If you work in an industrial- or construction-based job, there’s a good chance that you’ve bought your own fire-resistant clothing before. Many employers provide their own FR clothing, especially if required, but sometimes it’s nice to have extras or ones with higher levels of protection than those provided. If you’ve gone shopping for them yourself, you’ve likely stopped and wondered what exactly makes clothing fire-rated. If you haven’t, you sure are now, because it’s an interesting question.
Well, there’s no more reason to wonder because we are here to get to the bottom of it. In this article, we will go over the different kinds of testing and which types of materials hold up best against the tests performed.
We’ll start by going over the three main tests performed that determine how a piece of material gets rated and what each rating checks for in the material.
Vertical Burn Test
For this test, a strip of fabric is held vertically over a flame for about 12 seconds. After the time is up, the fire gets removed and whatever flames are left put themselves out, which is known as the afterflame. During the section of the test, the time it takes to dissipate and how far the flame spreads get recorded. If the afterflame lasts for too long or extends past a certain point, then the material fails the test and can’t progress to the next step.
The purpose of this test is to gauge the duration of time the user of the clothing will get burned after moving away from the fire source. Obviously, that means the lower the time and distance, the better for the user.
Instrumented Mannequin Test
The fabric from before now gets made into a standardized coverall, similar to the ones we sell in the fire-resistant outwear section of our store, and gets put on a mannequin that has heat sensors all over its body. The coverall is then exposed to fire on all sides for a few seconds while the sensors take in the data on which areas would have received second- or third-degree burns.
Since keeping a potential user completely unharmed from a fire is impossible, if the total area of those high burn levels is less than half, the material will pass the test. If it goes over that amount, it will fail and not move on.
Arc Rating Test
The final test is specifically for the arc rating that a fire-resistant (FR) piece of clothing will receive. Arc flashes are performed on three sections of the fabric in order to measure the amount of energy that gets through. Once that energy reaches a second-degree burn level, testers will be able to determine the arc rating.
There is no failing this test like with the previous ones. Lower scores simply mean that it won’t perform as well against arc flashes, which is then clearly communicated to the potential buyer.
Now that we know the process of what exactly makes clothing fire-rated, we will look at some of the various types of materials that go through this testing in order to get those ratings.
We’ll start with the one that is best used as the outer layer of protection for FR clothing. Nylon is naturally resistant to extremely high temperatures, and it thus also has a very high melting point. In addition, the extra coating gives it a stronger resistance to wear and tear, making it a durable choice for FR clothing manufacturers.
There is a large misconception that pure cotton materials are fire-resistant, but this is simply not true. Cotton does have a high melting point, but it never makes it to those temperature levels because it will combust way before it gets there.
Because of that, it has to be combined with other materials in order to avoid that issue. A common material cotton gets mixed with is the previously mentioned nylon. Giving it a mixture of 88% cotton and 12% nylon is enough to keep the clothing from combusting when encountering an open flame.
This is probably one of the more popular types of fire-resistant materials, not because of its durability, but more so due to its high thermal and radiation resistances. It’s also much more breathable and comfortable for everyday use, which is why many firefighters and race car drivers opt to use clothing made from this material.
Most people know this one since it is frequently used in bulletproof vests. What those people usually don’t know is that its tensile strength helps keep out flames as well, no matter how hot or cold the fabric gets. It is very similar to Nomex, although lighter and thinner than its counterpart.
While firefighters mostly use Nomex for their undershirts and pants, PBI is used primarily for outerwear since it does an excellent job of keeping out moisture while protecting its users from intense flames. It is also very durable, lightweight, and has an extremely high melting point. It seems like there are no flaws to this product other than the price, but it looks like it’s well justified.
This material is one of the most durable on the market for FR clothing. Even though it is an excellent choice for resisting thermal induction, modacrylic materials mainly get used by manufacturers as a way to make clothing last longer than it would without it. The main goal here is longevity, but it’s also quite soft and easy to dye, making it the perfect fit for more casual use.
Our final material isn’t even classified as a fabric. It’s actually a treatment applied to fabrics that aren’t as naturally fire-resistant, like cotton, to increase their FR rating. The process of adding proban is done after the clothing gets woven into shape. The main reason why this product exists is to make fire-resistant clothing more affordable for the base consumer. More affordable base materials and a simpler process can help lead to lower costs, and thus higher appeal for someone who doesn’t need extraordinary levels of fire protection.