Straight from the NHRA 2007 rulebook:
IMPORTANT TECH UPDATE: Effective 1/1/07 Snell 95 Helmets will no longer be valid for use in drag racing. Please check your helmet and if you have a Snell 95 you will need to replace it prior to competing in any competition at any NHRA sanctioned racetrack. The Snell 95 helmets are expired and no exceptions will be made for use of this model of helmet if you are running 13.99 and quicker in the 1/4 mile or 8.59 in the 1/8th mile. Acceptable helmets are the Snell K-98, Snell 2000 and Snell 2005. Please also remind your fellow racers to check their helmets as well!! Thanks.