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Increasing The Probability Of Surviving Loss Of Consciousness Underwater When Using A Rebreather

With divers soon returning to the loop, the Rebreather Training Council (RTC) is currently considering a number of initiatives to improve rebreather diving safety. One of those is to recommend the use of mouthpiece retaining straps to prevent drowning in the event of loss of consciousness (LoC). Accordingly, we offer this seminal paper by ex-British Special Forces dive instructor turned tech instructor trainer Paul Haynes on their efficacy and use. Can you or your mates survive a LoC underwater?

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by Paul Haynes
Header image by Barry McGill.

Header image: Deep wreck diver Gareth O’Neill giving scale to one of the impressive 13.5″ gun barrels on the wreck of the King George V-class dreadnought battleship HMS Audacious, which lies in 64m (210 ft.) off the coast of North Donegal, Ireland.

Mouthpiece Retaining Strap Resources:

Where do Agencies and Manufactures Stand on Mouthpiece Restraining Straps?

A Mouthpiece Restraining Strap Just Might Save Your Life

We surveyed CCR divers from around the world. Here are the results.

The paper was first published in the Diving and Hyperbaric Medicine Volume 46 No. 4 December 2016 253

When compared to open circuit scuba, it is acknowledged within sport, military and occupational diving organisations that the probability of exposure to an inappropriate breathing gas is increased when using rebreathers. 1

As a result, a serious or fatal incident is more likely when rebreather diving. 2

Inappropriate breathing gas scenarios most frequently associated with rebreather use are: (1) hypoxia; resulting from respiring an hypoxic gas,  (2) hypercapnia, resulting from increased levels of inspired carbon dioxide (CO2), or hypoventilation, (3) hyperoxia, resulting from respiring an hyperoxic gas. 3

The sport diving community, defined here as manufacturers, diver training agencies, instructional cadre, and divers, frequently refers to these maladies as the rebreather ‘3H hazards’, all of which can lead to loss of consciousness (LoC) with little or no warning.

The most common interface between the rebreather and the diver’s respiratory system is a mouthpiece valve assembly, frequently called a dive surface valve. This human-machine interface is referred to in this paper as a “mouthpiece” and is used in conjunction with a sport diving “half-mask.” The mouthpiece typically requires manual operation by the diver to change from “surface mode,” which isolates the rebreather re-circulation system (breathing loop) from the environment, to ‘dive mode’, which allows access to the breathing loop and breathing gas.

The mouthpiece retaining strap in place. Photo by Marcus Blatchford.

As tone is lost from the mandibular muscles following LoC, the likely consequence is loss of airway protection as the mouthpiece/breathing loop falls from the mouth of the diver. If this occurs underwater, unless there is immediate intervention by a diving partner, the following outcomes are highly likely: (1) fluid aspiration and asphyxiation, (2) venting of breathing loop gas via the open mouthpiece, (3) whole or partial flooding of the breathing loop, (4) loss of buoyancy, (5) drowning.

Although other factors (triggers) are inevitably responsible for initiating the accident, loss of airway protection and subsequent drowning is most frequently the actual cause of death (CoD). This paper examines a potential means of delaying or limiting this cycle, thus increasing the probability of surviving LoC underwater when using a rebreather.

Paul Haynes’ webinar on rebreather safety (above) is one of series of webinars hosted by BSAC, which are of interest to Technical Divers. Non members can access them by following the BSAC Technical Group Facebook page where they are advertised.

Background

The mid-1990s saw the beginning of an upsurge in the use of rebreathers by sports divers. At that time, the sport diving industry had limited rebreather experience and so in anticipation of a growth in rebreather popularity, in 1996 the diving industry organised Rebreather Forum Two (RF2). The conference was organised to address the major issues involved in bringing rebreather technology to the consumer market-place and was divided into working sessions to identify the key technology, safety, training, and risk management issues. Drawing on the collective experience of numerous delegates from sport, military, and occupation diving backgrounds, a consensus was developed in order to help shape future sport rebreather diving practice.4

Rebreather Fatality Analysis

As anticipated, sport rebreather use increased post RF2.  Subsequently, with consideration to the relatively low number of rebreather sport divers, there appeared to be a disproportionately higher number of reported rebreather fatalities when compared to open-circuit scuba. As a consequence, Divers Alert Network (DAN) conducted a study comparing sport diving open circuit and rebreather scuba fatalities from the period 1998 to 2006.5   Due to the difficulty in attaining comprehensive rebreather accident data specific to each fatality, in particular CoD as determined by a Medical Examiner (Coroner), the DAN study was restricted to a low number of rebreather fatalities (80 cases). However, study conclusions appeared to support the following related 1996 RF2 consensus points:

 “Rebreathers are much more complex than open circuit with insidious risk.”

Fig. 1: Triggers in open circuit and rebreather diving fatalities.

