Although NASCAR has made huge advances in protecting drivers from injury in crashes, the danger posed by fire hasn’t lessened much over the years. If you talk to any driver, their worst fear isn’t a wreck: it’s being knocked unconscious in a car that’s on fire. In that terrifying situation, the driver is totally dependent on how fast the emergency crews can get to the car and how quickly they can either put out the fire and/or extract him (or her) from the car.
Race cars are designed with a lot of precautions to prevent fire from breaking out, and from spreading if it does break out, but the fact is that you are putting a human being in a small area with a large amount of flammable liquid and it’s all going 200 mph. So let’s look at why little has changed in racing with respect to fire safety.
Three elements are required in order to have fire:
It follows, then that in order to stop fire, you must eliminate or diminish one (or more) of those things. So the three ways of minimizing a fire involve
- Displacing oxygen with other gases, such as carbon dioxide or water
- Keeping fuel away from the fire
How Hot is Fire?
The temperature of a flame changes, with the color of the flame telling you its temperature
Exception! Chemicals can change the color of flames. The materials you can use to colorize your fireplace fires are chemicals, as are fireworks.
Gasoline ignites at 495 F and burns at around 1500 -2000 F.
Bonus Myth Debunk: Gasoline is not flammable. Liquid gasoline doesn’t catch fire — it’s the vapor that can start a blaze. Whenever you have something volatile, like acetone (in nail polish remover, for example) or gasoline, you can smell it because some molecules have escaped the liquid and are hovering in a vapor just above the liquid surface. When you flame something in a pan like cherries jubilee, you don’t put the flame to the liquid. You put it just above, to ignite the vapors. That’s why volatile liquids like gasoline are so dangerous: You can’t see the vapor — which is the most dangerous (flammable) part.
A Brief History of Flame-Resistance: When Science Beats Nature
Humans have been worried about fire since forever. The first attempts were finding chemicals that you could coat flammable materials with. In 83 BCE, the Romans coated their siege towers with alum (aluminum potassium sulfate) to protect them from fire. This formula was improved upon, mainly in the 1820’s, when the chemist Gay-Lussac came up with as formula that included one set of chemicals that formed a glassy layer around the flammable material and a second that produces a non-flammable vapor that displaces oxygen. (Two of the three ways to stop fires noted above!)
The problem with coating something flammable to make it non-flammable is that when you wash the object, you wash off the flame-resistance. There were attempts to make chemicals that would be more difficult to remove, but what we needed was a paradigm shift.
The real problem is that almost all of the natural fibers (from animals, plants and minerals) are flammable. A notable exception is a set of fiberous minerals called asbestos, but asbestos turns out to be extremely bad for your health.
Since Mother Nature didn’t give us a solution, we had to make one ourselves. The first breakthrough was figuring out how to make artificial fibers. Rayon (1955) was the first: It’s made from cellulose, which is a component of wood. By crafting the fiber from scratch, we could change the properties of the fiber more to our liking. The first entirely synthetic fiber was nylon, introduced in the 1930’s.
Nomex’s 50th Anniverary!
2017 marks the 50th anniversary of the commercial availability of poly (m-phenylenediamine isophthalamide), aka Nomex, a totally synthetic fiber that is very flame resistant. Meet the Nomex molecule:
The silvery-grey atoms are carbon, the red atoms are oxygen, the blue atoms are nitrogen and the little white atom is a hydrogen. (There are actually a boatload more hydrogens, but chemists in their infinite wisdom decided early on that drawing all those hydrogen atoms just mucked things up and you just have to know that carbon makes four bonds and any bond that isn’t explicitly shown is to a hydrogen atom.
When you heat Nomex, it doesn’t melt and it doesn’t burn. It chars. A char is the black residue that is left over from heating something else. (For example, charcoal is what’s left over when you slowly and partially burn an animal or vegetable fuel source. When the Nomex fiber chars, it forms a layer of carbon on the outside.
The pictures below compare an image of a Nomex fiber before and after burning and the sorry drawings underneath are me trying to make the process a little clearer. The grey cylinder represents the char that forms on the outside of the Nomex fiber.
The thicker fiber does two very important things:
- Energy from the fire is used up in creating the char. Just as we talk about dissipating energy in a crash, the heat energy used to make the char is less heat energy available to burn the driver.
- The carbon layer (which isn’t flammable) surrounds the fiber and prevents the fire from reaching any more fuel.
There’s one more consequence of the thickening. Nomex fabric is made by weaving Nomex thread, so the material is a mesh with air pockets between the fibers (which is why woven materials breathe.) When the fibers thicken, they close up the air gaps in the woven fabric.
You can see that the thicker the fibers get, the smaller that gap in the middle becomes. I tried to illustrate it a little more clearly below.
