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County inspectors closed down La Conner’s Rainbow Bridge for about eight hours Thursday after a 911 caller reported they heard a small explosion and thought they saw something fall off the bridge.

The incident started around 1:30 p.m. Thursday when Skagit County 911 received a phone call from someone on the Swinomish side of the channel who said there appeared to be a small explosion on the bridge.

That prompted the Skagit County Department of Emer-gency Management to shut down the bridge and the roads to the bridge at approximately 1:50 p.m.

Soon, news helicopters were circling the bridge, TV crews set up at the waterfront end of Caledonia Street and drivers took the long way around via Highway 20 to travel between La Conner and Shelter Bay. After several rounds of inspections, the bridge reopened at about 9:30 p.m.

“We couldn’t find any new damage from what was in the inspection report from last April,” Torey Nelson, a bridge inspector with the County, said on Monday. The bridge goes through a routine inspection every two years.

County Public Works Lead Engineering Tech, Forrest Jones, went out to give a preliminary inspection of the bridge.

Skagit County Sheriff Sgt. Jenny Sheahan-Lee said the 911 caller told dispatchers that they thought a “piece of the bridge” had fallen off and there was a small explosion and a “cloud of rust.”

Nelson believes a shifting bearing which had become stuck may have caused debris to fall from the bridge.

“We suspect one of the bearings had gotten stuck and released violently. It was an isolated event,” said Nelson.

“Think of it like a knee joint in a ball, it just rolls around. The friction may have been too high, and once it released, it was violent.” Nelson says that when inspecting the bridge, they could hear the bearings moving. “It’s always happening, just not that violently.”

No new inspections are scheduled after Thursday’s incident. The next routine maintenance will take place in April of 2016.

The Coast Guard was immediately alerted to danger on the bridge, but decided not to close the waterway as the debris had been reported as falling over land.

The incident was said to have happened on the La Conner side of the bridge.

There was no sign of the rust cloud, but there was a small rock, possibly a piece of concrete, on the ground that appeared to be the same size as a small hole found under the bridge, Sgt. Sheahan-Lee said.

Jones did not appear to find evidence of damage during his over-the-side inspection on the La Conner side of the bridge. He made a second inspection on the Shelter Bay side of the bridge just before 3 p.m.

An inspector from the State Department of Transportation was on scene by 4 p.m. but the inspection truck, which had the equipment needed, had to come from Olympia and arrived shortly after 7 p.m.

The bridge was built in 1957 and state inspectors determined that it is still sound enough for traffic. It reopened at about 9:30 p.m.

Last May a section of the Interstate-5 bridge over the Skagit River between Mount Vernon and Burlington collapsed when an oversize truck struck one of the supporting beams. Although there were cars on the bridge that fell into the water, nobody was killed in the collapse.

There was no indication that there was damage caused by a vehicle on the Rainbow Bridge, however.