|
Ken Myers is the owner of I/O Port Racing and NASA's Safety Tech Inspector. He has stated the following in a couple of articles:
Currently, NASA allows 2-layer SFI-5 rated suits to be worn without underwear. This will allow you to wear just a cool cotton t-shirt under your suit to absorb sweat and keep you as cool as possible. When looking for a new suit, look for features to allow freedom of movement when sitting down and driving. Suits that are designed to look stylish in the pits may bind on you in the driver's seat. Suits that incorporate knit material for venting will be cooler and therefore, more comfortable.
AND
The driving suit is made of fire-resistant materials; yet not all suits are equal. Which is best, and what is good enough? The first question is easy, the second is a personal decision. There are five well-known materials on the market for fire protection: Proban, Firewear, Nomex, Kevlar, and PBI.
Proban is a treated cotton fabric. The treatment does not wash out, but like cotton jeans, the material gets thinner with washing. Therefore I do not recommend this material for the long run.
Firewear is relatively new on the market and is also a treated cotton. This material is unique as it will release a gas when exposed to heat and this gas will put out the fire. This material is used in balaclavas and underwear.
Nomex is the most known and used material in driving suits. Nomex is available in both regular and knit fabrics and a variety of colors. This is not true for Kevlar and PBI. If you want style, Nomex is the only way to go. However, if you want protection with an added benefit of comfort, Kevlar and PBI should be considered.
Kevlar is the same material used to make bullet-resistant vests for police use. This material is very tough and strong and also resists fire. But don't try to stop any bullets in a driving suit! Bullet-proof vests are made of many layers of this material; and I'm sure they incorporate other trade secrets too. Perhaps you've seen TV ads for Kevlar leggings choking a chain saw. Kevlar is expensive and hard to work with so it is used mainly in premium driving suits.
PBI will not melt or burn in the air and is as comfortable as cotton to wear. Nomex, on the other hand, will melt, become brittle and lose its strength rapidly. PBI, however has a problem with stretching so it is not used often in driving suits.
In a test in 1977, a state-of-the-art Nomex suit with two layers of Nomex underwear were worn into a ring of burning gasoline. This combination lasted less than 8 seconds! The person's legs were severely burned. Considering this, is a single layer Nomex suit worth wearing? Can one get out of a burning car is less than 8 seconds, especially if it has just crashed? Are you willing to take that risk? If not, read further.
Obviously, the more material you wear or the more the material resists fire, the more time you will have the escape the source of the fire. A lesser known fact is that the air between layers of material is an equally important factor in insulating you from fire.
NASA rules require a minimum of a 1-layer suit with underwear or a SFI 3.2A/5 rated suit without underwear. A SFI 3.2A/5 rated suit (usually referred to as a SFI-5 suit) will last about 9.5 seconds in a fire. When we talk about how long the suit will last, we are talking about the time it takes before you receive 2nd degree burns. Fire resistant underwear adds about 3 to 5 seconds of time.
In a non-scientific test, I put a Bic lighter flame directly on a single layer of Nomex material. The fabric charred, shrank, and burned through within seven seconds. Doubling the material layers resulted in the first layer doing the same thing but the second layer remained intact for over one minute. After charring, the first layer insulated the second layer from the heat source. However, the radiated heat through both layers would be unacceptably hot for this extended period. A second test proved this theory where a flame against the material against my hand was painful within 2 seconds with one layer and under 4 seconds with two layers.
|
