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Variable Gradient Model: An Approach To Create More Efficient Decompressions

British tech pioneer and inventor Kevin Gurr has been building dive computers since the early 1990s, including the world’s first mixed gas diving computer, the VR3, which he launched in 1997, through his former company VR Technology Ltd. based in Dorset, UK. He also designed and built three sport rebreathers. Now the Maritime Technology Officer at Avon Protection managing military rebreathers, Gurr discusses an innovative modification of gradient factors that he developed for use with his various devices.

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by Kevin Gurr

Header Image: by K. Davidson for Halcyon.

This article is not designed to go into the finite detail of decompression modeling; other people have achieved this far more successfully. It is intended as a snapshot view of what is currently available in Avon Protections’ MCM100 military rebreather, which I helped design, hopefully with a level of technical clarity so that the reader can evaluate for themselves the merits of the differing methods.

The human body cannot currently be mathematically modelled. Not only are individuals different because of age, fitness, pulmonary and cardiac (PFO) defects, but they also vary on a daily basis due to hydration, stress, exercise, micro-nuclei generation, and many other factors. 

So how does the diving community conduct thousands of safe dives per year? Some experimentation has historically been done to produce ‘reasonably safe’ decompression tables that ‘fit’ most people for a shallow water (primarily air diving) environment. In modern technical diving, much of the deeper diving we do is simply an extrapolation of the early shallow water research. We now know that this does not always work. 

Shallow water diving is relatively well documented and we have historical figures to work with, which  is only just starting to occur with deeper diving. Let’s review the basic decompression theory so that we may investigate possible ways to deal with the problem.

Consider the Buhlmann system of decompression: it is assumed that each of the hypothetical tissue compartments can safely experience an over-pressurization during a reduction in pressure (ascent) after a pressurized exposure (time at depth) which has allowed them to absorb gas.

The subsequent decompression profile that is generated on the ascent should not exceed the tolerated over-pressure value, or M value — a theoretical construct for the theoretical controlling tissue compartment within the body, in order to avoid decompression illness (DCI). As each compartment comes into play and the relevant M value is reached, a decompression stop profile is generated.

Figure 1 represents a very simplistic example involving just one of the fast tissues which will control the primary ascent phase. The M value for this compartment is shown as a straight line. If the diver controls the ascent, the inert gas loading in the compartment will stay on or below the M value line. If they do this, let’s assume they are using 100% of the available M value, which means there’s no extra safety margin for that dive; they are theoretically diving right on the edge of the model. 

Graph courtesy of Kevin Gurr.

For a typical bounce dive, Buhlmann standard practice has been to allow a rapid ascent to the first stop to generate a high level of off-gassing. Doing this, the gas loading in the fastest compartment will be on or near saturation at the bottom depth (the slow tissues are only partially saturated). This means that the fastest compartments will control the initial ascent since their gas loadings will be near or on the tolerated over-pressure value (M value). The first stop depth is set when the controlling (fast) compartment is nearest to the M value. The example only shows up to a point where the first stop starts and does not detail the other compartments or the remaining decompression. 

Using gradient factor terminology, the M value line is the 100/100 reference. The first 100 describes how close (in percentage) to the M value line the first stop is, and the second 100 describes how close the final stop is. Thus 100/100 has no added safety margin compared to the M value. In the complete picture, each compartments’ M value and each compartments’ internal pressure right through to the end of the dive (not just to the stop as drawn) would be displayed on the graph each with the same 100/100 gradient. The slower compartments would reach their M value during the final decompression phases while the faster compartments control the deeper decompression.

The gradient factor system modifies the M value by taking a percentage of the difference between the M value and the ambient pressure value. As a simple example to illustrate how Gradient factors work, using 80% of the M value as the controlling value (80/80 line) produces a line on the graph (figure 2) below the 100/100 line, having the effect of reducing the compartments allowed over-pressure value and generating a deeper decompression stop. 

Graph courtesy of Kevin Gurr.

Again, in the complete picture all the adjusted M values and compartment pressures would be plotted, adding safety to the whole decompression profile.

As most of these early dissolved gas based tables were formulated around relatively shallow water air range dives, they do not suit deep water dives, although historically they have often been extrapolated for use in deep-water. While these tables have a varying solution for different depths they were depth limited.

So what about Pyle stops? Technical diving pioneer, ichthyologist Richard Pyle developed a practical solution that divers could understand for modifying the decompression profile to reduce the excessive over-pressurization of the controlling compartment at the deep stops. He found that by stopping and venting a fish’s swim bladder below the first tabular stop depth, he ‘felt better’ at the end of the decompression. He was in effect allowing the faster compartments’ pressure to reduce before ascending to the tabular first stop and not reach its M value peak. 

The downside of this was that other compartments were still on-loading gas, which could generate an additional decompression obligation in shallow water. He was applying a safety factor that only had an effect on the deeper stops. This had the potential to allow the slower compartments to become closer to their M value during the shallow water decompression phase unless additional safety factors were applied.

Now we move onto bubble models (VPM etc.). Put very simply, bubble models attempt to explain the growth phases of inert gas bubbles and their subsequent effects. These models focus on the first part of the ascent where the bubbles grow, and by doing so, claim they can lead to a predicted reduction of the decompression obligation in shallow water. However, because of this decompression reduction, some dives generated decompression stress which could not be explained. In recent years, these bubble growth models have gone through several iterations as a result, and new evidence suggests that “deep stops” generated by bubble models may not be more efficient than shallower decompression.

A common (but complicated) solution to reduce the problem was to combine what was known about shallow water decompressions (Buhlmann) with the deep water bubble model. We know this is still an incomplete solution as phenomena such as arterial bubbles and other effects are not taken into account. Bubble models give an explanation and provide a working model of what Richard Pyle tried to implement practically from a technical divers standpoint. 

A recent tool, which provides a simpler solution between Buhlmann and the bubble models, has been to use gradient factors with a dissolved gas model which in turn modifies the M values of the controlling compartments (Baker). This has the effect of combining a bubble with a dissolved gas model style decompression profile.

Gradient factors can further mimic bubble models by using two different gradient factors to control the decompression: one that primarily references the deep stops, and one the shallow. 

So a 20/80 gradient factor, which has been commonly used on deeper dives, would allow an over-pressure value of 20% (instead of 100%) of the difference between the ambient pressure and the allowed M value for the controlling compartment of the first or “deep stop” and 80% (instead of 100%) of the M value for the controlling compartments’ pressure difference at the shallow stop. The stops in between are calculated by drawing an over-pressure value line between the two points and plotting the new adjusted M values for each compartment in between. It assumes a linear calculation between the adjusted first and last M values. 

In Figure 3 let’s assume that compartment 4 controls the deep stop and compartment 16 the shallow stop. Again, for clarity, the on-going compartment inert gas loading reductions are not shown past the M value point, neither are all the other compartment M values.

Graph courtesy of Kevin Gurr.

The major drawback of gradient factors is that the factors applied need to be adjusted for each depth/time exposure. For example, if you used the same 20/80 gradient factor for an 80 m dive, on a 30 m dive you might have an excess of decompression in shallow water because we know from experience that a gradient factor of close to 100/100 is reliable for this shallow water dive. 

What does this mean? First, it is not necessarily appropriate to apply one gradient factor to a range of dive depths. What works deep may not work shallow. Secondly, it means just applying gradient factors in the first place may be too coarse a solution. Just drawing a straight line between the M value points and assuming the mid-water decompression follows this linear approach may not work. So how do we generate a refinement?

Stochastic modelling has been around in diving for some time. Decompression tables are generated based on statistical dive data of incidents; basically, points are plotted on a graph and an algorithm generated. So how could we use this to improve gradient factor modelling? Assuming the 100/100 factor is OK for a certain shallow dive and the 20/80 is OK for a particular deep dive, would it not be best to have a varying gradient factor depending on depth/time exposure and other factors? If we can be fairly certain of key decompression times for a range of depth/time exposures that are ‘safe’ and generate reasonable decompressions, we could use them to generate a gradient factor that varies accordingly. My term for this approach is a Variable Gradient Model (VGM).

VGM has the ability to use stochastic data and historically ‘proven’ decompression values in an algorithm and automatically adjust it for a range of depth/time exposure scenarios. The VGM software can be embedded into the dive computer, for example, in the MCM100, and its parameters can be adjusted using the screen below. Note that I also used VGM in my previous company’s [VR Technology Ltd.] VRx computers.

The Ace, Ace Profile, VR3, VRx dive computers designed and built by Kevin Gurr, VR Technology Ltd.

In summary, a VGM profile has the effect of padding the stops at certain decompression points while reducing stop times at others for a specific exposure scenario. What’s more, it changes them again automatically for different exposure scenarios and allows varying degrees of user input dependent on the application. VGM is a useful tool based on our current culminated experience. It brings together in one approach much of what we know and may help predict some of that which we do not.

Once data is available, many other variables could be built into a VGM matrix, such that with time and information it could continuously evolve to give increasingly accurate decompression predictions. While the modelling of the human body eludes us, VGM would appear to be a good solution to the current issues.

Additional Resources:

REPROGRAMMING THE FUTURE: AN INTERVIEW WITH KEVIN GURR

 Gradient Factors in a Post-Deep Stops World by David Doolette.

DELVING DEEPER INTO DEEP STOPS By Mark Powell


Kevin Gurr has been involved with Technical Diving since its inception in Europe. As well as being the first Technical Diving instructor outside the USA, he has led and been a part of many expeditions; the first sport dives on the Britannic in 1997, treasure hunting in the Pacific (and several other locations World-wide), filmmaking, and a dive on the Titanic in the MIR submarines to name a few.

As an engineer and diver he has developed several ground breaking products for the diving industry from trimix computers to rebreathers, including the Ace Profile, VR3, VRx computers, Pro Planner desktop decompression software, and the Ouroboros, Sentinel, Explorer and the MCM100 rebreathers. He lives in Dorset, England with wife Mandy, daughters Leyla and Amberlee, Neo the black Labrador, and various motorcycles.



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Examining Early Technical Diving Deaths: The aquaCORPS Incident Reports (1992-1996)

The early days of technical diving were marred by an alarming number of fatalities that threatened the viability of this emerging form of diving. Here InDepth editor-in-chief Michael Menduno presents the original accident analyses of 44 incidents that resulted in 39 fatalities and 12 injuries, as reported in aquaCORPS Journal and technicalDIVER in the early to mid 1990s.

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By Michael Menduno

Unlike the military and commercial diving communities, which made the transition to mixed gas technology with the benefit of deep pockets, extensive infrastructure, and tightly controlled diving operations, the sports diving community’s adoption of mixed and rebreather technology was largely a do-it-yourself venture.  

We began reporting on these accidents in my magazine aquaCORPS Journal and its sister publication technicalDIVER in 1992 and continued until our final issue in January 1996. We tried to include all of the tech diving accidents that occurred in between issues, though there were undoubtedly incidents that were not reported. We formalized these in a column titled, “Incident Reports,” which first appeared in aquaCORPS #6 COMPUTING (1993) and quickly became the best-read section of the magazine. 

The reports were based on the accident analysis approach pioneered by famed explorer Sheck Exley in his book, Basic Cave Diving: A Blueprint for Survival, which is available as a free download from the National Speleological Society Cave Diving Section. I did much of the reporting, but we also received reports from Dr. RW Bill Hamilton, Dr. Bill Stone, Rob Palmer, Jim Bowden, Dr. Ann Kristovich, Denny Willis, and others.