The 2007 DAN analysis concluded that, of the cases studied, equipment trouble (human error or technical failure) was the trigger (something that turns an uneventful dive into an emergency) in over 40% of rebreather fatalities compared to just over 15% of open circuit fatalities (Figure 1). In addition, inappropriate breathing gas (insidious risk) was the disabling injury (something that causes death or makes drowning likely) in over 50% of rebreather cases compared to less than 5% of open circuit cases (Figure 2).

Fig. 2: Disabling injuries in open circuit and rebreather diving fatalities.

 “Loss of consciousness presents a significant hazard when using rebreathers, likely to result in death by drowning.”

The 2007 DAN analysis concluded that in 94% of cases studied, the actual CoD, as determined by a Medical Examiner, was drowning (Figure 3).

Fig. 3: Causes of death in open circuit and rebreather fatalities.

In an effort to quantify rebreather diving risk, in 2013, a separate rebreather fatality study concluded that of the 181 cases analysed between 1998 – 2010, study data suggested a four- to ten-fold increased risk of death when rebreather diving compared to open circuit scuba diving2.  The study also reported that a rebreather potentially has a 25-fold increased risk of component failure compared to an open circuit manifolded twin-cylinder scuba system. This study therefore also appears to further support the RF2 consensus statements discussed above.


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Human error

An incident is defined here as an unplanned event that degrades safety and culminates in equipment damage, diver injury, or death. Rebreathers are complex equipment that form one element of a broader life support system that includes: (1) the diver (attitude, skill set, knowledge, experience, health and fitness to dive), (2) dive partner / team (attitude, skill set, knowledge, experience, health and fitness to dive), (3) surface support team (attitude, skill set, knowledge, experience, emergency response protocols, emergency medical facilities), (4) diving ancillary equipment (functionality and fitness for purpose), (5) environmental protection equipment (functionality and fitness for purpose), (6) procedural/diving methodology (appropriateness and fitness for purpose).

Fig. 4: Generic human error rates.

Rebreather incident data suggests that a frequent contributing factor is knowingly or unknowingly violating diving and/or equipment protocols as opposed to equipment malfunction.2  This is in keeping with data from the marine oil and gas industry where approximately 80% of incidents investigated were related to human unreliability, and approximately 20% were related to technical causes.6  These figures support a widely held perception amongst the sport rebreather community that the diver is the “weak link” in the life support system “chain” described above.

To assist in the estimation and qualification of human error, Swain and Guttman developed a generic rate from experiment and simulation in the operation of nuclear power plants (Figure 4).7  If we consider an experienced rebreather diver in a benign environment, the assembly, testing, pre-dive donning and functionality confirmation (pre-breathe) procedures, all of which are essential to safe rebreather use, could be considered to fall into the fourth row of Figure 4, i.e., difficult but familiar task, little stress, sufficient time, very little distractions or impairments. The mean probability of human error or failure per task for such a scenario is between one in 1,000 events to one in 10,000 events. Thus, even under relatively benign conditions, experienced divers will occasionally make errors. It may be concluded, therefore, that to a lesser or greater extent, all levels of rebreather diver from novice to expert are prone to human error, the consequence of which could be exposure to an inappropriate breathing gas and LoC underwater.

Rebreather Accident Prevention

To help prevent rebreather diving accidents the following key measures are presently implemented or recommended by sport diving training agencies and equipment manufacturers:

  • Use of equipment that has been subject to independent third party testing against       a recognised international standard
  • Appropriate training standards and their strict application by diving instructors
  • Appropriate dive planning
  • Analysis and clear labelling of all gas cylinders
  • Use of assembly and test checklists
  • Remaining within manufacturer’s recommendation / performance guidelines
  • Remaining within training qualification parameters
  • Pre-breathe and function check prior to entering the water
  • Diving in pairs/teams
  • Frequent oxygen partial pressure display monitoring
  • Remaining within appropriate dive planning parameters
  • Application of appropriate preventive and corrective maintenance

These incident mitigation measures are also applied within military and occupational diving environments, often to a greater level of detail and enforcement.8, 9   However, despite what is often the rigorous application of equipment maintenance schedules, prescriptive diver supervision, and organisational management systems, in the author’s experience, human error remains a common characteristic of military and occupational rebreather diving incidents. Therefore, within the sport diving environment, it is reasonable to assume that, as a consequence of less formal diving equipment maintenance schedules, supervision, and management practices, human error will likely continue to remain a common characteristic of sport rebreather diving incidents with the resulting potential for LoC.

Airway Protection

Aspiration of as little as 1–3 ml∙kg-1 [0.02-0.05 oz/Ibs] per body weight of water produces profound alterations in human pulmonary gas exchange.10   It is also reported that average water aspiration in drowning is relatively small, rarely exceeding approximately 2.2 ml∙kg-1 [0.03 oz/Ibs] per body weight.11

Therefore, preventing or limiting fluid aspiration following LoC underwater is critical to surviving such an event. Whilst it is acknowledged that the diver may eventually die as a consequence of exposure to an inappropriate breathing gas, this can take a number of minutes or longer depending upon the breathing gas composition and ambient pressure (depth). If water aspiration is prevented or delayed following LoC, a diving partner may be able to affect a successful rescue. Alternatively it is conceivable that under certain circumstances, the distressed diver may regain consciousness, potentially enabling self-rescue.

