Garments made of Lenzing FR® blends- The best protection against heat and flame!
by Alexander Gstettner
Protection against thermal hazards (flash fire, electrical arc discharge, molten metal splash) has evolved from no protection, to uncomfortable and even dangerous products (asbestos fiber, glass fiber, synthetic flame resistant fibers) to todays highly advanced fabric composites.
Certainly, the best protection against direct fire is achieved with flame resistant materials. However there are other sources of heat to consider when designing protective garments, namely, convective, conductive and radiant heat. In some cases people may be exposed to all three kinds of heat at the same time, at least temporarily.
Take, for example, a molten metal factory where there is a high amount of conductive and radiant heat as well as a smaller amount of convective heat, not to mention the source of danger, liquid metal splashes and spots. The requirement for these workers goes far beyond simple protection from flames.
PCC should not only be protective- it should be functional as well
All physical activities require strength and movement. This movement, especially for a fire fighter in the line of duty, produces heat and heat, coming from the body, naturally produces moisture and perspiration. To keep the body at an optimal temperature, allowing for optimal performance, PPC must lift moisture away from the skin allowing the body to maintain an optimum temperature.
The Process:
PPC lifts and absorbs wetness, transporting moisture away from the skin and allowing the evaporation of perspiration.
Research has proven, that using functional PPC increases the efficiency and effectiveness of the wearer. Having a dry and comfortable feeling on ones skin enhances ones performance in any type of situation. Clothing which does not take these factors into consideration can lead to the fatigue or the mental distraction of the wearer increasing the probability of occupational injuries - not forget to mention the possibility of heat stoke resulting from heat stress. Not taking these factors into consideration can create a hazardous situation for both the individual and their team.
Using and understanding the fibers and their properties
Any PPC coming into contact with fire or heat must be flame resistant but it must also be comfortable and able to absorb moisture. Achieving the required effects requires the uptake and lift of moisture. Therefore, functional clothing always consists of two fibre components, one that absorbs and holds wetness away from the skin and one, which remains dry creating a feeling of comfort for the wearer.
There are many High Performance Fibres existing on the market (Meta Aramides, Para Aramides, Polyimide, Poly Amid Imid, PBI-fibres, etc.), which are being used for this application. These fibres have been proven to be excellent in respect to their flame resistance performance but their lack of moisture removing capability limits their functionality.
One alternative is flame resistant cotton, i.e. cotton treated with a special flame resistant finishing. This of course reduces the flexibility and comfort of the garment and research shows that with regular washing the chemical treatment can be washed out making the garment no longer flame retardant. In addition, when exposed to heat, the chemical releases toxic fumes, which may create a hazardous situation for the wearer and therefore reducing the usefulness of the clothing.
Science and nature joining forces
As with the majority of technological advances, the solution to the comfort issue was provided by a combination that exists in nature itself and some scientific ingenuity. Viscose fiber is derived from pure wood cellulose extracted from beech wood. By applying state of the art science, this cellulose is then transformed into viscose fiber. An environmentally safe fiber, which is biodegradable and does not harm the environment in any way.
The fiber is made inherently flame resistant through the incorporation of an environmentally friendly, totally non-toxic organic compound developed by a major pharmaceutical company particularly for this application.
Workers are only protected if they actually wear the protective apparel they are provided with
It goes without saying that workers are only protected if they actually wear the protective apparel they are provided with. In this respect, it helps if the garment is comfortable! Furthermore, the workers mobility and effectiveness has to remain as unimpeded as possible. It is in the realm of comfort and mobility that great strides have been made.
Prominent textile mills globally have recently picked up on this idea that a fabric does not have to be uncomfortable in order to provide full protection. These innovative mills have developed and commercialized new protective fabrics in several new styles and colors with great success. Through the use of these newly developed fabrics, the major garment manufacturers and rental laundries have, in turn, been able to meet the end users needs; apparel that is comfortable without compromising the demanding requirements for protection.
Thermal protection- a double-edged sword.
The issue of thermal protection has traditionally been a double-edged sword; if a protective garment insulated the wearer from outside heat and flame, it also insulated in the reverse direction. It could trap body heat and moisture inside the garment, leading to fatigue, discomfort, moisture buildup and loss of the bodys ability to maintain proper body temperature (heat stress). This resulted in the so called plastic wrap effect.
A new generation of thermal fabrics for specific endusers.
Using the inherently flame resistant viscose fiber Lenzing FR®, a whole new generation of thermal fabrics has now been developed. These fabrics effectively combine the historically mutually exclusive properties of permanent flame resistance and wearer comfort.
In addition to providing comfortable thermal protection the new generation fabrics also have some ancillary properties, which are of interest to specific end users.
For utility workers, innovative fabrics have been commercialized which are blends of Lenzing FR® and Aramids. These fabrics are comfortable yet offer excellent protection against flame and high voltage electrical arcs. Utility workers appreciate the natural comfort as well as superior UV stability of the new generation garments.
For hot metal splash protection, (for example, in aluminum smelters and foundries), fabrics composed of Lenzing FR® and wool are not only comfortable, but have superior metal shed and cryolite resistance properties compared to previous generation fabrics. Because of the hot environment where these garments are worn, the excellent wicking properties contributed by viscose add to wearer comfort. As with flash hoods, perspiration is wicked away from the skin and to the surface of the fabric. The subsequent evaporation helps to cool the wearer because of the latent heat of vaporization phenomenon.