Our goal, which was arguably in line with what human factor’s experts like Gareth Lock call “Just Culture,” was to present an objective, non-judgmental report of what went wrong, leaving out the names of the divers involved, so that we could all learn from others’ mistakes and experience. However, divers in three high profile accidents were named in reports published by aquaCORPS. They were Chris and Chrissie Rouse (1992), the subject of Bernie Chowdhury’s book, The Last Dive (2000); British cave diver Ian Roland (1994), who was part of Dr. Bill Stone’s Sistema Huautla expedition; and Sheck Exley (1994), whose accident report was reprinted in aquaCORPS with permission from the Undersea Hyperbaric Medical Society’s newsletter, Pressure.  

Arguably, though extremely valuable, this type of reporting is largely absent today and would likely be very difficult to conduct in today’s litigious environment. [See “The Case for an Independent Investigation & Testing Laboratory,” by John Clarke in InDepth 1.11]. In total, we reported on 42 incidents, 11 of which were non-fatal and six involving two or more deaths, for a total of 38 fatalities.

Though accidents typically involve numerous factors, some broad observations can be drawn from the reports.

  • 15/44 incidents (34%) involved “deep air” diving, which was still a thing for much of the 1990s
  • 10/44 (23%) involved breathing the wrong mix at depth. At the time, protocols for cylinder labeling and gas switching were not standardized
  • 5/44 (11%) involved “out of gas” incidents
  • 3/44 (7%) involved lack of training
  • 3/44 (7%) involved omitted decompression

The community was painfully aware of these incidents, and various efforts, including promoting “best practices”—for example through aquaCORPS’s “Blueprint for Survival 2.0” (an update of Exley’s  recommendations for mixed gas diving), improved training, and the creation of operational diving standards such as Woodville Karst Plains Project’s (WKPP) and later Global Underwater Explorers (GUE) DIR standards—were advanced to improve diving safety. By the mid- to late-1990s, it seemed as if tech diving safety had improved.

Not surprising, in all but two of the incidents presented, divers were using open-circuit scuba. There were only a small number of rebreathers available in the technical diving community during the early and mid-1990s. Rebreather use started growing in earnest in the late 1990s with the introduction of AP Diving’s “Inspiration,” the first production line sport rebreather in 1997, and the original KISS rebreather in 1998, which were soon followed by others.

Along with the growth of units, rebreather fatalities also grew, creating a second wave of tech diving fatalities beginning in the 2000s. In 2012, hyperbaric physician and rebreather diver Andrew Fock presented the findings of his research on rebreather fatalities, titled “Killing Them Softly,” at the Rebreather Forum 3.0 held in Orlando, Florida. Fock concluded that the risk of dying on a rebreather was 10 times that of open-circuit scuba. 

His paper, “Analysis of Recreational Closed-Circuit Rebreather Deaths 1998-2010,” was published in 2013 in Diving and Hyperbaric Medicine. From 1998-2018, there were approximately 313 fatalities, or an average of about 16 deaths per year. This average has improved slightly (14.8 per year) from 2013-2018, while rebreather use is seen  to have grown. The belief today among the community is that rebreather safety has improved—Michael Menduno

The aquaCORPS Incident Reports (1992-1996)

Here are the early technical diving incidents as reported in aquaCORPS and technicalDIVER.

technicalDIVER 3.2 (1992)

June 1992

“U-Who” Boat, New Jersey—An East Coast wreck diver blew up to the surface as a result of operational problems while diving trimix on the newly discovered, unidentified New Jersey U-boat, the “U-Who” at 66 m/215 ft. The diver  omitted about 30 minutes of decompression and suffered decompression illness during his evacuation. According to onsite observers, the diver, who had completed a trimix course, was “grossly overweighted and was diving new equipment including stage bottles that he was not well practiced with.” On descent, the diver missed the anchor line, got separated  from his partner, and sank straight to the bottom at about 66 m/215 ft, missing the wreck. Rather than trying to surface immediately or send up a lift bag indicating “diver in distress,” the diver searched for the wreck on the bottom under low visibility conditions, and he burned through approximately 200 cubic feet (cf) of gas/5,660 liters (l) in less than 10 minutes. Out of bottom mix, lost, overweighted with no ascent line, and unable to gain sufficient buoyancy with his drysuit or back mounted wings, the diver elected to ditch his weight belt and blew to the surface switching to his EAN 50 decompression gas fsw on the way up.

The diver showed no symptoms of decompression sickness upon surfacing and was immediately put on surface oxygen. He was evacuated by a Coast Guard chopper which did not have any oxygen onboard. Unfortunately, he wasn’t packed with an O2 cylinder and manifested symptoms in flight. Upon landing, he was successfully treated with a single Table 6. Clearly, this incident was a “blow up” and cannot be counted as a traditional DCI case. To date, there appears to have been only one known incident of decompression illness involving trimix in approximately 500-600 recent U.S. “technical” dives.

July 1992

Alachua Sink, Florida—A newly trained cave diver got lost in the cavern zone after being separated from the team’s line in zero visibility conditions at Alachua Sink and drowned. His partner survived. Instead of following the permanent line which begins at a log in the basin, the team ran a reel during the evening dive in order to make their way down through the sloping cavern zone to the main tunnel. The basin had near zero visibility conditions due to the seasonal algae bloom which usually clears up at about 40 m/130 ft at the upstream/downstream tunnel junction. About 18-23 m/60-80 ft into the dive, the team realized they had missed the main tunnel. After searching for the tunnel for several minutes in 1 m/3-4 ft visibility, they decided to tum the dive and lost visual and physical contact with each  other. The surviving partner reeled in believing his partner was ahead of him on the line. Reaching the surface alone and realizing his partner was still in the water, he attempted numerous line searches in order to locate the diver without success, and went for help. Though the lost diver had several hours of gas in his double 95’s he was unable to find his way up and out of the funnel-shaped cavern zone. A contributing factor may have been that he was only carrying a 50-foot “jump reel” rather than the 150-foot safety reel recommended by the cave diving training agencies. Ironically, if the dive had been conducted during the day, observers speculate that it should have been easy to find a way out.

Alachua Sink is considered an advanced dive by experienced cave divers due to low visibility conditions, depth, and the arduous climb out of the water. Most divers wait for the winter season to make the dive because of the low visibility in the basin during the spring and summer. Due to the poor conditions, it took threeand-a-half days for teams to recover the body, which was found wedged in the ceiling of the cavern.

Andrea Doria, New York—An experienced diver wearing double over-pressurized 72’s “ran out of gas” while making his eleventh penetration dive on the Andrea Doria (73 m/240 ft). His partner, who entered the water with a “half-filled” set of steel 120s—insufficient gas to safely make the dive—survived. Both were breathing trimix though neither was formally trained in its use. The team was separated during a penetration in the wreck. When the surviving partner exited at 67 m/220 ft with only several hundred psi remaining in his doubles and found his age bottles clipped off near the anchor line, his partner was nowhere to be found. The body was later recovered. His tanks were empty. A close friend who had trained with the diver reported that the diver had had problems managing his gas on several prior occasions. What’s more was that the diver was using trimix as a suit inflation gas in the chill  45 degrees Fahrenheit/7 degrees Celsius water which was possibly a contributing factor in the accident, one that could have impaired the diver’s judgment.

Andrea Doria, New York—Two weeks later another trained, experienced diver drowned after getting separated from the mainline during a wreck penetration on the Doria while the team worked as planned at two different places within the wreck. Though the trimix used to conduct the operation was a big safety factor, analysts on site believe the diver left the line to explore just a little further for artifacts before making his planned exit—contrary to the dive plan. He wasn’t running a gap reel. In addition, his primary light apparently failed, leaving only a single dim secondary light to exit the silted wreck. This probably added to his confusion. Lost in the wreck, he ran out of gas and drowned before the team was able to locate him. His body was later recovered at 65 m/230 ft. Though he was a cave-trained police diver who regularly dived solo and had been trained in mix, he did not have extensive wreck penetration experience and had gotten slightly disoriented on their previous dive. Sadly, the diver apparently told his partner prior to the dive that he just had to bring home a Doria artifact for his pregnant wife.

Arundo, New Jersey—A very experienced deep wreck diver knowingly dived beyond the NOAA oxygen limits while conducting an enriched air dive on the Arundo (42 m/135 ft), when he suffered an oxygen seizure and drowned. The diver was breathing an EAN 40 (40% O2, balance nitrogen). This mix had a rated Maximum Operating Depth or MOD of 87 f/27m (at a partial pressure of oxygen or PO2 of 1.45). However, the deck of the wreck is at 34m/110 ft with a maximum depth of 42m/132 ft, resulting in a PO2 of 1.7-2.0 atm which is well above the CNS toxicity threshold.

The diver had told others in the past that he didn’t follow the NOAA guidelines as he believed they were too conservative. An individual who knew the diver well believed he was probably diving the USN’s exceptional exposure limits for oxygen which are generally not considered conservative enough.

In one case, the diver recommended that another follow his example (After all, diving air at 250 fsw is a PO2 of 1.8 atm. No problem!). The problem is that CNS toxicity is a function of both PO2 time and other factors, many of which are not well understood. His body was found approximately 45-50 minutes into the dive with regulator out of his mouth and 1500 psi on his doubles. Maximum depth on his computer was 41 m/132 ft.

Chester Polling, MassachusettsAn experienced 45-year-old wreck diver suddenly lost consciousness during a 52 m/170 ft air dive on the Chester Polling and drowned in the arms of his partner. The exact cause of his death is unknown. The team descended on the “near virgin” wreck at 43-52 m/140-170 ft for what had been planned to be a short first dive of the day, leaving their inflatable boat unattended but anchored into the wreck. Conditions were good, and there was no current. About 10-15 minutes into the dive, the surviving partner called the dive and began to ascend to the bow at 43 m/140 ft to free their anchor.

The diver drifted back down to the bottom briefly for one more sweep of the area. When he returned to their ascent line, he didn’t look right to his partner who signaled, “OK?” The diver signaled, “NOnot OK,” but didn’t indicate what was wrong. His partner grabbed him by the harness to maintain contact during their ascent. As they ascended, the diver began moving his arms and legs and then his legs went limp at about 27 m/90 ft. At 24 m/80 ft, his regulator fell out of his mouth and the diver lost consciousness. 

The surviving partner was freaked and tried to resuscitate the diver without success. At 5 m/15 ft, the surviving partner elected to complete a portion of his decompression before surfacing, removed the diver’s weight belt, inflated his BC, and pushed him to the surface. There was no surface support person or anyone on their boat. The surviving partner completed about five  minutes of air decompression, surfaced, and went on oxygen. A nearby sailboat had picked up the drowned diver and had radioed the Coast Guard station which was only a few minutes away. CPR was applied to no avail. There were no life signs. The diver was evacuated to the hospital and pronounced dead. The autopsy stated the cause of death was drowning. It is highly unlikely that the event was an oxygen convulsion (a P02 of 1.26 atm at low to moderate work levels). The diver had no previous history of cardiac problems and was reportedly in great shape.

Ginnie Springs, Florida—A trained cave diver lost consciousness and drowned while making an enriched air stage dive at Devil’s Eye at Ginnie Springs. His partner survived. The multilevel dive was conducted using air as a travel mix and a bottom mix of EAN 40. The maximum depth of the dive was 32 m/104 ft. The dive team staged into the system on an aluminum 80 cf/2,264 l air stage which was breathed for approximately 15 minutes into the dive before the switch to EAN 40. About 60 minutes into the dive, the surviving partner turned to see the other diver stop and to begin shaking before losing consciousness and spitting the regulator out of his mouth. His partner tried unsuccessfully to resuscitate the diver and then attempted to swim the unconscious diver out of the cave. Soon realizing that his efforts were futile, the surviving diver exited the cave to get help. The body was recovered a short time later by a recovery team.

