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Diving the SOS: A Practical Discussion

The SOS meter was wildly popular in the 1970s and 80s prior to the advent and broad adoption of electronic diving computers like the EDGE. What’s more, according to avid users, like diving industry pioneer Bret Gilliam, who founded Technical Diving International (TDI) and was the former president of UWATEC, the device actually worked reliably, at least down to 55 m/180 ft. No Bend-O-Matic there! Gilliam, ever the name dropper, is positively bubbling.



Text by Bret Gilliam. Header image courtesy of Stephane Symes, other images courtesy of Bret Gilliam.

Wind the clock back five decades and re-enter an era when “square” dive profiles were the standard, and all divers used tables. Then, in 1959, Strumenti Ottoci Subacquei (SOS)—a small, Italian company led by founders Victor Aldo De Sanctis and Carlo Alinari—quietly introduced a new product. They called it a Decompression Meter or, simply, “Deco-Meter.” The device was distributed by SOS itself but also by a number of dive equipment companies.

However, the Deco-Meter got a major boost when it caught the attention of Scubapro founder Dick Bonin, a Naval officer and diver. It’s not clear exactly when Scubapro took on the actual distribution of the SOS product, but it was likely around 1967, a little less than a decade after its invention.

One of Bonin’s salesmen gave him an overview of the new SOS product while several other staff shared their practical experience with the meter. Jimmy Stewart from Scripps and engineer/designer Dick Anderson also chimed in with their own thoughts on methodology. NOAA underwater geologist Dr. Bob Dill undertook numerous deep, lengthy, repetitive dives and found that the two of us shared a common goal of making our dive exposures more efficient. He reached out to me while I was working on a US Navy project.

I was first introduced to the SOS meter in January 1971, while assigned to a Navy experimental deep diving team filming fast attack submarines in great depths. But, a lot of our standard operational and rigging protocols had us working between 18 m/60 ft and 45 m/150 ft during setups and breathing air. Our longest dive profiles resulted within the two to seven atmosphere range, and we’d already gotten input on alterations to mid-depth profiles from an experimental physiologist in Canada we were working with.

The diving medical officer on our ship was fascinated as I explained what I knew about the SOS meter as well as my conversation with NOAA diving director Dr. Morgan Wells—my first discussion about the concept of “multi-level” dive profiles—a radical departure from square table models and calculations of inert gas uptake and off-gassing. Dr. Wells had  been quite interested in explaining multi-level profile theory to my Naval team in more detail to show how such a calculative departure from the norm could make us more efficient and dive within an improved margin of safety.

Almost every professional diver I knew had embraced the SOS meter and used it exclusively. Virtually every filmmaker and photographer used the SOS meter since it gave them so much more time underwater.

What Works Works

The device was incredibly simple. It was a waterproof deformable flexible chamber with a semi-porous ceramic flow pathway (Bourdon tube) that channeled the pressure through the analog needle indicator to give a display of remaining no-decompression time (or required deco, if applicable). It sounds more complicated than it is. 

The mystery of the device was how the inventors were able to come up with a ceramic porous element that, incredibly, was seemingly able to match the flow rate of inert gas loading and outgassing from the diver’s tissues, and display it on analog display. From an engineering standpoint, to stumble on such a methodology so fundamentally and foundationally accurate with the barest minimum of decompression models was a physiological breakthrough of the first order. 

From the SOS Deco-Meter Manual

This was not anything that Haldane saw coming.

Legendary diving physiologist, Dr. RW “Bill” Hamilton, summed it all up with his precept for decompression tools, “What works is what works.” Bill had studied, led the development of, and created so many decompression models, but the SOS device was unique, with no timing device, no depth gauge, no bottom time display—only an analog needle indicating the diving profile status. Bill used to laugh and say, “There’s no explanation for the SOS meter. It shouldn’t work because it’s based on unknown models. But, somehow it does work… nearly perfectly down to about 55 m/180 ft. And I’ve never seen a case of DCS [decompression sickness] by divers using the SOS meter. It’s kind of crazy.”

