Wool, a natural fiber derived from sheep, is widely used in textiles for clothing, blankets, and furnishings due to its softness and warmth. This article explores how wool reacts to flame, the scientific reasons for its fire resistance, and practical safety considerations.
How Wool Reacts to Flame
When wool encounters a flame, its behavior differs significantly from many other common textile fibers. Unlike synthetic materials that can melt and drip, or cotton which ignites rapidly, wool typically chars and forms a protective layer. This charring process helps insulate against the heat source. Wool’s self-extinguishing property means it tends to stop burning once the flame source is removed. If wool does ignite, it often smolders rather than sustaining an open flame, and any smoke produced is minimal and less toxic compared to synthetic fibers. The smell emitted during this process is distinctive, often described as burning hair, and the residue is a soft, crumbly ash that does not melt or stick to skin.
Why Wool Resists Fire
Wool’s inherent fire resistance stems from its unique chemical composition and physical structure. The fiber is primarily composed of keratin, a protein also found in human hair and nails, containing a high percentage of nitrogen (around 16%) and a natural moisture content of 10-14%. This high nitrogen content makes wool less combustible because nitrogen acts as a fire retardant. Wool requires a higher temperature to ignite (typically 570-600°C, compared to cotton at approximately 255°C) and a higher oxygen concentration (about 25.2%) than what is naturally present in the atmosphere (around 21%) to sustain combustion. When heated, wool fibers swell and form an insulating char layer, which acts as a barrier to prevent the spread of flames and protect underlying materials.
Practical Safety Considerations
Wool’s fire-resistant properties offer a safety advantage in various applications, including clothing, bedding, and home furnishings. Its tendency to char and self-extinguish, rather than melt and drip, can reduce the risk of severe burns and fire spread. This characteristic makes wool a preferred material in environments where fire safety is a concern, such as in aircraft, public buildings, and specialized protective equipment like firefighter uniforms. While wool is naturally fire-resistant, it is not completely fireproof. All materials can burn under extreme and prolonged heat conditions. Therefore, general fire safety practices remain important, including never leaving open flames unattended and ensuring functional smoke detectors in all living spaces.