Page 52 - OHS, April 2020

ELECTRICAL SAFETY
Exploring the science of a flame unravels the mystery of fire into key principles that influence FR fabric creation.
ing a chemical reaction to form durable bonds that results in a permanently flame-resistant fabric. The engineering process allows the fabric to retain its original look and comfort benefits that are so desired in cotton and rayon fabrics, while providing permanent FR protection against short-term thermal hazards.
Gas-Phase Radical Scavengers
Another technology for suppressing flame is the gas-phase radi- cal scavengers. These are special molecules, usually chlorine-based, that are part of the fiber structure and have the unique property of forming relative stable radicals when exposed to heat. Recall that the fuel must break apart into radical molecules in order to react with oxygen. As these fuel radicals are formed, they will combine with the chlorine radicals instead of oxygen and become trapped or “scavenged”. This deprives the fire of the chemical chain-reaction that is one of the required components to maintain a flame.
These chlorine atoms are typically incorporated into an acrylic fiber forming a fiber commonly known as “modacrylic” (modified acrylic). Fabrics designed with modacrylic fibers generally main- tain their softness and are easy to dye for branding and visibility. Additionally, since the FR protection activates in the gas phase,
which occurs above the fabric, non-FR fibers are easily blended with FR fibers to provide effective protection at a more desirable price point. Many fibers blends incorporating modacrylic and other fibers currently available to optimize the desired properties.
High Temperature Fibers
These durable fibers have a molecular structure that does break apart when exposed to heat until it reaches very high tempera- tures of 750 degrees Fahrenheit or higher. They provide flame resistance by depriving the fire of its fuel by simply remaining intact at the temperature of most thermal events. FR benefits are a part of the fiber’s very structure, and as such, cannot be washed out or removed.
Aramid fibers are the most widely used, high-temperature fiber, but there are many different fiber structures available. Since there are no fire-retardant chemicals to consume, these fabrics can with- stand thermal events that are longer in duration. For this reason, high-temperature fibers are frequently used in military flight suits and firefighter turnout gear, where exposure times can be longer than typical flash-fires. This class of fiber makes these fabrics easily the most expensive FR technology; however, the resulting fabrics are very durable and provide excellent FR protection.
These fibers also are relatively stiff and have minimal moisture absorption, which results in a generally lower perceived comfort. But despite these limitations, fabrics made from high-temperature fibers are used extensively in many industries throughout the world due to their durability and excellent fire protection properties.
While each technology can provide excellent protection from thermal hazards, leading textile manufacturers with access to mul- tiple technologies can develop fabrics that incorporate more than one technology into a protective textile. Combining two FR tech- nologies into a fabric enables a manufacturer to utilize the best qualities and strengths of each technology to tailor optimized solu- tions for specific workplace needs in one fabric. Utilizing combina- tions of multiple technologies also allows manufacturers to meet industry requirements while offering performance characteristics, such as durability, lightweight, breathability or mobility.
All three FR technologies are able to help protect wearers from burns should a short-term thermal incident occur. Even though they offer critical protection, it is essential to specify the FR fab- ric that works best for your unique situation—not the other way around. Safety managers can specify the FR fabric that goes into PPE garments, which helps ensure that the garment will address the needs of your risk assessment. Identifying potential worksite hazards, environmental conditions and desired comfort features all contribute to selecting a durable and effective FR fabric.
Exploring the science of a flame unravels the mystery of fire into key principles that influence FR fabric creation. Both textile manufacturers and safety managers can benefit from a better un- derstanding of fire science to help guide technology development, deployment and selection of PPE through the lens of site-specific needs. Armed with this information, the PPE industry can provide those on the job with the best-possible FR fabrics to protect them when they need it most.
Drew Child is the Director of Technology and Program Director for Milliken’s Uniform and Protective Fabrics Business.
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