Six people have drowned in the past two weeks on Maui, prompting ocean safety advocates to ramp up efforts to warn visitors about the dangers of snorkeling and to study new types of masks that have become increasingly popular.

All six were males and their average age was 59. Two were local residents from Maui, two were from California, one was from Texas and the other was from Canada.

Officials have confirmed that two unrelated men from the Bay Area in California died after snorkeling off of Kamaole Beach Park III. Both were wearing full-face snorkeling masks, an alternative to the two-piece snorkel tube and mask.

Civil Beat has reported since March about the inherent dangers that lifeguards, doctors and others have identified in the use of full-face masks, including carbon dioxide buildup and difficulty removing the equipment quickly in an emergency.

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But there have been no studies to conclusively determine if it was the mask type that caused the drownings. Many people like using them, but others have reported near-death experiences and fatal incidents.

Nancy Peacock, a 70-year-old woman from California, drowned off the coast of Hawaii Island in September 2016 while wearing a full-face mask. Her husband, Guy Cooper, immediately began investigating the cause and started asking government officials for their help in raising awareness and collecting additional data in drowning incidents, which all four counties in Hawaii have agreed to do albeit with varying degrees of success.

Cooper said the people who manufacture or sell the full-face masks — which over the past year have become widely available to rent at hotels, purchase online or buy at stores throughout the islands — consistently point to a lack of evidence showing the masks pose a danger or have ever led to anyone’s death.

“Lack of evidence is a problem,” he said, “because up until just recently none has been collected, reported and analyzed.”

Cooper questioned the repeated claim that their products are safe and asked where the evidence is to support those claims.

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“There are so many uncounted anecdotal reports out there of the use of these masks leading to dangerous, life-threatening situations,” he said. “These are only the reports we can hear. We can’t hear from those no longer with us, such as my wife, or the two snorkelers in Maui who recently perished while strapped into these things.”

Snorkeling remains the leading cause of death among visitors to Hawaii, where they are drowning at nine times the rate of local residents.

There were 169 snorkeling drownings between 2007 and 2016, according to the state health department. Of those, 156 were visitors, with Maui leading the state with 69 deaths.

Cooper is still waiting for answers to questions about why there are so many drownings and under what circumstances.

“We need answers to these questions,” he said.

Dr. Philip Foti, an Oahu physician who specializes in pulmonary and internal medicine, is pursuing answers. He is developing a machine of sorts that will be able to test different types of snorkel tubes to see which ones create the most resistance while breathing through them.

There are other studies in the works to test for carbon dioxide buildup. There is dead space ventilation in some types of the full-face masks that seems greater than in the standard snorkel tube, Foti said at an ocean safety conference last year. There is concern that the carbon dioxide buildup in the mask could cause someone to become disoriented or lose consciousness.

Colin Yamamoto, who retired in December as Maui County’s Ocean Safety battalion chief after 30 years with the Fire Department, said some unscientific tests were conducted late last year to test for carbon dioxide.

The tests involved putting on a full-face mask and after five minutes inserting a probe that’s used to detect carbon dioxide in the atmosphere, he said. The readings showed the levels to be above what emergency responders call IDLH, immediately dangerous to life and health. The levels were also above STEL, short-term exposure limit.

Yamamoto, like other ocean safety advocates, does not want to jump to conclusions about the safety of full-face masks or other equipment. But he said it’s important to try to find out for sure, one way or the other, so the public can be fully informed.

Over the past five months, roughly one-fourth of the people who drowned snorkeling off the coast of Maui were wearing a full-face mask, Yamamoto said, cautioning that this could be interpreted in numerous ways.

“There is interest in looking at the mechanics of respiration across various types of snorkels/masks among members of the Advisory subcommittee,” said Bridget Velasco, state drowning and spinal cord injury prevention coordinator. “However, this is in preliminary stages and there is nothing to report at this point. It would also seem possible to assess respiratory strain under controlled, experimental conditions, but again this is out of the (Department of Health) purview.”

In the meantime, there’s a renewed focus on public safety messages.

“Tourists coming to Hawaii need to be urgently forewarned that they might be at risk of dying while ‘playing’ in these beautiful waters,” Cooper said.

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Ralph Goto, who chairs the Drowning and Aquatic Injury Prevention Advisory Committee, which includes key players from Hawaii’s various tourist and ocean safety agencies, said he and others on a snorkeling-focused subcommittee met Wednesday and again Thursday to discuss safety messaging.

“It’s taken too long,” he said. “People are still dying, dropping like flies.”

Last fall, the committee, after two years of work, approved messaging for four 25-second videos. They started airing in September every 90 minutes on the Real Hawaii TV channel that’s available in 25,000 hotel rooms on Oahu with plans to eventually air on the neighbor islands too.

Goto said that messaging was “pretty innocuous.”

“We need to come up with something a little more definitive and a little stronger,” he said.

Yamamoto stressed the importance of snorkeling and swimming at beaches with lifeguards, and to ask lifeguards or local residents about the conditions, which could include unseen rip currents, jellyfish or other hazards.

“We’ve got to send the message that snorkeling is a strenuous activity,” he said. “You need to be familiar with your equipment.”

Regardless of type of equipment used, Velasco said the health department and advisory committee strongly advocate for safe ocean activities as much as possible, which includes swimming or snorkeling with a “buddy” or in the presence of others and being aware of personal skill limitations and health issues.

Hawaii, which has had a record number of visitor arrivals for the past several years, is expected to top the 10 million mark in 2018.

“Hawaii needs to do a better job keeping our visitors safe,” Yamamoto said. “These are human beings with families in mourning.”

For more information on ocean safety, read Civil Beat’s special project, Dying for Vacation.