FLAME RETARDANT FABRICS
Fabric that is certified as FR has been topically treated in an immersion process with a chemical fire retardant after the fabric has been woven. All cottons and other natural fibers certified as flame retardant are FR topically treated. Some synthetic fabrics are also topically treated.
Because the treatment is topical, it will wear out in time, and repeated cleanings will cause the flame retardancy to dissolve sooner. Most flame proofing chemicals are water soluble and will also dissipate through dry cleaning. Draperies made from FR fabrics should be re-tested periodically for flame retardancy, as retreatment may be required. For this reason, “FR” flame retardancy is certified for only one year.
FABRIC FLAMMABILITY
Fabric flammability is an important issue to consider, especially for drapery that will be used in a public space such as a school, theatre or special event venue, since federal regulations require that drapery fabrics used in such spaces be certified as fire retardant. Although all fabric will burn, some are naturally more resistant to fire than others. Those that are more flammable can have their fire resistance drastically improved by treatment with flame retardant chemicals. Certain synthetic fibers are extremely flame resistant, including glass fibers and modacrylic. Other synthetics, including certain polyesters, are slow to ignite and may even self-extinguish. However, once synthetic fabrics ignite, they will melt rather than flame. The resulting substance can lead to severe burns if it comes into contact with the skin.
Natural fibers typically do not melt. Wool and silk burn slowly, are difficult to ignite, and may self-extinguish. With other untreated natural fabrics, such as cotton and linen, the fabric can ignite quickly, resulting in a fast moving flame spread. Fabrics that include a combination of natural and synthetic fibers, such as polyester-cotton blends, can be particularly troublesome, as they combine the fast ignition and flame spread of the natural fiber with the melting aspect of the synthetic fiber.
The ignition and burn factors of fabric are also affected by the weight and weave of the fabric. Lightweight, loose weave fabrics will burn more quickly than heavier fabrics with a tight weave.
In addition, fabric flammability can also be affected by the fabric’s surface texture, with napped fabrics (such as velvets and velour’s) igniting more easily than fabrics with a smooth surface.
FIRE RETARDANCY OF FABRICS
The flammability of fabric can be drastically reduced through the use of fire retardants. Many natural fibers, including cotton, can be topically treated with a chemical that reduces the fabric’s flammability to the extent that it becomes nearly non-combustible. During a fire, the chemical reacts with the gases and tars generated naturally by the fabric, converting the gases and tars to carbon char, thus drastically slowing the fabric’s burning rate.
Some polyester fabrics are considered permanently flame retardant. This is because the fabrics are manufactured utilizing fibers for which the flame retardant properties are built directly into the molecular structure of the fibers. Fabrics manufactured utilizing Trevira™ and Avora™ polyester fibers are considered inherently or permanently fire retardant. Other synthetic fabrics may be considered durably fire retardant, fire retardant, or non-fire retardant. “Durably fire retardant” refers to a process in which polyesters are chemically treated during the manufacturing process with a non-water soluble chemical. In other cases, synthetic fabrics may be topically treated with chemicals after the manufacturing process (in the same manner as natural fibers such as cotton), or may be untreated (or untreatable) and therefore considered non-flame retardant.
When a fabric is designated as “inherently flame retardant,” “permanently flame retardant,” or “durably flame retardant,” the flame retardancy will last for the life of the fabric. The drapery can be laundered or dry-cleaned as recommended by the drapery manufacturer. In the case of fabrics that are designated as “flame retardant,” that have been topically treated with chemicals, the flame retardancy of the fabric will dissipate over time, particularly with repeated cleaning. These fabrics must be dry-cleaned with a non-liquid cleaning agent. Typically, the flame retardancy of topically treated fabric is certified for one year, though the actual length of time in which the treatment remains effective will vary based on the number of times the drapery is dry-cleaned and the environmental conditions in the location in which the drapery is used. It is recommended that topically treated drapery be re-tested for flame retardancy on an annual basis, and re-treated by a qualified professional as needed.
DFR (Durably Flame Retardant): Fibers have been manufactured with a flame retardant process prior to being woven into fabric. As a result, the fabric is typically flame retardant for the life of the fabric. This is the case for many polyester fabrics (though not all).
PFR / IFR (Permanently Flame Retardant): The fibers themselves are non-combustible. Therefore the woven fabric is considered flame retardant for the life of the fabric. This is the case for most Avora™ polyesters, Trevira™ polyesters, some other polyesters, and some other synthetic fabrics.