Investigators believe that an oxygen seizure was the cause of death. Though PO2s for most of the multilevel dive were at or below 1.4 atm (25 m/83 ft on EAN 40), due to the configuration of the cave, there were multi-minute portions of the dive with PO2s as high as 1.5-1.7 atm (29-32 m/95-105 ft) placing the profile outside of the NOAA Oxygen Limits (a maximum P02 of 1.6 atm) which are based on moderate diver work levels. The team was reported to be swimming hard in the upstream system, which would have resulted in CO2 buildup and possibly increased the diver’s sensitivity to convulsion. The family refused an autopsy.

La Jolla Canyon, California—Two untrained recreational divers reportedly died in La Jolla Canyon attempting to beat their personal best depth records of 61 m/200 ft which they had made in the Canyon the week before using recreational scuba equipment. Their goal was to hit 76 m/250 ft. Apparently, neither of the divers had training or experience at these depths and had not done prior work-up dives. According to newspaper reports, when questioned by friends about their “record” dive the previous weekend, one of the friends said the divers got narked “big time,” and rather than dangerous or stupid, they believed their continuing push for depth was “cool.” Both of the divers were recreational divemasters. One of the divers had just received his divemaster certification earlier that month.

La Jolla Canyon begins about 130 m/450 ft offshore in 14 m/45 ft of water and quickly drops through a series of slopes and ledges to about 91 m/300 ft. The team apparently swam out alone sometime in the afternoon, covering probably about 549-732 m/600-800 yards on the surface (probably building up CO2 levels) before dropping into the canyon. They were conducting the dive on single aluminum 80’s without a stage or a pony bottle, and there was no descent/ascent line or surface support personnel. (Assuming a conservative surface consumption rate of 0.75-1.0 cf/min. [21-28 l/min] the transit to and from depth would have required between 30-40 cf/849-1,1132 l for each diver not including time on the bottom, decompression requirements, their surface swim, or reserves in the event of an emergency.) Since their bodies were never recovered and there were no witnesses, we can only speculate as to their dive and the exact events that led to their deaths.

Lake Jocassee, South Carolina—An experienced cave diver suffered an oxygen seizure during decompression following a special mix open water dive to 300 f/91m in Lake Jocassee, South Carolina, was treated for freshwater drowning and luckily survived due to excellent top-side support.

Utilizing a pair of large inflatables for surface support, safety divers, and a continuous ascent/decompression line system, the 8-minute planned jump to 91 m/300 ft was conducted on trimix 14/33 (14% oxygen, 33% He, balance N2. Max. working PO2 = 1.41 atm) with two intermediate mixes, an EAN 32 (@130 f/40m) and an EAN 60 (@ 60 f/18m) to be followed by surface supplied oxygen at 6 m/20 ft. Backup oxygen bottles were carried by team members. Total planned decompression time was 61 minutes. 

Prior to reaching the 6 m/20 ft oxygen stop, PO2‘s on the dive were at or below about 1.4 atm with the exception of 2 minutes at/37-40 m/120-130 ft (PO2 = 1.5-1.6 atm), and 6 minutes at 50-60 f/15-18m (PO2 = 1.5-1.7) during the intermediate gas switches. The dive team discussed and dismissed the need for “air breaks” (the practice of breathing air for 5 minutes every 20-25 minutes during oxygen decompression which greatly reduces sensitivity to convulsions) as unnecessary during the oxygen decompression phase of the dive due to the short time (36 minutes) involved.

The dive proceeded as planned without incident until about 20 minutes into the oxygen decompression. The diver unclipped from the decompression line, switching to his oxygen stage, in order to swim over and check on a second team on a nearby compression line on the second support boat. He did not communicate what he was doing to his partner, who lost visual contact with the diver as soon as he swam off. Swimming slowly, the diver lost some buoyancy, drifted down about 11 m/35 ft (PO2 = 2.06) and he believes he dozed off for several moments due to his excessive fatigue. He startled awake when his breathing became abnormal and quickly checked his depth as the onslaught of oxygen toxicity began. 

Fortunately, experience took over. Holding his regulator in his mouth with one hand, he hit his power inflator with the other as the seizure began. His actions saved his life. As he ascended uncontrolled, he was aware of losing his regulator at about 3 m/10 ft and hit the surface convulsing, face down, and helpless before losing consciousness. The diver was rescued within moments of surfacing by the team’s support personnel. His breathing had stopped. CPR was applied, and the diver was resuscitated. He was soon evacuated to a nearby hospital, treated for freshwater drowning, and recovered.

Though the diver’s profile would normally be considered light from an oxygen tolerance perspective, the short spike to 11 m/35 ft coupled with the lack of an “air break” apparently led to trouble. Extenuating circumstances appear to be his condition before making the dive. A paramedic by profession, the diver had just come off of a 4-hour shift and had less than 2 hours of sleep the night before the dive. Fluid intake had been minimal and little food had been consumed over the previous 14 hours. Diver fatigue was believed to be the main factor in the accident.

August 1992

Andrea Doria, New YorkA very experienced cave diver omitted approximately 68 minutes of decompression rather than executing a “free-floating” hang while conducting a solo air dive on the Andrea Doria and suffered a severe case of decompression illness. The diver was wearing double 104 pumped with air and an oxygen stage bottle for decompression, and there was a surface-supplied O2 system on board. Apparently, the dive had gone near picture-perfect in the 10-12 ft. visibility water when the diver’s guideline broke at his turn, and he was swept off the wreck by the heavy current. After spending precious minutes swimming hard at about 58 m/190 ft to regain the wreck and find the anchor line, the diver was forced to begin his ascent due to his dwindling gas supplies. In the resulting confusion, he neglected to deploy the reel and lift bag that he was carrying. He ascended without a line and completed his 15 m/50 ft stop and ascended to 12 m/40 ft at which point he had minimal air in his doubles. 

At that point, the diver reported he did not think of using his upline and bag and elected to surface rather than to ascend and pull his oxygen decompression free-floating in the current and risk getting separated from the boat. Upon surfacing his computer showed 31 minutes of runtime. The onset of symptoms was immediate and severe and progressed to include nausea, vomiting, and vertigo. Oxygen and fluids were administered immediately by a fellow diver and RN, and the diver was evacuated for treatment by helicopter. Reportedly, he spent nearly 40 hours in the chamber and was released with a slight deficit in his left leg.

aquaCORPS #5 BENT INCIDENT REPORTS (1993)

Double Fatality on the “U-Who”[U-869]On October 12, 1992, two highly experienced cave divers, Chris Rouse and Chris Rouse Jr., died exploring a U-boat wreck known as the “U-Who” off the shore of New Jersey. Both were trained in deep diving on air and mixed gases. This accident has had a major impact on the technical diving community. A formal report is being prepared, but aquaCORPS felt it important that a preliminary report be issued at this time.

The Rouses were diving with double 104’s filled with air for their travel and bottom mix. Each diver also carried an 80cf/11 l aluminum tank of 60% oxygen-enriched air intermediate decompression mix, and a 72 cf/8-liter steel tank of 100% oxygen.

After clipping off three of the four stage bottles (probably one EAN and two oxygen) near the anchor line, they proceeded to their point of penetration where a tie off was made and the 4th stage bottle (of EAN) was clipped. Shortly after entering the wreck Chris Jr. was trapped by falling debris; loosened silt reduced the visibility to nearly zero. Chris Sr. entered or was already just inside the wreck and began to dig out Chris Jr., further reducing the visibility. After Chris Jr. was freed, the two divers were unable to follow their line out; according to statements by Chris Jr., and examination of their equipment, they evidently began exploring with line for a new exit. During their exit, it appears Chris Jr. experienced some trouble with his primary regulator and switched to his secondary regulator, but it was taking in water. At this time Chris Sr. gave Chris Jr. his secondary regulator and they continued out of the wreck. After finding the exit, Chris Jr. noted it had taken 31 minutes for them to get out, 11 minutes longer then their planned bottom time. They were able to locate only one stage bottle (EAN60) and were so low on air with no more time at depth to search for the anchor line or the remaining bottles they left for the surface. They may have attempted some decompression in mid-water.

They arrived at the surface 41 minutes into the dive. Chris Sr. had limited use of his arms and hands. His eyes were glassy and he appeared calm but confused. While being assisted by surface help he went into respiratory failure, and 20 minutes later cardiac failure occurred. CPR was started immediately and continued to the hospital (approximately 3.5 hours later). He was pronounced dead on arrival at Bronx Municipal Hospital. While at the surface, Chris Rouse Jr. was hit by the tossing boat and his DIN adapter was sheared off the manifold; he lost a large amount of air before surface help could close the valve. He was quite alert on the surface, yelling about the ordeal, but he was paralyzed and had no feeling from the waist down. After reaching the hospital, he was placed in the chamber on USN Treatment Table 6A, during which he reportedly regained some feeling in his legs along with an increased level of pain. Early in the first air break at 1.9 atm (30 fsw), his heart stopped and resuscitation was unsuccessful.

Their bottom timer displayed a max depth of 68 m/223 ft for 41 minutes. Chris’s air tanks had 250 psi, and Chris Jr. had 150 psi. The one stage bottle recovered had 1200 psi. The investigation into this accident is still ongoing and a detailed report is being prepared for publication. Readers are reminded that hasty conclusions may be premature. Submitted by Denny Willis. Willis is a NAU/Instructor (#6988) and has been teaching since 1976.

aquaCORPS #6 Computing INCIDENT REPORTS (1993)

February 1993

Botany Bay, Australia—A diver experienced an out-of-gas emergency as a result of equipment failure, lost buoyancy control during descent, and blew to the surface following an 18-minute, 64 m/207 ft air dive on the SS Woniora, omitting 44 minutes of decompression. The surface support team returned the diver to the water within 5 minutes for in-water oxygen therapy beginning at 6 m/20 ft. After completing 30 minutes of oxygen decompression at 6 m/20 ft, she ascended to 3 m/10 ft where she completed an additional 30 minutes. She surfaced without apparent symptoms, was placed on surface oxygen, and evacuated to a hyperbaric center, which was 30 minutes away. 

The diver presented mild neurological decompression illness on admission and was treated on an USN Table 6 with two follow-up treatments of two hours each at 9 m/30 ft on subsequent days. She was discharged three days later with no apparent residual symptoms. Although in-water therapy was not condoned by hyperbaric officials, they stated that the diver probably would have presented in a far more serious condition had it not been carried out. Submitted by Rob Cason, Fun Dive Centre, Sidney, Australia. 

March 1993

Merida, Mexico—A full cave and nitrox instructor suffered an oxygen convulsion during a deep air dive in a sinkhole in Mexico and drowned. His partner, who experienced CNS toxicity warning signs during the dive, and a safety diver survived. The two later recovered the body. 

The team had planned a 20-minute air dive in excess of 71 m/230 ft—the depth of the saltwater halocline—in a cavernous open-water sinkhole near Merida on the Yucatan Peninsula. Because of the difficulty in obtaining helium mixes in Mexico, the team decided to conduct the dive on air followed by oxygen for decompression. Both were experienced deep divers. A weighted descent line was rigged for navigation and for staging oxygen and extra air cylinders. The safety diver was to descend with the team to 67 m/220 ft, ascend to a shallower depth and wait for the dive team.

