In industrial applications, the main thermal hazards against which workers need to be protected are heat and flame, fire, the heat of an electric arc and molten metal splashes.
DuPont developed two test methods which measure the thermal protection level of a fabric (the Thermal Protection Performance Test) or a garment (the DuPont™ Thermo-Man® 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.
In the test, fabrics made of Nomex® were compared with cotton and several cotton-blend fabrics which were treated with flame-retardant chemicals:
- Fabrics made of Nomex® better shield the wearer from the onset of body burns.
- Fabrics made of Nomex® provide considerably higher TPP.
- Fabrics made of Nomex® retain their protective performance even after 200 washes.
- On a kilo-by-kilo basis, fabrics made of Nomex® provide up to twice the thermal efficiency or FFF value compared to chemically treated cotton and cotton-blend fabrics.
- PPE made of Nomex® allows for comfortable lower-weight solutions while maintaining excellent protection against heat and flame.