Sign up for our monthly newsletter so you never miss the latest from InDepth!
Header photo by Jesper Kjoller
We surveys CCR divers from around the world. Here are the results.
Why GUE Has Not Adopted The Strap
First and foremost, GUE constantly evaluates and develops technologies and methodologies with the ultimate goal of offering increased safety, efficiency, and enjoyment to our divers. One such device is the Mouthpiece Retaining Strap (MRS) or more commonly called—the gag strap. The purpose of the MRS is to secure the diver’s mouthpiece (DVS or BOV) in place using an adjustable rubber band around the diver’s head. In theory, this would retain the mouthpiece in the diver’s mouth even during an adverse event leading to unconsciousness and thereby prevent drowning and death.
The origin of the MRS comes from the military diving community where it is used as an alternative to Full Face Masks (FFM). There is at least one study indicating a reduced risk of drowning while diving rebreathers under military operations with the use of a MRS. However, one should keep in mind that military rebreather diving applications are quite different compared to our technical diving application. Where the military divers carry no bailout, we certainly do. We also have more obvious and less concealed communication and information devices, such as bright head Up Displays (HUD) and controllers giving us a fair chance of detecting malfunctions.
Since our technical diving application is different, and our methods for bailout need to be uncomplicated and unrestricted, we have found that the use of the MRS would be unlikely to reduce the risks, and as such, we don’t advocate for the use. We don’t prevent the use per se, but we prefer a holistic and consistent approach when feasible.
-Richard Lundgren, GUE Technical Administrator
Haynes P. Increasing the probability of surviving loss of consciousness underwater when using a rebreather. Diving Hyperb Med.2016 Dec;46(4):253-259.
PADI’s Position on Retaining Straps
Community practice regarding the use of retaining straps in CCR diving remains divided, so at present, the choice to use them or not lies with the instructors and their students. The only exceptions are if the particular CCR manufacturer prohibits or requires strap use with their units, in which case manufacturer requirements should be followed. If and as community practices change, the requirements in PADI courses will change accordingly.
–Karl Shreeves, Technical development executive, PADI
RAID Encourages Their Use
RAID encourages the use of a retaining strap, but it is not mandated. Simple logic dictates that some CCR users do not have a true BOV installed and do not have off-board diluent (bailout gas) plugged into the unit. A retaining strap/gag-strap may not be the best option in that case. (Personal note: When diving my old pelagian rebreather, I have the mouthpiece “loose” and a bailout second stage on a necklace. I only had to use it in earnest once but I believe it would have been a slower switch from the loop to OC if I’d worn the strap.)
That said, the unit I dive most of the time has a BOV (good idea) and I always wear a retainer. I am thankful for it on EVERY long dive because it does an amazing job of helping to alleviate jaw fatigue. An added benefit is that it does prevent the mouthpiece dropping out of a diver’s mouth whenever they are gobsmacked by the behaviour of others.
–Steve Lewis, RAID training director
ANDI Says Usage is Optional
We have decided to add mouthpiece retaining straps to all of our CCR texts along with a few photos and explanations, in the same way that we explain the Full Face Mask. The benefits are these…The deficits are these…
This will show the students the safety advantages, how to use the device and when it would be used. Usage is optional. A limitation caused by the usage of a strap is increased difficulty and additional steps in performing off-board gas switches. Instructors agree that its use adds to potential issues during training.
Eduardo Jaimes Fabres, our training director commented that “During the last DEMA show I saw a good option made by AP Diving.” It’s basically a silicone strap with two soft large O-rings. It looks good, inexpensive and the user can still use his/her mouthpiece. My personal preference is a standard DSV or BOV with quick access to bail-outs. In the ANDI system a user can dive safely with the DSV and a redundant breathing system (RBS), which ANDI advocates for all divers and levels.
The primary reason for use of the mouthpiece retainer strap is its protection from drowning during a CNS seizure. That’s it. If one is running the bottom mix at a PO2 of 1.2-1.3 it seems to be a quite unnecessary precaution. Perhaps a better question for the industry; “Is there any evidence of CNS oxygen toxicity at 1.5, 1.45. 1.4?”
Sorry for the history lesson here but I remember discussions alluding to the dangers of a PO2 dosage of 1.6 atm for open-circuit SafeAir (nitrox) diving, even though no proven incidents were documented at that dosage. Then we stated that 1.5 is safer. Oxygen management is very difficult and unpredictable. 1.4 is even safer still. Well… for longer dives we should be using 1.3. Extended range diving is best served with 1.25 oxygen dosages. Keep going at this and we are back to diving air with fancy gas controllers.
