From section 4.3.1 of the SCCA Solo Rules:
Helmets meeting the following standards must be worn while on course:
All helmets meeting the latest or two immediately preceding Snell Foundation standards (SA2015, SA2010, SAH2010, SA2005, M2015, M2010, M2005, K2015, K2010, K2005); SFI standards 31.1, 41.1, 31.1A, 31.2A, 41.1A, 41.2A; ECE R22.05; FIA standards 8859-2015, 8860-2010, 8860-2004; or British spec BS6658-85 type A are acceptable.
Full face or modular helmets shall be worn while competing in an openwheel car, formula car, or kart. Face shield, goggles, or similar face protection (conventional eyeglasses are not sufficient) shall be worn while competing in any other vehicle with less than the standard-size windshield.
Formula Junior drivers must use helmets meeting the above, SFI 24.1 (Youth Helmets), Snell CMR2007 (Children’s Motorsports Restricted), or Snell CMS2007 (Children’s Motorsports Standard) specifications. Also, Formula Junior helmets must be of closed face design incorporating full face shields and chin bars.
For maximum protection, helmets must fit securely and should provide adequate peripheral vision. The chin strap must be securely fastened. Loaner helmets should be available to vehicle occupants not having their own.
Helmets sold in the United States typically have a Snell sticker affixed to the inside of the shell, beneath the helmet lining. DOT-approved helmets are not allowed. The sticker will look like one of the following:
Loaner helmets are available in the grid area in several large black storage boxes.