So the charring of the Nomex fiber also helps put more of a barrier between your skin and the fire.
Myth: Firesuits are Fireproof
You will never hear people in the industry use the word ‘fireproof’. Nothing is fireproof. Not firesuits and not any of the accessories (shoes, gloves, helmets, etc.).
The term used is ‘fire-resistant’. Since you can’t stop fire entirely, the important question is how much protection a piece of equipment will provide the wearer.
We know how much heat energy human skin can take before it starts to burn. I plotted up some of that data, but the problem is that most of us don’t have any feel for heat energy as a scale. So let’s look at how long it takes water of different temperatures to cause 2nd-degree burns.
The important thing is to notice is that the curve is far from linear. It would take 15 minutes of water at 118˚F to burn you, but three seconds at 140˚F. The hotter it gets, the less time you have before injury.
Remember that gasoline fires are ten to fifteen times hotter than the temperatures here. Fire introduces one more variable, which is distance from the heat source. (The water data are for immersion.)
Myth: NASCAR Requires All Drivers to Wear Nomex Firesuits
This is a myth is the same way that it’s a myth that NASCAR requires all drivers to wear the HANS device.
A badly made (or even poor fitting) firesuit made of Nomex will not protect you from burns. While Nomex is amazing, it isn’t magic.
NASCAR subscribes to a motorsport industry standard established by the SFI Foundation. SFI is non-profit organization created in 1963 by the Speed Equipment Manufacturer’s Association (SEMA) as a way to raise the bar on the quality of products intended for use in motorsports. All NASCAR (and many other racing series) require is that drivers use equipment that meets particular SFI specifications.
Firesuits are evaluated using a metric called TPP: Thermal Protective Performance. TPP was established by DuPont (the creator of Nomex) in the 1970’s. A sample of a firesuit is exposed to a known heat source and how much heat energy passes through it is measured as a function of time. This data is matched to a curve of the heat energy at which we know second degree burns happen. (2nd degree burns blister the skin. They are painful. I speak from experience.)
You can learn more about how TPP is measured from SFI’s video, or from DuPont’s description on their webpage. The TPP correlates to the time you can be exposed to a flame while wearing the garment before you get second degree burns.
|TPP||Seconds to 2nd Degree Burn||SFI Rating|
(The TPP is just double the time for seconds to a 2nd degree burn.)
The last column is the SFI Rating column. The SFI 3.2A specification addresses firesuits. In order to get the official SFI approval, your firesuit must meet these standards. Not every suit is tested: manufacturers submit suits as representative In addition to testing the firesuit, SFI also tests:
- Ability to self extinguish; a material lit on fire must go out by itself within 2 seconds.
- Thread heat resistance
- Zipper heat resistance
- Thermal shrinkage (fire resistance does you no good if your ankles are exposed)
There are separate SFI specifications for everything else a driver wears: 3.3 is for driver accessories (underwear, gloves, sock, shoes, balaclavas, helmet skirts, etc.); 16.1 is for driver restraint assemblies; 31.1 is for flame resistant motorsports helmets and so on. All NASCAR specifies is that drivers must wear a suit that is certified SFI 3.2A/5 suit. (Note that anything 3.2A/10 or higher has to be re-certified every five years.) To meet the spec, the material has to be inherently fire-resistant. You can’t use chemical dips to meet the spec.
The SFI allows products that meet the specs to use an official label; they are constantly having to worry about idiots who make fake labels and try to pass off inferior firesuits as meeting the standard. As if racing weren’t dangerous enough by itself…
Ways to up the TPP
Layers. Many suits are double or even triple layer because air is an excellent insulation. It’s the same reason you find winter coats quilted: Air is an excellent way to prevent heat conduction. The tradeoff is that the more layers, the heavier and bulkier the suit. In general, the more layers, the higher the TPP. but it’s possible for a single-layer suit made from one type of fire-resistant fabric to have a higher TPP than a two-layer suit made from another type of fabric. That tells you the construction of the suit plays a big part in how it protects you.
A simple way to increase the TPP of your outfit is to wear fire-resistant underwear. One more layer gives you another 3 seconds (on average) of protection.Fire resistant underwear and socks aren’t mandated, but they are recommended. If you can’t afford Nomex, think about what you are wearing. Cotton burns — but synthetic fibers like nylon and rayon melt, stick to the skin and are very difficult (and painful) to remove. So for the weekend racers, if you can’t afford a full set of Nomex undies, at least make sure everything else you’re wearing is 100% cotton. And ladies – no metal hooks, clasps or underwires. Metal heats up faster than fabrics and you’ll get burned in particularly bad places.
