Talk of beddings and wool is often a brilliant choice. But do you know that, unlike other fabrics like cotton and linen, wool poses a little fire hazard?
Well… in this article, we will talk about the properties of wool that not only makes it a comfortable bedding but an overall safe fabric you need in your home.
Is Wool Flammable?
According to the classical consensus, anything considered flammable should have a flash point below 100°F.
However, a flash point, which is the lowest temperature that a liquid vapor can burn after ignition, is not applicable to solids and gases. So, we can’t describe wool as a flammable material.
Besides that, wool can resist fire to a certain degree. So, many people consider it to be non-flammable and some people consider it to be natural flame resistant. In the next section, we will look at some reasons for that.
Why is Wool Non-flammable and Flame-resistant?
Under normal conditions, wool doesn’t support combustion. But when things get too hot (about 1,058⁰F), it burns, though not with the same intensity as other fabrics like linen and cotton. Let’s look at some of the underlying reasons for the flame resistivity of wool:
Wool has a high limiting oxygen index (LOI).
Limiting oxygen index is the least amount of oxygen you need to burn a polymer. The higher it is, the lower the tendency of the polymer to burn under ordinary conditions.
In fact, any polymer with an LOI higher than the oxygen content of the atmosphere, we describe them to be fire retardant. Wool has an LOI between 24%- 25% because within its molecules, it has a large amount of water and nitrogen.
In the atmosphere, we have only about 21% of oxygen. That means wool’s LOI is greater than what we have in the air.
To burn it, you need a lot more oxygen than you can find in the air. So, wool is a good example of a natural fiber that’s also a fire retardant.
Wool has a rather high ignition temperature.
Wool’s flame resisting ability only remains at optimal temperatures. At high temperatures close to or greater than its ignition temperature of 1094⁰F, wool burns.
The wool will keep burning as long as the heat source is still present. But once you remove the heat source, the wool would only smoulder for a while before it kills the fire.
The wool molecule mesh is inherently insulating.
At the molecular level, wool has a cross-linking arrangement of its structural cells with a keratin layer. When heated, these cells will rise to form an insulating layer.
This insulating layer does two things; prevent the flame from spreading and snuff out flames from other fabrics.
Besides that, the layer also helps to reduce the amount of smoke and toxic gas that wool produces during burning. And no matter how hot the fire, wool doesn’t melt, drip, or stick to the skin. This gives it an edge over fire-retardant synthetic fibers.
Why Wool Does Not Melt.
For solid substances to melt, you need to heat their molecules so much that they travel at high speeds.
This speed generates kinetic energy high enough to break the bonds between the molecules. After a while, the molecules become free to move as you see in liquids.
This same phenomenon occurs in fire-retarding synthetic fibers because of the chemicals they contain. On heating, these chemicals melt rather than turn to ash.
Unlike synthetic fibers, wool is a natural fiber with high moisture content. So, when heated, its water molecules make it hard for it to keep burning for long. Thus, it’s hard for the heat to reach the melting temperature.
So, instead of melting, wool rather turns to ash that even has an insulating property to prevent further burning. It produces smoke as well, but not as much and not as toxic as you would see in synthetic fibers.
However, note that some synthetic fibers like Kevlar and Nomex do not melt as well. But compared to wool, they burn at a lower temperature.
Kevlar, for instance, burns at 800⁰F, and Nomex burns at 700⁰F. Wool, on the flip side, burns at 1,058⁰F or higher.
Steel Wool: A Special Kind of Wool.
For about a century now, steel wool has been a thing in the industry. It is otherwise called wire wool, wire sponge, or iron wool. Like the name, iron wool contains a lot of fine steel filaments.
Since steel is often coarse, steel wool is often coarse as well. But there are other finer grades like superfine and moderate-coarse.
Whether fine or coarse, steel wool works well as abrasive. Artisans often use it to sharpen and smoothen iron, porcelain, glass, and other surfaces, except oak and a few others.
Is Steel Wool Flammable? Can It Catch Fire?
You can’t call steel wool a flammable material because it has no flash point. But it can catch fire because, unlike normal steel, it has a higher surface area and lower burning point.
In fact, steel wool can serve as a tinder, can burn even when wet, and you can use it to start a fire. So, you need to keep it far from naked flames, sparks, and other ignition sources.
However, you shouldn’t expect steel wool to burn like alcohol or as explosively as gasoline. But at any temperature above 12920F, steel wool will continue to burn until none of it remains.
Besides that, some steel wool contains copper. These are copper steel wool, and unlike ordinary steel wool, they are non-flammable and incombustible.
Is Glass wool flammable?
According to its safety data sheet, glass wool is non-hazardous, non-flammable, and heat-resistant. The FBS-1 Glass wool Insulation, especially, can withstand extreme heat to about 2642⁰F.
However, most glass wool products come with a plastic wrapping made of resin. When exposed to heat above 572⁰F, some facets of the wrapping can smolder or burn.
If the glass wool comes in direct contact with a naked flame, hot, toxic fumes may come as a by-product of the combustion. Although, the resulting effect depends on the ambient condition.
Is Mineral wool flammable?
Mineral wool is another kind of wool insulation like glass wool. But unlike glass wool made from glass fibers, mineral wool comprises artificial vitreous fibers other than glass.
Mineral wool is non-flammable and non-combustible. Their heat-resistant ability is inherent and you don’t need to treat them with any fire-retardant.
For that reason, mineral wool insulation can be a part of the fire protection system of a building.
However, mineral wool products come with wrappings and facings from Kraft paper or foil. These can catch fire. But when kept away from a naked flame, they do not pose any fire hazard.
Is Sheep Wool flammable?
Both glass wool and mineral wool are synthetic. Sheep wool, however, contains a natural fiber base because the wool comes from a real sheep and is then treated with boric acid.
The boric helps to repel insects and reduce the tendency of the wool to catch fire. To further reduce flammability, sheep wool producers often add ammonium sulfates and other compounds.
In the end, sheep’s wool will be as non-flammable as other types of wool insulation. Besides that, each sheep’s wool fiber is rich in water and nitrogen. So, it won’t burn or support any flame below 1,040⁰F.
Safety Tip on Wearing Wool in a Hot Weather
While wool may indeed be heat-resistant, wearing woolen clothes in hot weather needs some caution, and it’s best to choose lightweight wool.
That is because summer days can be sweltering. But wearing lightweight Merino wool, for example, would be like wearing mobile air-conditioning on your skin. This is because merino wool absorbs heat and sweat from your body pretty fast.
Then again, lightweight wool fabrics have a natural UV protection factor of 3+. That means they can protect your skin from the effects of excess sun radiation like wrinkles and others.
Thicker and heavier wool offers this kind of protection as well. But wearing heavyweight fabrics on hot days can make you uncomfortable.
Besides that, some of them absorb more heat than they lose. If things get too hot, you may even suffer from mild skin burns.
Final Words.
In this article, we noted that wool is non-flammable and fire-resistant. The major reason for this flame resistance is because of the high limiting oxygen index of wool.
Other reasons include its high moisture and nitrogen content, high ignition temperature and keratinized cells.
However, this doesn’t make it fireproof. At high temperatures, wool and steel wool can burn. But even when wool burns, it doesn’t melt, and it releases less smoke and toxic gas compared to other fire-retardant fibers like polyesters.
Although, some synthetic fibers like Kevlar and Nomen can also resist melting at high temperatures. However, wool (sheep’s wool) for example, has a natural fiber base, making it more eco-friendly.
That said, you can check out other Flamevenge articles here and learn more about flammable things around you.
