The first generation of frontal air bags saved the lives of thousands of drivers and adult or teenage right front passengers. But they harmed occupants positioned close to the air bag at the time of deployment, especially infants and children. In 1998-1999, air bags were redesigned by depowering - by removing some of the gas-generating propellant or stored gas from their inflators - and/or by reducing the volume or rearward extent of air bags, positioning them further from occupants, tethering and hybrid inflators. NHTSA facilitated the redesign by permitting a sled test in lieu of a barrier impact to certify that air bags would protect an unrestrained occupant ("sled certification"). Statistical analyses of crash data through 2004 from NHTSA's Fatality Analysis Reporting System (FARS) and the Special Crash Investigations (SCI) compare fatality risk with sled-certified and first-generation air bags.