To mitigate fluid aspiration following LoC underwater, a 1996 RF2 consensus statement endorsed the use of the full-face mask (FFM). However, a FFM adds to equipment complexity, and restricts access to alternative breathing gas supply systems whilst increasing maintenance, training requirements and associated cost. These factors likely account for the sport rebreather diving community having not embraced the widespread use of FFMs despite their potential safety benefits.

One occupational diving equipment manufacturer has developed an innovative hybrid FFM/half mask design.12   This mask system enables the ready separation of the lower oral section of the mask, which incorporates the rebreather mouthpiece. This design offers FFM airway protection benefits whilst also facilitating ready access to alternative breathing gas delivery systems. However, the sale of this hybrid design has generally been confined to government and occupational diving organisations. This and the relatively high cost appear to have restricted its wider use by sport rebreather divers.

Fig. 5: The author modeling a mouthpiece retaining strap. Image courtesy of Charles Hawks.

In recognition of the possibility of encountering inappropriate breathing gas and the associated potential for LoC underwater, when a FFM is not used, the mouthpiece retaining strap (MRS), combined with related training, has been employed by militaries worldwide for over half a century. It is a common safety design feature of the vast majority of both classic and contemporary military rebreather designs where the manufacturer has endeavoured to provide airway protection in the event of LoC underwater. In its simplest form the MRS is an elasticated adjustable strap secured to the breathing loop/mouthpiece. To optimise its effectiveness, the MRS is worn over the crown of the head and adjusted to positively hold the mouthpiece in position without causing undue discomfort. More sophisticated versions incorporate a padded flange. When retracted around the face by the distended strap, the padded flange enhances the lip seal whilst also helping to secure the mouthpiece in position (Figure 5). The MRS is a relatively low cost, simple and available alternative to the FFM.

Mouthpiece Retaining Strap Efficacy

A literature search has failed to identify any formal evaluation of MRS efficacy. The subject was discussed at Rebreather Forum Three (RF3), Orlando, Florida, in May 2012, and a RF3 consensus statement reads: “The forum identifies as a research question the issue of whether a mouthpiece retaining strap would provide protection of the airway in an unconscious rebreather diver.13   However, it is unlikely that a meaningful prospective experimental evaluation of the MRS could be undertaken in human subjects. In the absence of a specific formal study, the suggestion of MRS efficacy is principally based upon observational (anecdotal) evidence from military diving sources.

As a measure of the perceived potential effectiveness of the oral seal achieved by a correctly worn MRS, when conducting a diver rescue, some closed circuit oxygen rebreather military user groups are trained to break the MRS oral seal by partially inserting a finger under the unconscious diver’s lip at the corner of the mouth. This is believed to help facilitate the venting of expanding gas from the distressed diver’s lungs and reduce the risk of pulmonary barotrauma on ascent.14   Military groups who train this technique believe that an appropriately designed MRS results in an effective seal between mouth and breathing loop mouthpiece. Anecdotal evidence from various experienced military rebreather divers/diving supervisors, including the author, suggest that the use of a MRS has on various occasions been a key contributory factor to surviving LoC underwater. It is also the author’s experience as a passenger in a free-flooding combat submersible swimmer delivery vehicle, that whilst in an upright fetal position, the MRS has provided airway protection during periods of sleep lasting up to 10 minutes.

These perceptions are corroborated by one notable study that analysed 153 accidents amongst French military rebreather divers.15   Fifty-four of these events led to LoC underwater; however, this resulted in drowning in only three cases. The military report states: “gas toxicities are frequently encountered by French military divers using rebreathers, but the very low incidence of fatalities in over 30 years can be explained by the strict application of safety diving procedures. These procedures include:

“Systematic linking of divers in pairs, so that a diver can find his buddy regardless of diving conditions (particularly if visibility is poor) and can lend assistance in the event of rescue”.

“Using a strap to hold the mouthpiece in position, along with a lip guard, so that an unconscious diver can still breathe without risk of drowning. The rescuer can then concentrate on the quality of assistance and respecting the diving parameters for regaining the surface”.

The report gives no weighting to either of these factors, so it is unclear which, if any, played a larger role in preventing drowning in 51 out of the 54 LoC events. However, protecting the airway from water aspiration and effecting rescue at the earliest opportunity are cited as key factors to surviving LoC underwater. The related benefit implied by this military diving study is likely to be translatable to the sport diving setting.

Rebreather Solo Diving?

