ORLANDO, Fla. — A late-night fireball that set off a series of spectacular explosions at a propane depot in Lake County, Fla., may have been sparked by equipment failure and human error, Tavares Fire Chief Richard Keith said as federal authorities joined the inquiry.

Investigators were forced to suspend their probe Tuesday amid the smoldering hunks of metal at the Blue Rhino plant because of the risk posed by a leaking storage tank.

The tank, one of three bulk containers holding about 30,000 pounds of liquefied propane, withstood the intense heat that melted vehicles in a parking lot but may have been damaged by propane cylinders that flew like missiles from the flames.

Keith wouldn’t elaborate on the possible cause, but said sabotage was not suspected.

The plant, which refurbishes and fills 20-pound cylinders commonly used to fuel outdoor barbecue grills, passed inspections by the Florida Department of Agriculture and Consumer Services in March and as recently as July 19 with no violations, according to state records.

Fire officials said fleeing employees did not manually activate waterlines designed to protect the bulk tanks.

Firefighters, police and paramedics listed injuries to nine people, eight of whom were workers. Five of the injured employees were listed in critical condition Tuesday.