, 140 decibel sound blast, or 35,000 degrees Fahrenheit heat. Proximity of the worker to the hazard, temperature, and time for circuit to break dictate the severity of an injury.
Watch what an electric arc flash looks like in the video below.
What are flash fires
A flash fire is defined by NFPA as a “type of short-duration fire that spreads by means of a flame front rapidly through a diffuse fuel, such as dust, gas, or the vapors of an ignitable liquid, without the production of damaging pressure.” The flash fire consumes all the available fuel in the area (oxygen) which creates a dangerous environment. It’s predominately present in Oil & Gas and Manufacturing industries since combustible dust is commonly created.
United States Safety Standards
National Fire Protection Association (NFPA) created NFPA 70E for electrical safety. The code covers all industries who work in environments that are exposed to arc flashes. Typical occupations that NFPA 70E covers are industrial electricians, machine operators, and maintenance workers. NFPA 70E mandates employers to perform a hazard assessment to determine the arc level exposure. It is also the standard that created the 4 Category (ATPV/EBT) system that’s displayed on clothing.
aRC rATED oVERVIEW
NFPA 70E standard states that “Employees shall wear Arc Rated (AR) clothing wherever there is a possible exposure to an electric arc flash above the threshold incident energy level for a second-degree burn (1.2 cal/cm2)”. Keep in mind that Arc Rated clothing is also Flame-Resistant clothing.
Arc Rating is defined as the amount of energy a given fabric can withstand before a 50 percent likelihood of the onset of second-degree burn through the fabric. It’s measured in Arc Thermal Performance Value (ATPV) or Energy to Breakopen Threshold (EBT). In laymen’s terms, Arc Rating is a measurement of insulation so the higher the Arc Rating value the greater the protection is.
It is important to know that not all Arc Ratings are the same as there are two different measurements for Arc Rating.
- ATPV is measured in calories per cm2 (heat per square centimeter). ATPV value represents the heat exposure from an electric arc that will create a second-degree burn 50% of the time tested. The higher the ATPV the greater the protection is.
- EBT will break open at their Arc Rating by design leading to EBT less desired. Breaking open at a lower threshold than ATPV may cause exposure to flame on skin.
Look at the clothing tag when shopping for coveralls. The coveralls will have a category rating (1 through 4) if they are Arc Rated. Remember that coveralls can be Flame Resistant but have no Arc Rating.
NFPA 2112 is the standard for flame resistant clothing. It’s primarily for oil and petrochemical workers. The code requires an organization to conduct a thorough hazard assessment of the working environment to determine if there is a flash-fire risk. NFPA 2112 mandates that Flame-Resistant clothing must be worn if a flash-fire risk is present.
Another component of NFPA 2112 is the standardized method to determine if a clothing garment is flame resistant. Similar to NFPA 70E, textiles are tested to determine if a maximum of 50% total body burn will occur when ignited for 3 seconds. In addition, the material cannot melt, drip, or have after-flame burning. The tests are performed by two independent laboratories: Intertek Testing Services and Underwriters Laboratories (“UL”). The labs certification will be shown on the clothing after successful tests. Lastly, all testing labels must be in an easy-to-see location on the garment.
Institute of Electrical and Electronic Engineers (IEEE) produces a safety standard called National Electrical Safety Code (NESC). NESC sets the standard for safe installation, operation, and maintenance of electric power and communication utility systems. These include power substations, power and communication overhead lines, and power and communication underground lines that is designed for the electrical utility industry. NESC and NFPA 70E are alike in that the standard focuses on electrical arcs and arc flashes.
Similar to NFPA, the organization is required to conduct a thorough hazard assessment of the working environment to determine potential exposure to electrical arcs.The code requires clothing that has an arc rating at least equal to the estimated level of arc energy present (if 2 cal/cm2 or higher will be present). ATPV rating will be used once the 2 cal/cm2 threshold is met or exceeded.
NESC is easy and simple since the code uses NFPA 70E 4 category ratings.