After a long, slow descent past the halocline, the team tied into the descent line to explore the well at a leisurely pace. Informed sources estimated their maximum depth to be close to 91 m/300 ft (A PO2 in excess of 2.0 atmed.). The surviving partner experienced a tingling in his lower lip and turned back to call the dive only to see the diver headed back as well. When he reached the line, he sensed that the diver was in trouble. The diver grabbed the line and began a hurried hand-over-hand ascent. The partner reached the diver, gained control, and they began to ascend together. The diver continued to pull on the line creating slack and getting himself tangled. His partner cut him free. The diver then darted, got tangled again, and apparently convulsed. By the time his partner reached him the diver’s regulator was out of his mouth. At that point they were still deeper than 71 m/230 ft. After repeated attempts to force the regulator back into the diver’s mouth with no success, the surviving partner realized the diver was gone and, leaving the body entangled in the line, ascended to complete his decompression. Following decompression, the partner and safety diver were able to pull up the line and recover the body. 

March 1993 

Pompano Beach, Florida—An experienced 47-year-old spearfisherman apparently switched to his oxygen regulator by mistake while chasing down a grouper at about 68 m/220 ft during a deep air dive, convulsed, and drowned. He was found on the railing of the RB Johnson with his regulator out of his mouth by his partner, who was reportedly diving trimix. The body was later recovered by the charter boat captain. 

The diver was wearing twin “independently configured” 100 cubic foot cylinders, and an oxygen pony for decompression. Using this configuration, a diver must repeatedly switch regulators during the dive in order to balance the gas supplies. Though the diver used a distinct oxygen regulator which was labeled in green, his primary, secondary, and oxygen regulators were banded together and mounted over his right shoulder. It is believed he mistakenly switched to his oxygen regulator in the heat of the chase (A PO2 of 7-8 atm), having speared his first grouper at 74 m/240 ft earlier in the dive. He convulsed, spitting the regulator out of his mouth, and drowned. Vomit and blood were found in his mask. 

May 1993 

St. Croix, US Virgin Islands—A deep air diver was reported missing and is presumed dead after he failed to return from an afternoon solo dive. The diver had been training for some time in hopes of setting a new record for deep air diving and had spoken about his plans to several individuals in the States who tried to dissuade him. According to local observers, the diver had made air dives in the 144-160 m/470-520 ft range, qualifying him for some kind of record. 

The diver was last seen late on a Wednesday afternoon when he typically made solo dives. Later, friends found his car parked near the dive site, Twin Palms, and reported him missing when he did not show up by 9:30 pm. The local dive store apparently said he went out at 4 PM. Search divers were unable to find the body. Excerpted from Compuserve and the Virgin Island Daily News.

May 1993

Key West, Florida—A diver mistakenly switched to his “labeled and color-coded” oxygen regulator instead of EAN 36 at his 28 m/90 ft decompression stop following a 25-minute exposure to 64 m/210 ft conducted on trimix 17/50. The diver seized approximately 4 minutes later at his 21 m/70 ft stop during the mix training dive and spit his regulator out of his mouth. 

A second diver was on the scene in seconds and, unable to reinsert the regulator and having a substantial decompression obligation, inflated the diver’s BCD and sent him to the surface. The diver was picked up immediately by the surface support crew and displayed faint irregular breathing. He was cut out of his equipment, lifted on the boat, and placed on oxygen when he became semi-conscious. Emergency evacuation procedures were initiated and the boat left to rendezvous with an ambulance dockside about 50 minutes away. 

The diver regained full consciousness within about 15 minutes and did not exhibit DCI symptoms. He was evacuated from the hospital to a chamber within an hour and a half. Still not exhibiting symptoms, he was treated with a Table 6. The diver has little memory of events following his/27 m/90 ft stop until regaining consciousness at the surface. Apparently, his only warning was a vague feeling that something was wrong after switching to O2. Reported by Key West Diver Inc. 

aquaCORPS #7 C2 INCIDENT REPORTS (1994)

July 1993 

South Coast of England—An experienced wreck diver failed to surface following an air dive to 58 m/190 ft on the Merchant Royal and is assumed dead. The diver had become separated from her partner on the wreck who surfaced with the minimum required decompression and raised the alarm. Though visibility was excellent, the body was never found during the ensuing two-day search. The diver had been wearing twin 12-liter independent cylinders (about 200 cf/5,660 l) and a pony with decompression gas. She dived regularly to these depths and was reported to be a strong dependable diver. Submitted by Simon & Polly Tapson, London, England.

August 1993 

Sydney, Australia—A wreck diver lost consciousness during a 15-minute deep air dive to 78 m/254 ft on the paddle tug Koputai and drowned. The diver lost consciousness while returning to the anchor line after a 15-minute planned bottom time to make his ascent. Though his three partners attempted to ascend with the diver in tow, they were unable to maintain a regulator in his mouth and he subsequently drowned. The team preceded to lift the unconscious diver to 15 m/50 ft and released him to the surface. Surface support personnel radioed for emergency assistance/evacuation. 

The diver did not regain consciousness and was pronounced dead a short time later. Though the Coroner’s report has not been released, CNS toxicity (working PO2= 1.85 atm) compounded by possible CO2 build-up and narcosis—characteristic of deep air dives—is suspected as the primary causal factor. The incident raised government concerns about local deep diving practices. Though mix training has just gotten started in Australia, most deep dives are still conducted on air. Submitted by Richard Taylor, Sydney, Australia. 

September 1993 

Little River, Florida —A novice cave diver ran out of gas and drowned on a solo dive in the Little River cave system. The diver was found with no air in either of his independent 104 tanks about 1300 feet back in the cave on the mainline. Though the individual frequently made solo dives he was not diving with a buddy bottle.

The diver was known to use “creative” gas management rules outside of the basic tenets of cave diving, and on at least one occasion had explained the gas management strategy he utilized to a group of cave students. Basically, the diver reserved sufficient gas to exit from known points in the cave using the outflow in the system. The problem is that liberalized gas management rules such as this leave no margin for error or the unexpected compared to the golden “rule of thirds” or better (i.e. use at least 1/3 of your gas for penetration and exit on the remaining 2/3).

Members of the recovery team speculate that the diver ventured into an unfamiliar part of the cave and got lost in the low, silty tunnels and “tees.” Having silted out the area, the diver spent precious time searching for the main line connection and likely missed the tee on the way back. Eventually he found his way to the line, but it was too late. A long time aquaCorps subscriber, he had renewed his subscription only a week before.

September 1993 

Wakulla County, Florida—A very experienced 24-year-old cave diver lost consciousness and drowned while negotiating a restriction on the way back to the team’s decompression stages following a deep mix exploration push to about 66 m/220 ft with a planned bottom time of 120 minutes. 

The inbound leg of the dive, which was the latest in a series of progressive pushes intended to connect several major sinks, had gone as scheduled. The team of three reached the end of the line in good time and added about 800 feet of line (7800 feet back at a depth of about 66 m/220 ft) when the diver unexpectedly called the dive. The team turned for home. Upon reaching their staging area, the lead diver turned to see the diver tangled in the line struggling with his stage. The third diver freed him and they continued, although the diver appeared shaken. 

As the diver negotiated the shortcut restriction at about 61 m/200 ft deep and 2000 feet back in the cave, then his scooter prop caught and ate the line, halting his forward motion and pinned him between the floor and the ceiling just as his stage bottle ran out of gas. He flashed an Out-of-Gas signal to the lead diver, who responded with his long hose. Thinking the diver was out of gas (he actually had 1000 psi in his 104s and 1000 psi in his other stage), the lead diver passed him a stage bottle. The diver gave back the long hose and jettisoned his old stage. At this point the cave silted up and the lead diver lost visual contact.

From the rear, the third diver saw his teammate wedged in the restriction and initiated touch contact as the cave silted out. The third diver squeezed his leg to indicate “Go” and the diver kicked. He backed off then squeezed again, with no response. He tried to pry him free and at some point, realized the diver was dead. The third diver unclipped his scooter and stage bottles and was able to squeeze around the unconscious diver in the cloud of silt and made physical contact with the lead diver. Silted out and under the time constraints of their gas supply, the remaining two divers linked up and motored back to the safety of the decompression bottles. The two had about six hours of decompression remaining.

The incident generated serious discussion in the cave community regarding the role of a dive team and how much push is too much. Reportedly the deceased diver couldn’t sleep the night before, had ill feelings about the dive, and exhibited anxiety. He told at least one person that this was the last of these dives he would do. It was reported that the diver was “off” that day and that he may have chosen to go ahead so as not to miss the “big” dive and lose status.

October 1993

Honduras—A novice deep diver lost consciousness and drowned during a “deep air” wall dive beyond 92 m/300 ft. The diver and his two partners, all experienced recreational instructors, were attending a combination charter and week-long seminar on “Advanced Diving,” and had been conducting progressively deeper air dives between 61-91 m/200-300 ft during the week. Though the boat apparently had a “You’re on your own” policy, a mix instructor on the cruise made a “deep air” dive with the team to about 77 m/250 ft to check them out and give them pointers on their technique. He reported that based on their skills, he discouraged them from diving deeper. The captain was concerned as well. In fact, a fourth diver associated with the team was reportedly asked not to dive deep or his trip would be curtailed.

The divers were utilizing dual independently rigged 80 cf/11-liter cylinders and decompressing on air (oxygen was apparently not available). The dive was planned for 5 minutes to 91 m/300 ft using USN Exceptional Exposure Tables with backup tables to 15 minutes. The diver was carrying a video camera to film the team’s escapades and was the only member of the team with a decompression tool—a computer—for depths beyond 91 m/300 ft.

According to one of the team, the group overstayed their planned bottom time by a minute or so, and then the diver and one partner began to drift further down the wall (beyond 91 m/300 ft). Having emptied his first cylinder “unexpectedly” (the divers did not switch regulators during the dive to balance their gas supply) and feeling that the dive “was starting to go wrong,” the shallow member of the team executed a “rocket ascent” (of 100 fpm or more) that he had learned in the course to “get out of the danger zone,” and ascended to his first stop. Apparently, moments later, the first diver lost consciousness somewhere around 99-107 m/325-350 ft. His partner began to haul him up using his BCD for added buoyancy when one of his single cylinders also ran out of gas. He lost his grip on the unconscious diver while switching regulators and due to buoyancy differences was separated from the diver. Short on gas he ascended and survived. The diver’s body was never recovered off the wall. 

October 1993

Pompano Beach, Florida—A diver experienced what appeared to be the first onslaught of a CNS oxygen toxicity hit during an air dive to 70 m/228 ft on the RV Johnson, was able to make a rapid ascent to about 32 m/105 ft, and survived. The diver and two others descended towards the wreck in order to set the anchor. Missing the wreck, and being deeper than they had planned, the divers began a hard swim at about 70 m/228 ft (PO2 =1.66 atm) for about 5 minutes out of what was planned to be a 10-minute bottom time. He reached the mast at 58 m/190 ft and tied off the anchor.

As he was working, he got a severe pain in his molar, his lip began twitching, and his jaw started chattering. Feeling a convulsion coming on, he held his regulator in his mouth, tried to signal to his partners, and hit his BCD inflator just as he began to lose his vision and experience a mild convulsion. The symptoms began to clear during the rapid ascent, and he was able to regain control at about 35-37 m/115-120 ft and stopped himself at about 32 m/105 ft. The diver was then able to pull himself together. 

He completed his scheduled decompression and included a 20 f/6 m oxygen “hedge” stop on EAN 80 (80% O2, balance N2). He surfaced without incident. An extenuating factor may have been the prescription decongestant, Entex LA. The drug had been used by the diver at recommended doses during the preceding week of diving. He had previously bought a regulator retainer strap but “forgot” to bring it that day. According to the Divers Alert network (DAN) there is no data to link the drug to the incident.

