KITTERY — A Maine shipyard is investigating what caused a small fire outside a nuclear-powered submarine that was severely damaged by another blaze last month.

The fire was reported about 7 p.m. Saturday in the dry dock where the USS Miami is located, The Portsmouth Naval Shipyard said.

Additional Photos

The May 23, 2012, fire on the USS Miami severely damaged living quarters, the command and control center and a torpedo room. Seven people were hurt dousing the flames. The fire caused an estimated $700 million in damage. 2004 file photo provided by the U.S. Navy

A shipyard employee doused the fire with a portable extinguisher before the shipyard’s fire department arrived, and the ship’s reactor was never in danger, officials said. No one was hurt. The shipyard did not release additional information.

The latest fire was reported less than four weeks after a May 23 fire heavily damaged the submarine while it was in dry dock for an overhaul. That fire damaged the torpedo room, crew quarters, and command and control areas in the front of the submarine, but the nuclear propulsion components at the back of the sub were spared.

The Navy has estimated repair costs at $400 million. The fire started when an industrial vacuum cleaner sucked up a heat source that ignited debris inside the vacuum, officials say.

In the aftermath of the fire, the Navy directed all public shipyards to empty their industrial vacuum cleaners after each shift or remove them from ships.

The Naval Sea Systems Command is reviewing all models of vacuum cleaners now used aboard ships and will issue a directive by the end of June on which models are authorized for use.

The Portsmouth Naval Shipyard Fire Department responded to a report of another potential blaze aboard the USS Miami submarine on June 6, but it turned out to be a false alarm.

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