It has made for some interesting discussions over the years. 

Dive tables and square profiles were slowly falling out of favor by many professional divers and numerous sport divers as well. Divers embraced the new SOS device and multi-level diving as an alternative—and safer—approach.

This was over fifty years ago, and many divers had an SOS meter if they worked in the military, commercial, scientific diving communities or with filmmaking, and underwater photography, for example on Hollywood movies, and on documentaries. And so did serious sport divers. The SOS meter was the great liberator for so many divers, since it gave them more freedom and variables.

But How Did It Work?

Since it was an analog instrument with a manual movable needle to indicate allowable no-deco or required deco, there were no batteries required. The only maintenance required was rinsing with fresh water after dives. 

The lower left side of the meter contained the needle—the “blue zone” indicated no inert gas exposure. Once the dive was initiated, the analog needle traveled across the no decompression zone that spelled out SURFACE. If the needle remained within the SURFACE zone, you could immediately surface with no decompression. It was very common for divers to say, “I’m on the C,” or “Are you on the E?”

The face of the SOS Deco-Meter

If you went into the red zone beginning with the “10 Ft.” display, you were going to be there for quite awhile. Probably a good thirty minutes or so. If you hit a “20 Ft.” stop, you were going to be there for about a month or so. And you better have a backup breathing source.

The concept of multi-level dive profiles was an extraordinary enticement to longer periods with no deco obligations. But, a lot of divers still had a hard time getting their heads around the theory and wrestled with understanding the nuance of such deco models.

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It was exactly this type of misunderstanding that led some divers to be critical of the SOS meter and call it the “Bend-O-Matic.” Nothing could have been further from reality. The SOS meter had certain ranges that needed to be carefully observed to remain within no-deco limits. But, if used correctly, the SOS device had an amazing safety record. In fact, of the tens of thousands of divers using the meter, none of us were aware of a single case of decompression sickness (DCS) as long as the meters were used within their design range. That’s phenomenal. 

In 1971, I was one of the diving supervisors on a commercial diving project with 126 divers doing 10-12 dives a day in depth ranges between 15 m/50 ft – 43 m/140 ft. Every aspect of the dives was controlled by the SOS meter. This went on for over two months with a perfect safety record.

Gilliam on a film shoot for Skindiver magazine, St. Croix 1978

When we were filming the movie “The Deep” in 1976, the entire cast (including Robert Shaw, Jackie Bissett, and Nick Nolte), Al Giddings, Stan Waterman, location crew, technicians, and divers all controlled their exposures with the SOS meter. It made everything more efficient. The same was true for countless movie, television, and documentary projects—all done on the SOS meter.

The same was true for plenty of explorations, photo shoots, and sport dives. Every diver I knew used the SOS meter with success.

Evolution Was Coming

Though the adoption of the first electronic dive computers, including Orca Industries’ EDGE, which was launched in 1982, grew throughout the 1980s, the SOS meter remained popular. But, interest waned when Dacor released the Micro-Brain in 1988, which featured a decompression algorithm designed by Dr. Albert Buhlmann, and continued to pave the way for dive computers. I later worked with Dr. Buhlmann as a consultant on later versions of the Micro-Brain’s software program.

Even though dive computers changed the sport forever by making it safer and more efficient, the SOS meter laid the foundation for the early breakthrough into modern multi-level diving profiles. That simple, amazing device incorporated the conceptual transition from tables to an alternative protocol for diving. 

It was all done with the barest of technological design—yet it worked efficiently and safely. 

The lateTom Mount in 1969 sporting his SOS Deco-Meter (look above the tanks).

It was not created from a mind-numbing algorithmic deco model. It was crafted from an unknown ceramic element that theoretically represented inert gas flow loading and outgassing in human tissue. When first released, it sold for $18 retail, and it was still attracting buyers over two decades later. 

The SOS meter quickly went into the collectors’ cabinets and is remembered fondly as a pioneering piece of gear that launched a new technology closely followed by another revolutionary innovation: nitrox.