October 1993 

High Springs, Florida, — An experienced cave diver lost consciousness at the start of a pleasure cave dive at Devil’s Ear in Ginnie Springs and drowned. The dive was intended to be a fun dive to practice scooter techniques. The team of two mounted their double stage bottles and scooters and descended into the “Ear” of the cave against the normal outflow. The lead diver went through the first restriction after exchanging OKs with his partner, who appeared preoccupied. The lead diver got to the “Lips” of the cave about 61 m/200 ft into the cave, turned, and waited. The diver, his dive buddy, wasn’t there. Not seeing any  lights, he turned and backtracked and found the diver unconscious with his regulator out of his mouth in about 30 to 40 feet of water.

The diver was immediately brought to the surface, CPR was initiated, and the diver was flown to Shands Hospital where he was placed on life support but never regained consciousness, and was pronounced dead the following morning. The Coroner’s report didn’t shed light on the cause of his trauma. He had no history of heart problems, no predisposing medical conditions, and no signs of embolism. Individuals can only guess that the diver had a serious problem, turned to exit following the floor of the cave, missed the exit, lost consciousness and drowned.

aquaCORPS #8 HARD INCIDENT REPORTS (1994)

March 1994

Huautla Expedition Fatality Report: On March 27, 1994, British cave diver Ian Roland died whilst exploring the terminal sump in the Sótana de San Agustín cave, part of the Systema Huautla, in Oaxaca, Mexico. A member of the expedition team, Roland was diving the prototype rebreather system under development by Bill Stone.

At 8 AM  on the 27th, Roland  had dived from Camp Five for a 380 m/1246 ft penetration. Dive time was 53 minutes at a maximum depth of 26 m/85 ft. At 11 AM  Kenny Broad continued the exploration, surfacing in a large air bell at 430 m/1410 ft. The chamber was approx. 20 meters wide and 20 meters high (66 ft by 66 ft) with large sandbars. There was no sound of running water or air movement. Kenny returned to base without exiting the water. At 4 PM  Roland set out to explore the chamber. He estimated a return time of three hours but said not to worry for six. 

At 7 PM Broad, concerned by Roland’s absence, began to assemble the second rebreather rig. At 10 PM  he set out to Camp Three to alert the support party. They returned to Camp Five in due course and completed the assembly and checking of the second rig. At 12:15 AM on March 28, Broad began the dive through the chamber. He carried emergency medical supplies (Roland was diabetic), food, and bivouac equipment. At 12:41 AM he surfaced in the chamber and noted footprints on the sandbar. He swam alongside the bar, in clear water, and continued beyond its end for 10 m/33 ft at which point he located Roland’s body resting on its right side. Resuscitation was futile.

Broad noted that the line reel appeared to have fallen out of Roland’s hand. Four out of five tanks were full, and the control system was functional. The mouthpiece was in closed position and out of the mouth. The O2 “setpoint” was 0.5 atmospheres; the O2 control valve was in manual shutoff position and the PO2 was 0.17 atmospheres (heliox 14/86). There was no sign of struggle or distress. The body was recovered by team members, assisted by Mexican cavers and members of a British expedition, in an operation which took six days.

Observations during the recovery showed that the control system was still active, and the heads up and buddy displays were both flashing red, indicating PO2 below 0.21 atm. The left diluent tank was empty. Black box data records that were retrieved from the rig show that the tank was emptied over a seven-minute interval following Roland’s loss of the mouthpiece as the rig attempted to maintain counterlung volume. Functional tests were made on the rig back at the base. All systems were operational and within specification. 

Roland had eaten a normal breakfast in the morning but was suffering from mild diarrhea. He had taken two food bars which were not eaten. There was no sign that he had doffed and donned the rig when leaving the water. These items had a combined weight of approximately 140 pounds, therefore traversing the air bell would have involved a significant exertion. The oxygen injector unit on the rig was manually switched off. This is a common procedure upon surfacing in order to conserve oxygen. Normal procedure would have been to re-enable the unit upon re-entering the water.

Given that Roland’s  rebreather appeared to be fully functional, it was initially presumed that his  death was due to operator error based on the closed position of the O2 valve. However, black box data clearly indicated that at the time of what was apparently an uncontrolled descent from the surface to 2.8 m/9 ft, the PO2 of the breathing mix was 0.24 atm, i.e. not hypoxic, indicating Roland’s blackout was due to some other cause. The observed PO2 of 0.17 atm resulted from purging of the gas processor with 14/86 heliox during the descent. Its subsequent stability at 0.17 atm indicates that Roland was not breathing from the rig following initiation of the descent.

Based on his dive line, it was clear that Roland was returning to the sandbar from the head of Sump 2 after apparently realizing something was wrong. Given that Roland was a diabetic and had not recently eaten, and that heavy exercise and mental impairment were present (evidenced by the failure to re-enable to O2 valve), it has been concluded that the blackout was caused by hypoglycemia and/or related events, such as arrhythmia or seizure. Roland was an extremely meticulous cave diver and had logged more than 60 hours on rebreathers. He was, however, a recently-diagnosed diabetic and did not have a blood sugar glucose test kit in the cave. Submitted by Rob Parker and Bill Stone. 

March 1994

Sydney, Australia—A very experienced technical diver, PADI and NAUI instructor and ANDI nitrox instructor trainer, mistakenly breathed his EAN 50 (50% O2, balance nitrogen) decompression mix during a wreck dive to 50 m/165 ft (PO2 = 3.0) on the wreck of the Coolooli and convulsed and drowned 18 minutes into the dive. Efforts to resuscitate the 47-year-old diver were unsuccessful.

The diver was diving air supplemented with an EAN 50 mix for decompression—a common practice among Sydney wreck divers. Reportedly, the diver carried both his bottom and decompression mix on his back and ran both through a switchable manifold block. Several colleagues apparently talked about the shortcomings of this configuration with the diver without success. An analysis of the contents of the tanks showed that the diver breathed EAN50 during the duration of the dive. He convulsed just as he and his two dive partners began their ascent.

April 1994 

Abaco, The Bahamas—Three untrained open water divers ran out of gas and drowned in the Big Boil Blue Hole cave system. None of the divers were cavern or cave certified.

It was reported that the three divers entered the low and silty Big Boil cave with only two guidelines. Two of the divers carried single 72 cf/8-liter tanks. The third carried a single 80 cf/11-liter tank. The team leader, who reportedly had “dived Big Boil many times before,” made the dive without a depth gauge, BC, knife, or redundant second stage. The team apparently made about a 46 m/150 ft penetration to a depth of 23 m/75 ft.

Two of the bodies were recovered on the main line at what is believed to have been their point of maximum penetration. One of the divers was tangled in the line. After an extensive search, the body of the team leader was located in a restricted side passage approximately 46 m/150 ft off the main line. Submitted by Al Pertner.

May 1994 

Grand Bahamas—Two very experienced divers who were not cave certified got lost in a popular Blue Hole during a liveaboard dive trip, ran out of gas, and drowned. Neither diver was running a line or carrying multiple lights. One of the divers was found within 30 m/100 ft of the cavern zone in about 28 m/90 ft. The second body was recovered by a cave recovery team the next day at about 122 m/400 ft from the cave entrance in about 37 m/120 ft of water. Both were wearing single 80 cf/11-liter tanks. It is not known if the bodies were separated by the tidal flow in the system or if the team had been separated during the dive.

The cavern zone at the site is often dived by recreational divers from a liveaboard. A partner of one of the deceased who was on the dive boat believed that the two “had no intention of making a cave dive,” and in fact, had left line reels on the boat. One of the divers was going shell collecting. The other was apparently planning to shoot video. The partner believes that the two got intrigued and ventured out of the cavern zone into the cave system. Ironically, the two were considered the most experienced divers on the liveaboard trip. One of the divers was a former commercial and military diver who was open circuit mix trained, and who had worked as a divemaster with a technical diving operation. The other was a dive store owner, a 20-year instructor who was in the process of completing a cave course.

June 1994

Scituate, Rhode Island, USA—My son Jonathan asked if he could scuba in our backyard pool. Jon is almost 12 years old and has been using scuba in the pool for two years. I didn’t really want to, but after his relentless asking, I gave in. It was around 7 PM so instead of using his usual 30 cf/849 l pony bottle, I grabbed a yellow 14 cf/396 l pony for him from the stack. He geared up and we went in the pool.

I sat on the diving board as Jon entered the low end of the pool. My younger son Byron sat on the stairs. Jon went underwater and, after a few minutes, something seemed wrong. I went to the low end of the pool and Byron shouted, “Something’s wrong, Dad.” Byron grabbed the skimmer pole and poked Jon, who was floating face down. He didn’t respond. I jumped in the water and pulled him up. He was blue and not breathing. I got him out of the pool onto the deck and started CPR. He had a pulse but was not breathing. After rescue breathing for what seemed like an eternity, I was able to restore his breathing. My wife Jean had called 911 (U.S. emergency hotline) and the rescue personnel arrived several minutes later.

As I was explaining what happened to one of the rescue team, I looked into the pool and saw the yellow 14 cf/396 l pony floating where Jon had been. Then it struck me like a ton of bricks. When I first started using argon gas for suit inflation, I committed a cardinal sin: I failed to paint the bottle brown or to properly label it as containing argon. After obtaining a proper argon bottle, I thought I had drained the pony, but I hadn’t. Somehow I had it mixed up with my other pony bottles. When Jonathan went diving, I had picked that bottle out of the stack. It was lack of caution, and it almost cost me my son. Thank goodness, Jonathan has completely recovered with no lasting effects.

It is of the utmost importance that all types of gases be properly marked, that the required types of values and regulators be used, and that different gases be stored independently of each other [Note that Compressed Gas Association [CGA] conventions require that special connectors be used for each type of gas to avoid mix-upsed.]. I consider myself a careful and responsible person, however negligence, whether intentional or not, can be deadly in our sport. If writing this letter averts just one tragedy, then the horror we went through will not be in vain. Submitted by Bill Delmonico, Scituate, Rhode Island.
aquaCORPS #9 Wreckers Incident Reports (1995)

April 1994

What Happened To Sheck Exley?

by Bill Hamilton, Gordon Daughtery, Ann Kristovich, and Jim Bowden. Excerpted with permission from the Undersea Hyperbaric Medical Society’s newsletter, Pressure.  

On April 6, 1994, well-known and much-respected cave diver and explorer Sheck Exley died attempting to reach the bottom of the Zacatón sinkhole in northeastern Mexico. This physiological analysis relates the conditions and events of the dive as well as we can reconstruct them, and it speculates on possible causes of his death. It is neither intended to endorse or glorify record-setting exploration nor to judge it in any way; that stands on its own merits as the prerogative of the explorers. These are the facts of the case as well as we can put them together, plus some speculation. 

Exley, 45, died while exploring a sinkhole, or cenote, at Zacatón, located in northeastern Mexico, not far from Mante, the site of his previous record dives. At a depth of 332 m/1080 ft or more, Zacatón may be the deepest water-filled pit in the world. Exley was diving with Jim Bowden as part of Bowden’s “El Proyecto de Buceo Profundo” project. On the day of the fatal dive, Bowden and Exley dived independently, but at the same time and with similar techniques. 

Bowden and Exley descended on separate weighted guidelines 25 to 30 feet apart. Bowden started a few seconds before Exley; the descent was expected to take 10 to 12 minutes. The divers kept track of the line visually. From a decompression and gas management point of view, the more rapid the descent the better, but a rapid descent potentially may exacerbate the effect of High Pressure Nervous Syndrome (HPNS) (See aquaCORPS Journal N8, “High pressure nervous Syndrome,” by R.W. Bill Hamilton). Both divers had experienced HPNS symptoms on previous dives and planned to slow their descents to less than about 100 ft/min (30 m/min.) at about 229 m/680 ft. Air was breathed by both divers to 92 m/290 ft at which point Exley paused to “stage” his air cylinder by clipping it to the line at 290 ft. Bowden used a small pony cylinder carried on his back as his air supply. The divers switched to a “travel” mix, trimix 10.5/50 (10.5% O2, 50% He, bal. N2), for the descent from 89-179 m/290 to 580 ft. 