Durably fire retardant refers to a process in which polyesters are chemically treated during the
manufacturing process with a non-water soluble chemical. In other cases, synthetic fabrics may be topically treated with chemicals after the manufacturing process to produce flame retardant fabrics
Aramid, like Twaron is used in modern fabrics to withstand high temperatures in industry and fire-fighting.
HOW RETARDANTS WORK IN GENERAL?
In general, fire retardants reduce the flammability of materials by either blocking the fire physically or by initiating a chemical reaction that stops the fire.
Physical action
There are several ways in which the combustion process can be retarded by physical action:
• By cooling: Some chemical reactions actually cool the material down.
• By forming a protective layer that prevents the underlying material from igniting.
• By dilution: Some retardants release water and/or carbon dioxide while burning. This may dilute the radicals in the flame enough for it to go out.
One commonly used fire retardant coating is aluminium hydroxide. When heated, it dehydrates to form aluminum oxide (alumina, Al2O3), releasing water vapor in the process. This reaction
absorbs a great deal of heat, cooling the material over which it is coated. Additionally, the residue of alumina forms a protective layer on the material's surface.
1. Reactions in the gas phase: chemical reactions in the flame (i.e. gas phase) can be interrupted by fire retardants. However, there are situations where the released gas might be more dangerous when this type of retardant is involved.
2. Reaction in the solid phase: some retardants break down polymers so they melt and flow away from the flame.
3. Char Formation: Solid phase flame retardants are those which cause a layer of carbon char to form on the polymer surface. This carbon char layer is much harder to burn and prevents further burning.
4. Intumescents: These types of retardant materials add chemicals which cause swelling up behind the protective char layer, providing much better insulation behind the protective barrier. In additions to being added to plastics, these are available as paints for protecting wooden buildings or steel structures.
HOW DO FLAME RETARDANTS WORK IN FABRICS?
Flame retardant chemicals that are applied to fabrics are intended to inhibit or suppress the combustion process. These fire retardants interfere with combustion at different stages of the process like during heating, decomposition, ignition or spreading of flame. As with any matter, a textile fabric exposed to a heat source experiences rise in temperature. If the temperature of the fire source is high enough and the net rate of heat transfer to the fabric is great, pyrolytic decomposition of the fiber substrate occurs. The products of this decomposition include combustible gases, non combustible gases and carbonaceous char. The combustible gases mix with the surrounding air and its oxygen. The mixture ignites, yielding a flame. It happens when the composition of textile and the temperature, both are favorable. Part of the heat generated within the flame is transferred to the fabric to sustain the burning process and part is lost to the surroundings.
Now, if the textile is flame resistant then the flame retardant can act physically and/or chemically by interfering at particular stages of burning. There are different mechanisms of flame retardants.
APPLICATION METHODS/ TEXTILES
1. Immersion - The most efficient method of impregnating fibers is to immerse unpainted fabric.
2. Brushing on - Brushing the flame retardant on is less efficient, but generally successful if done thoroughly. It is sometimes necessary to brush on to both sides of the fabric.
3. Spraying on - Spraying on is also less efficient, but generally successful if done thoroughly and if before and after weighing of the fabric is done to determine that an adequate quantity of the retardant has been absorbed. A substantial portion of sprayed retardant is wasted as it falls to the floor.
FLAME RETARDANT FINISHES
Fabrics can be coated with chemicals to produce durable flame retardants. Flame Retardants on fabric can be applied through conventional padding, padding with multiple dips and nips. If followed by 30 to 60 seconds dwell, it gives good results. The pH of the pad bath is optimally kept at approximately 5.0. The amount of flame retardant required depends primarily on the fabric type, application conditions, and test criteria required to be met with. Screening experiments should be conducted to determine the minimum application level for a fabric
Fibres given an additional flame protection finish (right) can lose the protection as a result of wear, age or frequent washing. Flame retardant Trevira fibres (left) are inherently flame retardant. For this reason materials made from these fibres and filament yarns are likewise permanently flame retardant.This is an important argument from the ecological aspect as well. Apart from their environmentally friendly manufacture materials in Trevira CS require no
additional fire protection treatment, such as normally combustible materials need. Treatments of this kind are harmful to the environment. Flame retardant Trevira fibres and filaments are, furthermore, certified to Oekotex 100 Standard. In comparative terms only very slight amounts of toxic fumes develop in the event of a fire. This is particularly important, since in a fire the danger of suffocation from smoke fumes is greater than the risk of injury from flames.