–Edward A. Betts, founder and Executive Director, ANDI International
Did not wish to take a position at this time.
AP Diving Is Favorable And Supplies A Strap
On balance, we are in favour of mouthpiece straps. On longer dives they can reduce jaw fatigue, but this can also be done by ensuring the mouthpiece hose lengths are correct for you—too many divers look like they’re wearing a set of bagpipes when they dive.
Of course, straps are like a seatbelt in a car from a safety point of view, they’re there to help if you have an accident. Prevention of accidents is of course the first priority, but it is clear a lot of things have to line up for a mouthpiece strap to be of any use in an emergency situation; the mouthpiece strap would only be of use if a dive buddy is present AND is capable of offering assistance, AND if the diver does still manage to make a seal at the mouthpiece despite being unconscious. So you can see a lot of things need to be in line for the strap to be of any use in an emergency, and for that reason, many divers don’t see the benefit in one. We do mention the benefits of the strap in the instruction manual and do offer a strap as an optional extra.
–Martin Parker, Managing Director AP Diving
Divesoft Encourages and Supplies A Simple Strap
We supply our Liberty rebreathers with an elastic bungee cord, which serves as a simple retaining strap. But it is just a simple solution. We also offer the gag strap as an option in our configurator. Unfortunately, we do not currently mention retainer straps in our user manual, but it is a good idea to add it to the manual and also mention it in official factory training powerpoint slides as well.
We definitely advocate their use. I was a part of a team which researched the probability of rescuing an unconscious rebreather diver. The result of the study was absolutely clear. A diver with the gag strap has a much higher chance to survive going unconscious, and a very low chance without it. I really appreciate InDepth’s effort to address this, because I think this is a very important but unfortunately neglected topic.
-Jakub Šimánek, Factory Instructor Trainer Divesoft
rEVO Has Supplied and Advocated from Day One
Since the start of the rEvo production, we have always been (and we were the first for civilian use) supplying mouthpieces with lip seal and retainer straps standard on all units. It’s the same for training on rEvo units: the use of this mouthpiece with straps has always been mandatory, and it is mentioned in the user manual and in all training material.
Why? Simple! Because underwater, people never die because of bad gas (almost never…). If they die, they do because they breathe water. So if you can prevent, or delay, the breathing of water, you increase the likelihood of survival. Furthermore, a correctly fitted gag strap prevents buoyancy loss in case of unconsciousness .
–Paul Raymaekers, rEvo Rebreathers founder & CEO
Hollis Offers A Strap for the European Market & When Requested
With the recent CE approval of the Prism 2, we are offering a mouthpiece retention strap for the European market purchases and for anyone that requests one. However, real world use of a strap is very low. Our statement in our user manual is as follows, “A mouthpiece retaining strap is included with the Prism 2 Rebreather. This part minimizes the ingress of water during normal use and ensures the mouthpiece is held in place and the diver remains on the loop in the event of a diver falling unconscious or having a convulsion while underwater.”
–Nick Hollis, Brand Manager, Oceanic & Hollis
Dive Rite Says Watch Your PO2s
We have looked at the issue, but the only one I know of is the Drager strap. I have tried variations, but I just don’t like it and we don’t provide one. It can only help in the case of O2 toxicity? Survive the seizure? With regard to CO2 build-up or hypoxia, I’m not sure what the results would be. At the end of the day, should we react to divers not watching their PO2 or maintaining gear, by forcing everyone to use what I see as an uncomfortable strap because it has saved a few lives? Or could the incident have been avoided in the first place?
–Lamar Hires, Founder and president Dive Rite
Inner Space Says Good For Jaw Fatigue
My experience with a head straps began in the military with Draeger LAR V (oxygen) rebreather. Their purpose was not to prevent drowning but to prevent jaw fatigue during the endless hours we spent in the water with a diver surface valve (DSV) in our mouth. You put it on and secured it. Did we always use it? No, and I was a Special Forces Combat Diver, Diving supervisor, and trained with Seal Team Five.
