Why is wool flame retardant

The fire triangle below shows that three components are required to support conbustion. The presences of fuel, oxygen, and heat are all essential: remove any one of the three and the fire self extinguishes. Of the normally encountered textile fibres, wool is the most flame resistant. Wool has the most complex fibre structure optimised through evolution to provide thermal protection to mammals. Several factors in this structure are also responsible for wool's natural flame resistance.

Specifically, compared with other common fibres, wool:. While most textile fibres are polymers containing mainly carbon and hydrogen that can burn easily, wool also contains high levels of nitrogen and sulphur. In fact many fire retardant additives used for other materials are high in nitrogen. Wool therefore requires higher levels of oxygen in the surrounding atmosphere to accelerate combustion.

Therefore it is difficult to ignite wool, but once ignited, the flame speads slowly and it is easy to extinguish. Wool fibres are assembled from keratinised cells. The elongated cortical cells in the centre of the fibre are protected from the environment by a layer of cuticle cells.

These outer layer cells contain high levels of sulphur. On addition, the fibre is held together by a lightly crosslinked cell membrane complex.

When wool is heated to the point of combustion this structure tends to foam providing an insulating layer of pyrolysed material separating heat and oxygen from the fuel. Due to its natural low flammability characteristics, wool has traditionally been the fibre of choice in many technical applications, ranging from nightwear and protective garments, to transportation andspecialized military requirements. Fabric structure and density mass per unit area together with considered product design are important parameters when considering the flammability performance of textile products.

As you can see from these numbers, the total heat release from their mattresses did not even come close to passing the limit. For those of you who are serious about your research this is an amazing article that discusses wool throughout time and different cultures.

The article also discusses some on the innate properties of wool including its flame retardant nature. It also contains keratin, which has a degree higher flash point than wool alone, and that combined with the higher amounts of water means that it requires a much higher temperature to ignite. Wool burns slowly, smoldering and charring, and ultimately giving off less heat.

The structure of wool also contributes to its flame retardant nature. The structure of wool is unique in that each fiber is covered with microscopic scales, such that the outside of each fiber looks a bit like a pinecone. These tiny scales are what allows wool to be carded, weaved, or felted. There is no pass or fail for the E84 test. Its interior composition explains why wool is fire resistant and its ability to self extinguish. Wool has high nitrogen and water content so it needs higher levels of oxygen to burn than the surrounding environment provides.

The United States, as well as many other countries, have rules that certain materials must be fire retardant. Public places such as public theaters, schools, or community halls must have draperies that are fire retardant. This is to prevent injury in public places or to prevent injury to children. These laws are put in place because of how quickly other fabrics such as cotton, silk, or synthetics can catch fire and burn. This can easily be avoided by using more fire-resistant materials such as wool.

When wool catches fire, it can burn. Once removed from the source of the heat, it usually will self extinguish the fire. To keep a flame ignited on this material, a lot of oxygen is needed due to its high water and nitrogen contents.

Because of this, it is unlikely to burn for long and will then smolder and create dry ash. Because of how difficult it is for wool to burn, many people who work with fire or near explosives wear it as protective gear. For example, the material is used in personal protective equipment by firemen, the military, and occasionally policemen. People who work in welding use this textile to protect against sparks that can come off their equipment.

The textile is very insulating which makes it hard for heat to seep out from under the fabric or build up inside of it. This helps welders and firefighters alike stay close to a constant temperature while they are exposed to excessive heat. This is incredibly important since being near high temperatures is basically their job description.

Wool may not catch fire until it reaches a temperature of anywhere between 1, — 1, degrees Fahrenheit or — degrees celsius. Usually, the material will self-extinguish any flame or will smolder before turning it into ash. At the temperature wool can ignite, it would need a vast amount of oxygen for the flame to burn. Otherwise, it would be snuffed out because of a lack of oxygen.

The thickness of this textile makes it difficult for air to get into the fabric and harder for a fire to stay burning. Also, it has cross-linked cell membranes which means that when ignited, the fabric swells which will also cause the fire to extinguish, making it difficult for wool to burn. Melting is caused by molecules being exposed to so much heat they speed up so fast that they move past each other forming a liquid.

Different elements require different amounts of heat to reach this liquid state. Fire retardant fabrics melt because of the chemicals used to manufacture them and because of the synthetic fabrics they are made with. These synthetic materials can resist ignition up to high temperatures, but because of their chemical composition instead of turning into ash, they will melt. Wool cannot melt because it is a natural fabric that is not treated with the same chemicals. When the textile catches fire, it can turn to ash or smolder, but it will never melt.

The material naturally contains a lot of water which makes it difficult to reach the heat necessary for melting as well as making it difficult for the fabric to stay lit for very long. Since it contains so much water in it, it cools down any flame that may ignite.

Man-made fabrics like acrylic , nylon, or polyester melt because of the synthetic process they undergo to make them more fire retardant. If these materials caught on fire, not only would they melt but they would also produce harmful chemical gas.