Of the 80 rebreather fatalities reviewed in the 2007 DAN study, 33% (26 cases) involved solo diving as a result of either deliberately diving alone or becoming separated from a diving partner. In support of this finding, whilst its accuracy cannot be readily verified, a publically available on-line collation of sport rebreather fatalities suggests that solo diving continues to remain a prominent characteristic of sport rebreather deaths that have occurred since 2007.16   Due to the increased probability of respiring an inappropriate breathing gas when using a rebreather and the absence of a dive partner to witness early signs of diver distress or performance impairment and to implement rescue, solo rebreather diving appears to present additional risk.

Gareth O’Neill on a decompression stop while ascending from King George battleship HMS Audacious (64 m/210 ft.) off the North coast of Donegal, Ireland. Photo by Barry McGill

Even a well-designed and correctly fitted MRS is unlikely to provide airway protection over an extended period following LoC. Therefore, to realise any safety benefit accruing from delaying or preventing drowning, the maintenance of close contact with a dive partner is also considered an important component to surviving LoC underwater. This proposition appears to be supported by the French military study, in which divers have survived LoC as a result of MRS use and early rescue by a dive partner.

Sport Rebreather Design And Performance Standards

European standard EN14143:2013 sets minimum design and performance parameters for sport rebreathers sold within the European Union, where compliance is a mandatory aspect of consumer law.17  It is also setting a broader global benchmark for rebreather design standards. However, human error and equipment failure will likely remain a characteristic of sport rebreather use.  It follows that the provision of airway protection is a desirable safety design feature regardless of rebreather performance and reliability. Indeed, EN14143:2013 specifies a design requirement regarding a ‘face-piece’, which the standard defines as: “a mouthpiece assembly, a half mask, a full-face mask or a helmet”. The standard goes on to state: “The face-piece shall aid ear clearing by allowing the diver’s nasal passages to be occluded.  It shall also minimise the ingress of water during normal use and in the event of a diver falling unconscious or having a convulsion.”  

Whilst it is not specified how the minimisation of water ingress is to be implemented, EN14143:2013 states: “The face-piece harness shall be designed so that the face-piece can be donned and removed easily. It shall be adjustable or self-adjusting and shall hold the face-piece assembly firmly and comfortably in position.   The standard subsequently defines the design and functional requirements of a retaining strap, if fitted.

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The European rebreather standard therefore recognises the potential safety benefit of protecting the airway and breathing loop in the event of LoC and as a consequence incorporated the requirement into its design specification (Anthony G, personal communication, 2014; principal author of ENI4143:2013).

Market Trends

To extend the exploration parameters of self-contained sport and scientific diving to date, relatively small groups of “technical divers” have been the most prevalent users of rebreathers. However, a considerably larger sales potential is thought to exist amongst mainstream sport divers. As a consequence, considerable resource is presently being applied by the sport diving industry to introduce rebreathers into this larger market place.18, 19

To help facilitate mainstream rebreather diving, the world’s largest recreational diving training agency has defined a generic recreational closed circuit rebreather (rCCR) specification and developed what it considers to be appropriate rCCR training standards. As a consequence, manufacturers are either producing dedicated rCCR models or adapting previous rebreather designs to comply with this rCCR specification.20, 21   Rebreather use will likely continue to increase amongst sport divers.

Fig. 6: Rebreather open circuit bail out valve. Image courtesy of AP diving.

A mandatory rCCR specification safety feature is the bail out valve (BOV) (Figure 6).  In an emergency, it enables the diver to manually access a source of open-circuit breathing gas without the need to remove the mouthpiece. However, it is worth noting that the MRS is not a mandatory rCCR safety feature. Despite the EN14143:2013 design requirement previously discussed, the reason for this remains unclear but may result from the fact that the MRS has historically not formed part of sport rebreather design. Therefore, awareness and experience of its application and potential safety benefit is limited amongst the sport rebreather community. In addition, whereas a BOV is increasingly an integral part of sport rebreather design, contrary to EN14143:2013, it continues to remain the norm for the vast majority of manufacturers to sell sport rebreathers without “a means to minimise the ingress of water in the event of a diver falling unconscious” or a means to “hold the face-piece assembly firmly and comfortably in position.17

Airway Protection Spectrum

We may consider the upper end of the airway protection safety ‘spectrum’ is an occupational diving helmet interfaced with a rebreather. An example is the Secondary Life Support saturation diving emergency bailout rebreather manufactured by Divex.22   Assuming the watertight integrity of the breathing loop and helmet, water aspiration and, therefore, drowning following LoC, is highly improbable. At the low end of this ‘spectrum’ is the absence of any means of protecting the airway following LoC. Despite acknowledging the increased potential for exposure to an inappropriate breathing gas and LoC when rebreather diving, the sport diving community largely remains posiioned at the low end of this “spectrum.”