TREAT & TEST
Treated materials should be tested after an initial treatment, after cleaning and periodically as prescribed by the flame retardant manufacturers. To test a material, hold a flame source to the lower edge of a small sample for 10 - 15 seconds, and then remove it. A properly flame retardant material will self-extinguish after a few seconds.
Many flame retardant products are water-soluble and are removed or weakened by laundering and wet conditions. Some are unaffected by dry cleaning, however they should always be retested after cleaning.
NFPA 701 TEST
Fabrics used in most public spaces require by law in many states and cities to be certified as flame retardant, according to standards developed by the National Fire Protection Association (NFPA). NFPA has various standards depending on how the fabric will be used.
In the case of draperies, curtains, and similar hanging textiles, the standard that applies is NFPA 701: Standard Methods of Fire Tests for Flame Propagation of Textiles and Films. This test measures the flammability of a fabric when it is exposed to specific sources of ignition.
NFPA 701 (Small Scale) testing measures the ignition resistance of a fabric after it is exposed to a flame for 12 seconds. The flame, char length, and flaming residue are recorded. The fabric will pass the test if all samples meet the following criteria:
1. An after flame of less than 2.0 seconds 2. a char length of less than 6.5”
3. the specimen does not continue to flame after reaching the floor of the test chamber Fabric certified as flame retardant is certified to have been tested and passed the NFPA 701 test.
LIST OF FIRE-RETARDANT MATERIALS USED IN CLOTHING
• Twaron• Nomex (a DuPont trademark) • Arselon (Khimvolokno trademark)
• coated nylon • Carbon Foam
• M5 fiber
• Kevlar
• Proban fr cotton
• PYROMEX (a trademark of Toho Tenax) • Pyrovatex fr cotton
• Dale Antiflame
• Indura fr cotton
• Technora
• Teijinconex
• Lenzing FR (fire retardant Rayon)
• Carbon X • Kanox • Mazic • Modacrylic • Kermel • PBI
FLAME RETARDANT YARNS
There are a wide range of flame retardant yarns in single or blended forms for both industrial and military applications by using the following inherently flame resistant fibers:
Para Aramide Anti-static Fiber Fr-Viscose Modacrylics
INHERENTLY FLAME-RESISTANT FABRICS
Fabric type
Fabric Content
Common Applications
Nomex® IIIA 93% Nomex, 5% Kevlar, 2% antistatic fiber
Flashfire, Electricarc
Comfort Blend® 65% Nomex IIIA, 35% FR Lenzing Flash fire, Electric arc Advance ™ 40% Nomex IIIA, 60% Kevlar Welding
PBI Gold ® 40% PBI, 60% Kevlar Flash fire, Electric arc Protera ™ 65% modacrylic, 23% Nomex, 10%
Kevlar, 2% antistatic fiber
Electric arc, particularly 70E applications
CXP ® 93% Nomex, 5% Kevlar, 2% antistatic fiber
Flash fire, Electric arc Fire Service station uniforms Firewear® 55% Fibrous Flame-Retardant Fiber
(FFR), 45% combed cotton
Electric arc, particularly knits Fire Service station uniforms
FLAME-RETARDANT TREATED FABRICS
Fabric type Fabric Content Common Applications Indura
UltraSoft®
88% cotton, 12% nylon, FR treated
Flash fire, Electric arc, particularly 70E applications Welding, and molten ferrous metals
Indura® 100% cotton, FR treated Electric arc Welding, and molten ferrous metals PRO-C FR ™
Knit
100% cotton, interlock knit, FR treated
Electric arc, particularly 70E applications, Flash fire Fire Service station uniforms
As the whole environment is going highly technical and risky, the demand for specially treated textile such as flame retardant fabrics has grown significantly. In the process of meeting with these demands, synthetic fiber has played a significant role. The textile industry has found the solution by developing flame retardant finish for synthetic fibers like polyester fabrics, nylon fabrics, polypropylene fabrics etc. Fire-retardant fabrics protect people in a diverse range of occupations, including military personnel, racecar drivers, industrial workers, special effects technicians and, of course, firefighters. And new innovations in fire-retardant fiber and fabric products are raising protection of life and limb while keeping users more comfortable and giving them a greater range of fit and mobility. New clothing options are being designed for a wide range of body types, including products designed specifically for women. As a whole, there is a great potential need of flame retardant fabrics in the global scenario.
