Some info on NHRA helmet rules:

• If your car goes faster than 14.00 in the quarter mile, then you must wear a helmet.
• The helmet must be SNELL certified. (M2000, M2005, M2007, M2010, SA2000, SA2005, SA2007, and SA2010 certified are all acceptable, however, avoid M2000 and SA2000 if possible)
• If your car goes faster than 10.00 in the quarter mile then you must wear a full-face SNELL SA certified helmet.

Notes about helmet certifications:

• Almost all motorcycle helmets meet DOT safety standards, but that's not as good as SNELL.
• SNELL dates their certification. NHRA accepts the last 10 years of certifications.
• The older the SNELL certification, the older the helmet. Avoid M2000 and SA2000 and earlier.
• SNELL has two common certification levels: M and SA. M is for motorcycles and SA is Sports Automotive. The SA is a more rigorous certification, and includes fire retardance and side-impact with roll cages. SA helmets are typically quite expensive compared to M helmets.

Lastly, I'll mention that I've never seen a tech inspector check the certification on a helmet. If you're dumb enough to wear a cheap uncertified helmet, then I guess they figure you don't have anything in it to protect.

So, if you don't have a helmet, but need one, borrow one from a motorcycle riding friend. Just be sure it fits and is SNELL certified.