LOS ANGELES — Federal safety investigators revealed Wednesday that crew members aboard two Coast Guard boats involved in collisions in California and South Carolina last year were using wireless devices for conversation or text messaging unrelated to vessel operations. The collisions killed one person and injured 10.

The NTSB said that it has not determined the probable causes of the collisions in San Diego Bay and the Charleston, S.C., harbor, but was urging the Guard to develop a thorough policy on use of the devices by the service and to issue a safety advisory to the maritime industry.

The National Transportation Safety Board did not say how many members of each crew were using the devices or what their roles were on the boats, but said the accidents raise concerns about the potential for distraction.

It noted in a letter to the Guard that the service considers all crew members to be lookouts when a vessel is under way.

The Coast Guard issued a policy on July 16 that prohibits use of the devices by the boat operator — the person at the wheel and throttles — at all times while under way, said Lt. Cmdr. Chris O’Neil, chief of media relations at Guard headquarters in Washington, D.C.

The policy prohibits other crew members from using the devices unless expressly approved by the boat operator, known as the coxswain, O’Neil said.

A copy of the Coast Guard’s policy shows it is essentially a three-paragraph statement with two sentences of orders to crews.

O’Neil defended the existing rule as very specific on the use of the electronic devices. That policy does not define the purposes or situations in which use can be authorized.

“It allows the coxswain to exercise judgment … to determine whether it is prudent to allow use of that device,” O’Neil said.

The NTSB said the Guard must identify specific risks associated with distraction while using the devices and address them in the policy. It said that policy was only a “first step” in safety improvements recommended for the Guard.

The hazardous use of cell phones was also the focus of a probe into the 2008 collision of a commuter train and a freight train that killed 25 people in Los Angeles. Investigators believe the commuter train engineer ran a red light seconds after he was text messaging.