The Combat Diver school did not advocate the strap. I used it but didn’t think it was necessary. It was more in the way with a DSV. I did use a head strap for airborne operations when breathing hoses would flutter during the jump. I also used it with a scooter when hoses can also flutter. However, the LAR V does not have a bailout valve (BOV). I never advocated a strap as a diving supervisor, though I do think you should use one in airborne operations.
As I said, the head strap worked well for preventing jaw fatigue while diving. Also, the metal adjustment clasps on the Draeger strap worked great. I pondered whether to advocate and use a head strap when I started Inner Space. I think it is a good idea if you have a BOV. If you don’t it just slows down your gas switch. Also a lot of BOVs are big and heavy and can easily cause jaw fatigue so it is a good tool for that. In addition, if you passed out, it would aid in your rescue. It is a handy tool.
We looked at alternatives for preventing drowning. An old school half-facemask will prevent wet drowning. I have a good one from the fifties that seals around the mouth and buttons on the side. You still need a mouthpiece with it however to prevent CO2 build up. I think if the community got together it could create a new version of this for tech divers. The advantages are: no jaw fatigue, it seals around the mouth to prevent drowning in case the diver loses consciousness. It could be a little piece of insurance against wet drowning.
–Leon Scamahorn, founder and CEO Inner Space Systems
Note that Kirby Morgan Diving System makes half-mask called their M48 MOD-1 and the M48 SUPERMASK.
Rebreather Forum 3 (2012) Advocated Further Research
Mouthpiece retaining straps were addressed at Rebreather Forum 3, held in Orlando, Florida in 2012 and formed the basis (along with full face masks) of a Consensus Statement by the assembled body. See Rebreather Forum 3 Proceedings (pg 287-302).
Design and Testing 5. The forum identifies as a research question the issue of whether a mouthpiece-retaining strap would provide protection of the airway in an unconscious rebreather diver.
This is a unique statement as the only one in which we are proposing a research question to the research community. This arose out of Paul Haynes’ advocacy for the use of gag straps. In fact, the resulting discussion made it clear that here was a lot of ambiguity around people’s perceptions. To my knowledge, there are no data or even substantial practical experience that answers that question for us. This statement says, “The forum identifies as a research question the issue of whether a mouthpiece-retaining strap would provide protection of the airway in an unconscious diver.” We need to find a confident ethics committee or an imaginative way of figuring it out. Is there anyone who would like to speak to this?
PAUL RAYMAEKERS: I was not able to follow the presentation. I just hear that the question has no proof or any evidence that a mouthpiece-retaining strap has any efficiency. We did have a fatality a few years ago where it was clearly proven that when the jaw stress completely falls away, a correctly attached gag strap keeps the mouthpiece in place and no water comes into the driver’s lungs.
MITCHELL: If I am interpreting correctly saying there, there has been a case that you know of with a gag strap and mouthpiece [that stayed] in place. John, do you want to speak to this?
CLARKE: I think research would include looking at prior history. One case does not mean this has been solved.
FRANBERG: We come from the military community. I think that if we look at our own data from the fatalities, we may find information on the presence or absence of water in the airway.
MITCHELL: I like that idea. So, what we need is someone who has perhaps a Naval group with keen, young, research-hungry doctors who can start phoning up every navy in the world. My tongue in in my cheek. I have got a smile on my face. I think there probably may be enough information out there already to form this debate. We have just got to find it. It would be great to have that reported. If someone could compile the cases and report them, I think that would be a pretty powerful case. Is there anyone who objects to this statement in it’s current form? Carried as unanimously.
What Happened to Solid State Oxygen Sensors?
The news in 2016 that Poseidon Diving Systems would be incorporating a solid state oxygen sensor in their rebreathers sent a buzz through the rebreather community. Galvanic sensors, along with their legacy-1960s “voting logic” algorithms to boost reliability, had long been considered the weakest link in closed circuit rebreathers. Many heralded Poseidon’s subsequent 2017 roll-out as the dawn of a new era in rebreather safety. Five years later, Poseidon remains one of two companies (the other strictly military) to have adopted optical sensors. Technology reporter and tech diver Ashley Stewart examines some of the reasons why.
by Ashley Stewart.
