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Where Have All the Sensors Gone? Assessing the Global Oxygen Sensor Shortage

Tried to purchase O2 sensors for your rebreather lately—to no avail? You are not alone. As Reilly Fogarty explains, there’s both a global shortage of sensors as well as long lead times because of the pandemic-induced medical demand. Note that diving applications account for less than 2.5% of global usage.

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By Reilly Fogarty
Header image courtesy of AP Diving

Our community has weathered a number of drastic and unexpected changes this year, not the least of which is the current shortage of oxygen sensors for gas analyzers and rebreathers. These electro-galvanic oxygen sensors were first developed in the 1960s and have found uses in the automotive, medical, scientific, and manufacturing fields as well as at home in our dive kit. However it’s the pandemic-induced demand in the medical field that has posed the most recent challenge to the sport diving community. 

Inspiration head showing its three O2 sensors. Photo courtesy of AP Diving.

The types of galvanic oxygen sensors used in rebreathers are nearly identical to many of those used in medical devices, and even those that differ in form often share the same structure and manufacturer. The most common use for these sensors can be found in medical ventilators and anesthesia machines. These devices pump air, usually with an increased fraction of oxygen, into a patient’s lungs to help oxygenate their tissues and support life when they cannot breathe for themselves. The patients are anesthetized and intubated—an endotracheal tube is placed in their airway to prevent airway obstruction—and the ventilator is used to push air into their lungs via a bellows system. 

As COVID-19 symptoms progress in some patients and they develop acute respiratory distress syndrome (ARDS), the alveoli in their lungs fill with fluid and they lose their ability to adequately oxygenate themselves. This, and other complications that result in a patient losing the ability to breathe on their own, requires the use of a ventilator to maintain life. These ventilators, anesthesia machines, and a wide array of associated devices used for pulmonary interventions all require the careful monitoring of oxygen exposure. 

For many of the same reasons that divers manage their oxygen exposure, physicians must carefully monitor the time spent breathing and the fraction of oxygen they give their patients. CNS toxicity isn’t typically a concern in these situations, but long-term oxygen exposure can lead to a litany of inflammatory responses and damage to the pulmonary, ocular, and circulatory systems. 

An Unprecedented Demand for Sensors

The result of the influx of serious COVID-19 cases is that these ventilators and other medical devices that require oxygen sensors have been put under unprecedented demand. Machines are being repurposed, pulled from storage, and manufactured at breakneck speed to meet an impossible need. Researchers are innovating new solutions to provide care in areas where ventilators cannot be used or sourced as well, but even while ventilator bellows can be redesigned, the inspired gas must be measured with oxygen sensors. 

Ventilators require oxygen sensors. Here is the low cost Corovent ventilator developed by Divesoft founder Ales Prochaska, and others. Photo courtesy of Divesoft.

The result of the influx of serious COVID-19 cases is that these ventilators and other medical devices that require oxygen sensors have been put under unprecedented demand. Machines are being repurposed, pulled from storage, and manufactured at breakneck speed to meet an impossible need.

TEMC DE-OX Oxygen Analyzer with uses an O2 sensor.

This means the few companies that do make oxygen sensors for diving uses, like Vandagraph and Analytical Industries, have had to put their normal business on hold and retool their manufacturing to meet medical demands. The logistics of this are immense, but the products are quite often similar; medical oxygen cells can sometimes share the same connectors as some rebreathers, and many differ only in the way they’re attached to a device.

Despite what your dive buddy’s Salt Life bumper sticker may imply, diving is a recreational sport—at best a professional endeavour—so it’s difficult to find fault with the industry’s redirection of oxygen sensor supplies and manufacturing. All the same, it’s frustrating not being able to access the sensors we need to keep diving, and there’s undoubtedly a temptation to inappropriately extend sensor life in the face of a shortage. [Ed note: JUST SAY NO!]

