Understanding Arc Flash Ratings on FR Shirts
Choosing the right flame-resistant shirt can feel complicated when a product label includes terms such as ATPV, EBT, cal/cm², NFPA 70E, and arc flash PPE category. For workers who perform electrical maintenance or work near energized equipment, these ratings are important because ordinary workwear may ignite, melt, or continue burning after an arc flash.
An arc flash is a sudden release of electrical energy through the air. It can produce extreme heat, intense light, pressure, molten metal, and hazardous debris in a fraction of a second. An FR shirt cannot eliminate the arc flash hazard, but it can help reduce burn injury by resisting ignition and limiting the spread of flames.
Understanding the rating on an FR garment helps you select clothing that matches the electrical task, the calculated incident energy, and the rest of your protective equipment. The shirt should always be part of a complete electrical safety program rather than treated as a substitute for de-energizing equipment or following safe work practices.
What an arc flash rating measures
Arc flash clothing is commonly rated in calories per square centimeter, written as cal/cm². A calorie in this context is a unit of thermal energy. The number indicates the amount of heat energy the fabric can expose a wearer to before reaching a level associated with a second-degree burn.
For example, a shirt marked 8 cal/cm² has a higher thermal performance rating than one marked 4 cal/cm². That does not mean the wearer can safely work in any 8 cal/cm² environment. The garment rating must meet or exceed the incident energy analysis for the specific task and equipment.
The arc rating reflects thermal protection, not every hazard created by an electrical fault. It does not certify a shirt as protection from electric shock, arc blast pressure, flying objects, noise, or hazardous chemicals. Additional equipment and procedures may be required.
ATPV and EBT on garment labels
Two common terms appear on arc-rated clothing labels: ATPV and EBT. ATPV means Arc Thermal Performance Value. It represents the incident energy level at which there is a 50% probability of a second-degree burn when the garment is tested under specific conditions.
EBT means Energy Breakopen Threshold. It describes the energy level at which the fabric develops a break or opening during testing. A break may allow heat to pass through the material and expose the wearer’s skin. Some fabrics reach their breakopen limit before their calculated burn threshold, while others perform in the opposite way.
The label usually displays the lower applicable value as the garment’s arc rating. A shirt may show an ATPV of 6 cal/cm², an EBT of 6 cal/cm², or simply an arc rating of 6 cal/cm². For everyday selection, the key point is to compare the garment’s stated arc rating with the required incident energy, while referring to the manufacturer’s documentation for technical details.
How NFPA 70E relates to FR shirts
NFPA 70E provides electrical safety practices for workplaces in the United States. It addresses risk assessment, approach boundaries, energized work, training, and personal protective equipment. Its tables and methods can help determine the clothing and equipment needed for a particular job, although the final selection should be based on the applicable task assessment.
Older references often use Hazard/Risk Categories, or HRCs. Current terminology commonly uses PPE Categories. These categories can help organize protective requirements, but they should not replace an incident energy analysis when one is available. A garment’s cal/cm² rating is a more direct way to compare thermal protection with the calculated hazard.
An arc-rated FR shirt may be required with FR pants or coveralls, an arc-rated face shield or hood, voltage-rated gloves, leather protectors, hearing protection, safety glasses, and other equipment. The shirt alone does not create a complete arc flash ensemble. Open areas at the neck, wrists, waist, and front closure should also be considered when building the system.
| Label term or rating | What it means | How a beginner should use it |
|---|---|---|
| Arc rating | Thermal performance stated in cal/cm² | Compare it with the task’s required incident energy |
| ATPV | Energy level associated with a 50% chance of a second-degree burn during testing | Use the stated value as part of the garment’s protection rating |
| EBT | Energy level associated with fabric breakopen during testing | Check the lower applicable value shown on the label |
| FR | Flame resistant; the material resists ignition and self-extinguishes under specified testing | Confirm that the garment is also arc rated when electrical exposure is involved |
| PPE Category | A collection of PPE requirements for certain task conditions | Use it as guidance alongside the job hazard assessment |
| cal/cm² | Unit used to express incident thermal energy and garment arc rating | Higher numbers generally indicate greater thermal protection, not unlimited safety |
Matching a shirt to the work
The first step is to identify the incident energy associated with the equipment and task. This information may come from an electrical study, equipment label, employer procedure, or qualified safety professional. If the hazard is rated at 7 cal/cm², a shirt rated at 8 cal/cm² may meet the shirt-level thermal requirement, provided the rest of the clothing system is suitable.