Conclusions

Rebreathers incorporate a high number of inherent failure modes and the potential for human error. Individually or in combination this can lead to inappropriate breathing gas and spontaneous LoC underwater. If the airway is unprotected, water aspiration and asphyxiation is the likely immediate outcome. Whilst FFMs are considered to offer a high level of airway protection, due to cost and complexity they are unlikely to be widely adopted by sport rebreather divers.

Military rebreather manufacturers consider the MRS a safety-critical design feature, which is extensively employed throughout the global military rebreather diving community. Observational evidence suggests the correct use of a MRS can be an effective means of preventing or limiting water aspiration immediately following LoC. This potentially extends the window of opportunity for effective rescue or conceivably, self-rescue should consciousness be regained.

In the vast majority of sport rebreather fatalities, drowning is the actual cause of death. Therefore to directly mitigate the immediate consequences of loss of airway protection following LoC underwater, an effective MRS should be a standard component of all rebreathers used by sport divers. In addition, in order to raise awareness of the potential safety benefits, its use should be mandated within sport rebreather training standards.

References

1. Vann RD, Mitchel SJ, Denoble PJ, Anthony TG, editors. Technical Diving Conference Proceedings. Durham, NC: Divers Alert Network; 2009

2. Fock AW. Analysis of recreational closed-circuit rebreather deaths 1998–2010. Diving Hyperb Med. 2013; 43:78-85.

3. Doolette DJ, Mitchell SJ. Hyperbaric conditions.Comprehensive Physiol. 2011;1:163-201.

4. Richardson D, Menduno M, editors. Rebreather Forum2 Proceedings. Redondo Beach, CA: Diving Science and Technology; 1996.

5. Vann RD, Pollock NW, Denoble MD. Rebreather fatality investigation. In: Pollock NW, Godfrey JM, editors. Diving for science 2007. Proceedings of the American Academy of Underwater Sciences 26th Symposium. Dauphin Island, AL: AAUS; 2007.

6. Bea RG, Roberts KH. Human and organisational factors in design, construction and operations of offshore platforms. Offshore Technology Conference. Houston, TX. 1995.

7. Swain AD, Guttman HE. Handbook of human reliability analysis with emphasis on nuclear power plant applications. Washington, DC: US Nuclear Regulatory Commission; 1983.

8. US Navy Diving Manual, rev 6. Vol 4. Washington, DC: Department of the Navy; 2008.

9. National Oceanic and Atmospheric Administration (NOAA). Diving manual, diving for science and technology, 4th ed. Flagstaff, AZ: Best Publishing Company; 2001.

10. Orlowski JP, Abulleil MM, Phillips JM. The hemodynamic and cardiovascular effects of near-drowning in hypotonic, isotonic, or hypertonic solutions. Ann Emerg Med. 1989;18:1044-9.

11. Modell JH, Graves SA, Ketover A. Clinical course of 91 consecutive near-drowning victims. Chest. 1976;70:231-8.

12. Kirby Morgan.com [internet]. Santa Barbara, CA. [cited 2016 August 1].

13. Mitchell SJ. Rebreather Forum 3 consensus. In: Vann RD, Denoble PJ, Pollock NW, editors. Rebreather Forum 3 Proceedings. Durham, NC; AAUS/DAN/PADI; 2014. p. 287-302.

14. Royal Australian Navy Diving Manual. ABR 155. 2005 Vol2. Rev 2. Ch 12. Para 12-70.

15. Gempp E, Louge P, Blatteau JE, Hugon M. Descriptive epidemiology of 153 diving injuries with rebreathers among French military divers from 1979 to 2009. Mil Med. 2011;176:446-50.

16. Deeplife.co.uk. [internet]. Deep Life Design Group. Rebreather fatal accident database. [cited 2016 July 28].

17. European standard EN14143: 2013. Respiratory equipment- self-contained re-breathing diving apparatus. European Committee for Standardisation. Para 5.10. 2013.

18. Diver Magazine [internet]. Menduno M, Caney M. Interview. PADI on rebreathers – are they safe for recreational divers. 2011 (Pt1).

19. Diver Magazine [internet]. Menduno M, Caney M. Interview. PADI on rebreathers – are they safe for recreational divers. 2011 (Pt2).

20. Menduno M. The future of diving. Diver Magazine. 2011;37(3):18-25.

21. Menduno M. Rise of the recreational rebreather. Diver Magazine. 2011;38(8):18-25.

22. Jfdglobal.com [internet] JFD / Divex commercial rebreathers. [cited 2016 August 1].

Dive Deeper:

InDepth: Can Mouthpiece Retaining Straps Improve Rebreather Diving Safety?