It’s easy to see how diving applications get lost in the scope of the industry, but Eugenio Mongelli, CEO of TEMC DE-OX, an analyzer manufacturer, says the shortages we’re seeing now are complicated by the choices in sensor compatibility that diving equipment manufacturers have been making. “I do not believe using a custom made oxygen sensor in your analyzer is a good policy,” Mongelli said. “In case you are in the middle of nowhere you must [be able to] replace the sensor with any kind available.” Notably, TEMC DE-OX designs their analyzers to accept a wide range of oxygen sensors for this purpose, and Mongelli contends that applying the same methodology to other diving equipment could alleviate some shortage concerns in situations like the one the industry is facing now. 

Supply Chain Blues

At the time of this writing (OCT 2020), some sensors have been available sporadically, but widespread shortages and delays in supply have been noted across the industry. The manufacturing supply chain has been estimated at approximately three months behind schedule, and it’s unclear when the situation will improve. 



“Production oxygen sensors have been prioritized toward medical requirements since the pandemic started. Nearly all production has been used to supply government ventilator projects around the world,” explained Ryan Swaine, International sales manager for Vandagraph Ltd., a major manufacturer of oxygen sensors for surface gas analyzers and sister company to Vandagraph Sensor Technologies. “[Vandagraph] has also prioritized some of our products toward the emergency ventilator projects in the UK, such as our VN202 scuba analyzer, which is being used in some of the UK hospitals”. 

BBC News. Photo courtesy of Ryan Swaine.

Rebreather manufacturers have managed to ford the gap in supply in a few ways. Inspiration product manager Nicky Finn, of UK rebreather manufacturer AP Diving, said that AP “views this as a short-term issue” with the hope that “with time, normal stock levels will return. Unfortunately, it’s difficult to predict a time frame for this,” she explained.  AP has managed to maintain some supplies of oxygen sensors via the use of two separate product sources, which has resulted in a small waiting list that they are working through as sensors become available. 

Pieter Decoene, operations manager for rEvo Rebreathers, has taken a similar approach, noting that maintaining a large stockpile of sensors is not “the best approach, due to the limited shelf life of the sensors.” The rEvo team has found that customers are largely understanding of the shortage, and that while delivery times were somewhat longer, the sensor supply chain has not been entirely lost. “An interesting fact that we saw during the worst of the shortage was that divers who followed the rEvo sensor replacement policy (one sensor replaced every six months) were never forced to stay out of the water for lack of oxygen sensors,” Decoene said, adding that “having true redundancy and following the sensor exchange policy permitted [these divers] to continue diving without compromising safety.”

Poseidon Solid State Oxygen Sensor.
Photo courtesy of
Poseidon Diving Systems

In another interesting turn, Poseidon Diving Systems has seen a shift in the configurations of rebreathers they are selling, from approximately 50% of divers choosing to outfit their unit with a Poseidon Solid State Oxygen Sensor, manufactured for Poseidon, to 100% in recent orders. However, Jonas Brandt, CEO of Poseidon Diving Systems, said that while they do have “a huge order backlog from customers having rebreathers that only facilitate the “old” [galvanic] sensors, [he] does not see any change in lead times. However in terms of quantity, galvanic sensors are being delivered in lots of 25 bimonthly, rather than 200.”  

 It’s difficult to say exactly when this shortage of sensors will end because, as we enter fall, so much depends on how successful global efforts are in stemming the pandemic. The good news is that there may be a light at the end of the tunnel, as Vandagraph has begun to meet some of their demands from ventilator projects and has begun producing non-medical sensors in small batches once again. Cautious but optimistic, Swaine says that there “is a large backlog to get through, so there are still delays in supply, but the situation has started to improve.” 

Another large sensor manufacturer, who did not want to be named, shared that same optimism. “To say that the medical industry has dominated our production for the past seven months would be an understatement. We are running 10-12 hours a day, six days a week and it is still not enough, but both the industrial and diving industries are extremely important to us and we are hoping to have this backlog up to date shortly,” a representative explained.

No matter how hopeful manufacturers may be, Mongelli says that the future availability of diving sensors is unlikely to improve until the global COVID response gains ground. Due to the sheer demand from anesthesia device requirements, he predicts that supplies will remain sparse until next year, when he is hopeful a vaccine becomes available to control the spread of the pandemic.