Time moves on, but somehow manages to get it right sometimes.

See companion story: The SOS Automatic Decompression Meter: Bendomatic or Game Changer? by Stephane Eyme

Dive Deeper:

Shearwater blog: On The EDGE by Michael Menduno

BluTime History: DECO BRAIN HANS HASS, the first dive computer by Andrea Campedelli

Dacor’s Micro-Brain Pro Plus Manual

Bret Gilliam is president of the consulting corporation OCEAN TECH, following his entrepreneurial successes in the diving and maritime industries. Bret is also a prolific writer and photographer on various subjects related to diving. He has been published in virtually every diving magazine internationally as well as National Geographic, Sports Illustrated, Outside, Time, Playboy, and many others. Author of nearly 1500 published articles, his photography has graced over 100 magazine covers, and he has been primary author, editor, or contributor to 72 books and training manuals on diving and other topics such as hyperbaric medicine, emergency treatment of diving patients in remote locations, scientific papers, maritime operations and engineering, and decompression models and algorithmic adaptations for diving computers.


Hyperbaric Chambers Are Turning Away Divers. Will There Be One Nearby When You Need It?

Unfortunately, it’s hard to make a business case for treating divers versus wound and burn care victims. As a result, many hyperbaric chambers no longer treat divers, leaving fewer facilities available for divers in need and increasing their post-dive time to treatment. InDEPTH editor Ashley Stewart reports on this growing crisis in the US and what can be done!




By Ashley Stewart

The hyperbaric chamber at the University of California San Diego. Photo courtesy of Sherri Ferguson

Steven Wells was diving on the scuttled wreck of the USS Oriskany off the coast of Florida in 2016 when a problem with his buoyancy compensator caused a rapid ascent to the surface.

Wells’ dive buddies followed the emergency action plan for the Oriskany listed on the Florida Fish and Wildlife Conservation Commission’s website at the time and brought Wells straight to Naval Air Station Pensacola, the nearest facility with a hyperbaric chamber. The facility turned him away because there was no one there to run it.

Wells was taken 30 minutes away to Baptist Hospital, which also has a chamber capable of treating his injuries, but the hospital had years earlier decided only to use it for wound care. Doctors there decided Wells would be taken by ambulance more than an hour away to Mobile, Alabama, the nearest facility that accepts divers.

By the time Wells arrived at the only chamber that would help him, it was too late.

Steven Wells

“I got a call from the hospital saying, ‘Your husband is on life support. You need to get here now,’” Rachel Wells said of her late-husband of more than 23 years. 

Julio Garcia — the program director of Springhill Medical Center’s wound care and hyperbaric facility where Steven Wells was to be treated — told InDEPTH that while no one can be certain how sooner treatment would have affected the outcome of Wells’ case, it would have given him the best chance for a full recovery.

Each year in the US, there are about 400 serious cases of decompression illness (DCI) — a category including both arterial gas embolism and decompression sickness — in divers, according to one 2020 paper. The Divers Alert Network (DAN) hotline dealt with 587 cases annually over the past five years.

The availability of hyperbaric chambers to treat decompression illness is something many divers take for granted. We try to avoid dive-related injuries through training, but expect treatment to be available when we need it. 

The reality — as Steven and Rachel Wells tragically learned — is that only a minority of divers are close to care for diving-related injuries, according to medical professionals in the field. The estimates vary, but it’s generally believed there are about 1,500 hyperbaric medicine facilities in the US and only 67 are currently treating diving accidents, according to DAN.

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The estimates vary, but it’s generally believed there are about 1,500 hyperbaric medicine facilities in the US and only 67 are currently treating diving accidents, according to DAN.

“The problem is only getting worse, not better,” Garcia, the Springhill Medical Center program director, said. Garcia has been sounding the alarm about this problem for more than a decade. His hospital takes patients from as far away as Florida cave country and treated 20 DCI cases in 2022. Those patients had an average transportation time of 11.5 hours, according to an InDEPTH analysis of Garcia’s records.