InDepth: A Mouthpiece Restraining Strap Might Just Save Your Life

InDepth: RTC Launches New Rebreather Safety Initiative


Paul Haynes is a former UK Special Forces (SF), Special Boat Service (SBS) Combatant Diver Instructor, Diving Supervisor and Swimmer Delivery Vehicle (SDV) Operator. Upon leaving UKSF, he worked for Divex Ltd (now JFD) the world’s largest manufacturer of professional diving equipment. As a result, Paul has remained at the forefront of defense underwater life support systems research, development, design, test and training for over two decades.
Paul is a RAID advanced mixed gas diving and rebreather Instructor Trainer, as well as a PSAI and BSAC instructor, and has authored several rebreather training manuals and numerous safety related articles for civilian diving publications. He has been an invited keynote speaker at numerous technical diving conferences to discuss rebreather development, safety and training, and has provided civilian rebreather accident investigation assistance to U.S. law enforcement. He provides consulting services through his firm Haynes Marine Ltd.
Paul is a prolific shipwreck explorer and has participated in the discovery of numerous deep shipwrecks in the North Sea off the East coast of Scotland, and is a member of the Explorers Club of New York. In addition, he has been the diving safety officer on a number of high profile diving expeditions including UK Ministry of Defence sanctioned 2016 survey of HMS Hampshire, and the joint UK Royal Navy/civilian expedition to recover of the bell from the Battleship HMS Prince of Wales sunk during WWII in the South China Sea.

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Hal Watts: Plan Your Dive

Known for his deep air diving exploits back in the day, 86-year-old Hal Watts, aka “Mr. Scuba,” is one of the pioneers of early scuba and credited with coining the motto, “Plan Your Dive. Dive Your Plan.” He founded the Professional Scuba Instructors Association International (PSAI) in 1962, which eventually embraced tech diving, but never relinquished its deep air “Narcosis Management” training. Italian explorer and instructor Andrea Murdock Alpini caught up with Watts and teased out a few stories from the training graybeard.

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Interview by Andrea Murdock Alpini 
English text by Vincenza Croce

Hal Watts, Terrence Tysall, and Bill Stone in March of 1993.  This was the last stop in the U.S. for a test dive of the Cis-Lunar Mk-4 rebreather prior to Stone’s San Agustin expedition (1994) for its first real sump dive.

“Plan your dive, dive your plan,” is a common refrain in diving, but it’s easy to forget the meaning of this phrase has changed over time.

The underwater explorers of the early days learned to plan their dives with watches, depth gauges, and US Navy tables. Back then, decompression tables were the Bible for divers—something miraculous, halfway between alchemy and physiology. Those trail-blazing divers defined what it meant to “plan” a dive.

But, at the time, the term “technical diving” did not exist; divers breathed air on the bottom as well as during decompression. Only after many years was oxygen added, followed by the famous jump into the hyperbaric chamber.  

Later came new innovations after a few decades of experiments: hyperoxygenated binary mixtures, the NOAA tables, Heli-air (i.e. the addition of helium in tanks loaded with air), the change in the speed of ascent, new molecules to be studied, new physiological and narcotic effects, and their consequent impacts on humans and their psyches.

In a very short time, diving traditions underwent a metamorphosis. The spool and the coral tank became a proper reel, the ascent bin and the plastic bag disappeared in favor of the buoyancy control device (BCD), the surface marker buoy appeared—and then, even later on, wrists were adorned with underwater computers instead of decompression slates.

Divers later renewed and revolutionized a niche discipline, transforming it into a sporting phenomenon and a vocation. Faced with imminent change, there is often nothing that can be done when an anomalous wave arrives; you cannot stop its irresistible force with the wave of a hand. And thus was the American revolution of underwater technique, where the means of exploration—read mixed gas and scooters—have become the end.

The self-proclaimed originator of the “plan your dive, dive your plan” motto was 86-year old Hal Watts, the founder of American didactic Professional Scuba Association International (PSAI) and a diving pioneer who once held the Guinness Book of World records for deep diving. Though the use of trimix grew in popularity, Hal continued to believe in deep air, in the ancient technique of coral fishermen. He supported wreck and cave diving—with decompressive mixtures and new configurations through PSAI; but, above all, he believed (and continues to believe) that deep air, if properly practiced, is a discipline with unique logistics, hidden dangers, and irresistible charms that can take you to a parallel world.

Hal Watts speaking at aquaCORPS tek.93 Conference

First of all, Hal, what was the dive that changed your way of seeing scuba diving? I mean, a dive that was like an epiphany, a dive which changed your point of view on a technical matter?

Hal Watts: Wow, you sure are really trying to test my old man memory. Now I’ll have to review some of my old logbook entries. 

The first scuba dive that really got my attention as to just how serious and dangerous scuba diving can be was on December 2, 1962. I was diving with Bob Brown, co-owner of Florida State Skindiving School in Orlando, Florida. I was a member of a dive club in Orlando known as Orlando Sport Diving Club. Bob and I had heard of a sinkhole in Ocala known locally as Zuber Sink as well as Blue Sink. Years later, I later leased the property and renamed it as Hal Watts’s 40 Fathom Grotto, and I eventually purchased the Grotto in mid-1979.