Additional Resources:


Reilly Fogarty is an expert in diving safety, hyperbaric research, and risk management. Recent work has included research at the Duke Center for Hyperbaric Medicine and Environmental Physiology, risk management program creation at Divers Alert Network, and emergency simulation training for Harvard Medical School. A USCG licensed captain, he can most often be found running technical charters and teaching rebreather diving in Gloucester, Massachusetts.

Equipment

The Right Tool, For the Right Job: My De-Evolution on the Question of Urinating Underwater

Condom caths and p-valves are arguably the best way to go during tech dives, until they’re NOT. Here InDepth editor-in-chief Michael Menduno goes old school to beat the heat!

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By Michael Menduno
Header image of the author, Capt. Mark Nease and Capt. Billy Deans at Key West Diver, Stock Island, FL before p-valves were invented (1992). Photo by Dan Burton.

“To pee, or not to pee?” is NOT a question for tech divers. With the possible exception of British expat picture-maker extraordinaire, Tom St. George—who swears he never pees underwater in a drysuit—good hydration and long dives dictate that the urine will flow. The question is, how are you going to deal with it? [Obviously, easy peezy for wetsuit diving—just let it wizz.]

Today, of course the solution de rigueur for drysuit diving is the condom catheter and a p-valve for men—just slide on the sheath, connect it to the one-way p-valve hose, and you’re good to go. Women commonly use the She-P external catheter or the Shewee Go, which is a little more complicated, or resort to diapers. Problem solved! For the most part anyway. However, it turns out that might not always be the case, as I discovered on my recent diving trip to Mexico.

Plug and go with the Halcyon P-valve. Photo courtesy of Halcyon Dive Systems.

A Wee Bit of History

Siebe Gorman & Co Ltd.: Portable rubber urinal circa 1909

Male commercial divers enjoyed the privileges of an in-water urinary solution as early as 1876. By 1909, legendary British equipment manufacturer Siebe Gorman & Co Ltd. was touting its “Portable Rubber Urinal” in its catalog. According to the entry, the pouch-like device, which is attached to the male diver by means of a belt, was so constructed that “The diver can urinate without fear of the urine entering his dress, no matter what position he may be working.” Urine was captured in a tube with a non-return valve and emptied at the end of the job. The accompanying dry suit featured a watertight metal port with a screw-down plug enabling the diver to pee without undressing. Unfortunately, it took the sports diving industry a bit longer to get on with it. 

Ironically, early dry-suited cave divers—predecessors of today’s tekkies—were slow to heed the call of nature. According to underground graybeard Paul Heinerth, who was a member of Bill Stone’s original 1987 Wakulla Project, “We would just hold it till we were in the deco habitat and pee through the doorway in the water just before changing depth as it would act as a flush.” And these were long decompression dives to depths between 75-100 m/244-326 ft. 

Adult diapers were available but not regarded as an acceptable solution. I once asked the late great underwater filmmaker, Wes Skiles, who was also at Wakulla, about his urinary practices for a story that I was researching, “Us manly men were too stupid and/or too embarrassed to slip on diapers,” he sheepishly admitted. Underground patron saint Sheck Exley, also on the project, used a wet suit supplemented with chemical heaters, or his red Parkway neoprene drysuit, where he could “just cut it loose” for extended cave dives. 



1987 Wakulla Springs Project (L to R) Paul Deloach and Sheck Exley decompressing in the habitat. Photo by Wes Skiles.

Diapers, aka nappies, briefly came into vogue in the early 1990s as tech diving was just emerging from the closet. Explorer Jim King and his team began using diapers on their 1991 Diepolder #2 Project. So did tech pioneer Capt. Billy Deans and his Key West Divers team on deep wreck dives (Full disclosure: I was a member of Dean’s team and we used “Depends”). 