Both Bowden and Exley selected a bottom mix that would produce a tolerable PO2 of less than 2.0 atm and an equivalent narcosis depth (END, the equivalent depth on air) of 84 m/274 ft at 298 m/970 ft. These levels were accepted by both divers since the exposure to maximum depth would be brief. (Note that a higher PO2 would minimize the lengthy decompression at the cost of increasing the risk of CNS oxygen toxicity. Technical divers are recommended to run their working PO2s at less than 1.4 atm. See aquaCORPS N7, “Blueprint for Survival Revisited”ed.) Bowden used trimix 6.4/31 and Exley used trimix 6/29 (mixed by adding helium to air). Both divers used gas from the back-mounted bottom mix supply to fill their buoyancy compensators (BCs). 

Sheck carried a total of about 369 cf of bottom mix in two large back-mounted tanks. He also had two side-mounted tanks (aluminum “80s” filled to 3600 psi) of trimix 10.5/50. Jim carried 426 cf of trimix 6.4/31 in two back-mounted tanks and in one-side mounted aluminum “80” tank. A second side-mounted “80” tank contained trimix 10.5/50. Tanks filled with specific decompression mixtures had been staged on each individual’s descent line during the two days prior to the dive. The extended decompression called for mixes of air, enriched air nitrox, argon-oxygen, and oxygen. 

It is difficult to overemphasize the importance of gas management and careful gas planning for a dive of this magnitude. At 30 atmospheres (970 ft/298 m) the amount of gas in a normal 72cf scuba tank is reduced to less than 2.5 effective cubic feet—good for 2 or 3 minutes, less if exercising. Bowden and Exley followed a rigorous pattern of breathing, taking slow, deep breaths at a practiced rate in order to optimize the tradeoff between excess gas consumption and hypoventilation—which leads to CO2 buildup. A small change in the breathing pattern, especially in rate, can quickly alter usage calculations. 

Bowden checked his gas volume at about 268 m/874 ft. He had expected to have approximately 1800 psi (pounds per square inch) at this point and had only 1000. He realized the need to turn the dive and arrested his descent at the 276 m/898 ft mark. On the line during decompression, Bowden observed Exley’s unused decompression tanks and correctly assumed that Exley had not survived. The support team realized this 18 minutes into the dive when the trail of bubbles on Sheck’s line disappeared. Bowden completed his nine-plus hours of decompression, surfaced with shoulder pain, and was treated with oxygen, corticosteroids, and hydration. 

The post-dive analysis does not adequately explain the shortage of gas. In December 1993, Bowden dove to 238 m/776 ft in the same system, confirming his anticipated gas usage, as had previous dives to 222 m/722 ft and 150 m/489 ft. Sheck’s gas usage in an earlier dive in Bushmansgat confirmed that his gas management technique was adequate. 

Bowden concedes that even a slight elevation in breathing rate, beyond his practiced 5-6 breaths/min, would account for the added gas consumption on this dive. Both divers had planned to slow their descents at 209 m/679 ft using their BCs, which consumed precious bottom mix. Additionally, Exley, who had started the dive with less volume than Bowden, slowed at 84 m/291 ft to drop his air tank used in the initial stage of the dive. 

The day after the dive, topside team member Kristovich and others returned to recover equipment from both lines. Exley’s was heavy with his staged steel tanks, and plans were made to raise the entire line with a pulley assist from the surface. Two days later, during this process, Exley’s body surfaced. The line was wrapped several times around both arms and the valves of his side-mounted bottles. Entanglement did not involve the back-mounted bottles, valves, mounting plate, or BC. His mask and all other equipment were in place. He did not have a regulator in his mouth. His BC contained gas and the inflator was functional. His wrist-mounted dive computer revealed a maximum depth of 270 m/879 ft. The gauge for his back-mounted tanks read 500 psi, the lowest pressure that would effectively supply gas to the diver’s regulator at bottom depth. One regulator of his two side-mounted tanks was unhooked, and the pressure was 500 psi. The second tank had 3600 psi and the regulator was stowed. A later analysis of the gases for the oxygen component revealed accuracy in the expected mixes. An autopsy was ordered but nothing reported explained the accident. Three days passed since his death, and that combined with the effects of immediate decompression made a confident postmortem analysis difficult. 

What went wrong?

We will never know for sure. Most likely, Exley reached a point where he was unable to inflate his BC mechanically with compressed gas and wrapped the line around himself to stabilize himself while sorting things out. His maximum depth was 270 m/879 ft. Exley may have ascended to 23 m/75 feet or more, but that cannot be determined for certain from the recovered line, since it was cut during removal from the water. The manner in which the line was wrapped around his upper body makes it unlikely that the entanglement could have happened accidentally, even if a convulsion had occurred. Exley’s experience level makes this unlikely as well. 

If we accept this, the primary  uncertainty is why or how he became so low on gas. It was not like Exley to fail to check his gas supply, but the physiological stress of the rapid compression (HPNS) could have occupied him enough that he was not aware of his situation until it was too late. The equivalent narcotic depth of his mix was approximately 75 m/242 ft at a depth of 270 m/879 ft, an air depth easily within his comfort level, but also a potential contributor to the probable cascade of problems. The gas density was 14 g/l at this depth, the equivalent of breathing air at 106 m/334 ft. Resistance to breathing plus intentional slow breathing undoubtedly resulted in an increased level of CO2, possibly high enough to impair performance.

Exley had used some of his trimix 10.5/50 travel mix for the descent, but would not have consumed gas down to 500 psi on that portion of the dive. The travel mix could have been lost to free flow, but more likely Exley breathed it when the supply of trimix 6/29 was exhausted. This was a “hot” mix at 270 m/879 ft, where the pO2 would be 2.9 atm; the equivalent narcosis depth was 130 m/423 ft, and the gas density 21 g/l, equivalent to breathing air at 154 m/487 ft. It could have been breathed during a quick ascent if everything else were under control. However, with the contributing factors of the neurological hyperactivity due to HPNS, his exertion, and an inevitable CO2 buildup, it is possible that central nervous system (CNS) oxygen toxicity caused incapacitation or a convulsion. A phenomenon known as “deep water blackout” has caused many divers under less stress to lose consciousness without convulsing. Its exact physiological course, including the cause, is not known. 

In addition, equipment failure cannot be entirely ruled out. A free flow of the primary regulator at depth would have contributed to a very rapid loss of volume and consequent reduction of vital gas reserves. 

Conclusions

The most likely sequence of events was that Exley got behind on his gas management, ran low on bottom gas, and could not control his buoyancy so could not ascend. The cause is not clear, but a combination of factors could include stress of HPNS exacerbated by the narcotic effects of nitrogen and CO2. He stabilized his position by wrapping his descent line around his arms, was forced to switch to his trimix 10.5/50 at a depth of at least 246 m/800 ft, and was subsequently incapacitated by the prevailing conditions of HPNS, hyperoxia, exertion, CO2 buildup, and nitrogen narcosis.

The accident could have occurred as a physiological consequence of an illness, known or unknown, that could lead to death or incapacitation on any day in an individual involved in strenuous activity. Likewise, mechanical failure, such as something that could cause unexpectedly fast gas consumption or loss, cannot be ruled out. 

R.W. Bill Hamilton, PhD, is a physiologist and editor of Pressure. C.G. Daugherty, MD, is a diving doctor specializing in occupational medicine. Ann Kristovich, DDS, is an oral surgeon and diver and medical officer for the Zacatón project. Jim Bowden is a diving instructor at the University of Texas and produced much of the material used in this article. 

July 1994 

Bakerton Mine, Harpers Ferry, West Virginia—A certified cave diver apparently embolized and died when his DPV trigger stuck in the “on” position, dragging him to the ceiling of the cave following a gas switch from trimix to air at a depth of 61 m/200 ft on the return leg of an exploration run. Prior to the switch, the diver had drained his doubles—violating the “thirds rule”—and was forced to share gas with his partner and swim for safety when his reserve cylinder regulator failed to function, the regulator hose being too short to permit scootering. 

The team’s objective was to explore beyond the end of the existing permanent line at approximately 503 m/1650 ft at a depth of 88 m/285 ft. The team began the dive by motoring in 274 m/900 ft to a depth of 61 m/200 ft, where they switched from air to trimix. The dive continued to a landmark known as “The Rock” at a depth of 78 m/250 ft at 366 m/1200 ft. At this point the cave sloped to 83 m/270 ft over a distance of several hundred feet (around 61 meters). The diver dropped his DPV due to the limited depth rating of the vehicle and swam as his partner slowly motored along. The end of the line was reached without incident at a depth of 86 m/285 ft and the team added another 46 m/150 ft of line to a depth of 94 m/305 ft. The dive was called and the exit began. 

The team returned to the staged DPV at 83 m/270 ft, at which point the diver attempted to switch to his reserve cylinder, his doubles being empty. Apparently, his regulator would not deliver any gas. Realizing there was a problem, his partner handed the diver a regulator from one of his two trimix stage bottles. However, the short hose made it impossible to motor so the team swam their DPVs back to The Rock. At this point, the diver switched back to his air stage, and the team motored approximately 91 m/300 ft up the ledge to the big room at a depth of 61 m/200 ft. 

Once they entered the room, his partner felt a DPV blast and saw a flash of light. He turned to find the diver unconscious on the ceiling—the DPV running circles around him. The trigger was stuck “on.” There was blood in the diver’s mask. He cut away the DPV and tried to hold a regulator in the diver’s mouth with no response. The partner then attempted to tow him out but had to leave the diver to complete his own decompression. 

The recovery team had no problems locating and extracting the body. All equipment was functioning properly, including all regulators. The doubles were empty and the single 80 cf with trimix was full with the regulator working properly.

The diver had a reputation for violating the thirds rule, had previously run out of gas on at least three cave dives, and had experienced deep water blackout (where a deep air diver is rendered unconscious) at 65 m/210 ft, while switching from bottom mix to air during a previous dive to the site and survived. An astute dive partner held his regulator in his mouth until he regained consciousness. 

August 1994 

Lusitania, Kinsale, IrelandTwo months after the Tapson expedition was completed without incident, a 37-year-old diver blew up to the surface from a 86 m/280 ft trimix dive on the RMS Lusitania, incurring severe injuries. 

After descending to the wreck, the diver’s partner began to lay line from a descent line. The two became separated when the diver’s stage cylinder came undone from his harness. He tried unsuccessfully to reattach the cylinder and, in the process, became severely entangled in the line. He then dropped a cutting tool that he had intended to use to disentangle himself. His partner returned to assist and cut him free, but the diver apparently panicked and blew up to the surface legs first. He was diving a trimix 12/26 (12% O2, 26% He, balance N2) and his surface-to-surface interval was about 12 minutes. 

The injured diver was flown to the Naval recompression chamber at Haulbowline near Cork, Ireland. On arrival, the injured diver was weak but moving all limbs with good preservation of cortical function and absolutely no evidence of pulmonary barotrauma. His condition continued to worsen, and he was treated with little success. 