Do not select a shirt based only on the voltage of the equipment. Voltage influences electrical hazards, but arc flash energy also depends on available fault current, clearing time, working distance, equipment design, and other factors. Two pieces of equipment with the same voltage can have very different incident energy levels.
Layering also affects the selection. Multiple arc-rated layers may offer a combined rating only when the manufacturer or applicable standard provides a recognized method for determining that performance. Do not assume that adding ordinary cotton, synthetic fabric, or an untested jacket automatically increases protection. Some synthetic materials can melt and worsen burn injuries.
Reading an FR shirt label correctly
Look for a permanent label that identifies the manufacturer, fiber content, care instructions, and applicable performance information. An arc-rated shirt should clearly state its arc rating, usually in cal/cm². Product descriptions may also identify compliance with relevant ASTM or NFPA requirements, but the sewn-in label and manufacturer documentation are especially important.
FR and arc rated are related terms, but they are not interchangeable. FR describes resistance to flame, while an arc rating indicates tested thermal performance for an electrical arc exposure. A shirt advertised only as flame resistant may be appropriate for welding, heat, or flash-fire work but may not be suitable for an arc flash hazard.
Inspect the shirt before every use. Look for holes, torn seams, damaged closures, heavy contamination, or areas worn thin. Oil, grease, solvents, and other flammable substances can affect performance. Garments that have been exposed to hazardous contamination may need special handling or removal from service.
Care, fit, and everyday comfort
Correct laundering helps preserve the garment’s protective properties. Follow the care label and avoid chlorine bleach, hydrogen peroxide products, fabric softeners, or other chemicals that the manufacturer prohibits. These products can damage fibers, leave residues, or reduce the garment’s flame-resistant performance. Industrial laundering may be preferable for heavily soiled workwear.
Fit matters because a shirt that is too tight can restrict movement and leave gaps between garments. A shirt that is too loose may catch on equipment or create uncomfortable bulk under a jacket or harness. Choose sleeves that cover the wrists during normal movement, a length that stays tucked when required, and closures that remain secure during work.
Breathable FR fabrics, articulated sleeves, durable stitching, and practical pockets can make protective clothing easier to wear consistently. Direct-to-customer workwear manufacturers such as UR Shield offer FR shirts and related protective gear with an emphasis on practical use, accessible pricing, and sizing for demanding trades. Product specifications should still be checked against the precise requirements of the job.
Practical selection checks
Use these checks before purchasing or wearing an arc-rated shirt:
- Confirm the required incident energy in cal/cm² from the employer’s assessment or equipment documentation.
- Choose a shirt whose arc rating meets or exceeds that requirement.
- Verify that the label states an arc rating, rather than relying on an “FR” description alone.
- Check compatibility with arc-rated pants, jackets, gloves, face protection, and other PPE.
- Follow the care label and remove garments with serious damage or permanent contamination.
An arc-rated FR shirt is a practical line of defense when electrical work cannot be performed in a de-energized state. Selecting the correct rating begins with the hazard assessment, then continues with label verification, complete PPE coordination, proper fit, and regular garment inspection.
Browse UR Shield’s flame-resistant shirts and protective work gear to find options suited to electrical work, welding, and other heat-exposed tasks. Review each product’s arc rating, construction, sizing, and care information before ordering, and use bulk purchasing or direct-to-customer options when outfitting an entire crew.