P-valves with male condom caths made their debut in the mid-to-late 1990s. “A few of us were playing with homebuilt designs,” GUE founder and president Jarrod Jablonski explained to me. “[Early cave explorer] Roger Werner is also one that comes to mind. He was building some of his own and essentially selling them to others.” In the early days of cave diving, it was not unusual for divers to make their own gear. 

Halcyon was one of the first manufacturers of p-valves. Photo courtesy of Halcyon Dive Systems.

According to Jablonski, Extreme Exposure dive centre based in High Springs, FL was the first to commercially produce and distribute p-valves back in the late 1990s. Production was soon moved to Halcyon Dive Systems (Ed.—Jablonski is a co-owner of both). As a result, the relief zipper—remember them?—became a thing of the past.

The She-P 3.0 revealed. Photo courtesy of She-P.

At the time, female tech divers were stuck with diapers or nothing at all. That is until Netherlands DIR (“Doing It Right) diver Heleen “Wethorse” Graauw, invented the first underwater female catheter system, which Fred Devos, cave explorer and co-owner of Zero Gravity in Puerto Aventuras, Mexico, dubbed the “She-P” when Graauw visited Mexico, and the name stuck. She-Ps mostly do too, thanks to help of ex-surgical tech Laura James, who teamed up with Graauw to perfect the adhesive system and distribution. Another external device on the market is the Shewee Go. For more information see: Urination Management Considerations for Women Technical Divers by Payal Razdan in InDepth V 1.9.

The Shewee Go. Photo courtesy of Shewee.

The Joys of Nappies

Condom caths and p-valves work great for men except when they don’t. Assuming that your p-valve is functioning and properly maintained, the condom may refuse to stay in place. Which brings us back to Mexican cave diving. 

As anyone who has dived Riviera Maya during the spring or summer months knows, the air is hot and humid. As a result, your entire body stays dripping wet, before, during, and after you get in the water. The result? Much to my chagrin, on our first couple of dives, my condom refused to stay on. As they say, “No glove, no love.” My p-valve was definitely NOT showing me any love. We’re talking spillage.  What to do?

I consulted with tech and cave instructor Kelvin Davidson, proprietor of Third Dimension Diving in Tulum, who offered a couple of solutions. Option one: buy condoms two sizes too small (Davidson buys “Ls.” Wreck diver! ), and be prepared to stuff your junk. Option two: purchase a bottle of rubbing alcohol and pads, wipe your willy after your morning shower, and put on your condom before the humidity gets out of hand.

The author suiting up for a dive at Cenote Angelita. Photo by Kelvin Davidson.

Instead, I opted to go old school. I walked down to the local farmacia and bought a twelve-pack of high tech (gel-based) adult diapers for US$8. They even featured rip-away sides for easy removal post-dive. Yeah, I had to put up with some ribbing from the guys, but I happily dived nappies for the rest of the trip with just a hint of nostalgia. More importantly, I didn’t have to worry about slippage! (Full disclosure: I peed twice on some dives. Well, OK, two and a half times.It was not a problem). As they say in GUE circles (usually when they are referring to rebreathers or sidemount configuration), “The right tool, for the right job!”  

Additional Resources

InDepth: Urination Management Considerations for Women Technical Divers  by Payal Razdan

Diver: The Divine Secrets of the She-P Sisterhood by Michael Menduno


Michael Menduno/M2 is InDepth’s editor-in-chief and an award-winning journalist and technologist who has written about diving and diving technology for more than 30 years. He coined the term “technical diving.” His magazine aquaCORPS: The Journal for Technical Diving (1990-1996), helped usher tech diving into mainstream sports diving and he produced the first tek.Conferences and Rebreather Forums 1.0 & 2.0. In addition to InDepth, Menduno serves as an editor/reporter for DAN Europe’s Alert Diver magazine, a contributing editor for X-Ray mag, and writes for DeeperBlue.com. He is on the board of the Historical Diving Society (USA), and a member of the Rebreather Training Council.

Be A Part of History: To access our treasure trove of dive history and become a member, visit us at: www.HDS.org. We are also on Facebook: Historical Diving Society USA

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