Florida stands out because it’s a popular diving destination, DAN Research Director Frauke Tillmans said, but the situation is not much better across the US. Many of the 1,500 hyperbaric medicine facilities, like Pensacola’s Baptist Hospital, have transitioned to treating wound care only for economic reasons. Emergency hyperbaric services are expensive to train and staff, and come with increased liability.

Patient briefing before treatment at the Environmental Medicine and Physiology Unit at Simon Fraser University. 

Time to treatment can be important in DCI cases

Time is of the essence when treating DCI. Divers Alert Network Director of Medical Services Camilo Saraiva told InDEPTH time to treatment is a “pivotal determinant” when it comes to outcomes for DCI patients. “Swift intervention significantly influences the effectiveness of therapeutic recompression,” Saraiva said.

Decompression sickness, for example, results from rapid changes in pressure and can form gas bubbles in body tissues. Initiating recompression therapy minimizes bubble size and number, Saraiva said, enhancing their elimination and reducing the risk of further vascular obstruction and tissue damage.

“The timely provision of hyperbaric oxygen therapy not only aids in bubble resolution but also mitigates the potential for neurological deficits and other severe complications, highlighting the critical role of early treatment in optimizing outcomes for DCI patients,” Saraiva said.

The 2018 paper “In water-recompression” stated delays to recompression in military and experimental diving are typically less than two hours and more than 90% of cases are completely resolved during the first treatment.

Frank K. Butler and Richard E. Moon, hyperbaric medicine experts, wrote in a 2020 letter to the Undersea and Hyperbaric Medicine journal editors suggesting a minority of patients who need life-saving hyperbaric oxygen treatment (HBO2) are close to a major hospital with a 24-hour emergency hyperbaric facility.

Julio Garcia’s log on patient time to treatment at Springhill Medical Center. Click to enlarge

“Despite the urgent need for treatment, most hyperbaric chambers will decline to accept emergent patients at present,” Butler and Moon wrote. “Patients may eventually receive HBO2 but after a significant delay and a transfer of several hundred miles. Many never receive indicated HBO2, often resulting in poorer patient outcomes.”

Patients who are delayed treatment, they wrote, face the possibility in some cases of “death, permanent neurological damage, permanent loss of vision, or loss of an extremity, most of which would have been readily preventable had emergent HBO2 been administered.”

Why fewer chambers treat dive injuries

As recently as two decades ago, according to Butler and Moon, the majority of hyperbaric treatment facilities were available 24/7 to treat emergency patients. The percentage of those facilities now treating emergency patients is unclear, but it’s universally agreed the number has fallen significantly.

The reasons for the loss of emergency HBO2 facilities, Butler and Moon suggest, include “a better economic return when chambers focus on wound care patients as opposed to emergencies; the greater legal liability involved with treating high-acuity emergency patients; and the increased training and staffing requirements that would be required to manage critically ill patients — especially diving injuries and iatrogenic gas embolism patients.”

A letter from an administrator at Baptist Hospital — which sent Steve Wells to Springhill Medical Center — viewed by InDEPTH shows the hospital discontinued hyperbaric emergency services in December 2010, citing lack of staffing for specialty trained hyperbaric physicians who can provide 24-hour patient care. Baptist has yet to respond to InDEPTH’s request for comment.

Julio R. Garcia at Springhill Medical Center Hyperbaric Center

There’s also the issue of pay. Garcia, the Springhill program director, said the current rate of pay for doctors who administer hyperbaric treatments regardless of length is around $150. A typical hyperbaric treatment for other conditions is about two hours. Diving treatments are usually six or seven, he said. “What doctor wants to get paid $150 to be up all night for seven hours, at that point making less than the technician?” Garcia said. “The fix is that healthcare payers need to pay more for the supervision of the treatment for diving injuries. Make it something that’s worth a doctor’s time besides the goodness of their hearts.”