The diver had been certified for nitrox and trimix diving less than four months before his accident, and he had been advised by his instructor that his experience level was insufficient to attempt the Lusitania in 1994 without more experience. It is unknown whether the diver, who is now a quadriplegic, will ever walk again. 

aquaCORPS #10 Imaging INCIDENT REPORTS (1995)

October 1994 

US Detroit, Lake Huron, MichiganA deep-wreck diver made an emergency ascent from a depth greater than 61 m/200 ft and got severely bent during a mix dive on the  US Detroit, a paddle wheeler sunk in 1854. The injured diver had ten years’ experience diving deep wrecks in the Great Lakes, having logged 200-300 dives, according to one of his companions. The Detroit was discovered last year and lies 18 miles offshore in an area of Michigan known as The Thumb. 

The diver was using trimix and independent doubles. He switched tanks and regulators when one of his regulators began to free flow. The diver decided to make an emergency ascent to an oxygen supply staged at 6 m/20 ft for decompression, but ascended to the surface instead. The support crew administered oxygen and called a Coast Guard helicopter for medical evacuation. The diver underwent repeated recompression treatments and is walking today, but suffers residual damage from the incident.

Ethel-C, Virginia—A diver died during a charter expedition to the freighter Ethel-C, sunk in 1960 off the Virginia coast. The 33-year old diver experienced a problem during his final decompression stop on the second dive of the day, lost consciousness, and sank when other divers could neither inflate his BCD nor hang onto him. His body has not been recovered. 

The former military diver was reportedly in good physical condition and had extensive experience diving, although he had not done deep diving previously. He and two partners were diving air on the wreck, which rests at 57 m/185 ft depth with the deck at 52 m/170 ft. On both dives of the day, the team descended to 57 m/185 ft for a minute, then ascended to 52 m/170 ft for 19 minutes. A decompression schedule of three minutes at 9 m/30 ft on air, six minutes on O2 at 6m/20 ft and 18 minutes on O2 at 3 m/10 ft was followed. The divers had a five-hour surface interval between the two dives. 

After about 2 minutes into their 13 m/10 ft dive, the diver’s head fell and his regulator came out of his mouth. One of his two partners came to assist, but the other was not in the vicinity, apparently following a different decompression schedule. The partner tried unsuccessfully to inflate his BC using a power inflator button, but for an unknown reason could not, and was having difficulty holding onto the unconscious diver, who was not clipped to the station. Another diver came to assist and the partner ascended to the surface to notify the boat crew of the problem. The assisting diver could neither inflate the BC nor hold onto the diver, who sunk to the bottom. The surviving partner suffered decompression illness and had to be flown out by helicopter for treatment. 

Neither the partner nor the assisting diver tried to remove the diver’s weight belt, and the partner did not attempt to orally inflate the BC. While the reason the BC did not inflate is unknown, one member of the group speculated that either the diver left his power inflator hose detached intentionally, without informing his partner, or could have run out of air, although the other divers believe he had 1000 psi remaining in his tank. One report attributed the death to O2 seizure, while another theory is that the diver suffered from a heart condition called Prinzmetal’s angina, which has been linked to other diving incidents. 

April 1995 

Maya Cenote, Mexico—Two experienced cave divers ran out of air and died after missing a turn while trying to exit a cave dive in Mexico. The two were among a group of seven cave divers who had broken into three teams for a 45-minute dive on air at depths no greater than 18 m/60 ft. The pair was on the third team to enter the cave. Besides making an incorrect turn while trying to exit, the divers failed to use safety reels to mark a jump and apparently missed or disregarded a series of line markers pointing the direction to the exit. 

On their way into the cave, all three teams used a main tunnel known as B. They passed in sequence through a T-turn, where the divers expected a jump. However, instead the cave came to a T, with three line markers marking the correct direction to turn while returning to go to the exit. A member of the second team repositioned one of the markers to make it more visible.

The third team into the cave called their dive earliest as planned, since the first two teams were stronger swimmers and wanted to penetrate further. The two divers then headed back, but turned in the wrong direction at the T, apparently missing all three line markers at the spot. Their mistake led them 91 m/300 ft to the end of B tunnel, where another route leads to the A tunnel. The divers headed into the A tunnel, which also led to an exit, crossing a visual gap without setting up a safety reel to mark their path.

The divers then made a series of errors, apparently missing several indicators that should have told them that they were following a different path than the one they’d taken in. The divers made it to the end of the line marking the start of the A tunnel, about 30 feet from an exit. Rather than exiting, the team headed back into the A tunnel, passing as many as 14 line markers pointing back toward the entrance they’d just left. The divers then swam past the unmarked jump which might have led them back to the other dive teams. 

When the third team did not return from the dive, the other five divers notified local authorities and asked for help. Later that day, the divers returned to the cave and recovered the bodies of the two divers. Their moves were reconstructed by the other members of the team, one of whom had entered the A tunnel after completing his dive in an attempt to find the missing divers. He noticed silt at the entrance, indicating that the missing team had recently been there, but because of low air had to turn back before going far enough into the tunnel to find them. One of the divers who died was 38 and had made between 75 and 100 cave dives; the other was 45 and had some 150 cave dives. 

Correction

In the incident report from Maya Cenote, Mexico, we have two clarifications: (1) It is not known whether or not the deceased divers actually made it to the end of the A line; (2) The recovery team, not the divers from the original group, re-enacted the dive the following day. 

aquaCORPS #11 Xplorers INCIDENT REPORTS (1995)

May 1995 

Lake Wazee Brockway, Wisconsin—A 32-year-old cave diver is believed to have overexerted himself, narked out, and drowned during a 61 m/200 ft plus air dive in an open-pit iron mine quarry. The diver had separated from his partner during a deep air class dive that was planned for 46 m/150 ft.

The maximum depth limit of the four-person class was set at 55 m/180 ft by the instructor, but the diver and his partner had apparently planned to “sneak off” and dive to 61 m/200 ft. Visibility was about 6 m/20 ft. The two separated from the class as soon as the dive began, and the instructor remained with the two less experienced students. The pair then traveled close to 500 feet in doubles and twin stage bottles in 12-14 minutes in order to reach the deep section of the quarry, several hundred feet of which was beyond 55 m/180 ft. 

The surviving diver then turned the dive, thinking his partner was with him. He ascended to about 49 m/160 ft, realized his partner was not following, descended back to 58 m/190 ft, and tried to signal to the diver with his light. However, the two had lost contact. The partner was found drowned at 65 m/213 ft with gas in his tanks. Calculations suggest the diver was breathing at about 2 cf/min (56 l/min) surface equivalent. Reportedly, the deceased diver had abandoned his partner during a previous class dive and had a reputation for wanting to go deep. 

June 1995 

Matterhorn, Channel Islands, California— A cave diver, 7 to 8 minutes into his dive at approximately 92 m-plus/300 ft on the Matterhorn seamount, apparently drained his 72 cf/8-liter stage of trimix and switched back to the air in his doubles, and shortly after rocketed to the surface, where he died of a massive embolism. It is not known if a convulsion proceeded his rapid ascent, though there was bruising at the back of his head. His computer showed 11 minutes of bottom time with a one-minute ascent. 

The diver, who was not mix certified but had some mix training and had supposedly made mix dives, was last seen swimming off the anchor line at 92 m/300 ft by his two dive partners, who turned their “air” dive at77 m/250 ft (PO2 = 1.8 atm) to complete their decompression. Contrary to the dive plan, the diver reportedly left his two partners at 77 m/250 ft, descended to 92 m/300 ft, and swam off the line horizontally, where his partners lost sight of his bubble trail. He was later spotted at the surface, and his body was recovered. The team made the dive from a 25-foot inflatable approximately 25 miles offshore. The deceased diver’s girlfriend, who was not able to operate the vessel, was the only one on the boat during the dive.

June 1995

Offshore Broward County, Florida—A 27-year-old diver never returned from a deep air dive to 138 m/450 ft. The dive was a practice run for his attempt at a 169 m/550 ft deep air record scheduled for this summer. Prior to his fatal dive, the diver reportedly had completed twenty air dives beyond 123 m/400 ft, with a maximum depth of 147 m/480 ft. The current record is 156 m/513 ft held by Dan Manion (U.S.). It was reported that members of the local technical diving community—many of whom practice extreme deep air diving themselves—tried to discourage him from attempting to set the record. 

The dive was scheduled during the surface interval of a recreational, two-tank dive. The diver wore a single large-volume cylinder and an oxygen pony for decompression. The crew rigged a descent line, and the diver went over the side while the boat’s recreational divers looked on. The diver had no in-water support team. 

About 7 to 8 minutes into the dive, a crew member jumped into the water, free-dived down, and reported that he saw bubbles. The crew member then pulled on the line in a pre-arranged signal to ascertain if the diver was okay. The diver supposedly returned the pull signal. About 20 minutes later with no sign of the diver, the captain sent down another diver to 33 m/100 ft to look for him. There were no bubbles. He was not seen again.

July 1995 

Thunder Hole Cave System, Florida—A highly experienced cave explorer suffered an oxygen convulsion at 25 m/80 ft and drowned after mistakenly switching to an EAN 50 decompression mix (50% O2, bal N2) instead of an EAN 32 at 37 m/120 ft (PO2 = 2.3 atm) following an extended trimix dive beyond 61 m/200 ft.

The diver and his partner were conducting a trimix dive which utilized two nitrox mixes (EAN 32 and EAN 50) for decompression. Reportedly, the bottles and regulators were numbered but not marked for depth, and the diver matched the regulators to the wrong cylinders during set-up. The diver then staged the EAN 50 mix at 43 m/140 ft [EAN 50 has a “maximum operating depth” (MOD) of 22 m/72.6 ft at a PO2 of 1.6 atm] instead of the EAN 32 mix, which was staged at 21 m/70 ft. During decompression, the partner heard the diver’s scooter kick in and looked over to see the diver convulsing at 25 m/80 ft. The partner freed the diver from the scooter but was unable to save him. With no support or safety divers, it wasn’t possible to get the diver to the surface and resuscitate him.

July 1995

Moody, Southern California—A non-technical diving trained father and his 14-year-old son ran out of gas and drowned while trying to free the anchor on a wreck dive on air to the Moody at 40-43 m/130-140 ft. A third diver ran out of gas, surfaced unconscious, and was revived. Two other divers on the trip were bent after they shortened their decompression. 

The anchor line snagged following the first dive on the wreck, and five individuals on the boat decided to dive the Moody a second time instead of cutting the line and going to dive another, shallower wreck. The father, who organized and led the trip, partnered up with a second diver and decided to include his 14-year-old son, who had not yet dived that day. The father wore a dry suit and twin steel 72s with a single outlet manifold (no first stage redundancy) that were not over-pressurized. The second dry suit diver wore doubles and carried a pony. The son wore a wet suit and carried an aluminum 80 cf/11-liter tank. Reportedly, the team carried no decompression gas. Visibility was said to be about 15-18 m/50-60 ft, water temperature on the bottom was about 50-55 degrees Fahrenheit, and there was a strong surface current that necessitated running a leader line from the stern to the anchor line to assist the divers’ descent. A second team of two divers followed the three down.

After descending and working to free the anchor line, the father’s partner surfaced about 8 to 9 minutes into the dive and told the captain they needed more slack to free the line. He then went back down to the bottom. Upon his return, the father indicated he was low on air and headed up the anchor line. The second team of divers also ascended. The son and the partner remained.

