Businesses scrambled to find emergency generators and city crews hustled to lay new cable a day after a fire caused a 40-block blackout in Seattle that officials feared could last until the weekend. The fire, of undetermined origin, destroyed a double underground vault containing two transformers and switching equipment Wednesday, cutting electricity to much of the city’s retail, financial and hotel center. Officials said it was Seattle’s worst outage, eclipsing an 80-block downtown blackout that was limited to five hours in 1966. Police patrols were doubled and no looting or injuries were reported. Hundreds of workers were sent home early, many night spots were dark and some restaurants served free food rather than have it spoil.