Understanding the basic differences between “inherent” and “treated” flame-resistant (FR) technologies is very important for those responsible for evaluating, selecting and wearing FR garments.
The Merriam-Webster Dictionary defines “inherent” as being involved in the “constitution or essential character” of something. As it relates to FR clothing, the word “inherent” means that FR properties are part of the fibers used in the fabric, and always have been. The flame resistance is intrinsic, permanent and cannot be washed away or worn out.
“Treated” or “topically treated” fabrics, on the other hand, have had chemicals added to them to make them flame resistant. The FR properties of chemically treated FR fabrics—which are usually cotton or cotton/nylon blends—may be diminished or removed altogether depending on how they are laundered and/or which chemicals they are exposed to in the work environment. One way to remove flame resistance is to use chlorine bleach while washing the garment. Test results shown in the chart below demostrate this.
Click to Enlarge
DuPont™ Nomex® IIIA and DuPont™ Nomex® MHP fabrics are inherently FR and provide excellent protection from fire and arc flash hazards. Fabrics and garments made from Nomex® IIIA have been third-party certified to meet the requirements of NFPA 2112, and deliver superior protection across a range of fire-exposure conditions. Nomex® MHP fabric is engineered to protect against electric arc hazards and meets NFPA 70E Category 2 requirements. Like Nomex® IIIA, the FR properties of Nomex® MHP fabric are inherent—they cannot be washed out or worn away.
Evaluating flame resistance
Char damage length is one of the key criteria used to qualify fabrics as FR. NFPA 2112 sets a requirement of less than or equal to four inches of char damage length. While the FR cotton/nylon fabric passed this requirement when new (0 washes), by 10 washes with regular detergent and chlorine bleach, its char length had increased to 12 inches, (i.e., the entire length of the sample burned). While manufacturers may recommend against the use of chlorine bleach, its use in the real world is routine, and just a few washes with chlorine bleach can damage a chemically treated FR cotton or cotton/nylon garment. Unfortunately, the wearer cannot tell this through a visual inspection of the garment.
Note that for DuPont™ Nomex® IIIA and Nomex® MHP fabrics laundered and tested in the same way, even at 30 washes with detergent and chlorine bleach, both fabrics still meet the NFPA 2112 requirements for char damage length.
Frequently asked questions
- What will happen if I home launder FR-treated cotton/nylon, Nomex® IIIA or Nomex® MHP garments?
If you follow home laundering instructions for Nomex® IIIA, Nomex® MHP and (FRT) cotton/nylon garments precisely, nothing negative should happen to them. Be aware, however, that in specific instances where FRT cotton/nylon garments were laundered using hydrogen peroxide (a type of oxygen bleach), the FR properties were compromised.
- When should I retire my FR garments from service?
Any garment with visible holes, rips and/or tears or contamination from flammable materials should be repaired, cleaned or removed from service. A garment made with FRT fabric, such as FR cotton/nylon blends, may need to be retired from service long before the fabric shows any visible wear. It is difficult to judge the remaining level of flame resistance in treated garments because there are no visible cues; it can only be determined through a destructive test. The FR properties of an inherent FR fabric like Nomex® IIIA and Nomex® MHP do not change with use or laundering.
- If inherent FR garments and FRT garments perform differently, how can they both be certified to the same standard?
The two main garment performance standards for FR clothing, NFPA 2112 and ASTM F1506 (used for NFPA 70E), only specify minimum performance levels for fabrics and garments. They do not address all factors related to durability of the FR properties. It is the end user’s responsibility to determine if these minimum standards provide an appropriate performance level for their particular application.
- Other than chlorine bleach, what else could damage the FR properties of FRT garments?
- The combination of hydrogen peroxide (a type of oxygen bleach) with hard water during laundering could compromise the FR properties of garments made with FRT fabrics.
- Exposure to oxidizing (e.g., chlorine-containing) chemicals in the workplace may, over time, compromise the FR properties of garments made with FRT fabrics.
- How will I know if the FRT garment’s FR properties have been compromised?
Without performing destructive testing, such as vertical flammability testing, you would not know. This is dangerous, because the wearer cannot see the difference between an FRT garment that is still effective and one that has lost its FR properties.
- If Nomex® IIIA and Nomex® MHP fabrics are inherently FR, why do the DuPont laundry instructions advise me not to use chlorine bleach?
Repeated use of chlorine bleach can affect fabric color and strength and shorten the useful life of the garment. However, exposure to chlorine bleach will not affect the FR properties of inherently FR fabrics like Nomex® IIIA and Nomex® MHP.
- How does Nomex® MHP compare to FRT cotton or cotton/nylon blends?
Nomex® MHP fabrics and garments provide inherent protection against electric arc hazards. This means that the thermal protection cannot be washed out or worn away as compared with chemically treated FR products such as UltraSoft®. Garments made from Nomex® MHP fabric are lighter than FRT cotton/nylon blend garments, such as UltraSoft® (6.5 oz/yd2 vs. 7.0 oz/yd2), and they retain their professional appearance throughout extended use and repeated launderings. Nomex® MHP garments demonstrate a better life-cycle value than less durable FRT cotton and FRT cotton/nylon blend garments.
*Reported by Westex in their “Update to Industrial Laundry Care Advisory,” October 2, 2003.