We had never talked to anyone about the sinkhole; therefore, we had no idea about the visibility or the depth. Up to this point, I had constructed my favorite BCD, using a large white Clorox plastic jug, which we tied to our twin tank system. We put air into the BCD from our “Safe Second Stage” mouthpieces. 

Bob and I tied our safety line to a tree on the bank of the sink and reviewed our dive plan. I am reminded of the motto I came up with, many moons ago—Plan your dive, dive your plan. 

We all know that motto. I didn’t realize that it was you who coined it.

It was back in the 1960s when I was writing course manuals for NASDS [National Association of Scuba Diving Schools] and opened up my Mr. Scuba dive shop.

Mr. Scuba’s Magic Bus!

But back to the dive at Zuber. I’ve failed to mention the fact that neither of us had been doing any dives below 30 m/100 ft. We followed the cave line down slowly, not paying enough attention to our depth. Before we realized it, we had hit the bottom, stirred it up, and had no clear water.

Lucky for us, I kept the cave diving reel in my hand, and Bob kept his hand on the line. I couldn’t see; however, I could feel Bob’s hand, squeeze his fingers tight on the line, grab his thumb, and give it the “thumbs up” signal. I don’t know how we managed it, but we were both able to use our NASDS safe second stages and add air into the Clorox “BCDs.” We were actually fated to begin an uncontrolled, too-rapid ascent. All of a sudden, we hit an overhead wall, which stopped our ascent at a depth of 9 m/30 ft. 

We looked at each other, and gave the OK hand signal. While decompressing, following the old Scubapro SOS mechanical computer, I started to pull up the loose line until the dive reel appeared. Wow, we sure had an awful lot of loose line floating around us. Were we extremely lucky? Of course, we were. Our problem was that we never planned our dive, and consequently, were unable to dive a plan.

After that dive, I worked with Scuba Pro and Sportsways to create the “Octopus,” or “safe second.” A while later, the octopus appeared for the first time in Scuba Pro catalogs. I was also the first to add a pressure gauge along with the Octopus.

Hal Watts set the world deep air record to 120m/390 ft in 1967

Ah yes, the “Safe Second.” That’s what NASDS called backup second stages, right? Sheck Exley (1949-1994), the legendary cave explorer with whom you were friends, was also credited with fitting a redundant second stage reg with a necklace. I want to ask you more about Exley, but first, I want to know: What are the best wrecks you ever dived?

This is really very hard to answer. I’ll have to list four, in the order that I dived them: the USS Monitor, Andrea Doria, Japanese wrecks located in Truk Lagoon, and the Lusitania in Ireland.

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The most important would have to be the USS Monitor, a submarine used during the Civil War. A group of well-known USA divers applied to the National Oceanic and Atmospheric Administration (NOAA) for a permit to dive the Monitor, as she was located in protected waters. In addition to myself, the group consisted of: Gary Gentile, attorney Peter Hess, and several other well-known expert divers. At first, NOAA refused. Then, Peter Hess filed proper papers asking that we get the NOAA permit. To that end, we presented my Deep Air training material to the concerned NOAA group. I appeared as an expert witness and provided NOAA staff and their legal representatives with my internationally accepted training material and my record of training several world record deep air divers. Our deep air training has been accepted worldwide with zero diving deaths. After that, we received the permit. 

Other than the Monitor, my favorite deep wreck dive would be the Lusitania, which is a very personal and proud story for me. The main reason is because venture capitalist Gregg Bemis owned the diving rights to the Lucey at the time. Gregg had contacted me requesting that I train him on PSAI Narcosis Management Level V, on air—which is 73 m/240 ft—and then train him on trimix so he and I could dive to 91 m/300 ft on the Lusitania lying off the coast of Ireland. 

When word got out that I had enrolled Gregg in my Narcosis Management Course, a well-known international course director (a personal friend of mine) called and told me, “Hal, do not teach Gregg deep diving.” 

PSAI’s ad in aquaCORPS Journal circa 1994 offering deep air training.

He told me that he had been training Gregg at his facility, and that he was a “train wreck.” “He is from a very well-off family in Texas, and if you cause him any injuries, you will be sued and put out of business,” my friend said. Well, guess what? Gregg completed the 240 Level V Deep Air course, then our PSAI Trimix course. My wife, Jan Watts, Gregg, and I went to Ireland to dive the Lusitania. He and I made an awesome 91 m/300 ft trimix dive to the deck.

Diving on the Andrea Doria with Tom Mount, Peter Hess, and several great wreck divers was also an awesome dive. Last but not least was a great trip to Truk to dive on some of the Japanese wrecks.

Please tell us about Sheck.  What was your relationship with him like?

