Navy officer Brian Bugge jumped off the dive boat, was handed his underwater camera, and probably took a handful of breaths from his dive rig before he lost consciousness and sank beneath the waves.

That’s the conclusion of the Honolulu Medical Examiner’s Office, the dive equipment maker and Bugge’s wife, following his drowning death on May 20 while conducting a training dive using a complex “rebreather” device off Waikiki.

Used by Navy SEALs, the exotic closed-circuit rebreathers — which don’t emit bubbles — recycle exhaled air, remove carbon dioxide and add oxygen and other gases through a “loop” mouthpiece. Divers can go far deeper and stay under far longer than with traditional scuba gear.

Rebreathers can also be fatal in a hurry if not used properly.

Bugge, 35, had not turned on the oxygen supply to his Liberty rebreather, according to an equipment inspection by maker Divesoft.

Reports indicate he was “breathing on his loop on the boat. He got in the water. He was able to talk to some people on the boat while in the water — and then within moments after that, he was gone,” said Ashley Bugge, his wife, who was not on the dive.

Retired submarine officer, nuclear engineer and rebreather instructor Mike Jones said a lot of people don’t realize is that the feeling of needing to take a breath is caused by a rising level of carbon dioxide in the body — not by a lack of oxygen.

But a “scrubber” in the rebreather removes exhaled carbon dioxide, “so you don’t get that feeling that you need to take a breath. You don’t get the feeling there’s a problem,” said Jones, who also was a science advisor to the commanders of U.S. Pacific Command and Pacific Fleet.

Unconsciousness can occur in about five breaths, he said.

As he waited in the water for the dive group, without anyone watching him, Brian was essentially rebreathing his own air, each time with less and less oxygen content, until he passed out and sank to the seafloor, his wife and experts said.

Ashley Bugge, who has three young children with Brian, with the third born two months after his death, posted an account of the events to a Scuba Accidents and Risk Management Techniques for Divers Facebook page as a cautionary warning.

“I’m sharing this with you because my husband’s death was preventable, and after what I’ve been through the past 12 weeks since his death, I’m hoping sharing his story and the details of his final minutes will help any and all of you from having your family suffer the same fate as I/we are now,” she said on the page.

At the time of the planned dive on the Sea Tiger wreck, which lies in 120 feet of water, Brian Bugge was a student in rebreather training and diving for the first time on trimix — a combination of helium, oxygen and nitrogen, Ashley said.

Brian Bugge, an ensign limited duty officer assigned to the U.S. Pacific Fleet submarine force’s Integrated Undersea Surveillance Systems department, was diving off duty. An avid underwater photographer who was already a scuba diver, he liked the technical challenge of rebreathers and the diving capabilities that came with them, his wife said.

He had previously sailed the couple’s 36-foot sailboat from Washington state to Hawaii, and “started daydreaming about expeditions to untouched wrecks in the South Pacific,” Ashley Bugge said.

On the May 20 dive, he was eventually spotted sinking, the breathing loop out of his mouth, she said. He was retrieved from the seafloor, but was later pronounced dead at a hospital.

“What they call the error chain is so short and so subtle (with rebreathers) that if you don’t recognize the symptoms immediately, it’s too late,” said scuba instructor and rebreather diver Matthew Kuderik. “In this case, if he would have realized, ‘Oh, I’m starting to black out a little bit,’ he might have been able to hurry up and switch something on — take the regulator out and put on his regular scuba gear, because we all go in with a regular scuba tank on our side as a bailout. … But it can happen so fast that you don’t realize it.”

Andrew Fock, then with the Department of Intensive Care and Hyperbaric Medicine at The Alfred Hospital in Victoria, Australia, authored a research paper in 2013 that said rebreathers have a 25-fold increased risk of component failure compared with scuba. Fock noted that the 181 recreational rebreather fatalities between 1998 and 2010 occurred at about 10 times the rate of deaths among scuba divers.

Jones, the rebreather instructor, said Oahu probably has about 30 to 40 rebreather divers — which is a lot compared to other locations. By comparison, Hawaii likely has thousands of scuba divers.

Rebreather divers can descend to more than 300 feet and stay down for several hours. But that capability comes with a steep pricetag. A Liberty rebreather rig can cost $9,000.

Rebreathers are used for more aggressive dives, and Jones said he doesn’t dispute that the recreational death rate is higher, “but the bottom line is, rebreathers are just less forgiving than I think open-circuit (scuba) is, so you have to be detail-oriented,” he said. “And you have to do things right every time. So we have a culture of using checklists and following checklists.”

Dive instructors “should have been reinforcing that mentality of following a checklist and doing the procedures — which makes it even more shocking that he somehow didn’t open that (oxygen) valve,” he said.

Ashley, now living temporarily with family in Boise, Idaho, said it’s been an emotional process that she has to take day by day.

“I lost my best friend. The kids lost their dad. I had a baby during this time. I’ve moved away from our home (in Hawaii) to a place I’ve never been before,” she said.

Ashley had Brian’s body cremated. He loved adventure that had to do with the sea, she said.

“The kids and I will come back (to Hawaii) in May — probably for the rest of our lives, I hope — and do something special for him there,” she said. “… I’ll probably ask some of his friends to scatter some of his ashes down by the Sea Tiger, and then some of his sailor friends are going to take some out on the ocean on the boat for me, just to a couple other special spots that we have.”