The Science of Firesuits

Crashes are scary, but most drivers will tell you that being in a burning race car is even more frightening. Luckily, their firesuits give them a few more seconds of protection. Let’s see how firesuits make the difference for drivers and pit crew members.

The Scariest Part of Racing?

In a 2015 XFINITY race at Richmond, a malfunctioning fuel injured gasman Josh Wittman, rear tire changer Anthony O’Brien and Clifford Turner, a crew member for a team pitting nearby. All three went to the hospital, with O’Brien released after spending a weekend there.

What It’s Like in a Burning Race Car

The danger is even greater for drivers, who don’t have safety officials standing nearby ready to put out a fire. For example: Stephen Cox’s account of his experience at Circuit of the Americas. Cox sustained first, second and third-degree burns over 7% of his body despite wearing all recommended protective gear. A second article includes a video.

His one-year reflection, Five Things You Won’t Expect When Your Race Car Catches Fire, mentions things drivers do that the public often doesn’t know.

  • Drivers practice getting out of their cars with all safety equipment on and eyes closed. Smoke in an enclosed space like a car cockpit blinds you.
  • In addition, the in-car fire suppression system in the drivers’ cockpit that puts out the fire also makes it hard for you to see and breathe.

Three Requirements for Fire

Let’s understand fire first. Then we’ll know how to put it out.

The Fire Triangle shows the elements needed for a fire: Heat, Fuel and Oxygen
  • Oxygen. Air is about 21% oxygen, with 78% nitrogen and 1% other gases.
  • Fuel, which can be anything from clothing to wood to (ulp) people
  • Heat – with the caveat that there must be enough heat to sustain the chain reaction that becomes fire.

I’m using the triangle, even though there is a fire tetrahedron now. I don’t like the tetrahedron because ‘chain reaction’ is not an element, it’s a process.

It’s a good thing we need all three to have a fire because oxygen and fuel surround us most of the time. Stopping a fire requires you to eliminate one (or more) of these elements.

NASCAR Fires are Different

Racing puts a driver in a small, enclosed space with 20 gallons or so of fuel, plus oil and grease. Gasoline ignites at 495 ºF and burns at about 1500 – 2000 ºF, so putting out the fire quickly is really important. But how?

Water puts out fires by cooling, thus eliminating the ‘heat’ portion. Energy from the fire vaporizes the water, which takes energy away from the fire and eventually breaks the chain reaction.

Water won’t put out a gasoline fire for the same reasons it doesn’t work on a grease fire in your kitchen. Liquids like gasoline, paint thinner, etc float on water and don’t mix with it, which makes water useless for a gasoline fire.

NASCAR uses two different protection mechanisms: a chemical fire suppressant for the car and firesuits for the driver and crew.

A Brief History of Flame-Resistance

It takes 15 minutes of holding your hand in 118 ºF water before you get a second-degree burn, but only three seconds if the water were at 140 ºF. The situation is worse with gas fires, which burn more than ten times hotter than.

Every millisecond counts, so it’s important to buy time so they (or someone else) can put the fire out.

In the early days of NASCAR, drivers and crew dipped their street clothes in fire-retardant chemicals. Those chemicals come off in the laundry and have to be reapplied constantly.

Almost all natural fibers are flammable, and it wasn’t until the 1960s that Nomex came on the market. Nomex is a polymer closely related to Kevlar. Instead of being superstrong like Kevlar, it’s super resistant to burning.

Firesuit Science

Current firesuits protect their wearers in three ways: insulation, more insulation and blocking oxygen

Insulation

Firesuits are quilted with two, three or more layers of material. Quilting traps air between the layers and air is a great thermal insulator. The structure of the firesuit actually contributes to its flame resistance.

Nomex firesuits add two more types of protection.

More Insulation

When Nomex fibers are heated, they don’t burn: They char. Charring is forming a layer of carbon around the fiber. That carbon layer insulates the driver from the heat of the fire.

Nomex doesn't burn when heated: It chars, forming an insulating layer of carbon around the fiber.

But that’s not the only thing the expanding Nomex does.

Block Oxygen

In addition, the char cuts off oxygen by making the weave of the fabric tighter.

When woven Nomex expands, the holes in the fabric get smaller, which prevent oxygen and hot air from getting in through the suit.

After charring, the holes in the firesuit are smaller, allowing less oxygen in, and less hot air.

Additional Protection for Fuel Handlers

A fueling apron

While we think of drivers as being in the most danger, when it comes to fire, the gas man may actually be more at risk. Liquid fuel will go through a firesuit. Anyone handling fuel must wear a fueling apron made of non-permeable material.

But the apron doesn’t cover the extremities, so there’s still room for a fueler to be badly burned in there is a large spill.

Fireproof?

There is no such thing as fireproof. While Nomex is amazing, it is not magic. Firesuits are, at best, fire resistant.

The SFI Foundation is a non-profit created in 1963 that develops standards and tests for motorsports safety equipment. They evaluate firesuits using a metric called TPP: Thermal Protective Performance. DuPont (who created Nomex) established the TPP. The SFI 3.2A specification uses the TPP for evaluating firesuits.

TPP Ratings

TPPSeconds  to 2nd Degree BurnSFI Rating
63 seconds3.2A/1
147 seconds3.2A/3
1910 seconds3.2A/5
3819 seconds3.2A/10
6030 seconds3.2A/15
8040 seconds3.2A/20
The TPP is just double the number of seconds to a 2nd degree burn.

NASCAR requires drivers to wear firesuits certified SFI 3.2A/5. (Note that anything 3.2A/10 or higher has to be re-certified every five years.) To meet that spec, the firesuit material must be inherently fire-resistant. You can’t use chemical dips to meet the spec.

And it’s not just the material, the specification includes things like

  • The suit’s 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)

Specs Include More Than Firesuits

There are SFI specifications for everything. 3.3 is for accessories (underwear, gloves, sock, shoes, balaclavas, helmet skirts, etc.); 16.1 is for driver restraint assemblies; 31.1 is for helmets and so on.

Crew members who go over the wall must wear 3.2A/1-rated suits, although the NASCAR rulebook recommends 3.2A/5.  In addition, anyone handling gas must have the the 3.2A/5 suit and wear a fire-resistant apron.

Fire resistant underwear and socks aren’t mandated, but are recommended. The danger here is that if you’re close enough to a fire, synthetic fibers like nylon and rayon melt. Then they stick to the skin and are very difficult (and painful) to remove.

So for you 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 fabric and you could be get burned in particularly sensitive places.

Conclusion

As you might expect, the higher the level of protection, the more expensive the suits are. But a day in the hospital costs a lot more.

If you want to learn more about firesuits, take at look at my blog on the materials used for fire protection, and this video we made with the National Science Foundation.

You can also learn more about fire-resistant materials.

Note: This post was revised and updated on May 6, 2020 from the original.


Also published on Medium.

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