Burning of fiber is actually a process which flammable fibrous material severely reacts with oxygen in high temperature environment. During this process, the combustible material, oxygen and the heat are the three basic elements, and the absence of any one of them will terminate the combustion phenomena. So, the flame retardant of fabric is mainly to reduce the generation of flammable substances or oxygen, and the fabric stop burning after the heat disappeared or removed.
The Meaning of Flame Retardant
There is a quite high probability of the occurrence of deflagration or other fire accidents in the field of industrial or some other explosive field. And many survey showed that the majority of thermal injury does not come from combustion sources, but from the continuous burning of non-fire-retardant clothing. For example, flammable gas in the air will be burn out in 3 to 5 seconds after the detonation phenomena, but the high temperature during the time of intense burning will ignite flammable substances in the environment, including people’s non-flame-retardant clothing. Even if the combustion sources have been burned or people have fled from the deflagration area, the clothes will still burning, and it is the continuous burning of clothes led to serious burns or even death. So the meaning of flame retardant clothing lies in that the fire will immediately self-extinguish (without generating melt, drip or piercing) after the fire source disappeared and does not cause the secondary harm to people.
The Classification of Flame Retardant
Nowadays, there are mainly two kinds of flame retardant technologies:
The first one is put flame retardants into non-flame retardant fibers. The flame retardants will be “active” by high temperature and release non-combustible gas and accelerate fibers’ dehydration so as to retardant the flame. This kind of flame retardant called Post-Processing Flame Retardant, including flame-retardant cotton, flame retardant viscose, nylon flame retardant polyester etc.
The other kind is a change in the internal structure of the fiber by chemical process. Making fiber itself does not support combustion, so as to achieve the purpose of fire-retardant. This kind of flame retardant called Natural Flame Retardant or Permanent Flame Retardant, such as NOMEX®, KEVLAR®, PBI® etc.
Since the function of post-processing flame retardant fabric will gradually reduce and eventually disappear with time and washes, and it will be gradually be replaced by Natural Flame Retardant fabric.
Fires are unpredictable. So in order to test fabric under the most realistic conditions, DuPont invented Thermo-Man®. This life-sized, instrumented mannequin system is one of the most advanced thermal burn injury evaluation devices in the world. Covered with 122 heat sensors and dressed in test garments, Thermo-Man® helps ensure optimal product performance. With this type of testing, we can supply safer personal protective clothing for workers and improve upon personal protective equipment available today. Since the 1970s, Thermo-Man® tests have been conducted for a broad range of fields, including the petroleum, petrochemical, and chemical industries, electric and gas utilities and fire services. As different as these industries may be, they all have one common goal: protecting workers from fires. And we’re happy to help these industries with their hazard assessments so that they have the protection needed for their particular hazard.
The Survival Chances of Burn Injury ＆ Product Performance Comparison in Thermo-Man Experiment
The diagram below is from American Burn Association, in which the abscissa represents four age groups, and the vertical axis represents the survival chances, the blue column represent 25 percent of the burn area (second degree and third-degree burns), the red column on behalf of 50% burn area, yellow represents 75 percent of the burn area. According to the diagram, The higher the age, the larger the burn area, the lower the chances of survival.
The following video is from Dupont’s Thermo-Man Experiment (with audio commentary). From which you can visually see the burn degree of different clothing materials in fire deflagration accidents.
Thermal Protection Performance (TPP) Test
The Thermal Protection Performance (TPP) Test was developed by DuPont for Europe in the 1970s. It sets realistic conditions of an exposure to combined radiant and convective heat. A fabric sample is subjected to circumstances typical for fires: a constant combination of 50% radiant heat and 50% convective heat, at a constant heat flux of 84 kW/m² (approximately 2 cal/cm²/sec.). The test then measures the time that elapses and the amount of heat energy per surface area (TPP value) at which the temperature and energy transferred to the back of the fabric reaches a level which would cause a second-degree burn to the wearer of the Personal Protective Equipment (PPE).
By dividing the TPP value (cal/cm²) by the fabric basis weight (in g/m²), the Fabric Failure Factor or FFF value is obtained, indicating the thermal insulation performance of the fabric. The higher the TPP and the FFF, the higher the protection. The FFF allows for an objective comparison of materials on an equal basis, as it takes the protection/weight ratio into account. This test cannot predict the thermal performance of a garment, as other factors such as design and fit of the garment and accessories are important.
The TPP test has been adopted by ISO as a test method standard (ISO 17492) with a heat flux exposure of 80kW/m².
The US NFPA 1971 standard requires the ISO 17492 test to be carried out at a modified, increased heat flux exposure of 84 kW/m².
Functionality and Comfortableness of Flame Retardant Clothing
I Background and Present Situation Analysis
According to statistics, there are about 1000 deaths each year from fires and burns in the UK, and the number in the USA is bigger, about 8000 deaths and over 150000 people injured form fire and burns, causing $ 400 million economic losses. It is the continuous burning of clothes led to the most serious burns or even death, not the flame itself. If people wear flame-retardant clothing in the scene of fire, the burn damage can be greatly reduced. High quality flame-retardant clothing will also give firefighters confidence and courage to have a better performance in rescue people’s life and properties, minimizing the losses. In addition, as a kind of safety and health protective product, fire-retardant protective clothing is widely used in metallurgy, petrochemical, welding etc. Therefore, the research and development of flame retardant textile has became an important subject for us. In the past, flame retardant clothing is mainly put flame retardants into non-flame retardant fibers. Its flame retardant properties is temporary, and it will gradually decrease and eventually disappear with time and washes. Besides, the abrasion resistance ability, anti-static ability, anti-chemical ability and thermal protective ability are poor. Nowadays, the fabrics of flame retardant clothing are more advanced, such as aromatic polyamide, aromatic polyimide, polybenzimidazole etc. Those are permanent flame retardant fibers with high strength, well anti-static performance, well anti-flame performance and well anti-chemical performance. But with the improvement of its functionality, the cost also increased significantly, and comfortableness did not keep up with the pace of it. This is the problem we are dealing with at the present.
II Performance Requirements of Flame Retardant Clothing
1. The Functional Requirements of Flame Retardant Clothing
1) Outer shell-permanent flame retardant performance
2) Well water-proof performance
3) Well Heat Insulation Performance
4) Well anti-static performance
2. The Comfortableness Requirements of Flame Retardant Clothing
1) Well breathable performance
2) Flexibility of the whole structure
III The R＆D Strategies of Flame Retardant Clothing
1 Improve fiber’s performance ＆ reduce the cost
2 Pay attention to the development of flame retardants and flame retardant technology, and adopt advanced technology
3 Strengthen the research of flame retardant fabric’s structure ＆ realize the combination of functionality and comfortableness
4 Strengthen the coordination and cooperation in the process of development
IV Ending words
With the advancement of technology, the human self-awareness and awareness of environmental protection, there is growing emphasis on the research and development of functional and environmentally friendly new fabrics. Among the newly developed fabrics, the kind with a special protective function has a booming development, and it will be a leading force in the development of the textile industrial. With the improvement of the quality of fire-retardant protective clothing, reduction of cast, expansion of apply field and formulation of relevant laws and regulations, Flame retardant clothing with good quality will play a more and more important role in people’s daily life. So, the research on flame retardant clothing will be deeper, the protective performance of it will be more perfect, and it will have far-reaching effect for our human beings.