The 6D helmets are DOT and ECE (European standard) but not SNELL.
After knocking myself out and getting a concussion, I threw away my helmet and started looking into new ones. Through some connections I could get pretty much any helmet i wanted at a mid-pack price point. I decided to stick with a Shoei. I looked into the 6D's, tried them on and liked the fit. They are a slightly bigger helmet but i really couldn't say that I noticed the difference. they are a local company, about 4 miles from my house. i didn't go visit them though, thought about it.
This is off of their website 6D's website:
The 6D ATR-1 Helmet is certified to meet and exceed the U.S. DOT (Department of Transportation) FMVSS218 and the ECE (Economic Community of Europe) 22.05 safety standards. The ECE 22.05 standard is the most recognized international helmet standard, required by over 50 countries worldwide. The combination of our dual certified helmet to both DOT and ECE assures a broad range of high performance protection. While the DOT certification provides for penetration protection and max G loads at controlled dwell times, the ECE certification provides for high velocity impacts similar to Snell testing.
The ATR-1 off-road helmet is not Snell approved. Snell is a totally voluntary program, which is not required by any U.S. government safety authority or any major U.S. racing sanctioning body. Meeting Snell’s criteria would require the shell to be both stiffer and heavier than necessary, which, in the case of the 6D ATR-1 helmet, is contradictory to meeting the safety objectives set forth by our company.