About 12-15 minutes into the dive, the son indicated that he was out of air. The partner gave him a second stage and the two started up. During their ascent, the partner ran out of air, switched to his pony, and tried to drag the son, now presumably drowned, up the line. The partner then ran out of air in his pony. In the process, he apparently dropped his weight belt before ascending unconscious to the surface. The son’s body, being negatively buoyant, drifted back down. It is believed that the father either witnessed this event from the anchor line or saw the partner ascend alone and went back down to save his son. The father and son were found together on the bottom.

aquaCORPS #12 Survivors (1995)

September 1995

Blunt Avenue Quarry, Knoxville, Tennessee—An experienced, mix-trained cave diver and dive software developer grabbed the wrong tanks and suffered a CNS convulsion at depth during a 61m/200 ft body recovery. He was brought to the surface unconscious, resuscitated, and evacuated to a chamber where he suffered massive heart failure and died. The independent double cylinders contained EAN 34 (34% O2, bal. N2) with a maximum operating depth of about 33m/108 ft.

The diver, who was the only member of the local Sheriff’s Volunteer Rescue Squad trained for depths beyond 40m/130 ft, had slept only three hours before receiving an early morning call requesting his help in recovering a drowned swimmer’s body from the 92m/300 ft quarry. It was reported that he regularly used the same sets of doubles for air, EAN, and trimix, never labeled his cylinders, or used contents tags, and did not own an analyzer. He instead relied on memory, much to the consternation of his friends. The diver apparently grabbed the doubles containing EAN instead of air and arrived at the dive site.

It is believed that the diver descended breathing from one of his stage bottles containing EAN 23, and switched to his doubles containing EAN 34 at depth (PO2=2.4 atm @ 61m/200 ft). A second member of the recovery team was breathing air. The two found the body approximately 30 minutes into the dive and tied it off at about 61m/200 ft. The rescue team signaled to surface. Just then the partner reported hearing the diver moan and start kicking hard for the surface. The partner tried to stop the diver to no avail, and followed him up. The diver was found face down with his regulator out of his mouth at 52m/170 ft. His partner began to haul him up and handed him off at about 34m/110 ft to support divers who then got him to the surface. The diver regained consciousness briefly as he was being evacuated to a chamber, where he died of heart failure likely the result of an embolism. Sadly, the use of content tags on his cylinders would likely have prevented his death. Damn.

August 1995

Oxtox Hit On The ‘Lusey’, Celtic Sea 

by RW Bill Hamilton 

In August, 1995, a diver who was decompressing at the 6m/20 ft stop suffered an oxygen convulsion and was rescued successfully on a dive on the Lusitania by the Starfish Enterprise team.

As a technical diving operation, this one appears to be exemplary, and this incident bears that out. The group was correctly criticized for not having an onboard chamber, but it should be pointed out that their dives have something sorely lacking in most other open sea technical operations: an organizational structure and an operations plan.

Briefly, Starfish uses two standby divers, one in the water and one on deck, and has a second chase boat which tends to offset the use of a small dive boat as the main platform. The divers take their oxygen decompression while hanging on a semi-rigid “station,” so all can drift as a unit. This minimizes the problems of fighting current, and reduces the wind chill factor. A chase boat makes drift decompression a new ball game.

The divers used a profile generated (“cut”) with MigPlan. The important issue here is the actual profile, which shows the diver deeper than 87m/287 ft for 16 min (maximum depth 93m/307 ft) after a three-minute  descent. He made planned stops while ascending to 6m/20 ft, switched to air at 51m/170 ft and to EAN 50 at 21m/70 ft. After 14 minutes at 6m/20 ft, he convulsed. His partner and another diver were not successful in putting an air regulator into his mouth. His head was tilted back, his eyes were closed, and blood came out of his mouth. He still had a tight grip on the john line. They tried to force gas out of his chest but saw none escape, and took him to the surface.

He was given some meaningful expired-air resuscitation while still partly in the water, his BC and tanks were removed, and he was hoisted on board. It took about two minutes to get the diver onto the deck. A helicopter was called.

He looked dead and he did not appear to be breathing. His mouth was open and his tongue protruded about half an inch. His mask was full of vomit, and some light pink fluid, not frothy, escaped from his mouth. His neck seal was cut away, and resuscitation was continued. Within moments he began to breathe on his own. He was placed on a dry, warm, engine hatch cover which had been cleared in advance for just such an event. A constant flow oxygen mask with a good seal was used at first while his breathing was weak; however, as it became stronger, he was switched to a demand mask set for slight positive pressure. He recovered consciousness and was given a quick neurological check, which showed no DCI abnormalities. A support diver gathered up the records and his dive computer. The helicopter picked him up 50 minutes after he surfaced, and in another 15 minutes, he was at the chamber, disoriented but with few other DCS symptoms. He was given a Table 6 (RN 62) (aquaCORPS N5/BENT] about an hour later; no oxygen toxicity symptoms were noted. He was hospitalized for two days.

The diver does not remember anything from the time he felt the convulsion coming on until the arrival of the helicopter. He will not be allowed to dive for three months, but no residual effects are expected. From the point of view of non-commercial diving operations, the rescue and resuscitation were classical.

Several points are worth noting. There was some, but not much warning of the impending seizure. It was impossible to reinsert the mouthpiece; this is to be expected, and further points up the value of a full-face mask.

There is always concern about embolism when ascending a convulsing diver. This team tried to expel air out of his lungs, a sensible move. Although embolism from such ascents is relatively rare, ascending is the better alternative if drowning is the other. If the diver is able to breathe, then ascent should be delayed until the diver is breathing regularly.

Because there were standby divers to take over, the dive partner went only part way to the surface with the unconscious diver (because of his own decompression obligation). To surface for a minute or two after being several minutes at the 6m/20 ft stop on oxygen is acceptable for lifesaving efforts and entails very low extra risk as long as the obligated decompression is completed. If more than two or three minutes are spent at the surface, it would be advisable to add some oxygen time, as a guess about three or four times as much as the time spent at the surface, plus any remaining obligation.

Constant-flow oxygen is normally not ideal for surface treatment of DCI, where the patient needs to receive 100% oxygen. A demand system is better. In this case, constant flow was appropriate when the diver was not breathing strongly. Having another diver accompany a diver going for treatment is highly recommended. Although it is desirable to make an immediate switch to air or a lower-PO2 mixture, in the event of a convulsion, this need not be done if it requires unusual effort or risk.At this point, we have no clues as to why this diver convulsed. He had made over 100 similar trimix dives so had been exposed to substantial oxygen profiles before. He was not taking medications, got sleep the night before, his equipment seemed to be functioning normally, and he was not exercising or doing anything else known to cause a CO2 buildup. The highest PO2 on the bottom was 1.24 bars, and on decompression was 1.56 for only 3 minutes; the diver was at 1.61 during the oxygen breathing for 14 minutes, and had used about 50% of his allowable exposure (by at least two widely used methods against the NOAA 1991 limits). He normally takes his oxygen in cycles, but in this case had not even used one cycle. He had no toxicity symptoms during the Table 6 (RN 62) two hours later. At this time we have no confident explanation. This shows the fickle nature of CNS oxygen toxicity, and highlights the need to have rescue capability. This incident further shows the value of strong organization and support divers.

aquaCORPS #13 O2N2 INCIDENT REPORTS (1996)

October 1995 

Catalina Island, California—A diver suffered hypoxia and went unconscious in about 5 m/15 ft while diving a refurbished CCR-1000 rebreather during a “Rebreather Experience,” and was pulled to the surface by the safety diver and dive partner. She was revived with no ill effects. 

The cause of the incident was attributed to battery failure on the unit, which left the primary PO2 sensors and oxygen addition value inoperative and resulted in no oxygen being fed to the diver. In addition, the diver failed to properly monitor the primary and backup PO2 displays which would have alerted her to the problem. This would have prompted her to manually add oxygen to the system as per standard protocol and abort the dive. 

According to personnel conducting the dives, the batteries on the unit, which had been dived twice earlier that day, were checked according to a pre-dive checklist prior to the dive. There was some discussion that the batteries had been tested without a load and therefore gave an inaccurate reading. Reportedly, the unit was turned on before the dive, which would have delivered a load. Others also questioned whether the canister was packed correctly, and whether the antiquated units were reliable enough to dive at all. 

The diver, a physician’s assistant, stated that she “analyzed” the oncoming hypoxia symptoms (euphoria, confusion, incoherence) into unconsciousness. The safety diver and partner realized that something was wrong and pulled her out. 

November 1995 

Bahamas—A 27-year-old recreational and enriched air instructor died while conducting a deep air dive with three other divers to about 92 m/300 ft or more. He used a single 100 cf/12-liter cylinder with redundant regulators (H-valve) and EAN 50 stage bottle. The body was never recovered. 

Reportedly, the diver, who was working the charter, tagged along with a private instructor and his two students who had completed a deep air diving course the day before. They were making a bounce dive to 92 m/300 ft on air along the wall using recreational gear. 

According to his employer, the diver was not overly involved in technical diving but had 4000-5000 dives under his belt, including 1000 dives to depths between 46- 61 m/150-200 ft and had dived several times to 123 m/400 ft on air. Although the diver was aware of the dangers involved, he “liked” deep air diving. 

The group with which the diver descended along the wall was not using a decompression line or support divers. The instructor reported that he signaled his two students to ascend after about 4 four to 5 minutes of bottom time. He then reported that he noticed that the diver, who was at about 84 m/275 ft, was heading up the wall at an angle, at which time the instructor began his own ascent and lost track of the diver. Another instructor who had trained the diver challenges this report and believes that the diver may have actually planned to make a deep plunge at that point and never returned.

The instructor surfaced after about 29 minutes of run time. Several recovery dives were made to no avail. This is reportedly the fourth recreational diving death this year on the wall in the Bahamas. One observer questioned the judgment of an instructor who dives to 92 m/300 ft on single air cylinders with students in tow. 

November 1995 

Oahu, Hawaii—A fish collector suffered a spinal hit on a 61-92 m/200-300 ft air dive to collect fish after he got separated from his down line (and his travel decompression gas) when the boat broke loose. He was forced to surface prematurely, swim 20 minutes to reach the boat, and then complete his decompression. 

The diver and his 19-year old partner, who reportedly had no formal deep diving training, left their boat unattended while they descended to deeper than 61 m/200 ft to collect a specific fish, which apparently could bring up to $3,000 for a matched pair. They reportedly attached their travel gas (air stage) and oxygen to the anchor line. The 19-year-old got so narked that he decided to remain on the line while the fish collector swam to collect the fish. The anchor pulled away, and the boat and decompression gas drifted away. 

When the collector surfaced because of a gas shortage, the boat was a 20-minute swim away. The collector got to the boat and breathed all the remaining gas (including O2) in an attempt to decompress. It is not known when the collector began to experience DCI symptoms. The two drove several hours to reach a chamber, crossing the Liki Liki Pass (1,500 feet above sea level) in the process. When they arrived, the collector was unable to climb out of the truck unaided and had lost all feeling below his chest. After 15 days of treatment, the diver improved to having feeling in his waist. The prognosis is that he will never walk again. Based on a report from Dennis Pierce/Epic Dives.

Additional Resources:

Diver Alert Networks Annual Diving Reports on Diving Incidents, Injuries and Fatalities (1988-2016) can be found here.
Get a free copy of aquaCORPS #4 MIX, which was published in 1992 as technical diving was just emerging. The issue provides a window into what mixed gas diving looked like in 1992.


Michael Menduno is InDepth’s editor-in-chief and an award-winning reporter and technologist who has written about diving and diving technology for 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. He also produced the first Tek, EUROTek, and ASIATek conferences, and organized Rebreather Forums 1.0 and 2.0. Michael received the OZTEKMedia Excellence Award in 2011, the EUROTek Lifetime Achievement Award in 2012, and the TEKDive USA Media Award in 2018. In addition to his responsibilities at InDepth, Menduno is a contributing editor for DAN Europe’s Alert Diver magazine, and X-Ray Magazine.

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