FLAME PROTECTION 177
FLAME PROTECTION
INHERENT FLAME RETARDANCY
Flame retardant fabrics are used to make garments harder to ignite and to reduce the spread of fire, but it does not mean that the material is not flammable. The purpose of flame retardancy is to halt the combustion process in various ways. Most synthetic fibres ignite easily, but usually go out quickly and melt. Cotton, on the other hand, is harder to ignite but burns for longer and more fully. Wool is, in principle, not flammable – it can cope with tests with a glowing cigarette without starting to burn – but extra flame retardant treatments are added in certain cases. Due to the properties of these different materials, we have developed flame retardant treated cotton fabrics and inherent flame retardant synthetic fabrics.
Inherent flame retardancy is built into the fibres – it is not on top of the fabric – and cannot be washed off or worn away. Our ATH, ATS, ATG, GXH, SFLA, PFLA and Nomex fabrics have inherent flame retardancy. They consist of modacrylic, cotton and antistatic fibres. Modacrylic is a modified acrylic with inherent flame retardancy. On contact with fire a gas is formed that forces out the oxygen, suffocating the fire. There is no afterglow. Flames do not spread outside the carbonised area. The fabrics do not melt or form a hole where the flames could get through. Nor do they form a hot molten area which could stick to the wearer’s skin. Modacrylic has many advantages. It is soft, light and easy care. Modacrylic can be combined with cotton to provide better flame retardancy and better comfort. The difference between GORE-TEX® (GXH) and other inherent flame fabrics is that GXH has an anti-static membrane and is waterproof, while the rest have anti-static fibres in the weave.
LOI VALUE Limited Oxygen Index (LOI) measures the lowest oxygen content at which the material burns by itself after being ignited. Ordinary air contains approximately 21% oxygen. Easily flammable material has an LOI value of about 20% or lower, e.g. cotton which has an LOI of 16–18%. The lowest limit for fabrics that are difficult to ignite is about 25%, which is roughly the case for wool. Wool Flame retardant treated cotton Flame retardant treated wool Meta-aramid Modacrylic Modacrylic/cotton mix
25% 28% 30-32% 30% 33% 35%
FLAME RETARDANT TREATED FABRICS Our FLAM, FV, and NEG fabrics are all flame retardant treated fabrics. The chemical impregnation is long-lasting if the washing instructions are followed, and no subsequent fabric treatment is necessary. Abrasion can, however, affect the impregnation and therefore the lifetime of the garments is somewhat limited. Flame retardant treated fabrics carbonise when subjected to fire. There is no afterglow. Flames do not spread outside the carbonised area. The fabrics do not melt or form a hole where flames could get through. Nor do they form a hot molten area that could stick to the wearer’s skin. Regarding allergy risks, flame retardant treated fabrics have been tested against extremely stringent criteria. Tests show that the fabrics don’t irritate the skin or create hypersensitivity. Examples of flame retardant treated fabrics are Proban® and Pyrovatex.