Seams and zippers on flame retardant garments. How do they work?

These humble little things have been keeping us dry since Whitcomb L. Judson patented the first modern zipper in 1890. Judson was a prolific inventor, but his "chain-and-lock fastener" remains his most recognized achievement and the basis for the zipper we use today.

On the surface, it can be difficult to tell one zipper from another. But what about when your clothing needs to withstand dangerous situations? You can't put out a fire with your fly loose. Fasteners on many workers' clothing are needed to keep things together under a variety of conditions.

How to make a zipper fireproof?

The cheapest solution is to use brass or oxidized brass for the zipper buckles and teeth. As a copper alloy, brass is non-sparking and suitable for situations where static build-up is dangerous. Oxidizing brass improves its protective qualities by reacting copper molecules with oxygen, creating an outer layer that prevents further corrosion.

However, cheap doesn't mean happy, especially when deadly conditions are involved. Brass has a relatively low melting point of 900 – 940°C; candles burn at 1000°C. For work environments that require reliable protection, fully flame-retardant threads and fasteners are required to hold the overalls together.

Hello Nomex

Add the original flame retardant material Nomex. Nomex was created by DuPont over forty years ago and remains the industry standard for fire resistant clothing. Unlike flame-retardant treatments such as Pyrovatex, which add protective properties to existing materials, Nomex fibers are inherently fire-resistant. Nomex uses natural cellulose from wood to make "aramid" fibers.

The molecules in aramid polymers are structured along a horizontal axis and are therefore held together by extremely strong amide bonds. It is these bonds that Nomex uses to achieve fire resistance: when ignited, the fibers carbonize and expand to form a protective layer. Another synthetic fire protection material, Lenzing FR, uses polyamide chains in the same way.

Nomex is pigmented and available in sheet or fabric form. This means the material can be processed into fire-resistant seams, fabrics and zippers. It's lightweight and tear-resistant, and because the material's flame-retardant elements are present in the material's fibers themselves, Nomex's fire-resistant, antistatic properties won't wash away or erode.

However, it should be cleaned somehow. Nomex is flame-tested for five seconds and won't melt, drip, or burn; wearers can last 35 percent longer in heat without suffering second-degree burns. Certain forms of material are also resistant to arcing.