SAN JUAN, Puerto Rico (AP) — A broken fuel gauge at a Puerto Rican gasoline depot contributed to an explosion that forced the evacuation of hundreds of people, a U.S. federal agency said Tuesday.

The faulty equipment prevented Caribbean Petroleum Corp. workers from discovering that one of the tanks was overflowing before the fuel vapors ignited, according to the preliminary findings of the U.S. Chemical Safety and Hazard Investigation Board.

"Filling the tank without a functioning control system is the type of activity the CSB will examine very closely," said Jeffrey Wanko, the lead case investigator.

He said the agency will examine Caribbean Petroleum's operations as well as practices across the industry to prepare recommendations for improving safety.

The tank exploded on Oct. 23 as a ship piped in gasoline from San Juan Bay, shattering windows and sending tremors across the capital. The fire destroyed 21 of the depot's 40 fuel storage tanks and more than 1,500 people were evacuated out of fears of contamination from the plume of toxic smoke. There were no deaths.

Federal law enforcement authorities have said there was no evidence of sabotage, but they were still investigating whether negligence was involved.

Caribbean Petroleum officials did not immediately respond to messages seeking comment.

The company supplies 200 Gulf gas stations in Puerto Rico and operated a refinery at its plant west of San Juan until 2000.