Federal Motor Vehicle Safety Standard #213. This is the safety standard that that discusses that all car seats on the market need to meet certain safety guidelines in order to be sold for use. Every car seat on the market for sale has met or exceeded these safety standards, so on some level, no matter which seat you purchase, you are getting a seat that has already passed relatively stringent guidelines.
FMVSS 213 requires that child restraint systems must pass a 30 miles per hour frontal sled test that simulates a crash. There are padding requirements for the area around the head of car seats for children weighing 22 pounds or less. The seat must meet flammability standards, and buckle release pressure. The seats need to have permanent, visible labels on the restraint that include verification that it conforms to federal standards, offers basic instructions for correct installation and use, the name and address of manufacturer/distributor, and the date of manufacture. The publication FMVSS 213 Highlights of the Regulation for Child Restraint Systems provides more information and can be found on the NCPSB website.