Header image: Karst Underwater Research (KUR) rebreather divers at Weeki Wachee. Photo by Kirill Egorov
For years, it’s been said there’s a revolution coming for the closed-circuit rebreather— a new, more reliable, safer replacement for the traditional electro-galvanic oxygen sensor, widely considered the weakest component of rebreathers. In March 2017, that revolution looked to be just over the horizon. Poseidon Diving Systems began shipping an offboard solid state sensor to supplement the MKVI’s and SE7EN’s galvanic sensors and offered to license the technology to other manufacturers. Though Poseidon subsequently incorporated the solid state sensor into its SE7EN rebreathers, nearly five years have passed, and not much else has changed.
Poseidon remains the only manufacturer using solid state sensors in recreational rebreathers. No other companies have licensed Poseidon’s technology. Major tech diving manufacturers—including JJ-CCR and Divesoft—say they don’t believe the technology in general is ready for use in rebreathers. Some manufacturers worry that the sensors won’t function accurately in humid environments over a wide range of pressures, and they claim that addressing these challenges will be costly. Meanwhile, divers who tested Poseidon’s sensors offered mixed reviews, and even the inventor who sold the sensor validation technology patent to Poseidon believes they should be used along with traditional sensors. (Poseidon gives divers the option of combining the sensors).
Oxygen sensors are the enabling technology that made mixed gas rebreathers possible, replacing rebreathers that could only be used with pure oxygen. In 1968, marine scientist Walter Starck introduced the first commercial CCR, called the Electrolung, which used polarographic sensors. The next year, BioMarine Industries launched its CCR-1000, the predecessor of the US Navy’s Mk-15/16. The unit was the first mixed gas rebreather to use galvanic sensors, which do not require a power supply.
In addition to removing a diver’s exhaled carbon dioxide, a rebreather must measure and maintain a safe and efficient level of oxygen, as measured by the partial pressure of oxygen, or PO2, via oxygen sensors.
Measuring PO2 correctly is critical, and failures can be fatal. Too little oxygen can cause hypoxia and loss of consciousness, and too much can result in central nervous system toxicity and convulsions. Since sport divers began using CCRs over twenty years ago, both conditions have caused numerous drowning fatalities.
With the exception of Poseidon and military manufacturer Avon Underwater Systems, modern close circuit rebreathers have more or less used the same type of sensor since the 1960s. Rebreathers typically use three galvanic sensors, averaging the readings of the two closest sensors and ignoring the third in a protocol called “voting logic,” originally created by Starck in response to the sensors’ noted unreliability.
Even with this voting logic, however, the sensors can be unreliable (See “PO2 Sensor Redundancy” in Additional Resources below). The galvanic sensors are cheap and time-tested, but they need to be recalibrated before every dive and expire after about a year. The new sensors—called “solid state sensors” or optical sensors—are expected to be more precise, reliable, and durable, though significantly more costly.
Galvanic sensors are essentially wet-cell batteries that generate a millivolt current proportional to the PO2 in the loop. Conversely, Poseidon’s solid state sensor uses luminescent quenching, wherein a red LED light excites the underside of a special polymer surface, which is covered with a hydrophobic membrane and exposed to the gas in the breathing loop. A digital color meter then measures the responding change in fluorescence, which is dependent on oxygen pressure, and an algorithm calculates the PO2.
Experts more or less agree that the right solid state sensor could make rebreathers safer, but the market is split on whether the technology is ready for use in rebreathers and just how much better they’d have to be to justify the cost.
Field Test Results
Poseidon advertises its sensor as “factory-calibrated and absolute, delivering unsurpassed operating life, shelf life, and calibration stability.” Richard Pyle, a senior curator of ichthyology at Hawaii’s Bishop Museum who works with Poseidon-affiliated Stone Aerospace, has tested Poseidon’s sensors for years, initially as a passive offboard check against Poseidon’s traditional galvanic sensors. Later, in November 2019, he said he began testing Poseidon’s prototype with the solid state sensor as the primary sensor in the unit. “From my perspective as a rebreather diver, this is the most significant game-changing way to know what you are breathing,” Pyle said. “We will never go back to the old oxygen sensors.”
Pyle said he’s yet to fully analyze the data he’s collected to compare the performance of the solid state sensors against the galvanic sensors, but that he’s had zero failures with the solid state sensors in the time he would have expected to have 50 to 100 failures with the galvanic sensors.
Likewise, Brian Greene, a Bishop Museum researcher who has tested the Poseidon sensors with Pyle, estimated that he’s made hundreds of dives with the solid state sensors without failure. But, not everyone has had this experience.