Sheck and I became friends and made several dives together, and one of my favorites happened when Sheck, his Mary Ellen, my wife Jan, and I were diving at 40 Fathoms. Sheck wanted to practice gas switches during descents. Sheck was practicing, getting ready for a planned very deep dive (I think in Mexico with Jim Bowden). The four of us swam to the east side of The Grotto, slowly following the wall during our controlled descent, watching Sheck practice gas switching. 

Sheck Exley and Hal Watts at a NSS-CDS conference

After reaching our planned depth of 73 m/240 ft, we began our controlled ascent up to our first planned deco stop. During our last deco stop on our 4.5 m/15 ft platforms, I noticed that Sheck had a funny look on his face and was messing with his drysuit between his legs. I remembered then that he had told me that he had an attachment installed in the drysuit that would allow him to pee underwater. He was clearly in a bit of discomfort and Mary Ellen, Jan and I just floated nearby and watched.

I’ve heard that Sheck later used diapers, or just cut it loose in one of his old neoprene drysuits on his big dives, so evidently he didn’t get that early p-valve to work. What about your friendship and job collaboration with Gary Taylor, your brother-in-arms and a co-owner of PSAI?

Andrea, get comfortable, since this question will take some time to properly answer.

I first met Gary in Miami, which is where we became friends when I was staying in his home and taking Tom Mount’s nitrox course.  I have a photo of Tom, Gary, and me gas blending on the floor of Tom’s garage. During the course, Tom was still using his worn-out hand written paper flip charts as his notes.

Gary was impressed with my deep air program and offered to put together an updated slideshow presentation for me to teach with. PSAI still uses an updated version of this system to date. Gary stayed with Tom until Tom thought he had sold IANTD [International Association of Nitrox and Technical Divers] to another individual. After that sale came about, Gary contacted me wanting to get more involved with PSAI. Being smarter than folks thought I was, I jumped at the chance to have Gary on the PSAI Team. Tom’s deal fell through, but Gary was totally involved with PSAI, and now is a partner and president of our agency. Thanks to Gary and Tom. 

Many, many years ago I was still taking some type of classes—I think regarding mixed gasses, maybe with Rebreathers—at Tom’s house. In fact, I was one of Tom’s instructors who did the final proofreading of one of Kevin Gurr’s manuals. Too far back to recall much about this mixed gas stuff—remember my reputation for being a deep air diver.

Tom Mount and Gary Taylor mixing up some trimix in the garage.

Speaking of the people with whom you’ve dived, was the aim of The Forty Fathom Scubapros Club?

Before I invested in a sinkhole in the Ocala, Florida, area—which was locally referred to as Blue Sink or Zuber Sink, and is now referred to as 40 Fathom Grotto—several diving buddies whom I had dived with and trained for extreme deep air diving—as well as cave exploring—got together and planned to dive The Grotto at least one Friday night per month. Within a short period of time, several other buddies joined our group, which eventually became known as The 40 Fathom Scubapro’s dive club. Each diver had to meet my requirements of training. 

Forty Fathom Grotto aka Zuber Sink
An early Sheck Exley mix course at Forty Fathom Grotto
An Eric Hutcheson drawing of Forty Fathom Grotto

Eventually, our group set specific personal requirements—being a good person, supporting our club safety rules, and making at least one 40 Fathom Grotto dive per month. We set a limit of 14 or 15 members. Three 40 Fathom members eventually set World Records for deep air: I was one, A. J. Muns, and Herb Johnson set ocean records, and later I set the air depth record for cave diving. Naturally, as time passed and we got older, our membership got smaller. It is notable that none of our club members have died during any scuba dive.

Finally, what led you to create the iconic motto, “Plan Your Dive. Dive Your Plan?” 

I used to be a private pilot, and we used to say, “Plan your flight, fly your plan.” This was back in probably 1961 when I had just started diving and there were so many instances where all the other divers would get in the water without saying anything. I’ve seen so many incidents and fatalities that could have been avoided through proper planning.

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Dive Deeper

ScubaGuru: LXD 029 : Hal Watts – Record Deep Diver & Technical Diving Pioneer

Netdoc: Netdoc chats with Mr Scuba, Hal Watts

InDEPTH: The First Helium-based Mix Dives Conducted by Pre-Tech Explorers (1967-1988) by Chris Werner

Alert Diver.Eu: Rapture of the Tech: Depth, Narcosis and Training Agencies

Professional Scuba Association International: PSAI History


Andrea Murdock Alpini is a TDI and PSAI technical trimix and advanced wreck-overhead instructor based in Italy. He is fascinated by deep wrecks, historical research, decompression studies, caves, filming, and writing. He holds a Master’s degree in Architecture and an MBA in Economics for The Arts. Andrea is also the founder of PHY Diving Equipment. His life revolves around teaching open circuit scuba diving, conducting expeditions, developing gear, and writing essays about his philosophy of wreck and cave diving. He published his first book, Deep Blue: storie di relitti e luoghi insoliti (2018) and IMMERSIONI SELVAGGE, the new one is on the way, out on fall 2022. 

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