Fabrics made with wool and Lenzing FR® fulfil Norm EN 531 with the following results:
- EN 532 Limited flame spread Pass
- EN 366 Radiant heat Level 2
- EN 367 Convective heat Level 1
- EN 373 Molten metal splash (aluminum) Level D-2 - Molten metal splash (iron) Level E-2
Several companies throughout the world in the aluminum, steel and iron sector have clothed their workers in garments made of wool/Lenzing FR® blends and the results have been highly satisfactory.
For welding industry applications, new generation fabrics composed of Lenzing FR® and para aramids have been developed. They are proving to be the lightweight, comfortable solution for protecting the welder. There is also an added benefit; the wear life of these garments is up to 10 times that of traditional treated cotton products, providing excellent cost effectiveness, despite the higher initial cost.
For petrochemical and general industrial applications where protection against flash fire is required, Lenzing FR® / aramid blends are replacing heavier, less effective, chemically treated cotton shirts, trousers and coveralls. These new blends have resistance to a wide variety of solvents, acids, alkalis and other industrial substances. Yet, these new generation fabrics are comfortable, inherently flame resistant and cost effective.
Fabrics made with a blend of wool and Lenzing FR® offer natural protection. Highlights include:
- Permanent flame resistance regardless of the amount of laundering
- Good protection against convective heat
- Good protection against radiant heat
- Excellent resistance against molten metal splash
- Excellent wear comfort
- Easily dyed produces brilliant colors
- Good color fastness to light and laundering
- Breathable and non-irritating to the skin
- Inherently anti-static
- Easy care
- Right cost
Features of aramid/Lenzing FR® blends include:
- Lightweight, comfortable fabrics with higher moisture regain than 100% aramid.
- Soft, smooth and comfortable against the skin
- Long lasting durability versus FR treated cotton and cotton blends
- Natural chambray appearance
- Better light fastness than piece dyed aramids
- Excellent pilling resistance
- Easy care; no touch up ironing required
Finally, testing has concluded that the toxicity of pyrolysis gases for Lenzing FR® is no different than that of regular viscose. Additional Gas Chromatographic analysis of pyrolysis gases confirmed that there were no phosphorous compounds or sulphur dioxide (SO2) detectable. Formation of hydrogen cyanide or hydrogen chloride in the smoke gas is not possible because the flame retardant agent used does not contain nitrogen or chlorine.
The balance between protection and comfort
So, for numerous applications, Lenzing FR® flame resistant viscose fibers would seem to be the perfect solution.
But we all realize that in an imperfect world, there are seldom-perfect solutions...
By way of analogy, in the consumer market, polyester was introduced years ago as a solution to enhance the care properties of pure cotton garments. But, simply replacing the cotton with polyester would solve one problem and simultaneously create another. Pure polyester was not very comfortable. Eventually, the consumer determined that a blend of cotton and polyester gave the best of both worlds. Cotton for comfort, polyester for easy care. Ultimately, the optimum blend ratio was determined by the balance that the consumer wanted between comfort and easy care.
Similarly with thermal protection fabrics there are balances to be determined. Let us consider the properties of two widely used fibers with inherently flame resistant properties.
At one end of the spectrum are the synthetic fibers, such as aramids, which are inherently flame resistant and extremely durable. At the other end of the spectrum are the viscose fibers, which are inherently flame resistant and extremely comfortable.
Here, as in the cotton / polyester example above, a balance has to be achieved between two competing properties - durability and comfort. Or, to be more precise; advantage can be taken of the synergy between flame resistant viscose fibers and aramid fibers. The balance is determined by the end use application of the fabric / garment.
For example, for firefighters bunker gear, physical strength and durability is of the essence, so 100% aramid construction makes sense. Alternatively, for childrens nightwear, comfort is of the essence, so 100% inherently flame resistant Lenzing FR® makes sense.
For most industrial applications, however, the best balance between protection and comfort lies somewhere in between. Research in this area shows that Lenzing FR® / aramid blend levels of 50/50 are a good starting point. But these levels can range from 20/80 to 80/20 depending on the balance of properties to be achieved.
Lenzing AG, in cooperation with other fiber producers, developed yarns and, subsequently, fabrics based on varying blends. The results obtained from several tests clearly showed that this new generation of fabrics was a great improvement in many ways. Compared to 100% aramid fabrics, these new blends offered equal or better protection against heat and flame and at the same time brought about a whole new level of comfort.
The three Cs
The protective apparel industry speaks of the three Cs that it needs to address on an ongoing basis Compliance, Cost and Comfort.
Compliance is a given; today there is an array of fabrics available which are compliant with current government, military and industry requirements and standards.
Cost of compliant fabrics is determined by the competitive nature of the protective apparel industry. Effectively this has resulted in increasingly better protection at lower prices.
Comfort is an ongoing and increasingly more important issue. Comfort can now be incorporated as a permanent feature in thermal protective apparel. And in most cases with simultaneous cost savings to the end user.
Prominent fabric manufacturers, in close cooperation with garment makers are ready to offer fabrics made of Lenzing FR®, blended with aramids, high performance fibers or simply wool and garments on a worldwide basis in order to ensure healthiness, protection and comfort on the workplace.
(Lenzing FR® is the inherently flame resistant viscose fiber produced, sold and marketed by Lenzing AG).