When was the last time you were at a race that went caution free? Yeah, that's what we thought. Accidents are a part of racing, and at some point we are all going to be involved in at least one. It's not a matter of "if" but "when." Many different things can happen to your safety equipment in an accident, one of the most obvious being belt stretch. This is so commonplace that some tracks even cut your belts out of the car after a hard hit to ensure that you replace them before racing again.

While belt stretch is obvious, there is a potentially more sinister result of a hard hit and that has to do with your head. A good helmet is essential to racing safely and you should always check your helmet carefully after a hard wreck. Spiderwebbing or outright cracks are obvious damage but is it possible to damage a helmet's interior beadliner, thus compromising its integrity, without cracking the outer shell?

We decided to find out if the Phantom Impact exists.

Our theory started out that if you are wearing a head/neck restraint such as a HANS Device and you crash, the helmet gets restrained but your head keeps moving within the helmet. Since the inner liners of helmets have some amount of give to them, after all that is how they protect your noggin, when your head keeps moving it will damage the inner liner. To find out if our theory held water we contacted five major helmet manufacturers, a head and neck restraint company and an independent industry expert.

Interestingly they had differing opinions on whether or not you could actually damage an inner liner without hitting your head against something. Much of this has to do with a lack of data. "I don't know that anybody has ever measured the liner crush due to an SFI test," admitted HANS' Dr. Bob Hubbard. "The head accelerations in an SFI 38.1 test for head and neck restraints (HNR) are typically below 100g. The accelerations in Snell helmet testing are typically 300g or more. So, the acceleration and associated loads on the helmet liner in the SFI test are much less than for the Snell test."

So, while there is no specific test for our theory we did find out some extremely important factors about the Phantom Impact.

"Sometimes the evidence is not visible," says Bell's Kyle Keitzman. "During the 2006 Indianapolis 500, Darren Manning backed into the wall. The impact generated over 100g but there was no outward damage to the helmet's shell, however you could actually see the outline of the back of his head in the lining."

If you hit the wall hard enough that you can see the outline of your head in the inner liner, it's safe to say that your helmet is now junk. Every helmet manufacturer we talked to for this story told us the same thing-if that inner liner is damaged there is no way possible that it will provide the same level of protection in another accident. And that is the danger of the Phantom Impact.

But what about the not so obvious damage? Let's say you have a crash and you inspect the helmet, looks good on the outside, looks good on the inside. It's fine right? Wrong.

"There could definitely be non-visible damage," says Gary Peters of Simpson Race Products. "Hairline cracks in the shell could be hidden by a helmet's paint job, especially ornate designs with a lot of color changes, lines, etc."

Peters told a story of when Hank Parker Jr. was involved in a high-speed crash in a Craftsman Truck where he recorded one of the highest g-force impacts ever. "He did have a HANS on," said Peters. "I took the whole helmet apart myself and couldn't find anything wrong with it."

However, that doesn't mean that the helmet wasn't damaged and shouldn't have been junked (which by the way it was). There are two types of helmet inner liners, EPS or expanded poly styrene and EPP or expanded poly propylene. EPS (the common white liner) will show visible damage after an impact. Upon impact, the liner deforms and does its job of protecting your head. You can easily see dents and deformation after taking an EPS helmet apart.

However with EPP, you may never see the damage. EPP has a memory, conceptually similar to the Tempurpedic mattress, and will return to its original shape even after being subjected to a tremendous force such as Parker Jr's. So even though the EPP returns to its shape, its ability to keep you safe from additional impacts is compromised. This is compounded in accidents where you take multiple hits.

"In a multiple-impact accident, you use up the helmet's ability to attenuate an impact after the initial hit," says Peters. "The second and third hit will further compromise the helmet."