Flame Resistant (FR) Clothing Basics FAQs

Flame resistant clothing stops burning once the source of ignition, either a flame or an electric arc, is removed. Essentially, the fabric self-extinguishes and the secondary source of potential injury – clothes burning against the skin – is removed. All Tyndale-manufactured FR clothing passes the ASTM D6415 vertical flame test and meets the stringent requirements of ASTM F1506.

• Protective clothing selection must be based on the probable worst case exposure for a task.
• Flame resistant clothing should provide a good functional fit for protection and comfort.
• Sleeve cuffs should be fully rolled down and secured.
• All garments, including outerwear, should be fully fastened.
• Clothing should be free of flammable contaminants such as oil or grease, which can ignite and increase burn injury.
• Appropriate protective neck, face, eye, head, hand, and foot coverings should be worn.
• Outerwear must be flame resistant, since flammable outerwear can ignite and continue to burn, essentially eliminating the protection of flame resistant clothing worn underneath.
• Undergarments worn against the skin should be FR or 100% natural fiber (cotton, wool, silk).

The difference between clothing worn everyday and FR clothing is the fabric. In order to be considered flame resistant, an FR garment must undergo a complex and costly process—using special fibers or treatment and stringent testing—before it reaches your hands. Each garment that Tyndale offers conforms to stringent quality and safety requirements that your normal, everyday clothes do not require.

Both treated and inherently flame resistant fabrics are flame resistant for the useful life of the garment. The difference between them relates to the process used in making the final product flame resistant. Treated cotton fabrics are given a flame resistant chemical application, which the originally non-FR fabric is immersed in after it is woven together. Inherent fabrics contain fibers with an FR polymer base, so that there is no need for a topical treatment. Both types of fabric offer comparable protection.

Dozens of industries may potentially benefit from the use of FR clothing. Some of them include: electric utilities, electrical contractors, refineries, drilling companies, chemical companies, manufacturing companies, and construction companies. Wherever a known flash fire or arc flash hazard exists, FR clothing may keep workers from suffering severe burn injuries. Many industries beyond those mentioned above are affected by arc flash, flash fire, and low visibility hazards.

Tyndale embroiders all FR garments onsite with 100% flame resistant thread. Tyndale’s heat transfer logos, which comply with ASTM 1506, are safe to use on FR garments because they take on the FR characteristics of the fabric after application.

Arc ratings are described by ASTM 1506 as follows: “An arc rating is a value that indicates the arc performance of a material or system of materials. It is either the arc thermal performance value (APTV) or breakopen threshold energy (EBT), when the ATPV cannot be determined by Test method F 1959.” A garment’s arc rating can be found on the interior tag below the collar. Tyndale also incorporates an exterior label on its shirts that indicates both a garment’s arc rating and its hazard risk category, so that a shirt’s protective levels are obvious at all times.

An acronym for Arc Thermal Performance Value, APTV is, in arc testing, “the incident energy on a fabric or material that results in sufficient heat transfer through the fabric or material to cause the onset of a second degree burn based on the Stoll curve.”

An acronym for Energy Breakeven Threshold, EBT is “the average of the five highest incident energy exposure values below the Stoll curve where specimens do not exhibit breakopen.” Note: EBT is similar to ATPV, but is determined when breakopen occurs before the onset of a second degree burn.

The PPE category (formerly known as hazard risk category, or HRC) is a number representing a “range” of arc ratings for easy reference. These categories were first defined by NFPA 70E Table 130.7(c) (11). PPE categories are an easy-to-remember guide for employers looking to standardize on acceptable arc ratings for the hazard level employees might be exposed to while working on specific tasks. For example, many companies standardize on CAT2 or above for most tasks. This would mean that the employer will allow only garments that carry arc ratings of 8.0 and above. Here is the breakdown of PPE categories and their corresponding Arc Ratings:

• PPE Category 1: 4 cal/cm2
• PPE Category 2: 8 cal/cm2
• PPE Category 3: 25 cal/cm2
• PPE Category 4: 40 cal/cm2

Arc rating measures the amount of heat (calories/cm2) the flame resistant fabric blocks when exposed to electric arc. Arc rating is, in essence, the level of protection provided to you.

All arc rated clothing that Tyndale carries includes labeling with the six required and recommended elements listed below:

• Manufacturer
• Country of Manufacturing/Origin
• Garment ID Number
• Fiber Content
• Statement of Compliance with ASTM 1506
• Care Instructions

Additionally, all Tyndale-made shirts include an exterior label as an enhanced safety feature. This label includes a garment’s arc rating AND its CAT rating so that the protective specifics of each garment are highly visible. Even from a distance, Safety Managers can see that workers are protected at a glance. And, our Tyndale labels denoting “FR” are in a prominent location at the back neck on shirt, jackets, coveralls and sweatshirts and on the back pocket of jeans, pants and bib overalls.

Wearing clothes in layers – for example, a sweatshirt over a henley – oftentimes provides additional protection to the wearer. What does this mean? Wearing two layers of flame resistant clothing together may provide more protection than is provided by the sum of the arc ratings. On top of the added protection of extra fabric, the layer of air between the two garments often improves the overall performance.

For example: Tyndale’s U180T CAT 1 button down shirt with an arc rating of 6.0 layered over Tyndale’s F025T short sleeve T-shirt with a 4.7 arc rating delivers enhanced protection.

• Additive ATPV value of 6.0 + 4.7 = 10.7 ATPV (cal/cm2)
• Actual ATPV value is 20.4 ATPV (cal/cm2) – more than 50% higher than the additive value!

There are documented situations where the value of layered combinations actually tested lower than the additive value, so be aware! There is no formula that accurately calculates additional protection that may be achieved by wearing two or more layers of FR fabrics. To validate any additional protection achieved through layering, arc testing according to ASTM F1959 must be performed. As a wearer of FR, it makes sense to cover as much of your body as is possible with layered flame resistant fabrics.

Tyndale does not recommend using 100% cotton instead of FR clothing, even as a base layer. According to OSHA 1910.269, clothing that “could increase the extent of the burn injury” is not permissible. Untreated cotton is not in itself flame resistant and does not provide or claim protection against arc flash or flash fire hazards. Cotton may increase the burn injury of wearers because it will not self-extinguish after exposed to arc flash or flash fire. Tyndale offers many breathable, comfortable FR base layer options as a substitute for 100% cotton.