The Navy has directed all public shipyards to empty industrial shop vacuum cleaners each shift after combustibles inside a cleaner at the Portsmouth Naval Shipyard in Kittery ignited a fire that caused $400 million in damage to the USS Miami.

The Navy said there was no defect in the vacuum cleaner and it was unplugged when the fire broke out in the forward compartment of the nuclear submarine May 23, a fire that burned for 10 hours before it was put out by firefighters from three states.

The Navy is investigating the cause of the fire and corrective actions it should take and conclusions and recommendations are expected in two weeks. However, the Navy took the step of immediately warning all shipyards that vacuum cleaners should be emptied or removed from ships at the end of each shift, according to a release issued this afternoon.

“Additional inspections of ships have also been conducted for fire safety and fire fighting response with special attention on temporary services and the stowage of combustible materials on board,” the release said.

The release does not indicate whether the Navy has identified what heat source was vacuumed into the equipment’s container that ignited the fire.

Repairs to the nuclear submarine would cost $400 million plus another $40 million in disrupted work schedules and private contractor costs in the Kittery yard and other shipyards. The Navy is still assessing whether the steel hull of the sub was damaged too much by the fire to repair and won’t know that til later this month.

However, the Navy is operating under the assumption the sub will be repaired and is developing a schedule for when the Miami would be returned to service.