Kevin Kirk has been replaying his dive at the General Sherman Wreck site off the coast of Little River trying to figure out why a fellow diver died Tuesday.

Kirk, a master diver from Kentucky, and his wife were on the diving expedition led by Coastal Scuba when Karen Murphy, 43, of Massachusetts died.

Kirk and his wife realized something had gone wrong as they were surfacing from the dive.

“As we were coming up we noticed a diver go real fast by us giving us the thumbs up, then the rescue diver flew by,” he said. “I knew something was up.”

Murphy was already on the deck when Kirk and his wife surfaced from the dive. He said a crew member and a nurse on board were performing CPR. Kirk said his wife is a surgical technician and the couple helped perform CPR while the boat was driven back to shore.

That drive lasted about an hour, he said, but felt like three hours.

They tried to use an oxygen tank, but Kirk said it was empty. He said the group trying to resuscitate Murphy then tried a different tank, but couldn’t find a mask that would work so they continued taking turns with chest compressions and mouth to mouth until the U.S. Coast Guard met the boat in the inlet.

Horry County Deputy Coroner Tamara Willard said Murphy was pronounced dead at Seacoast Medical Center and the cause of death is still not known following an autopsy Wednesday.

A toxicology screening and other tests will be done to determine what happened to Murphy. There are several possibilities involved with a scuba diving accident and Willard said she couldn’t pinpoint one cause without further testing.

The autopsy report may take more than the normal 12 weeks to complete, she said.

Willard said the death does not appear suspicious and there are no signs of trauma.

Coastal Scuba owner Cameron Sebastian could not be reached for comment and the company was running dives as originally scheduled Thursday.

Kirk said the Sherman Wreck is considered an amateur dive site, only about 50 feet below the surface, but the dive was more advanced that day due to low visibility and a swift current.

“With the right conditions it would be a very easy dive,” he said. “But, visibility was only 10 to 15 feet with a decent current.”

Records with the National Oceanic and Atmospheric Association showed an advisory Tuesday for boats advising caution with wave heights between four and five feet.

The Coast Guard is also investigating. The Coast Guard office in Georgetown deferred comment about the investigation to a spokesman in Charleston who did not return phone calls for comment.

Kirk estimated about 20 people, plus a four-person crew were on the dive.