It was not immediately known just what chemicals were contained in the tank.
Fire Commissioner William Richmond said a 2-foot-thick film of the chemical methyl ethyl amine was on the top of the other contents of the burning tank. Richmond said the chemical could cause eye irritation and other minor ailments.
"It was a blessing in disguise that the roof actually flew off the top of the tank," Richmond said. "That way, we could get directly at the contents."
Richmond also expressed concern that the overflowing contents of the tank could catch fire. Firefighters coated the overflow material with foam.
The fire continued to burn out of control more than two hours after it started, although the flames had abated.
According to Fire Department spokesman Capt. Angelo Saggiomo, the department was "swamped" with telephone calls from residents who heard and/ or felt the blast.
The refinery, then owned by ARCO, was the scene of a number of fires in the 1970s, including a nine-alarm blaze in 1975 at which then-Mayor Frank Rizzo suffered a broken hip when he fell while trying to escape a flare-up.
The blast today broke windows in the neighborhood of 23rd and Shunk streets. Windows also were reported shattered in the area of 23rd Street and Oregon Avenue.