The five-member board's unanimous vote, coming after a two-day public meeting, wrapped up the longest and most expensive investigation in the agency's 33-year history.
Flight 800, involving a 25-year-old Boeing 747, was bound for Paris on July 17, 1996, when it broke apart in midair off Long Island minutes after taking off from New York's John F. Kennedy International Airport. All 230 people aboard were killed.
Meeting in Washington, the board endorsed investigators' findings that a mixture of fuel and air in the airplane's nearly empty center wing fuel tank blew up after being heated by the sun and air-conditioning packs attached to the outside of the tank.
Though investigators never found what ignited the explosion, they said the source was probably a short circuit that created a surge of electricity in a low-voltage wire attached to a fuel gauge inside the tank.
Accident investigators who have spent years searching for what sparked the explosion said the airlines and airplane manufacturers had not paid enough attention to the condition of electrical wiring on older aircraft like the one involved in the 1996 accident.
Safety board Chairman Jim Hall ordered a report by Nov. 15 to determine whether aircraft age and the frequency of accidents are related.
The four safety recommendations issued Wednesday call for improved training of maintenance personnel about potentially unsafe wiring in aircraft and for several actions to limit possible sources of ignition in fuel tanks.
The board previously issued 11 other recommendations as a result of the Flight 800 investigation; 90 percent of them have already been acted upon by the Federal Aviation Administration, the board said.