Sonia Rowley, an assistant researcher at the Department of Earth Sciences in University of Hawai’i at Mānoa, told InDepth that she experienced a variety of repeated failures when testing Poseidon’s system alongside Pyle beginning in 2016 and 2017, and Rowley dictated to InDepth specific dive logs detailing many of the failures. She wrote about her experience in the book “Close Calls.”
Poseidon CEO Jonas Brandt said the company has tested the sensors since 2017 at different depths and temperatures, and that it has only seen one possible failure.
Arne Sieber is a sensor technology researcher who said he developed the O2 sensor validation technology used in the Poseidon rebreather and sold the patent to Poseidon. Sieber is now researching uses for the solid state sensor including in the medical market. He told InDepth he believes the best way to incorporate the solid state sensors into rebreathers would not be to substitute one for the other, but to combine sensor types and design a rebreather that incorporates both.
Traditional galvanic sensors have advantages over the solid state sensors, Sieber said—they’re cheap, simply designed, low-voltage, and time-tested. Also, while solid state sensors are very accurate at measuring low PO2, they become less sensitive at about 1.6 bar, and are more prone to incorrect readings of higher PO2 levels than galvanic sensors. As for whether the sensors can function in humid environments, Sieber said the sensors can work well in liquids, such as when used for blood analysis (though the sensors are used to measure much lower partial pressures of oxygen) and for measuring oxygen content in the sea. Liquid can delay the amount of time it takes a sensor to read a partial pressure, but it does not falsify the results, Sieber said. Of Poseidon’s system, Sieber said, “It’s a good start. It’s very important that someone starts. Someone always has to be the first one.”
Brandt said divers have the option of combining sensors in the company’s SE7EN rebreather, using either two galvanic sensors, two solid state sensors, or one of each, and said it could be argued that using one of each sensor is the most reliable.
Meanwhile, a catalyst may be coming to encourage the development and adoption of solid state sensors in Europe, Sieber said. European Union rules restrict the use of hazardous substances in electrical and electronic equipment, but galvanic sensors (which have an anode made of lead) have been granted an exemption in medical products because there is not a suitable alternative. The exemption is set to expire.
Poseidon’s solid state sensor sells to end users for as much as around $1,500USD, and its SE7EN rebreather units use a maximum of two onboard sensors. [Note: Poseidon sells the sensor for 6800SEK plus VAT from its website, which equates to 944 USD, some outlets in the states sell them for much higher]. Galvanic sensors, meanwhile, cost around $100USD, last one year and divers use three at a time. And, that’s just the cost of the sensors themselves: Manufacturers have to make significant investments in, and upgrades to, electronics systems to accommodate solid state sensors.
As for how long the sensors actually last, even the manufacturers don’t yet know. Poseidon has some from 2014, and they still work but have to be factory calibrated every two years. Galvanic sensors need to be replaced annually, while solid state sensors are expected to last much longer.
Brandt chalks the debate about its sensors up to competitiveness in the market. “I don’t think anyone likes that somebody cracked the nut,” Brandt told InDepth. Poseidon is ready to share the technology with other dive companies and manufacturers, Brandt said, but there have been no deals to date. “We wanted to raise the bar in technology and safety with the rebreathers, and to be honest, we haven’t said to anyone in this business that this technology is exclusive or proprietary.”
When the company first debuted its sensor, Brandt reported that companies like Hollis and Shearwater Research expressed interest in licensing the technology, but nothing has come so far of those discussions. Brandt did say one manufacturer reached out right before the pandemic. He declined to say which, but shared that it was a European company. Hollis brand manager Nick Hollis said his team recalls a conversation with Poseidon, but that it was back in 2014 or even earlier.
Shearwater director of sales and marketing Gabriel Pineda said the company is still interested in solid state sensors, but they see an issue with the price. “If you make the economic case of traditional galvanic sensors versus solid state or optical sensors, you have to dive a lot, and it takes a long time for these to make economic sense for a diver.”
Of course, Shearwater is not a CCR manufacturer, but the company is interested in seeing whether the sensors would be viable for use with its electronic control system that is used by a majority of rebreathers on the market. Shearwater currently has no immediate plans to license the technology from any manufacturer but Pineda said the interest remains.
Meanwhile, Poseidon’s solid state sensor CCR is still making headway, Brandt said. The current biggest buyer of the Poseidon units is the military (Brandt said three European Union countries’ forces are actively using the sensors). The sales have continued throughout the pandemic, and, over the past six months, Poseidon has started an upgrading program, allowing divers to add the new sensors to their old units. Poseidon is looking into a program Brandt compares to Apple Care, where customers can pay a fee for maintenance throughout the life of the sensor.
