The National Transportation Safety Board has opened an investigation into 21 shipping containers that fell off an interisland barge, a move state Sen. Kai Kahele is heartened by because it will determine probable cause.

Kahele has alleged that there were possible improper actions by the company.

“Since damages from this accident are estimated to exceed $500,000, the U.S. Coast Guard has declared this to be a major marine casualty,” the NTSB wrote Kahele. “NTSB will be investigating this accident in conjunction with the Coast Guard and will establish probable cause.”

Kahele, a former Navy pilot, said the NTSB will be “looking for causes of the accident and probable cause. That’s pretty substantial. With the NTSB being involved, they are kind of like the FBI. They do forensic analysis.”

PHOTOS: Coast Guard investigating after 21 containers fall off Young Brothers vessel

On Monday morning, 21 containers fell off a barge traveling to Hilo Harbor from Honolulu, and a cluster of nine were found 8 miles north of Hilo. Of the 21, 12 are still unaccounted for after flyovers, the Coast Guard said Tuesday.

Young Brothers has secured a third party to conduct an independent investigation, and “we are working closely with state and federal authorities to determine the cause of the accident,” said Chris Martin, director of terminal operations for Young Brothers LLC, adding more information would be shared when the investigations are concluded.

“Notwithstanding this unfortunate incident, the first loss of containers overboard in more than 20 years, we are proud of our track record of safely transporting what matters most to Hawaii,” he said.

Young Brothers safely discharged the undamaged cargo from the barge Tuesday morning and made it available to customers in Hilo, it said. An additional salvage crew was hired to remove the damaged containers remaining on the vessel.

Coast Guard spokeswoman Sara Muir said, “The back row of containers, where the containers were lost from, have remained untouched.” In that section some of the containers are “tipped over or unsettled.”

Kahele, who has been in contact with people who are familiar with Young Brothers’ operations in Hilo Harbor, alleges the containers were improperly stacked five high on the stern (rear) and the midship.

He said videos of the barge show the midship and stern are left open. “It’s highly unusual to load a barge like that,” Kahele said. He suspects the company has been overloading the barge because it reduced its deliveries to Hilo from twice weekly to once a week.

That move was approved by the Public Utilities Commission due to the company’s losses during the pandemic, and it had requested $25 million in assistance from the state.

Kahele also alleges the barge may have remained outside Hilo Harbor until 4:30 a.m. in order to avoid paying overtime to workers manning a second tugboat that assists in bringing the barge into the harbor.

He said NTSB investigators would be able to determine the path of the tugboat and barge, when it left and when it arrived.

He suggests that the toppling and falling overboard of the containers may have been caused by the tug and barge moving in circles if it had been held outside of Hilo Bay for several hours.

“It wouldn’t have likely happened in a straight run to Hilo in virtually calm seas. … You don’t sit there. You have to be constantly moving.”

Muir said the Coast Guard’s news release Monday erred in saying one container was floating in Hilo Harbor when it should have said in Hilo Bay.

The company hired a Cates Marine salvage team to search for and locate the containers. American Marine is using a 250-ton crane to pull them out of the water in Hilo.

The containers are scheduled for removal this morning from the water in Hilo Harbor. Young Brothers will submit plans for offloading the remaining containers, which could take several days, to the Coast Guard for approval.

Only one container, which remained on board and was never in the water, contained hazardous materials in the form of household cleaning supplies, the Coast Guard said.

The Coast Guard continues to advise mariners to use caution in waters off Hilo and to keep a close eye out for any signs of the shipping containers, which could present a hazard to navigation.