Silence from lawmakers

Medical and diving organizations in 2020 sent a letter to the House and Senate, federal government agencies, governors of Florida and California, and the American Hospital Association expressing concerns about the lack of availability of chambers to treat diving injuries.

“There are approximately three million recreational scuba divers in the US,” the letter stated. “In the unlikely event that they suffer a diving-related injury, they trust that the US medical system will provide state-of-the-art care for their injuries, but the steadily- decreasing number of hyperbaric treatment facilities in the US willing to treat them emergently for decompression sickness or arterial gas embolism often places them at much greater risk than they realize.”

Garcia has on his own contacted lawmakers, reporters, medical systems — even private space companies like SpaceX because his facility is also the only one nearby treating altitude decompression sickness from space and air travel.

Little has changed, Garcia said.

Garcia showed InDEPTH a 2014 letter from a Defense Health Agency director who said, while there are three Undersea and Hyperbaric Medicine Society-accredited clinic hyperbaric medicine facilities and two additional facilities that can treat civilian emergencies, they are not staffed 24/7 and not designed for patients with other medical illnesses. Garcia at the time requested the creation of a federal grant to support the expansion of 24/7 hyperbaric services, but the director said that was outside of the agencies’ purview. 

The hyperbaric chamber at the University of California San Diego. Photo courtesy of Sherri Ferguson

Two years after this exchange, Steven Wells was taken to and turned away from one of these facilities — the NAS Pensacola, listed on the Florida Fish and Wildlife Conservation Commission’s (FWC) emergency action plan at the time. 

The Florida Fish and Wildlife Conservation Commission website now shows a map of the nearly 4,000 artificial reefs across Florida’s 1,350 miles of coastline. Two chambers, one in Mobile, Alabama, and one is Orlando, cover 500 of those miles densely packed with dive locations, according to Garcia.

The FWC website now shows a map of the nearly 4,000 artificial reefs across Florida’s 1,350 miles of coastline. Two chambers, one in Mobile, Alabama, and one is Orlando, cover 500 of those miles densely packed with dive locations, according to Garcia. A report from the University of West Florida estimated the sinking of the Oriskany, scuttled in 2006, generated nearly $4 million for Pensacola and Escambia County in the next year alone.

So many reefs, so few chambers! FWC map screenshot

An FWC spokesperson said the agency provides diver safety reminders and recommended actions on its website “as a courtesy” and is not intended for emergency response. FWC and Visit Florida did not respond to inquiries about how much Florida’s government spends on advertising the artificial reefs and other diving activities, or whether any effort to expand the availability of hyperbaric facilities to treat the divers who show up as a result.

“My question is what is my husband’s life worth compared to your chambers,” Rachel Wells, Steven Wells’ widow said. “Why did he have to die?”


DIVER: A Crisis in Emergency Chamber Availability by Dan Orr (April 2022)

Divenewswire: A Crisis Lurking Below the Surface Emergency Hyperbaric Treatment Availability by Dan Orr (August 2021)

Undersea and Hyperbaric Medicine (2020): Emergency hyperbaric oxygen therapy: A service in need of resuscitation – an open letter by Frank K. Butler, MD, and Richard E. Moon, MD

White paper: Access to emergent hyperbaric oxygen (HBO2) therapy: an urgent problem in health care delivery in the United States (2020)

InDEPTH: A New Look at In-Water Recompression (IWR) (2019) by Reilly Fogarty

Diving and Hyperbaric medicine (2018): In-water Recompression, Doolette DJ and Mitchell SJ 

aquaCORPS (1993): In-Water recompression As An Emergency Field Treatment for Decompression Illness by Richard L. Pyle and David A. Youngblood

InDepth Managing Editor Ashley Stewart is a Seattle-based journalist and tech diver. Ashley started diving with Global Underwater Explorers and writing for InDepth in 2021. She is a GUE Tech 2 and CCR1 diver and on her way to becoming an instructor. In her day job, Ashley is an investigative journalist reporting on technology companies. She can be reached at:

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