Meanwhile, Avon Underwater Systems is using three solid state sensors in its MCM100 military rebreather. Kevin Gurr, a rebreather designer and engineer who sold his company, VR Technology Ltd., to Avon, said the company uses the sensors “because of the increased safety and the decreased user burden as far as daily calibration.”
Gurr, who designed and produced the Ouroboris and Sentinel closed circuit rebreathers at his prior company VR Technologies Ltd., believes it’s the cost that has discouraged other manufacturers. “It shouldn’t be about cost at the end of the day,” Gurr said. “The digital interface is so much safer.”
Martin Parker, managing director of rebreather manufacturer AP Diving, said his company follows solid state sensor development but has yet to come across a sensor that meets its accuracy requirements. One such sensor using luminescence quenching can achieve good accuracy through a replacement disk the user must apply to the sensor surface after each use.
“Having been in the diving business for 50 years, we don’t believe it is on any diver’s wish list to have to re-apply every diving day a new component, as simple as that is to do,” Parker told InDepth. “With no easy external measure of accuracy prior to the dive, it is easy to foresee that many divers would ‘push their luck’ and use the discs for multiple days, then when they get away with it, they would encourage other divers to do the same… with the inherent risk of DCS or O2 toxicity.”
Parker said that he’s aware of two additional sensors under development, but neither has shown a working product yet. He declined to identify any of the manufacturers, citing commercial sensitivity. “Hopefully, we will get these to evaluate in the next 12 months,” Parker said.
Divesoft co-founder Aleš Procháska said he believes Poseidon’s approach to the sensor could “lead to success.” Speaking generally about solid state sensors rather than about Poseidon’s specifically, Procháska said his company isn’t yet utilizing solid state sensors because he believes the sensors are unable to function in humid environments with extreme water condensation and not applicable over a wide range of pressures. To be able to use one of these sensors in a rebreather, Divesoft wants it to be durable in high humidity, consume less energy, and have a good price-to-lifetime ratio.
“It is possible to build a CCR with the currently available O2 solid state sensor but not without sacrificing important properties of the breathing apparatus,” he said, such as size and energy. “Overall, the reasons why no one currently sells this technology on the market seems to be quite simple. It’s extremely difficult to come up with a suitable and functional principle that would lead to a cheap, small, and low energy consuming solid-state sensor. Despite this, I do believe that it’s only a matter of time until someone solves this one.” Asked via email about the status of DiveSoft’s own work on the technology, Procháska replied, “Well, as I said earlier, it’s just a matter of time,” adding the text, “Aleš smiles.”
Halcyon COO Mark Messersmith said that divers are slow to embrace new technologies in general, and the current sensors just aren’t deficient enough to merit widespread adoption or the investment from manufacturers. “It’s not unlike many other technologies,” Messersmith told InDepth. “People are often slow to embrace a new technology if the existing technology is functional. The existing tech needs to be vastly deficient, and existing oxygen sensors are still largely functional.”
The bottom line: Solid state sensors might very well be safer, but there isn’t enough incentive for the market to make them a reality.
David Thompson, designer of the JJ-CCR, told InDepth they don’t use the sensors because he doesn’t believe the technology is ready yet and research in that area is extremely expensive and difficult for what he believes is essentially a small market. “Analog cells have a long history, and in the right hands are very reliable, easily available, and have a long history of working in a rebreather environment which is very hostile,” Thompson said, adding that high humidity and temperature in a rebreather is a challenge for any sensor. “I am sure it will be in the future, but that future won’t be here yet.”
Rebreather Forum 3 Proceedings: PO2 Sensor Redundancy by Nigel A. Jones p. 193-202
Alert Diver: Oxygen Sensing in Rebreather Diving by Michael Menduno
Wikipedia: Electro-galvanic oxygen sensor
Ashley Stewart is a Seattle-based technology journalist and GUE Tech 1 diver. Reach her via email: firstname.lastname@example.org, Twitter: @ashannstew, or send a secure message via Signal: +1-425-344-8242.
Thank You to Our Sponsors
Top Tech Stories of 2021
We’d like to kick off the new year with a selection of 11 hand-curated stories from our deepening well of...