Some New Firesuit Technologies
Racing isn’t a huge market. If it were just racing, companies wouldn’t spend huge amounts of money on R&D; however, there is a huge market for fire-resistant clothing, including firefighting, welding, utility work, oil/gas and the military. Right now, about 95% of racecar drivers use Nomex firesuits – but there are things being developed.
CarbonX is a blend of oxidized polyacrylonitrile and other strengthening fibers. Oxidized polyacrylonitrile is pretty much pre-charred Nomex. The fibers are inherently fire-resistant – more than Nomex. CarbonX won’t combust unless 55% of the air around it is oxygen. In a normal environment, oxygen is 21% of air. You can hold Carbon-X at 2600˚F for two minutes and it won’t ignite or burn. Remember, though, that keeping the driver’s suit from catching on fire is only part of the task: the firesuit also has to protect the driver from the heat that would cause burns.
Prices have come way down on CarbonX since they first hit the market. You can get a CarbonX sport bra for about $80 and a CarbonX balaclava for about $65 and a pair of SFI 3.3 certified socks for $45. now. A good Nomex balaclava will cost you about the same amount.
You will notice that most of what I mentioned for sale are undergarments and accessories. There’s a reason for this. Look at the caption on the picture at right, which is take from the Carbon-X website. The fibers are basically burnt Nomex, which means you can buy those products in black, dark gray, navy blue and a dark olive green. That is the primary reason why you don’t see Carbon-X firesuits in racing; however, if you’re in the military or work in a metal foundry, color isn’t an issue and Carbon-X is finding a lot of applications in other industries.
The people I know who have tried both feel like CarbonX pieces are heavier, but more breathable and less scratchy than Nomex .
Sparco Racing has a new firesuit made from Hocotex, which it turns out isn’t a new material. It’s a new twist on Nomex. Woven materials all start with thread. From their promotional materials (and this patent), it looks like they’ve created a fabric that has aircells within the fabric. Normally, the protective air pockets are created in a firesuit by quilting together layers of fabric. There are about 300 air pockets in a normal suit.
Sparco is using a weaving technique that makes three layers, each of which is interwoven with the others. This makes a single piece of fabric, but with many air pockets. (It takes 7 miles of Nomex thread to make one square meter (about a square yard) of HOCOTEX fabric. I imagine it to be something like the batting you’d use for a quilt, but thinner. In traditional firesuit construction, you never see more than three-layer suits because they become very bulky and uncomfortable. The Hocotex patent claims they can make up to seven layers, with different patterns in each. The middle layers could be knit to have lateral air gaps, so there’s a huge amount of flexibility in this method. They claim their Extrema RS-10 suit has “60,000 microcells” in a fabric that is 0.6 mm thick, with a 10-12% increase in heat protection and two to three times the breathability.
Because, ultimately, it’s made of Nomex, it can be screen printed and made in many different colors. So you can make pretty much any design you could make out of regular Nomex, but with the advantage of the suit being lighter and easier to breathe in. They can also apply the method using other types of fibers
Sparco is an Italian company; most of their suits are FIA homologated (meaning “approved”), but they claim their Victory RS-4 suit is the only single-layer suit to pass the SFI 3.2A/5 spec.
DuPont is looking at improving Nomex as well, with Nomex Nano, a more breathable version of the Nomex fabric they already offer. Drivers wear suits for a couple hours; if you’re in the military or a factory job, you might be wearing the suit for 8-12 hours at a time, so breathability becomes even more important.
A First-Hand Account of Being in a Burning Race Car
If you want to read something truly terrifying, look at Stephen Cox’s account of his experience at Circuit of the Americas when his Porsche — and then he — caught on fire.
Cox, a writer at MotorSportNews.net and co-host of Mecum Auctions on NBCSN, had first, second and third-degree burns over 7% of his body despite wearing all recommended protective gear. While 7% may not sound like much, the part where he describes “the skin on the back of my right thumb dripped off my hand.” A second article shows videos of the fire, which one can watch only knowing that Cox recovered.
On the one-year anniversary of his accident, Cox reflected on the event with Five Things You Won’t Expect When Your Race Car Catches Fire. It’s a good read because he talks about things drivers do for safety that the public often doesn’t know.
- Drivers practice getting out of their cars with all safety equipment on and eyes closed. When there’s a fire in an enclosed space like a car cockpit, the smoke blinds your quickly.
- When you pull the fire suppression system most racing series require be installed in the drivers’ cockpit, the blast of chemicals can not only keep you from seeing, it can make breathing challenging.
He notes that when you’re actually in a situation like this, you won’t have time to think and your training will take over — which is why it’s so critical that drivers practice getting out of their car in the worst-case situation.
NOTE: Some images and materials were adapted from the Building Speed blog of April 1, 2015.